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 | |
| This is the day after tomorrow's (day 3) forecast for organized severe thunderstorms over the contiguous United States. Please read the description of the risk categories for further information. The latest Day 3 Outlook is available as well as all Outlooks that have been issued today. | Day 3 Outlook |
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mardi 30 septembre 2014
Convective Outlooks
Sep 30, 2014 0600 UTC Day 1 Convective Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1229 AM CDT TUE SEP 30 2014 VALID 301200Z - 011200Z ...THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF SD AND NERN NEB... ...SUMMARY... ISOLATED SEVERE THUNDERSTORMS WITH HAIL AND PERHAPS A TORNADO ARE POSSIBLE TUESDAY FROM SOUTH DAKOTA INTO NEBRASKA. A FEW STRONG STORMS WITH HAIL MAY ALSO DEVELOP FROM KANSAS SOUTHWARD INTO NORTHWESTERN TEXAS BY LATE AFTERNOON INTO THE EVENING. ISOLATED HAIL WILL ALSO BE POSSIBLE ACROSS PORTIONS OF PENNSYLVANIA. ...SYNOPSIS... A NEGATIVELY-TILTED SHORTWAVE TROUGH WILL MOVE ACROSS THE DAKOTAS WITH SURFACE LOW OVER CNTRL SD AT 21Z. AT THE SAME TIME...A WARM FRONT WILL EXTEND EWD FROM THE LOW ALONG THE SD/ND BORDER AND SEWD INTO WRN IA WITH A DRYLINE FROM E-CNTRL SD INTO ERN NEB AND SWWD INTO THE ERN TX PANHANDLE. LOW-LEVEL MOISTURE WILL BE SOMEWHAT MEAGER...BUT WILL LIKELY SUPPORT ISOLATED STRONG TO SEVERE STORMS DURING THE AFTERNOON WHERE FORCING FOR ASCENT IS STRONGEST NEAR THE BOUNDARIES AND WITH AMPLE SHEAR IN PLACE. TO THE E...A SMALL UPPER LOW WILL SHIFT SEWD ACROSS OH...PA...WV AND VA WITH COOL AIR ALOFT AND ENHANCED SHEAR HELPING TO SUPPORT A FEW STRONG DAYTIME THUNDERSTORMS. ...ERN SD AND NEB DURING THE AFTERNOON... A N-S ORIENTED ZONE OF NON-SEVERE THUNDERSTORMS WILL EXIST EARLY IN THE DAY FROM NRN KS ACROSS NEB AND SD IN ASSOCIATION WITH THE WARM CONVEYOR BELT AHEAD OF THE LOW. IN THE WAKE OF THIS EARLY ACTIVITY...COOLING ALOFT WILL PERSIST COINCIDENT WITH STRONG HEATING W OF THE DRYLINE ACROSS SD AND NEB. DEWPOINTS INTO THE MID TO UPPER 50S F ARE LIKELY TO EXTEND NWWD TOWARD THE SURFACE LOW OVER CNTRL SD. BY MID/LATE AFTERNOON...AN ARC OF STORMS APPEARS LIKELY...COMPRISED OF RELATIVELY LOW-TOPPED SUPERCELLS. A TORNADO OR TWO WILL BE POSSIBLE ALONG WITH LARGE HAIL. DUE TO THE NWD MOVEMENT OF THE UPPER LOW...FORCING FOR ASCENT WILL WEAKEN WITH SWD EXTENT INTO NEB...BUT ISOLATED HAIL WILL BE POSSIBLE THERE DURING THE AFTERNOON AS WELL. ...ERN NEB...KS...FAR WRN OK INTO NWRN TX OVERNIGHT... WEAK FORCING ALONG THE STALLING SFC TROUGH/DRYLINE MAY BE SUFFICIENT FOR ISOLATED STRONG STORMS CAPABLE OF MARGINAL HAIL FROM KS INTO NWRN TX. TEMPERATURES ALOFT WILL NOT BE PARTICULARLY COOL...AND SHEAR WILL BE MARGINALLY FAVORABLE FOR A LONG-LIVED CELL CAPABLE OF HAIL DURING THE PEAK HEATING HOURS. DURING THE EVENING...WARM ADVECTION WITH THE SWLY LOW-LEVEL JET WILL HELP INCREASE LIFT ACROSS NERN KS AND VICINITY...WITH PERHAPS MARGINAL HAIL. ...CNTRL AND WRN PA...NRN WV AND SWRN NY DURING THE AFTERNOON... A SHORTWAVE TROUGH WILL MOVE SEWD ACROSS MI AND ACROSS OH/PA/NY DURING DAY WITH COOLING ALOFT FAVORABLY TIMED WITH DAYTIME HEATING. A WEAK COOL FRONT WILL HELP FOCUS DEVELOPMENT ACROSS MAINLY WRN PA. ALTHOUGH MID TO UPPER-LEVEL FLOW WILL INCREASE ACROSS SRN AREAS UNDER THE JET MAX...WINDS IN THE LOWEST 3KM WILL BE RELATIVELY WEAK. THIS SHOULD RESULT IN LITTLE IF ANY TORNADO THREAT EVEN WITH A FEW CELLS PERHAPS EXHIBITING MIDLEVEL ROTATION...AND ANY WIND THREAT SHOULD BE QUITE LOCALIZED. COOL TEMPERATURES ALOFT WILL STRONGLY FAVOR HAIL PRODUCTION...WHICH WILL BE THE PRIMARY THREAT. ..JEWELL/ROGERS.. 09/30/2014
lundi 29 septembre 2014
European Storm Forecast Experiment
Storm Forecast
Storm Forecast
Valid: Tue 30 Sep 2014 06:00 to Wed 01 Oct 2014 06:00 UTC
Issued: Mon 29 Sep 2014 22:00
Forecaster: GATZEN
Valid: Tue 30 Sep 2014 06:00 to Wed 01 Oct 2014 06:00 UTC
Issued: Mon 29 Sep 2014 22:00
Forecaster: GATZEN
A level 2 was issued for parts of the west Mediterranean mainly for excessive precipitation and to a lower extend large hail and tornadoes.
A level 1 was issued for most of the west Mediterranean region mainly for excessive precipitation.
SYNOPSIS
The south-west-European trough is weakening. Its northern portions will move eastwards into central Europe, pushing the ridge south-east. At low levels, the moist air mass over France spreads eastward, before cold air advection sets in from the north late in the period. Across the west Mediterranean, the very moist easterly low-level flow will continue, but unfavourable large-scale forcing will limit severe potential.
DISCUSSION
West Mediterranean
On Tuesday, convective activity with the potential of excessive rain will go on along the eastern portions of Spain, the southern portions of France, and the west Mediterranean Sea. Upslope flow and frontogenetical forcing are still present. During the second half of the day, weaker QG forcing in the wake of the eastward moving short-wave trough can limit the potential of excessive rain. Given weak vertical wind shear, chance of hail and tornadoes is expected to be rather low.
Strong vertical wind shear is expected across the south-western Mediterranean area including south-eastern Spain and the Balearic Islands due to north-easterly surface winds and south-westerly flow at mid levels. A few well-organized storms are forecast along the sea-breeze convergence over Spain and near the frontal boundary over the Mediterranean Sea. These storms may be capable of producing large hail and tornadoes.
