Aug 31, 2014 0600 UTC Day 1 Convective Outlook

DAY 1 CONVECTIVE OUTLOOK CORR 1

   NWS STORM PREDICTION CENTER NORMAN OK
   0100 AM CDT SUN AUG 31 2014

   VALID 311200Z - 011200Z

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CENTRAL PLAINS TO THE
   UPPER MS VALLEY...

   ...THERE IS A SLGT RISK OF SVR TSTMS FROM PART OF THE MID-ATLANTIC
   STATES TO SRN NEW ENGLAND...

   CORRECTED TO INCLUDE THE EASTERN SLIGHT RISK AREA IN THE SUMMARY.

   ...SUMMARY...
   SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP ALONG A COLD FRONT
   SUNDAY AFTERNOON AND EVENING FROM MINNESOTA SOUTHWESTWARD ACROSS
   WESTERN IOWA...AND CENTRAL AND EASTERN NEBRASKA INTO KANSAS.  LARGE
   HAIL...DAMAGING WINDS...AND A FEW TORNADOES ARE EXPECTED WITH THIS
   ACTIVITY.  A FEW SEVERE STORMS WILL ALSO BE POSSIBLE THIS AFTERNOON
   AND EARLY EVENING ACROSS NORTHERN VIRGINIA AND MARYLAND TO SOUTHERN
   NEW ENGLAND.

   ...SYNOPSIS...
   A BROAD NWRN STATES UPPER TROUGH WILL AMPLIFY TODAY ACROSS THE NRN
   AND CENTRAL PLAINS.  A PROGRESSIVE SHORTWAVE TROUGH...CURRENTLY
   MOVING EWD THROUGH THE NRN INTERMOUNTAIN WEST PER WATER VAPOR
   IMAGERY...WILL TRANSLATE THROUGH THE PARENT LARGE-SCALE
   TROUGH...REACHING THE CENTRAL DAKOTAS/NEB BY 01/00Z.  THIS MIDLEVEL
   FEATURE WILL THEN MOVE THROUGH THE MID MO VALLEY...REACHING THE
   UPPER MS VALLEY BY 12Z MONDAY.  A COLD FRONT WILL ADVANCE EWD ACROSS
   THE UPPER MIDWEST...WHILE THE TRAILING PORTION MOVES SEWD ACROSS
   NEB/KS.

   AN EXTENSIVE CORRIDOR OF RICH TROPICAL MOISTURE /PW EXCEEDING 2
   INCHES/ WILL SPREAD THROUGH THE OH VALLEY AND MID ATLANTIC STATES TO
   SRN NEW ENGLAND TODAY.  A SHORTWAVE TROUGH...EMBEDDED WITHIN THIS
   MOISTURE PLUME...WILL TRACK FROM KY/TN TO CENTRAL PA/SRN NY BY LATE
   THIS AFTERNOON/EARLY EVENING...AND THEN UNDERGO SUBSTANTIAL
   WEAKENING AS IT MOVES INTO SRN NEW ENGLAND LATE SUNDAY NIGHT.  WEAK
   HEIGHT FALLS WILL PRECEDE THE KY/TN SHORTWAVE TROUGH ACROSS THE
   CENTRAL APPALACHIANS TO SRN NEW ENGLAND...AS A COMPACT SHORTWAVE
   TROUGH MOVES EWD FROM LOWER MI TOWARD NRN NEW ENGLAND THIS FORECAST
   PERIOD.

   ...UPPER MS VALLEY TO CENTRAL PLAINS...
   EARLY IN THE PERIOD...ELEVATED THUNDERSTORMS WILL LIKELY BE ONGOING
   ALONG THE NOSE OF LLJ ACROSS PORTIONS ERN ND AND NWRN MN.  THIS
   ACTIVITY SHOULD BE ROOTED AT OR ABOVE 850MB WITH THE GREATEST THREAT
   WITH THESE STORMS BEING MARGINALLY SEVERE HAIL BEFORE THEY PROPAGATE
   INTO SRN MANITOBA AND ADJACENT NRN ONTARIO ATTENDANT TO A
   PROGRESSIVE LEAD SHORTWAVE TROUGH AND SURFACE LOW. 

