samedi 20 septembre 2014
vendredi 19 septembre 2014
European Storm Forecast Experiment
Storm Forecast
Storm Forecast
Valid: Fri 19 Sep 2014 06:00 to Sat 20 Sep 2014 06:00 UTC
Issued: Thu 18 Sep 2014 21:10
Forecaster: TUSCHY
Valid: Fri 19 Sep 2014 06:00 to Sat 20 Sep 2014 06:00 UTC
Issued: Thu 18 Sep 2014 21:10
Forecaster: TUSCHY
A level 2 was issued for NE-Spain, S/CNTRL-France, parts of Italy and surroundings mainly for excessive rain, large to very large hail and severe wind gusts. An isolated significant tornado event can't be ruled out.
A level 2 was issued for NE France, Belgium and parts of W-Germany mainly for large hail and excessive rain.
A level 1 surrounds both level 2s mainly for excessive rain, large hail and severe wind gusts.
A level 1 was issued for parts of UK and S-Ireland mainly for excessive rain and large hail.
SYNOPSIS
Rex block continues as E-Atlantic trough retrogrades a bit to the westsouthwest. Numerous short-waves eject out of its base with the most pronounced one leaving NE Spain to the NE while weakening. Downstream ridge remains in place over the CNTRL Mediterranean and caps a very unstable air mass over the sea. Complex trough/ridge pattern occurs further north but none of the troughs will play a serious role for our forecast. Either they're cut off from the moisture or they initiate storms out of our forecast area (e.g. Turkey).
At the surface, a wavy front runs from the E-Iberian Peninsula to France and towards Germany. Crossing mid-layer waves and orographic effects induce an E-W oscillation of that front which serves as focus for enhanced deep moist convection.
...NE-Spain, Balearic Sea, Ligurian Sea, S/CNTRL-France N/CNTRL Italy to the N-Adriatic Sea ...
Many uncertainties exist due to supposable ongoing convection from the previous night, rather thick cloud cover and a decaying short-wave which passes by during the forenoon hours. Expect bulk of activity along the southern coast of France, which already has the chance to be severe as 15 m/s DLS and
roughly 1kJ/kg MLCAPE intersect.
Thereafter models diverge substantially. Weak short-waves circle the ridge, which itself reveals lowering thickness (e.g. over and north of Corsica). Capped air mass features unseasonably high BL mixed-layer mixing ratios in excess of 16 g/kg. Plume of mixed mid-layer air from the Atlas mountains over this air mass pushes MLCAPE to 2-3 kJ/kg. Shear oscillates a bit and peaks during the passage of any wave but remains aoa 20 m/s. Big question remains where and when new storms initiate. Otherwise expect favorable parameter overlap until the end of the forecast. With decreasing thickness over offshore areas, CI during the night becomes increasingly likely further south towards Corsica and Sardinia.
Latest model data indicates two peaks of DMC acitivty, one during the afternoon/evening hours and another one during the night. This time coincides with the passage of mid-layer waves.
Aside from ongoing uncertainties, confidence is high that any storm could become severe with very large hail (hail diameter in excess of 5 cm), excessive rain (selective QPF maxima in excess of 100 mm/12 h) and an augmented tornado risk (a significant event is possible as 200 m^2/s^2 and LCLs of 800 m or less overlap over SE-France and NW Italy). In addition, clustering storms will see enough CAPE/shear for long swaths of damaging wind gusts. We expanded the level 2 far east to account for such an overnight cluster, which rides along the CAPE tongue to the east. The level 2 was expanded south, too, to account for organized convection, developing over Corsica and racing to the E.
A similar setup evolves over NE Spain, where isolated DMC could evolve into supercells with all kind of severe. Despite uncertainties of thunderstorm coverage, adequate confidence for CI exists to upgrade.
... Rest of France, S-UK, Benelux and parts of Germany ...