A level 1 was issued for most of the west Mediterranean region mainly for excessive precipitation.
SYNOPSIS
The south-west-European trough is weakening. Its northern portions will move eastwards into central Europe, pushing the ridge south-east. At low levels, the moist air mass over France spreads eastward, before cold air advection sets in from the north late in the period. Across the west Mediterranean, the very moist easterly low-level flow will continue, but unfavourable large-scale forcing will limit severe potential.
DISCUSSION
West Mediterranean
On Tuesday, convective activity with the potential of excessive rain will go on along the eastern portions of Spain, the southern portions of France, and the west Mediterranean Sea. Upslope flow and frontogenetical forcing are still present. During the second half of the day, weaker QG forcing in the wake of the eastward moving short-wave trough can limit the potential of excessive rain. Given weak vertical wind shear, chance of hail and tornadoes is expected to be rather low.
Strong vertical wind shear is expected across the south-western Mediterranean area including south-eastern Spain and the Balearic Islands due to north-easterly surface winds and south-westerly flow at mid levels. A few well-organized storms are forecast along the sea-breeze convergence over Spain and near the frontal boundary over the Mediterranean Sea. These storms may be capable of producing large hail and tornadoes.
Convective Outlooks
| This is tomorrow's forecast for organized severe thunderstorms over the contiguous United States. Please read the description of the risk categories for further information. The latest Day 2 Outlook is available as well as all Outlooks that have been issued today. | Tomorrow's Outlook |
| |
| This is the day after tomorrow's (day 3) forecast for organized severe thunderstorms over the contiguous United States. Please read the description of the risk categories for further information. The latest Day 3 Outlook is available as well as all Outlooks that have been issued today. | Day 3 Outlook |
|
Sep 29, 2014 0600 UTC Day 1 Convective Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1244 AM CDT MON SEP 29 2014 VALID 291200Z - 301200Z ...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN CO INTO WRN NEB AS WELL AS OVER MUCH OF SRN AND ERN NM... ...SUMMARY... SCATTERED SEVERE THUNDERSTORMS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND PERHAPS A TORNADO OR TWO ARE POSSIBLE THIS AFTERNOON ACROSS MUCH OF EASTERN COLORADO...NEW MEXICO...AND SOUTHWESTERN NEBRASKA. ...SYNOPSIS... AN INTENSE SHORTWAVE TROUGH WILL MOVE FROM AZ EWD ACROSS NM AND CO DURING THE DAY...ENHANCING LIFT AND SHEAR FROM NM INTO THE CNTRL HIGH PLAINS. LOW PRESSURE WILL DEEPEN OVER NERN CO WITH A SHARP SURFACE TROUGH/DRYLINE EXTENDING SWD INTO CNTRL NM BY 00Z. SELY SURFACE WINDS WILL HELP TRANSPORT 50S DEWPOINTS INTO THE AREA WITH SUFFICIENT INSTABILITY FOR SCATTERED SEVERE STORMS BY AFTERNOON. THE SHORTWAVE TROUGH WILL CONTINUE NEWD IN A NEGATIVELY-TILTED FASHION DURING THE EVENING AS THE COLD FRONT SURGES NEWD WITH STORMS SPREADING ACROSS WRN NEB INTO FAR WRN KS. ...NM...ERN CO...WRN NEB... COOLING ALOFT AS WELL AS SURFACE HEATING WILL LEAD TO A STEEPENING OF LAPSE RATES ACROSS THE REGION WITH CIN BEING REMOVED BY AROUND 18Z ACROSS NM NWD ACROSS THE FRONT RANGE. AS SUCH...SEVERE STORMS MAY DEVELOP AS EARLY AS 19-21Z WITHIN THE DEVELOPING LOW-PRESSURE TROUGH FROM ERN CO SWWD ACROSS NM. STRONG DEEP-LAYER SHEAR WILL RESULT IN A PRIMARILY CELLULAR STORM MODE INITIALLY...WITH A FEW SUPERCELLS DEVELOPING BY LATE AFTERNOON WHEN LOW-LEVEL SHEAR WILL BE STRONGEST. LARGE HAIL AND PERHAPS A BRIEF TORNADO OR TWO WILL BE POSSIBLE DURING THE DAY...THEN STORMS SHOULD EVENTUALLY BECOME MORE LINEAR AS FORCING FOR ASCENT INCREASES. THIS MAY YIELD A DAMAGING WIND THREAT FROM NERN CO INTO WRN NEB THROUGH EVENING BEFORE STORMS WEAKEN AROUND 03Z AS INSTABILITY DISSIPATES. WHILE CELLS OVER CNTRL/SRN NM MAY BE MORE ISOLATED DUE TO THE MAIN FORCING PASSING TO THE N...CONDITIONS WILL STRONGLY FAVOR SUPERCELLS. ..JEWELL/ROGERS.. 09/29/2014
European Storm Forecast Experiment
Storm Forecast
Storm Forecast
Valid: Mon 29 Sep 2014 06:00 to Tue 30 Sep 2014 06:00 UTC
Issued: Sun 28 Sep 2014 22:17
Forecaster: GATZEN
Valid: Mon 29 Sep 2014 06:00 to Tue 30 Sep 2014 06:00 UTC
Issued: Sun 28 Sep 2014 22:17
Forecaster: GATZEN
A level 2 was issued fort he western Mediterranean mainly for excessive precipitation.
A level 1 was issued for northern Morocco, northern Algeria, south-western Mediterranean, and eastern Spain mainly for excessive precipitation, large hail, tornadoes, and severe wind gusts.
SYNOPSIS
A slowly weakening ridge over the central Mediterranean and central Europe is flanked by long-wave troughs extending into Iberia and Turkey. Main convective activity is expected ahead of the western trough due to warm air advection and frontogenesis across the Balearic Sea and northern Algeria, affecting a very moist air mass that is partly overlapping with steep lapse rates. Some instability will also evolve over France and the UK in the moist air mass. Further east, large-scale subsidence and drier low-level air are expected, and CAPE is not forecast except for the southern Aegean Sea. Over northern Europe, an intense short-wave trough will move over Scandinavia. It is associated with cold and dry low-level air spreading east, but some remaining moisture across Finland and north-western Russia may allow for weak CAPE in the afternoon hours.
DISCUSSION
Northern Morocco and Algeria into Balearic Sea and eastern Spain, southern France
Latest soundings indicate that rich moisture is present up to mid-levels in this area, yielding PWAT values between 30 mm (central Iberia and southern France) and more than 40 mm (west Mediterranean). Although lapse rates are limited, a few 100 J/kg weakly capped CAPE is well possible on Monday. Over northern Algeria, an elevated mixed layer is expected in the noon and afternoon hours that will spread across the south Mediterranean later on. CAPE may increase to more than 2000 J/kg according to latest GFS.
Main focus of initiation is again a frontal zone ahead of the trough, extending along the eastern border of the Iberian Peninsula. Continuing inflow of low-level moisture from the north-east and frontogenitical forcing can allow for larger clusters of storms moving north-east. Over eastern Iberia, upslope flow can evolve during the day and storms can initiate there as well.