   A PLUME OF STEEP MIDLEVEL LAPSE RATES WILL SPREAD E/NEWD FROM THE
   CENTRAL PLAINS TO THE UPPER MS VALLEY.  MEANWHILE...SOUTHERLY
   LOW-LEVEL WINDS AHEAD OF THE COLD FRONT WILL ADVECT MOISTURE NWD
   WITH SURFACE DEW POINTS IN THE MID-UPPER 60S SPREADING INTO ERN
   NEB/IA TO THE UPPER MS VALLEY.  THESE FACTORS COMBINED WITH SURFACE
   HEATING WILL RESULT IN STRONG INSTABILITY /MLCAPE 2000-3000 J PER
   KG/ ACROSS THE CENTRAL PLAINS TO CENTRAL MN.

   TSTMS MAY DEVELOP BY EARLY-MID AFTERNOON ALONG CENTRAL NEB PORTION
   OF THE COLD FRONT.  THIS WILL OCCUR AS FORCING FOR ASCENT ATTENDANT
   TO WEAK HEIGHT FALLS WITH THE LARGE-SCALE TROUGH AND AHEAD OF THE
   PROGRESSIVE NRN INTERMOUNTAIN WEST SHORTWAVE TROUGH REACH THIS AREA.
   EFFECTIVE BULK SHEAR WILL INCREASE ACROSS NEB/NRN KS AS A 50-60 KT
   WLY MIDLEVEL JET EMERGES FROM THE CENTRAL ROCKIES.  STRONGER SURFACE
   HEATING FROM CENTRAL NEB INTO KS RESULTING IN A DEEPLY MIXED
   BOUNDARY LAYER WILL TEND TO RESULT IN DAMAGING WINDS AND LARGE HAIL
   BEING THE PRIMARY THREATS IN THE CENTRAL PLAINS.  GIVEN VERY STEEP
   LAPSE RATES /EXCEEDING 8 C/KM IN THE 700-500-MB LAYER/...STRONG
   INSTABILITY AND EFFECTIVE BULK SHEAR OF 40-50 KT SUGGESTS VERY LARGE
   HAIL WILL BE POSSIBLE.

   MEANWHILE...STORMS ARE EXPECTED TO DEVELOP ALONG THE REST OF THE
   COLD FRONT BETWEEN 21-00Z FROM MN THROUGH ERN SD...ERN NEB...AND WRN
   IA WITH BOTH QUASI-LINEAR AND SUPERCELL STORM STRUCTURES.  ALL
   SEVERE HAZARDS CAN BE EXPECTED.  THE GREATEST SEVERE WEATHER THREAT
   IS EXPECTED ACROSS ERN NEB INTO WRN/CENTRAL IA AND SRN MN FROM LATE
   THIS AFTERNOON INTO THE EARLY EVENING.  THIS REGION WILL HAVE A
   JUXTAPOSITION OF A STRENGTHENING SSWLY LLJ ENHANCING LOW-LEVEL
   SHEAR...LOWER LCLS...AND EFFECTIVE BULK SHEAR VECTORS CROSSING THE
   COLD FRONT SUPPORTING SOME DISCRETE SUPERCELLS AND/OR EMBEDDED
   SUPERCELLS WITHIN THE DEVELOPING LINEAR STRUCTURE.  STORM MERGERS
   INTO THE EVENING SHOULD RESULT IN AN ELONGATED MCS-TYPE COMPLEX
   ADVANCING EWD ACROSS THE UPPER MS TO LOWER MO VALLEYS.

   ...NRN VA/MD/ERN PA/NRN NJ/SERN NY/SRN NEW ENGLAND...
   A CORRIDOR OF MODERATE INSTABILITY /MLCAPE UP TO 1000-1500 J PER KG/
   IS EXPECTED TO DEVELOP THIS AFTERNOON FROM NRN VA/MD TO SRN NEW
   ENGLAND...DESPITE THE PRESENCE OF WEAK MIDLEVEL LAPSE RATES.  THIS
   DESTABILIZATION WILL BE LOCATED ALONG THE ERN PERIPHERY OF EARLY DAY
   CLOUDS/PRECIPITATION EXPECTED TO EXTEND FROM THE OH VALLEY INTO
   CENTRAL PA/NY.  CONVERGENCE IN VICINITY OF A SW-NE ORIENTED
   DIFFERENTIAL HEATING BOUNDARY AND WEAK HEIGHT FALLS SPREADING ACROSS
   THIS REGION SHOULD PROVE SUFFICIENT FOR DEVELOPING TSTMS FROM
   AFTERNOON INTO THE EARLY EVENING.  EFFECTIVE BULK SHEAR OF 30-40 KT
   WILL SUPPORT ORGANIZED STORMS WITH DAMAGING WINDS BEING THE PRIMARY
   THREAT AS ACTIVITY SPREADS FROM WEST TO EAST.