Persistent advection of the marine layer from the W-Mediterranean towards France ensures deep and moist low-tropospheric profiles during the day. Hence, diurnal mixing should be suppressed and with mid-layer lapse rates of 7-8 K/km, MLCAPE forecasts of 1-2 kJ/kg seem reasonable. A forecast sounding just SW of Paris has MLCAPE of 2600 J/kg, PWs of 28 mm and less than 10 m/s of 6 km bulk shear. Differential heating helps to diminish CIN whereas residual outflow boundaries from yesterday's storms and the passage
of a weakneing mid-layer wave during peak heating induce enough forcing for widespread CI. Slow moving storms with torrential rain will be the main risk ... especially as storms grow upscale into numerous slow moving clusters. Initiating storms could bring large or very large hail and severe downbursts (LCLs above 1 km and augmented delta theta-e).An isolated tornado event can't be excluded due to enhanced LLCAPE along any convergence zone. This activity diminishes during the night, althoguh the air mass still supports severe events (large hail and excessive rain).
A similar kinematic/thermodynamic set-up extends towards Belgium and W/CNTRL Germany, where the same risks are
forecast. Concerns exist that with so much CAPE, an organized/long-lived cluster (MCS) could evolve over
CNTRL-France. SW-erly steering flow could bring any cluster towards W/NW Switzerland or SW/W-Germany. Aside from that, an E-W aligned convergence zone from N-France to W-Germany will be another focus for slow moving storms with excessive rain.
Further north, over S-UK, forecast soundings indicate less CAPE (1-1.5 kJ/kg), which is still noteworthy for this region. Persistent LL convergence signals, PWs in excess of 20 mm, weak upper divergence and storm motions of 5 kt point to an augmented risk for slow moving multicells with isolated large hail and excessive rain. High resolved models indicate selective amounts of 50 mm/3h, which would bring a flash flood threat to those areas. This risk also extends to S-Ireland and shifts north during the night, conform to the northbound advection of the unstable air.
... Portugal and parts of Spain ...
Beneath the upper low, scattered thunderstorms evolve. Weak lapse rates/warm mid-layers and thin CAPE profiles within the hail growth zone lower the risk for electrified convection. Heavy rain and marginal hail will be the main hazard. A few spout-type tornado events are possible along the coasts.
A level 2 was issued for NE France, Belgium and parts of W-Germany mainly for large hail and excessive rain.
A level 1 surrounds both level 2s mainly for excessive rain, large hail and severe wind gusts.
A level 1 was issued for parts of UK and S-Ireland mainly for excessive rain and large hail.
SYNOPSIS
Rex block continues as E-Atlantic trough retrogrades a bit to the westsouthwest. Numerous short-waves eject out of its base with the most pronounced one leaving NE Spain to the NE while weakening. Downstream ridge remains in place over the CNTRL Mediterranean and caps a very unstable air mass over the sea. Complex trough/ridge pattern occurs further north but none of the troughs will play a serious role for our forecast. Either they're cut off from the moisture or they initiate storms out of our forecast area (e.g. Turkey).
At the surface, a wavy front runs from the E-Iberian Peninsula to France and towards Germany. Crossing mid-layer waves and orographic effects induce an E-W oscillation of that front which serves as focus for enhanced deep moist convection.
...NE-Spain, Balearic Sea, Ligurian Sea, S/CNTRL-France N/CNTRL Italy to the N-Adriatic Sea ...
Many uncertainties exist due to supposable ongoing convection from the previous night, rather thick cloud cover and a decaying short-wave which passes by during the forenoon hours. Expect bulk of activity along the southern coast of France, which already has the chance to be severe as 15 m/s DLS and
roughly 1kJ/kg MLCAPE intersect.
Thereafter models diverge substantially. Weak short-waves circle the ridge, which itself reveals lowering thickness (e.g. over and north of Corsica). Capped air mass features unseasonably high BL mixed-layer mixing ratios in excess of 16 g/kg. Plume of mixed mid-layer air from the Atlas mountains over this air mass pushes MLCAPE to 2-3 kJ/kg. Shear oscillates a bit and peaks during the passage of any wave but remains aoa 20 m/s. Big question remains where and when new storms initiate. Otherwise expect favorable parameter overlap until the end of the forecast. With decreasing thickness over offshore areas, CI during the night becomes increasingly likely further south towards Corsica and Sardinia.
Latest model data indicates two peaks of DMC acitivty, one during the afternoon/evening hours and another one during the night. This time coincides with the passage of mid-layer waves.