Current thinking is that storms over northern Algeria and Morocco as well as across the south-western Mediterranean Sea. Deep layer vertical wind shear about 15 to 20 m/s will assist supercells and well-developed multicells, capable of producing excessive precipitation, large hail, severe wind gusts, and tornadoes. The hail threat is expected to increase in the southern and eastern portions of the risk area, where convection will be more isolated and CAPE will be higher.
Storm merger and upscale growth along the frontal zone may allow for one of two MCSs, moving north-east along the Iberian coasts. Excessive precipitation and severe wind gusts are possible and may even affect southern France late in the period. To the east of the main activity, storms across Spain may produce marginally severe hail and excessive precipitation.
A level 1 was issued for northern Morocco, northern Algeria, south-western Mediterranean, and eastern Spain mainly for excessive precipitation, large hail, tornadoes, and severe wind gusts.
SYNOPSIS
A slowly weakening ridge over the central Mediterranean and central Europe is flanked by long-wave troughs extending into Iberia and Turkey. Main convective activity is expected ahead of the western trough due to warm air advection and frontogenesis across the Balearic Sea and northern Algeria, affecting a very moist air mass that is partly overlapping with steep lapse rates. Some instability will also evolve over France and the UK in the moist air mass. Further east, large-scale subsidence and drier low-level air are expected, and CAPE is not forecast except for the southern Aegean Sea. Over northern Europe, an intense short-wave trough will move over Scandinavia. It is associated with cold and dry low-level air spreading east, but some remaining moisture across Finland and north-western Russia may allow for weak CAPE in the afternoon hours.
DISCUSSION
Northern Morocco and Algeria into Balearic Sea and eastern Spain, southern France
Latest soundings indicate that rich moisture is present up to mid-levels in this area, yielding PWAT values between 30 mm (central Iberia and southern France) and more than 40 mm (west Mediterranean). Although lapse rates are limited, a few 100 J/kg weakly capped CAPE is well possible on Monday. Over northern Algeria, an elevated mixed layer is expected in the noon and afternoon hours that will spread across the south Mediterranean later on. CAPE may increase to more than 2000 J/kg according to latest GFS.
Main focus of initiation is again a frontal zone ahead of the trough, extending along the eastern border of the Iberian Peninsula. Continuing inflow of low-level moisture from the north-east and frontogenitical forcing can allow for larger clusters of storms moving north-east. Over eastern Iberia, upslope flow can evolve during the day and storms can initiate there as well.
Current thinking is that storms over northern Algeria and Morocco as well as across the south-western Mediterranean Sea. Deep layer vertical wind shear about 15 to 20 m/s will assist supercells and well-developed multicells, capable of producing excessive precipitation, large hail, severe wind gusts, and tornadoes. The hail threat is expected to increase in the southern and eastern portions of the risk area, where convection will be more isolated and CAPE will be higher.
Storm merger and upscale growth along the frontal zone may allow for one of two MCSs, moving north-east along the Iberian coasts. Excessive precipitation and severe wind gusts are possible and may even affect southern France late in the period. To the east of the main activity, storms across Spain may produce marginally severe hail and excessive precipitation.
dimanche 28 septembre 2014
European Storm Forecast Experiment
Storm Forecast
Storm Forecast
Valid: Sun 28 Sep 2014 06:00 to Mon 29 Sep 2014 06:00 UTC
Issued: Sat 27 Sep 2014 23:32
Forecaster: PUCIK
Valid: Sun 28 Sep 2014 06:00 to Mon 29 Sep 2014 06:00 UTC
Issued: Sat 27 Sep 2014 23:32
Forecaster: PUCIK
A level 1 was issued for E Spain and the Balearic Sea mainly for excessive precipitation.
A leve 1 was issued for NW Algeria mainly for large hail, severe wind gusts and excessive precipitation.
SYNOPSIS
During Sunday, a large ridge will stretch from the Mediterranean towards Central Europe, with troughs on the either side - one over Iberia and another, deep one, over Turkey. Towards the north, lower amplitude, strong westerly flow will be observed, with deep low pressure system affecting Norway and Sweden.
Regarding DMC activity, most of Europe will be under stable and dry conditions, apart from Iberia and the Balearic Sea, where scattered to widespread tstm activity is forecast.
DISCUSSION
... E Spain and the Balearic Sea...
On the forward flank of the trough, mid to upper tropospheric flow will turn southerly, advecting steeper lapse rates from N Africa atop the warm and moist boundary layer of the sea. As a result, marginal to moderate CAPE build-up is forecast. Models reveal several subtle short-waves crossing over the sea to the north, as well as the surface cyclogenesis is forecast. To its north, easterly surface flow will impinge on the coastline, creating favorable setup for widespread convective initiation. It is likely, that in the environment of low CIN, a large cluster, perhaps an MCS will form. Relatively slow storm motion, along with high chance of cell training as convection backbuilds towards the moist easterly flow, will provide favourable setup for several excessive precipitation events. Because of the model inconsistency regarding the MCS track, Lvl 1 seems to be sufficient choice at the moment.
... NW Algeria ...
Compared to Spain, steeper lapse rates, higher CAPE values and also stronger DLS will likely allow for some well organised DMC. Here, besides the excessive rainfall threat, large hail and severe wind gusts may occur as well, especially if supercells manage to form.
A leve 1 was issued for NW Algeria mainly for large hail, severe wind gusts and excessive precipitation.
SYNOPSIS
During Sunday, a large ridge will stretch from the Mediterranean towards Central Europe, with troughs on the either side - one over Iberia and another, deep one, over Turkey. Towards the north, lower amplitude, strong westerly flow will be observed, with deep low pressure system affecting Norway and Sweden.
Regarding DMC activity, most of Europe will be under stable and dry conditions, apart from Iberia and the Balearic Sea, where scattered to widespread tstm activity is forecast.
DISCUSSION
... E Spain and the Balearic Sea...
On the forward flank of the trough, mid to upper tropospheric flow will turn southerly, advecting steeper lapse rates from N Africa atop the warm and moist boundary layer of the sea. As a result, marginal to moderate CAPE build-up is forecast. Models reveal several subtle short-waves crossing over the sea to the north, as well as the surface cyclogenesis is forecast. To its north, easterly surface flow will impinge on the coastline, creating favorable setup for widespread convective initiation. It is likely, that in the environment of low CIN, a large cluster, perhaps an MCS will form. Relatively slow storm motion, along with high chance of cell training as convection backbuilds towards the moist easterly flow, will provide favourable setup for several excessive precipitation events. Because of the model inconsistency regarding the MCS track, Lvl 1 seems to be sufficient choice at the moment.
... NW Algeria ...
Compared to Spain, steeper lapse rates, higher CAPE values and also stronger DLS will likely allow for some well organised DMC. Here, besides the excessive rainfall threat, large hail and severe wind gusts may occur as well, especially if supercells manage to form.
vendredi 26 septembre 2014
European Storm Forecast Experiment
Storm Forecast
Storm Forecast
Valid: Fri 26 Sep 2014 06:00 to Sat 27 Sep 2014 06:00 UTC
Issued: Thu 25 Sep 2014 17:29
Forecaster: TUSCHY
Valid: Fri 26 Sep 2014 06:00 to Sat 27 Sep 2014 06:00 UTC
Issued: Thu 25 Sep 2014 17:29
Forecaster: TUSCHY
A level 2 was issued for NE Morocco and N-Algeria mainly for excessive rain and large hail.