Aside from ongoing uncertainties, confidence is high that any storm could become severe with very large hail (hail diameter in excess of 5 cm), excessive rain (selective QPF maxima in excess of 100 mm/12 h) and an augmented tornado risk (a significant event is possible as 200 m^2/s^2 and LCLs of 800 m or less overlap over SE-France and NW Italy). In addition, clustering storms will see enough CAPE/shear for long swaths of damaging wind gusts. We expanded the level 2 far east to account for such an overnight cluster, which rides along the CAPE tongue to the east. The level 2 was expanded south, too, to account for organized convection, developing over Corsica and racing to the E.
A similar setup evolves over NE Spain, where isolated DMC could evolve into supercells with all kind of severe. Despite uncertainties of thunderstorm coverage, adequate confidence for CI exists to upgrade.
... Rest of France, S-UK, Benelux and parts of Germany ...
Persistent advection of the marine layer from the W-Mediterranean towards France ensures deep and moist low-tropospheric profiles during the day. Hence, diurnal mixing should be suppressed and with mid-layer lapse rates of 7-8 K/km, MLCAPE forecasts of 1-2 kJ/kg seem reasonable. A forecast sounding just SW of Paris has MLCAPE of 2600 J/kg, PWs of 28 mm and less than 10 m/s of 6 km bulk shear. Differential heating helps to diminish CIN whereas residual outflow boundaries from yesterday's storms and the passage
of a weakneing mid-layer wave during peak heating induce enough forcing for widespread CI. Slow moving storms with torrential rain will be the main risk ... especially as storms grow upscale into numerous slow moving clusters. Initiating storms could bring large or very large hail and severe downbursts (LCLs above 1 km and augmented delta theta-e).An isolated tornado event can't be excluded due to enhanced LLCAPE along any convergence zone. This activity diminishes during the night, althoguh the air mass still supports severe events (large hail and excessive rain).
A similar kinematic/thermodynamic set-up extends towards Belgium and W/CNTRL Germany, where the same risks are
forecast. Concerns exist that with so much CAPE, an organized/long-lived cluster (MCS) could evolve over
CNTRL-France. SW-erly steering flow could bring any cluster towards W/NW Switzerland or SW/W-Germany. Aside from that, an E-W aligned convergence zone from N-France to W-Germany will be another focus for slow moving storms with excessive rain.
Further north, over S-UK, forecast soundings indicate less CAPE (1-1.5 kJ/kg), which is still noteworthy for this region. Persistent LL convergence signals, PWs in excess of 20 mm, weak upper divergence and storm motions of 5 kt point to an augmented risk for slow moving multicells with isolated large hail and excessive rain. High resolved models indicate selective amounts of 50 mm/3h, which would bring a flash flood threat to those areas. This risk also extends to S-Ireland and shifts north during the night, conform to the northbound advection of the unstable air.
... Portugal and parts of Spain ...
Beneath the upper low, scattered thunderstorms evolve. Weak lapse rates/warm mid-layers and thin CAPE profiles within the hail growth zone lower the risk for electrified convection. Heavy rain and marginal hail will be the main hazard. A few spout-type tornado events are possible along the coasts.
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 |
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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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DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1156 PM CDT THU SEP 18 2014 VALID 191200Z - 201200Z ...NO SVR TSTM AREAS FORECAST... ...SUMMARY... A FEW THUNDERSTORMS MAY BECOME MARGINALLY SEVERE FROM EASTERN PORTIONS OF NEBRASKA AND SOUTH DAKOTA NORTHEASTWARD INTO PORTIONS OF MICHIGAN FOR THIS EVENING INTO TONIGHT. ...SYNOPSIS... THE SRN INFLUENCE OF THE POLAR MID/UPPER-LEVEL STREAM WILL GLANCE THE NRN STATES WITH EMBEDDED/PROGRESSIVE LOW-AMPLITUDE PERTURBATIONS FROM THE NRN PLAINS TO THE NE STATES. MEANWHILE...A MID-LEVEL CYCLONIC CIRCULATION NEAR THE CA COAST WILL BECOME INCREASINGLY DISASSOCIATED FROM THE AFOREMENTIONED STREAM...AS A RIDGE BUILDS OVER THE PACIFIC NW. AT THE SFC...A MODEST COLD FRONT WILL ADVANCE SEWD ACROSS PORTIONS OF THE NRN/CNTRL PLAINS TO THE UPPER MS VALLEY...WHILE AN ANTICYCLONE COVERS PORTIONS OF THE NERN STATES. ...ERN PORTIONS OF NEB/SD NEWD INTO PORTIONS OF MI... A QUASI-ZONAL SPEED MAX AT THE SRN EDGE OF THE POLAR STREAM WILL ADVANCE FROM THE NRN PLAINS TO THE ERN GREAT LAKES REGION. SHOWERS AND ISOLATED THUNDERSTORMS WILL LIKELY BE SPREADING EWD AT THE BEGINNING OF THE PERIOD FROM PORTIONS OF ND INTO MN...IN RESPONSE TO ASCENT ACCOMPANYING THE SPEED MAX AND WAA RELATED TO A SWLY LLJ. THE LLJ WILL PERSIST THROUGH THE PERIOD WHILE GRADUALLY SHIFTING EWD...ROUGHLY EXTENDING FROM THE CNTRL PLAINS TO THE GREAT LAKES REGION. THE COMBINATION OF WARMING ALOFT ASSOCIATED WITH LLJ-ENHANCED WAA AND THE INFLUX OF AN EML FROM THE WRN-CONUS PLATEAU WILL ENCOURAGE STRONG CAPPING AMIDST A PRE-FRONTAL WARM SECTOR. DESPITE RICH BOUNDARY-LAYER MOISTURE AHEAD OF THE FRONT CONTRIBUTING TO STRONG CONDITIONAL INSTABILITY FROM PORTIONS OF ERN NEB/SD INTO SRN MN...ASCENT ALONG/AHEAD OF THE COLD FRONT IS NOT EXPECTED TO INCREASE SUFFICIENTLY FOR MORE ROBUST CONVECTIVE DEVELOPMENT UNTIL THE EVENING HOURS. BY EARLY EVENING...MODEST MID-LEVEL HEIGHT FALLS SHOULD BECOME MORE PREVALENT ACROSS THE N-CNTRL STATES DOWNSTREAM OF A SHORTWAVE IMPULSE CROSSING THE CANADIAN PRAIRIE PROVINCES. RELATED COOLING ALOFT MAY BE SUFFICIENT FOR LOW-LEVEL PARCELS TO BREACH A WEAKENING CAP AS FRONT/LLJ-ENCOURAGED ASCENT CONTINUES. THIS SHOULD SUPPORT TSTM DEVELOPMENT/INTENSIFICATION FROM PORTIONS OF ERN NEB/SD NEWD TO PORTIONS OF MI INTO THE OVERNIGHT HOURS. CLOUD-BEARING SHEAR AND MODERATELY STEEP MID-LEVEL LAPSE RATES MAY SUPPORT ISOLATED INSTANCES OF MARGINALLY SVR HAIL WITH CONVECTION...WHICH IS GENERALLY EXPECTED TO BE ROOTED ATOP A NOCTURNALLY STABILIZING BOUNDARY LAYER. THERE MAY ALSO EXIST A BRIEF WINDOW OF OPPORTUNITY FOR NEAR-SFC-BASED CONVECTION TO EVOLVE FROM ERN NEB/SERN SD INTO SRN MN/NRN IA THROUGH MID-EVENING. THIS REGIME COULD FEATURE RELATIVELY WARMER SFC CONDITIONS WELL S OF EARLIER PRECIPITATION...TO LOCALLY ENHANCE REDUCTIONS TO SFC-BASED CINH...AND SUPPORT ISOLATED DMGG WIND GUSTS. CONFIDENCE IN GREATER-COVERAGE SVR-TSTM POTENTIAL OWING TO ANTECEDENT CAPPING PRECLUDES HIGHER PROBABILITIES AT THIS TIME. ...NERN ND AND NRN MN... A FEW STRONG TO PERHAPS LOCALLY/MARGINALLY SVR STORMS CANNOT BE RULED OUT ACROSS THE AREA IN THE WAKE OF EARLIER-DAY PRECIPITATION...AND AHEAD OF A MID-LEVEL VORT MAX CROSSING THE INTERNATIONAL BORDER REGION. MODERATE DEEP SHEAR WILL PERSIST. UNCERTAINTY IN THE EVOLUTION OF THE PRECEDING PRECIPITATION EXTENDS TO THE PROPENSITY FOR LATER-DAY DESTABILIZATION TO SUPPORT A SVR-TSTM RISK. AS SUCH...SVR-TSTM PROBABILITIES HAVE NOT BEEN INCLUDED AT THIS TIME.
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