A level 2 was issued for the S-Aegean Sea and Crete mainly for large hail, severe wind gusts, excessive rain and an isolated tornado.
A level 1 surrounds both level 2s for a lesser severe risk.
A level 1 was issued for CNTRL Sweden, the CNTRL Baltic Sea and S-Finland mainly for severe wind gusts and an isolated tornado risk.
SYNOPSIS
A progressive trough north of Scotland (26th, 06Z) crosses Norway, Sweden and most of Finland from west to east until 27th 06Z. A pronounced high is placed to the south and keeps regions from France to the W-Mediterranean stable. A strong cut-off evolves over SE Europe with another but weaker one over Portugal.
DISCUSSION
... Norway, Sweden, parts of the Baltic Sea and Finland ...
A rapidly eastbound moving occlusion/cold front will be the focus for enhanced convection. Left exit of a powerful 45 m/s mid-layer jet overspreads the front and most models produce MLCAPE of 200-500 J/kg. Combined with intense forcing, an organized line of showers/at least isolated thunderstorms is forecast. It remains questionable, when orographically induced subsidence wanes east of the rough orography of Norway/
Sweden. With LL trajectories from the southwest and extrapolating eastbound moving forcing, we began the level 1 over CNTRL Sweden and expanded it east. 850 hPa winds of 25 m/s or more and LL shear of 15-20 m/s will be enough for severe wind gusts along any line of showers/thunderstorms. Deeper updrafts take profit of even stronger shear. Low LCLs and modest SRH-1 favor a few tornadoes ... especially along the coast, where warmer SSTs enhance LLCAPE. Lightning activity diminishes during the night, but the wind gust risk remains with decaying convection. Hence the level was expanded far east. No upgrade to a level 2 due to uncertainties in magnitude of CAPE and E-displacement of strongest LL winds ahead of anticipated convective line.
... Ionian Sea, Aegean Sea, Greece, Turkey and Crete ...
Leisurely southbound moving cold front and abundant lift of the cut-off ensure scattered to widespread CI. Overall scenario becomes rather messy as cold front, a developing LL depression over Turkey and the upper low interact. Expect organized convection offshore and along the coasts, where CAPE approaches 1000 J/kg. Rapid decay of onshore CAPE is forecast, although models might exaggerate. DLS aoa 20 m/s will support organized multicells/isolated supercells with large hail and severe wind gusts. Despite meager LL shear, CAPE in the lowest 3 km increases substantially. Therefore a few tornadoes are forecast and overlap of 150 J/kg LLCAPE with 20 m/s DLS could support an isolated strong event. Back-bending occlusion keeps air mass over Greece unstable for a prolonged period, so excessive rain should add a flash flood risk.
Further south, initially capped environment becomes more conducive for CI south of Greece, around Crete and over SW Turkey. Despite rather strong capping conditions, strong lift should help to initiate numerous storms, which grow upscale into eastbound moving clusters. 30 m/s DLS and more than 1kJ/kg MLCAPE support organized thunderstorms with large hail (an isolated very large hail event is possible), severe wind gusts, torrential rain and an isolated tornado threat). This area was upgraded due to the highest confidence of more widespread severe.
... N-Algeria to S-Spain ...
A quasi-stationary boundary, trapped along the Atlas Mountains, keeps BL moisture high. A confined area of 500-1000 J/kg MLCAPE and 15 m/s DLS with daytime heating assist in scattered thunderstorms with large hail the main risk. Clustering storms along/south of the Atlas Mountains could also bring excessive rain with flash flood problems. Weak positive thickness advection lowers the risk for thunderstorms from E to W during the night. Effective PWs of 15-30 mm, slow moving storms, dry soil and anticipated scattered to widespread CI increase confidence in a more serious flash flood risk. Hence the level 2. Towards Spain, less PWs and CAPE lower the severe risk and we kept this area in a broad level 1.
A level 2 was issued for the S-Aegean Sea and Crete mainly for large hail, severe wind gusts, excessive rain and an isolated tornado.
A level 1 surrounds both level 2s for a lesser severe risk.
A level 1 was issued for CNTRL Sweden, the CNTRL Baltic Sea and S-Finland mainly for severe wind gusts and an isolated tornado risk.
SYNOPSIS
A progressive trough north of Scotland (26th, 06Z) crosses Norway, Sweden and most of Finland from west to east until 27th 06Z. A pronounced high is placed to the south and keeps regions from France to the W-Mediterranean stable. A strong cut-off evolves over SE Europe with another but weaker one over Portugal.
DISCUSSION
... Norway, Sweden, parts of the Baltic Sea and Finland ...
A rapidly eastbound moving occlusion/cold front will be the focus for enhanced convection. Left exit of a powerful 45 m/s mid-layer jet overspreads the front and most models produce MLCAPE of 200-500 J/kg. Combined with intense forcing, an organized line of showers/at least isolated thunderstorms is forecast. It remains questionable, when orographically induced subsidence wanes east of the rough orography of Norway/
Sweden. With LL trajectories from the southwest and extrapolating eastbound moving forcing, we began the level 1 over CNTRL Sweden and expanded it east. 850 hPa winds of 25 m/s or more and LL shear of 15-20 m/s will be enough for severe wind gusts along any line of showers/thunderstorms. Deeper updrafts take profit of even stronger shear. Low LCLs and modest SRH-1 favor a few tornadoes ... especially along the coast, where warmer SSTs enhance LLCAPE. Lightning activity diminishes during the night, but the wind gust risk remains with decaying convection. Hence the level was expanded far east. No upgrade to a level 2 due to uncertainties in magnitude of CAPE and E-displacement of strongest LL winds ahead of anticipated convective line.
... Ionian Sea, Aegean Sea, Greece, Turkey and Crete ...
Leisurely southbound moving cold front and abundant lift of the cut-off ensure scattered to widespread CI. Overall scenario becomes rather messy as cold front, a developing LL depression over Turkey and the upper low interact. Expect organized convection offshore and along the coasts, where CAPE approaches 1000 J/kg. Rapid decay of onshore CAPE is forecast, although models might exaggerate. DLS aoa 20 m/s will support organized multicells/isolated supercells with large hail and severe wind gusts. Despite meager LL shear, CAPE in the lowest 3 km increases substantially. Therefore a few tornadoes are forecast and overlap of 150 J/kg LLCAPE with 20 m/s DLS could support an isolated strong event. Back-bending occlusion keeps air mass over Greece unstable for a prolonged period, so excessive rain should add a flash flood risk.
Further south, initially capped environment becomes more conducive for CI south of Greece, around Crete and over SW Turkey. Despite rather strong capping conditions, strong lift should help to initiate numerous storms, which grow upscale into eastbound moving clusters. 30 m/s DLS and more than 1kJ/kg MLCAPE support organized thunderstorms with large hail (an isolated very large hail event is possible), severe wind gusts, torrential rain and an isolated tornado threat). This area was upgraded due to the highest confidence of more widespread severe.
... N-Algeria to S-Spain ...
A quasi-stationary boundary, trapped along the Atlas Mountains, keeps BL moisture high. A confined area of 500-1000 J/kg MLCAPE and 15 m/s DLS with daytime heating assist in scattered thunderstorms with large hail the main risk. Clustering storms along/south of the Atlas Mountains could also bring excessive rain with flash flood problems. Weak positive thickness advection lowers the risk for thunderstorms from E to W during the night. Effective PWs of 15-30 mm, slow moving storms, dry soil and anticipated scattered to widespread CI increase confidence in a more serious flash flood risk. Hence the level 2. Towards Spain, less PWs and CAPE lower the severe risk and we kept this area in a broad level 1.
mercredi 24 septembre 2014
European Storm Forecast Experiment
Storm Forecast
Storm Forecast
Valid: Thu 25 Sep 2014 06:00 to Fri 26 Sep 2014 06:00 UTC
Issued: Wed 24 Sep 2014 19:39
Forecaster: GATZEN
Valid: Thu 25 Sep 2014 06:00 to Fri 26 Sep 2014 06:00 UTC
Issued: Wed 24 Sep 2014 19:39
Forecaster: GATZEN
A level 2 was issued for north-eastern Algeria to northern Tunisia mainly for large hail.
A level 1 was issued for the south-western to central Mediterranean mainly for large hail.
A level 1 was issued for the western Balkans mainly for excessive precipitation.
SYNOPSIS
A long-wave trough covers eastern Europe. A strong westerly mid-level jet extends at its southern flank from Algeria to Turkey. Dry air masses have spread into most of Europe except for the Mediterranean Sea.
DISCUSSION
South-west to central Mediterranean
Relatively well-developed moisture is left across the Mediterranean Sea. Latest soundings indicate that this moisture overlaps with rather steep lapse rates over the warm sea surface. On Thursday, some QG forcing can be expected as the long-wave trough extends southward. Ahead of the axis of the trough, weak warm air advection is expected over the southern Adriatic Sea.
Current thinking is that latest convective activity will go on with scattered thunderstorms. These can organize into multicells given 10-15 m/s 0-3 km vertical wind shear. From the southern Adriatic Sea to Greece, larger hodographs in the warm air advection regime can also support supercells that move to the east.
Storms that form may produce severe weather, but overall threat is limited. Excessive rain seems to be not too likely given the rather isolated occurrence of rather fast moving storms. Large hail may occur but CAPE seems to be relatively weak in the hail growth zone. Although low-level vertical wind shear is weak, a few wind gusts and a tornado are not ruled out.
A higher severe potential exists across northern Africa, where 15 m/s 0-3 km vertical wind shear overlap with CAPE. Numerous thunderstorms are forecast in response to diurnal heating with large hail the main threat. Tornadoes and severe wind gusts are not ruled out.
Convective activity will increase in the northern portions of the Adriatic later on, due to an approaching short-wave trough from the north-west. Locally large hail may be possible due to 10-15 m/s 0-3 km vertical wind shear.
Late in the period, warm air advection and DCVA will take place over the southern Adriatic Sea, where storms may merge to clusters, moving onshore over the southern Balkans. Excessive rain may occur due to numerous storms in upslope flow.
A level 1 was issued for the south-western to central Mediterranean mainly for large hail.
A level 1 was issued for the western Balkans mainly for excessive precipitation.
SYNOPSIS
A long-wave trough covers eastern Europe. A strong westerly mid-level jet extends at its southern flank from Algeria to Turkey. Dry air masses have spread into most of Europe except for the Mediterranean Sea.
DISCUSSION
South-west to central Mediterranean
Relatively well-developed moisture is left across the Mediterranean Sea. Latest soundings indicate that this moisture overlaps with rather steep lapse rates over the warm sea surface. On Thursday, some QG forcing can be expected as the long-wave trough extends southward. Ahead of the axis of the trough, weak warm air advection is expected over the southern Adriatic Sea.
Current thinking is that latest convective activity will go on with scattered thunderstorms. These can organize into multicells given 10-15 m/s 0-3 km vertical wind shear. From the southern Adriatic Sea to Greece, larger hodographs in the warm air advection regime can also support supercells that move to the east.
Storms that form may produce severe weather, but overall threat is limited. Excessive rain seems to be not too likely given the rather isolated occurrence of rather fast moving storms. Large hail may occur but CAPE seems to be relatively weak in the hail growth zone. Although low-level vertical wind shear is weak, a few wind gusts and a tornado are not ruled out.
A higher severe potential exists across northern Africa, where 15 m/s 0-3 km vertical wind shear overlap with CAPE. Numerous thunderstorms are forecast in response to diurnal heating with large hail the main threat. Tornadoes and severe wind gusts are not ruled out.
Convective activity will increase in the northern portions of the Adriatic later on, due to an approaching short-wave trough from the north-west. Locally large hail may be possible due to 10-15 m/s 0-3 km vertical wind shear.
Late in the period, warm air advection and DCVA will take place over the southern Adriatic Sea, where storms may merge to clusters, moving onshore over the southern Balkans. Excessive rain may occur due to numerous storms in upslope flow.
Africa & Middle East Infrared Animated Satellite & Lightning Detection
http://www.eldoradocountyweather.com/forecast/europe/with-controls/africa-infrared-sat-loop.php
European Storm Forecast Experiment
Storm Forecast
Storm Forecast
Valid: Wed 24 Sep 2014 06:00 to Thu 25 Sep 2014 06:00 UTC
Issued: Wed 24 Sep 2014 06:23
Forecaster: PUCIK
Valid: Wed 24 Sep 2014 06:00 to Thu 25 Sep 2014 06:00 UTC
Issued: Wed 24 Sep 2014 06:23
Forecaster: PUCIK
A level 2 was issued for extreme E Tunisia and SW Sicily mainly for very large hail, severe wind gusts and excessive precipitation.
A level 1 was issued for much of the western Mediterranean, SE Spain, Sardegna, SW Italy mainly for large hail, severe wind gusts and excessive precipitation.
SYNOPSIS
A complex synoptic-scale setup evolved over Europe. When looking at the satellite loops, one immediately notices unseasonably deep low pressure system over extreme Eastern Ukraine. With pressure reading of 979 hPa and intense gradient, it is very likely that just south of the core, wind gusts have exceeded 30 m/s. To the west, situation looks more calm. Still, a pronounced trough filled with cold mid-tropospheric airmass is making its way from UK towards BENELUX and Germany. Its base is stretching all the way towards Iberia, slowly progressing eastwards and weakening.
As of 05 UTC, abundant DMC activity is already observed over the western half of the Mediterranean. This will also be the region of most interest regarding severe DMC for today.
DISCUSSION
... SE Spain through Balearic, Tyrrhenian Sea, N. Africa ...
00 UTC soundings from Dar-El-Beida and Trappani reveal presence of EML, while towards the north, lapse rates are not as pronounced (e.g. Mallorca or Decimonnanu soundings). It is likely that with an approach of the trough, lapse rates will be advected a bit more to the north than is the current situation. Combined with moist airmass over the sea surface, moderate CAPE values are simulated, with values on the order of 1000 - 2000 J/kg. Degree of wind shear will increase towards the south, where stronger southwesterly flow is observed. Generally speaking, DLS values should easily reach over 15 m/s over much of an area, so that supercells and well-organised multicells will be possible, capable of large hail and severe wind gusts.
CI will be at first tied to the lingerning, ill-defined frontal boundary, but will spread southwards towards the night hours. Models simulate possiblity of one or two MCS formation. The most likely location will be between Tunisia and Sicily after Thursday 00 UTC, where explosive environment is simulated, featuring CAPE above 2000 J/kg, along with more than 25 m/s of DLS. In case that storms attain supercellular characteristic, besides the MCS form, very large hail will be likely. With MCS, excessive precipitation and damaging wind gusts may be expected as the primary threats.
A level 1 was issued for much of the western Mediterranean, SE Spain, Sardegna, SW Italy mainly for large hail, severe wind gusts and excessive precipitation.
SYNOPSIS
A complex synoptic-scale setup evolved over Europe. When looking at the satellite loops, one immediately notices unseasonably deep low pressure system over extreme Eastern Ukraine. With pressure reading of 979 hPa and intense gradient, it is very likely that just south of the core, wind gusts have exceeded 30 m/s. To the west, situation looks more calm. Still, a pronounced trough filled with cold mid-tropospheric airmass is making its way from UK towards BENELUX and Germany. Its base is stretching all the way towards Iberia, slowly progressing eastwards and weakening.
As of 05 UTC, abundant DMC activity is already observed over the western half of the Mediterranean. This will also be the region of most interest regarding severe DMC for today.
DISCUSSION
... SE Spain through Balearic, Tyrrhenian Sea, N. Africa ...
00 UTC soundings from Dar-El-Beida and Trappani reveal presence of EML, while towards the north, lapse rates are not as pronounced (e.g. Mallorca or Decimonnanu soundings). It is likely that with an approach of the trough, lapse rates will be advected a bit more to the north than is the current situation. Combined with moist airmass over the sea surface, moderate CAPE values are simulated, with values on the order of 1000 - 2000 J/kg. Degree of wind shear will increase towards the south, where stronger southwesterly flow is observed. Generally speaking, DLS values should easily reach over 15 m/s over much of an area, so that supercells and well-organised multicells will be possible, capable of large hail and severe wind gusts.
CI will be at first tied to the lingerning, ill-defined frontal boundary, but will spread southwards towards the night hours. Models simulate possiblity of one or two MCS formation. The most likely location will be between Tunisia and Sicily after Thursday 00 UTC, where explosive environment is simulated, featuring CAPE above 2000 J/kg, along with more than 25 m/s of DLS. In case that storms attain supercellular characteristic, besides the MCS form, very large hail will be likely. With MCS, excessive precipitation and damaging wind gusts may be expected as the primary threats.
dimanche 21 septembre 2014
Sep 21, 2014 1300 UTC Day 1 Convective Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0753 AM CDT SUN SEP 21 2014 VALID 211300Z - 221200Z ...NO SVR TSTM AREAS FORECAST... ...SUMMARY... SCATTERED SHOWERS AND THUNDERSTORMS -- A FEW WITH GUSTS APPROACHING SEVERE LEVELS -- WILL BE POSSIBLE FROM THE LOWER GREAT LAKES ACROSS THE CENTRAL APPALACHIANS TO THE MID SOUTH. SCATTERED THUNDERSTORMS ARE ALSO EXPECTED ACROSS PARTS OF THE SOUTHWEST AND GREAT BASIN...WITH ISOLATED AND MARGINAL SEVERE STORMS POSSIBLE MAINLY OVER UTAH THIS AFTERNOON AND EVENING. ...SYNOPSIS... IN MID-UPPER LEVELS...GENERAL AMPLIFICATION OF PROGRESSIVE SYNOPTIC PATTERN IS FCST THROUGH PERIOD. LEADING PORTION OF STG SHORTWAVE TROUGH NOW OVER LOWER MI AND LM IS FCST TO PIVOT EWD ACROSS ERN/SRN ONT THROUGH PERIOD...REACHING SRN QUE AND HUDSON VALLEY REGION BY 12Z. BY THAT TIME...TRAILING VORTICITY BANNER SHOULD EXTEND SWWD ACROSS WV AND TN...CONTRIBUTING TO LARGER-SCALE TROUGH AMPLIFICATION. LEADING/SRN-STREAM PERTURBATION -- NOW EVIDENT IN MOISTURE-CHANNEL IMAGERY OVER COASTAL CAROLINAS -- WILL EJECT NEWD ACROSS ATLC TOWARD NOVA SCOTIA. FARTHER W...MID-UPPER-LEVEL CYCLONE NOW OVER CENTRAL CA AND ADJACENT SIERRAS WILL MOVE NEWD ACROSS CENTRAL/NRN NV...REACHING SRN ID/NERN WY AND DEVOLVING INTO OPEN-WAVE TROUGH NEAR END OF PERIOD. AT SFC...11Z ANALYSIS SHOWED LOW OVER LH WITH COLD FRONT SWWD ACROSS CENTRAL INDIANA...SWRN MO...SERN KS...NWRN OK AND ERN NM. WARM FRONT WAS DRAWN FROM LOW SSWWD OVER CENTRAL OH AND NERN/CENTRAL KY. LOW SHOULD EJECT NEWD OVER ST. LAWRENCE VALLEY TODAY...WITH COLD FRONT REACHING ERN PA...WRN VA...NRN MS...AND N TX BY 00Z. BY 12Z...FRONT SHOULD MOVE OFFSHORE MID ATLC AND REACH COASTAL CAROLINAS...EXTENDING SWWD ACROSS CENTRAL/SRN PORTIONS OF MS AND TX. ...NERN CONUS TO MID SOUTH... ONE OR TWO NARROW BANDS OF CONVECTION WITH EMBEDDED TSTMS SHOULD DEVELOP THROUGH EARLY-MID AFTN...POSSIBLY INCLUDING EWD SHIFT/EXTENSION OF CONVECTION NOW EVIDENT NEAR BUF-PKB LINE. AT LEAST ISOLATED GUSTS APCHG SVR LIMITS MAY OCCUR...AND POTENTIAL EXISTS FOR SUB-SVR GUSTS...BELOW 50 KT...TO PRODUCE MINOR WIND DAMAGE SUCH AS DOWNED LIMBS/TREES OVER SOME AREAS. NARROW CORRIDOR OF MID-UPPER-60S SFC DEW POINTS IS EVIDENT BETWEEN COLD AND WARM FRONTS ATTM...WITH LOWER 60S FARTHER E TO WRN PARTS OF NY/PA/WV. THIS WILL ACT IN TANDEM WITH SPORADIC DIURNAL HEATING UNDER VARIABLE CLOUD COVER TO YIELD 200-500 J/KG PREFRONTAL MLCAPE. BUOYANCY WILL INCREASE WITH SWWD EXTENT TOWARD MID SOUTH AS DEEP-LAYER FLOW DIMINISHES...AND FROM ABOUT OH RIVER NWD...MOST FAVORABLE LOW-LEVEL FORCING ULTIMATELY WILL OUTPACE EWD SHIFT OF RICHEST LOW-LEVEL MOIST PLUME. FLOW ALOFT WILL BE LARGELY PARALLEL TO COLD FRONT AND ANY PREFRONTAL CONFLUENCE/CONVERGENCE LINES UPON WHICH TSTMS MAY DEVELOP...INDICATING PREDOMINANTLY LINEAR MODE. THOUGH MLCINH WILL REMAIN WEAK...LACK OF MORE ROBUST PRECONVECTIVE SFC WINDS SHOULD LIMIT CONVERGENCE. THESE OFFSETTING FACTORS...AND LACK OF MORE ROBUST INSTABILITY OVER NRN AREAS...PRECLUDE CATEGORICAL UPGRADE FOR NOW. ...UT AND VICINITY... SCATTERED TSTMS ARE EXPECTED TO DEVELOP THROUGH EVENING OVER AREAS FROM SRN NV AND NRN AZ ACROSS MUCH OF UT. ISOLATED DAMAGING GUSTS ARE POSSIBLE. EXTENSIVE/ONGOING AREA OF CLOUDS/PRECIP AND EMBEDDED SHOWERS/TSTMS WILL LEAD TO FRAGMENTED...MUTED AND SLOWLY PACED DIURNAL HEATING ACROSS THIS AREA. MLCAPE ULTIMATELY MAY REACH 300-800 J/KG IN POCKETS BY MID-LATE AFTN...WHILE DEEP-LAYER FLOW INCREASE WITH APCH OF CA VORTEX ALOFT. ALTHOUGH CYCLONE WILL BE WEAKENING...RELATED DCVA SHOULD CONTRIBUTE SUBTLE COOLING/DESTABILIZATION ALOFT IN SUPPORT OF EPISODIC CONVECTIVE POTENTIAL. ..EDWARDS/MARSH.. 09/21/2014
European Storm Forecast Experiment
Storm Forecast
Storm Forecast
Valid: Sun 21 Sep 2014 06:00 to Mon 22 Sep 2014 06:00 UTC
Issued: Sat 20 Sep 2014 23:02
Forecaster: PISTOTNIK
Valid: Sun 21 Sep 2014 06:00 to Mon 22 Sep 2014 06:00 UTC
Issued: Sat 20 Sep 2014 23:02
Forecaster: PISTOTNIK
A level 1 was issued for N Italy, S Austria, Slovenia, Croatia, Bosnia-Hercegovina, Montenegro, Serbia and W Bulgaria for excessive precipitation, large hail and severe wind gusts.
A level 1 was issued for E France, Switzerland, S Germany, the W Czech Republic and W Austria mainly for excessive precipitation.
A level 1 was issued for S Portugal and S Spain mainly for large hail.
SYNOPSIS
An upper-level trough rapidly amplifies from Scandinavia into central Europe. It induces a strong surface cyclogenesis over the Baltic Sea and various weak ones in the triangle between Poland, Northern Italy and Romania. A tongue of polar air erupts southward into central Europe on their rear flank and replaces the unseasonably warm and moist air of the past few days.
An anticyclone is placed over the British Isles, to its south flanked by a stationary cut-off low off the Portuguese coast. A strong zonal flow (up to 30 m/s at 500 hPa) stretches from northwestern Africa into the central and eastern Mediterranean region.
DISCUSSION
... southern Alps and central Mediterranean into the Balkans ...
Still plenty of CAPE (700 - 2200 J/kg) was present across the central Mediterranean region according to the Saturday 12 UTC soundings. However, apart from Trapani (3100 J/kg), not the extreme values of the previous days were reached any more. Low-level cooling with increasing westerly winds will likely continue to quietly reduce CAPE and reinforce the capping inversion on Sunday. Central and southern Italy will therefore only see isolated, struggling storms or no activity at all, similar to the previous days.
A higher coverage of storms is expected from the southern Alpine region into the Balkans, where CAPE will be lower (probably below 1000 J/kg) but only weakly capped, and where a series of travelling vorticity maxima facilitate convective initiation. Especially over orographic features of the Balkans, quite many storms may form with a maximum in the afternoon and evening hours. Coverage in the southern Alpine and northern Adriatic region is somewhat more uncertain, but the arrival of the main trough may keep storms going well into the night there.
With still plenty of moisture and a possibility of repeated rounds of convection, excessive rainfall is again the main hazard. In addition, deep-layer shear between 15 and 25 m/s and regionally enhanced helicity may also promote better storm organization with a risk of large hail and severe wind gusts. Distinct upper-level cooling overnight could support the formation of one or two tornadoes (either supercellular or "spout-type") with offshore convection over the Gulf of Genoa and the northern Adriatic Sea late in the forecast period.
... France into Poland and east-central Europe ...
Ahead of the cold front, the same warm and moist air will again allow CAPE up to 1000 J/kg under 10 m/s deep-layer shear. Scattered to widespread, mostly disorganized thunderstorms will form. Due to slow storm motion and precipitable water around 30 mm, once more a few flash floods are possible.
Vertical wind shear will gradually increase from the northwest with the amplification of the main upper-level trough, but pronounced cold air advection and associated subsidence in the range of the southward slipping cold front will probably kill any deep convection before it can attain any better organization.
... Denmark, S Scandinavia, Baltic Sea ...
Showers and low-topped thunderstorms under limited CAPE and mostly weak shear in the polar air mass should not pose any severe weather risk.
... Iberia ...
Warm air advection and positive vorticity advection provide increasing lift ahead of the cut-off low. Rich Atlantic moisture will be advected well inland with southwesterly winds, and CAPE is expected to build to ~500 J/kg inland and probably to higher values near the east coast. Scattered to widespread, diurnally driven storms are expected.
Deep-layer shear increases from 10 m/s in the northwest to 20 m/s in the southeast, with slightly veering profiles. This may be sufficient for multicells and a few supercells with a primary risk of large hail. In case of supercells, severe wind gusts and an isolated tornado are not ruled out, either.
Activity may propagate offshore and spread towards the Balearic Islands overnight with an ongoing severe weather risk.
A level 1 was issued for E France, Switzerland, S Germany, the W Czech Republic and W Austria mainly for excessive precipitation.
A level 1 was issued for S Portugal and S Spain mainly for large hail.
SYNOPSIS
An upper-level trough rapidly amplifies from Scandinavia into central Europe. It induces a strong surface cyclogenesis over the Baltic Sea and various weak ones in the triangle between Poland, Northern Italy and Romania. A tongue of polar air erupts southward into central Europe on their rear flank and replaces the unseasonably warm and moist air of the past few days.
An anticyclone is placed over the British Isles, to its south flanked by a stationary cut-off low off the Portuguese coast. A strong zonal flow (up to 30 m/s at 500 hPa) stretches from northwestern Africa into the central and eastern Mediterranean region.
DISCUSSION
... southern Alps and central Mediterranean into the Balkans ...
Still plenty of CAPE (700 - 2200 J/kg) was present across the central Mediterranean region according to the Saturday 12 UTC soundings. However, apart from Trapani (3100 J/kg), not the extreme values of the previous days were reached any more. Low-level cooling with increasing westerly winds will likely continue to quietly reduce CAPE and reinforce the capping inversion on Sunday. Central and southern Italy will therefore only see isolated, struggling storms or no activity at all, similar to the previous days.
A higher coverage of storms is expected from the southern Alpine region into the Balkans, where CAPE will be lower (probably below 1000 J/kg) but only weakly capped, and where a series of travelling vorticity maxima facilitate convective initiation. Especially over orographic features of the Balkans, quite many storms may form with a maximum in the afternoon and evening hours. Coverage in the southern Alpine and northern Adriatic region is somewhat more uncertain, but the arrival of the main trough may keep storms going well into the night there.
With still plenty of moisture and a possibility of repeated rounds of convection, excessive rainfall is again the main hazard. In addition, deep-layer shear between 15 and 25 m/s and regionally enhanced helicity may also promote better storm organization with a risk of large hail and severe wind gusts. Distinct upper-level cooling overnight could support the formation of one or two tornadoes (either supercellular or "spout-type") with offshore convection over the Gulf of Genoa and the northern Adriatic Sea late in the forecast period.
... France into Poland and east-central Europe ...
Ahead of the cold front, the same warm and moist air will again allow CAPE up to 1000 J/kg under 10 m/s deep-layer shear. Scattered to widespread, mostly disorganized thunderstorms will form. Due to slow storm motion and precipitable water around 30 mm, once more a few flash floods are possible.
Vertical wind shear will gradually increase from the northwest with the amplification of the main upper-level trough, but pronounced cold air advection and associated subsidence in the range of the southward slipping cold front will probably kill any deep convection before it can attain any better organization.
... Denmark, S Scandinavia, Baltic Sea ...
Showers and low-topped thunderstorms under limited CAPE and mostly weak shear in the polar air mass should not pose any severe weather risk.
... Iberia ...
Warm air advection and positive vorticity advection provide increasing lift ahead of the cut-off low. Rich Atlantic moisture will be advected well inland with southwesterly winds, and CAPE is expected to build to ~500 J/kg inland and probably to higher values near the east coast. Scattered to widespread, diurnally driven storms are expected.
Deep-layer shear increases from 10 m/s in the northwest to 20 m/s in the southeast, with slightly veering profiles. This may be sufficient for multicells and a few supercells with a primary risk of large hail. In case of supercells, severe wind gusts and an isolated tornado are not ruled out, either.
Activity may propagate offshore and spread towards the Balearic Islands overnight with an ongoing severe weather risk.
samedi 20 septembre 2014
Sep 20, 2014 0600 UTC Day 1 Convective Outlook
DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1229 AM CDT SAT SEP 20 2014 VALID 201200Z - 211200Z ...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE UPPER MS VALLEY... ...THERE IS A SLGT RISK OF SVR TSTMS FROM LOWER MI TO NRN MO... ...SUMMARY... SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED SATURDAY FROM SOUTHWESTERN LOWER MICHIGAN TO NORTHERN MISSOURI. LARGE HAIL AND STRONG WINDS WILL BE POSSIBLE. SEVERE WIND AND MARGINALLY SEVERE HAIL ARE ALSO LIKELY ACROSS MUCH OF NORTHERN MINNESOTA AND VICINITY. A LOWER THREAT OF SEVERE WEATHER EXISTS ACROSS NEVADA AND WESTERN UTAH. ...UPPER MS VALLEY... EARLY MORNING WV IMAGERY CLEARLY DEPICTS A STRONG SHORT-WAVE TROUGH OVER CNTRL AB...DIGGING SEWD IN LINE WITH LATEST MODEL GUIDANCE. 00Z GUIDANCE SUGGEST 80KT+ 500MB SPEED MAX WILL TRANSLATE INTO WRN ND BY 18Z...THEN INTO SWRN MN BY EARLY EVENING. EXIT REGION OF THIS FEATURE WILL ENHANCE UVV ACROSS THE RED RIVER VALLEY REGION AND A STRONGLY FORCED SECONDARY COLD FRONT SHOULD ADVANCE TO A POSITION OVER ERN ND BY 18Z. DESPITE THE SOMEWHAT MARGINAL MOISTURE IN PLACE AHEAD OF THIS SYSTEM...COOLING PROFILES AND STRONG FORCING SHOULD ENCOURAGE A BAND OF CONVECTION TO DEVELOP ALONG WIND SHIFT BY EARLY AFTERNOON. THIS ACTIVITY WILL THEN SPREAD SEWD ACROSS MN AS EXIT REGION OF JET ADVANCES DOWNSTREAM. DAMAGING WINDS ARE POSSIBLE WITH THIS ACTIVITY...ESPECIALLY IF LINEAR MCS EVOLVES AS A FEW HIGH RES MODELS SUGGEST. MARGINALLY SEVERE HAIL COULD ALSO ACCOMPANY THE MORE ROBUST UPDRAFTS. ...MID MS VALLEY TO LOWER MI... BAND OF STRONG THUNDERSTORMS HAS EVOLVED FROM NERN NEB INTO SERN MN AT 05Z. THIS ACTIVITY APPEARS TO BE AIDED IN PART BY ENTRANCE REGION OF EJECTING SPEED MAX THAT WILL TRANSLATE INTO SERN CANADA DURING THE DAY. WHILE CONVECTION MAY BE ONGOING AT THE BEGINNING OF THE PERIOD OVER PORTIONS OF NRN LOWER MI...MORE SIGNIFICANT CONVECTION IS POSSIBLE LATER IN THE DAY AS BOUNDARY LAYER WARMS. AS MID-LEVEL SPEED MAX EJECTS INTO SERN CANADA LOW-LEVEL FLOW SHOULD VEER ACROSS THE MIDWEST AND A CONFLUENCE ZONE SHOULD ESTABLISH ITSELF FROM EXTREME SERN WI...SWWD INTO NRN MO. GREATEST BUOYANCY IS EXPECTED ACROSS THE MID MS VALLEY WHERE SBCAPE COULD APPROACH 3000 J/KG. AS TEMPERATURES WARM INTO THE MID 80S CINH SHOULD WEAKEN SUFFICIENTLY FOR SCT TSTMS...LIKELY BY 22Z. THIS ACTIVITY IS EXPECTED TO DEVELOP WITHIN INCREASINGLY SHEARED NWLY FLOW REGIME. LARGE HAIL AND DAMAGING WINDS ARE POSSIBLE WITH ORGANIZED MULTI-CELL CLUSTERS AND ISOLATED SUPERCELLS. ...GREAT BASIN... UPPER LOW OFF THE SRN CA COAST IS EXPECTED TO EJECT NEWD ACROSS CA INTO NV BY THE END OF THE PERIOD. MID-LEVEL FLOW WILL INCREASE ACROSS THE LOWER CO RIVER VALLEY INTO THE GREAT BASIN BY AFTERNOON AND HIGH-BASED CONVECTION THAT EVOLVES ACROSS THIS REGION MAY ORGANIZE WITHIN DEEP SELY FLOW. FORECAST SOUNDINGS SUGGEST ORGANIZED ROTATING UPDRAFTS ARE POSSIBLE BUT PW VALUES ARE NOT PARTICULARLY HIGH. GIVEN THE WEAK INSTABILITY WILL MAINTAIN 5 PERCENT SEVERE FOR ISOLATED SEVERE WIND GUSTS AND MARGINALLY SEVERE HAIL. ..DARROW/COHEN.. 09/20/2014
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