Tuesday, May 3, 2011

DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 030555
SWODY1
SPC AC 030554

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1254 AM CDT TUE MAY 03 2011

VALID 031200Z - 041200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM WRN NC TO CENTRAL AND ERN
PA...

...SYNOPSIS...
FURTHER PHASING OF A SRN STREAM SHORTWAVE TROUGH...NOW LOCATED OVER
THE OZARKS PER WATER VAPOR IMAGERY...AND A SYSTEM OVER THE UPPER MS
VALLEY/WRN GREAT LAKES WILL OCCUR TODAY ACROSS THE OH/TN VALLEYS.
THE PHASED TROUGH IS EXPECTED TO BECOME NEUTRALLY ORIENTED DURING
THE SECOND HALF OF THE FORECAST PERIOD WITH THIS DEEP TROUGH
SHIFTING EWD AND EXTENDING FROM THE SRN APPALACHIANS TO SRN ONTARIO
BY 12Z WEDNESDAY.

AT THE SURFACE...AN AREA OF LOW PRESSURE EXPECTED TO BE LOCATED OVER
ERN KY AT 12Z TODAY IS FORECAST TO DEEPEN SOME AS IT TRACKS ACROSS
WV REACHING SRN/CENTRAL PA BY LATE AFTERNOON. A COLD FRONT TRAILING
SSWWD FROM THIS LOW WILL ADVANCE EWD REACHING THE ERN SLOPES OF THE
SRN/CENTRAL APPALACHIANS FROM WRN SC TO THE BLUE RIDGE MOUNTAINS TO
CENTRAL/NERN PA BY 04/00Z. A BOUNDARY INITIALLY EXTENDING FROM ERN
KY THROUGH MD TO DELMARVA WILL MOVE NWD THROUGH PA AS A WARM FRONT
REACHING NRN PA AND FAR SERN NY BY LATE AFTERNOON. AS THE SURFACE
LOW TRACKS NE TOWARD NRN VT TUESDAY NIGHT...THE COLD FRONT IS
EXPECTED TO MOVE OFF THE MIDDLE/SRN ATLANTIC COASTS AND EXTEND
THROUGH NRN FL BY 12Z WEDNESDAY.

...WRN NC THROUGH MID ATLANTIC REGION...
POST-FRONTAL CONVECTION AND EMBEDDED TSTMS ARE EXPECTED TO BE
ONGOING FROM THE LOWER MS VALLEY TO KY/SRN OH AT THE START OF THE
FORECAST PERIOD. A 40-50 KT SWLY LLJ EXTENDING FROM ERN TN TO SRN
OH WILL TRANSLATE NEWD INTO WRN PA THIS MORNING...AND ANY CONVECTION
DEVELOPING NEWD WILL HAVE A POTENTIAL TO PRODUCE LOCALLY STRONGER
WIND GUSTS. OVERALL SEVERE WEATHER THREAT WITH THIS EARLY ACTIVITY
WILL BE LOW GIVEN THE LACK OF STRONGER INSTABILITY.

MEANWHILE...HEIGHT FALLS /30-60 METERS AT 500 MB/ SPREADING ACROSS
AND IN LEE OF THE SRN AND CENTRAL APPALACHIANS WILL SUPPORT A
STRENGTHENING SSWLY LLJ FROM NC TO NY BY THIS AFTERNOON. THE SLY
WINDS WILL AID IN SUSTAINING A MOIST AIR MASS ALREADY IN PLACE FROM
ERN-NRN VA/MD INTO CENTRAL/SERN PA WITH SURFACE DEWPOINTS RISING
INTO THE LOWER 60S. ALTHOUGH MIDLEVEL LAPSE RATES SHOULD NOT BE
VERY STEEP...SURFACE HEATING WILL CONTRIBUTE TO MODERATE INSTABILITY
FROM ERN WV AND CENTRAL/NRN VA INTO CENTRAL/ERN PA. FARTHER S INTO
WRN NC...WEAKER MOISTURE AND WEAK MIDLEVEL LAPSE RATES SHOULD RESULT
IN MARGINAL INSTABILITY.

CONVERGENCE INVOF THE SURFACE LOW AND SWD ALONG THE COLD FRONT
THROUGH ERN WV/WRN VA COMBINED WITH HEIGHT FALLS WILL SUPPORT NEW
TSTM DEVELOPMENT BY EARLY-MID AFTERNOON AS THE AIR MASS BECOMES
MODERATELY UNSTABLE. STRENGTHENING SWLY MIDLEVEL WINDS AND DEEP
SHEAR WILL SUPPORT LINE SEGMENTS AND SUPERCELL STRUCTURES. IN
ADDITION TO A THREAT FOR HAIL AND STRONG WIND GUSTS ACROSS THE
SLIGHT RISK AREA...INCREASING LOW LEVEL SHEAR /ESPECIALLY ALONG THE
SURFACE LOW TRACK/ AS THE LLJ STRENGTHENS WILL SUPPORT A TORNADO
THREAT. THE TORNADO THREAT SHOULD BE GREATEST DURING THE AFTERNOON
AND EARLY EVENING FROM ERN WV INTO CENTRAL VA AND NWD THROUGH
WRN/CENTRAL MD TO CENTRAL/ERN PA.

OVERALL SEVERE WEATHER THREAT IS EXPECTED TO DIMINISH BY LATE
EVENING AS INSTABILITY WEAKENS.

...ERN AL AND GA...
A MODERATELY UNSTABLE AIR MASS SHOULD DEVELOP AHEAD OF THE COLD
FRONT ACROSS THIS REGION TODAY SUPPORTING TSTMS INTO THE AFTERNOON.
WEAKER LOW LEVEL WINDS AND EFFECTIVE BULK SHEAR OF 20-30 KT SUGGEST
MULTICELLS WILL BE THE PRIMARY STORM MODE. A STRONGER MIDLEVEL WARM
LAYER PER FORECAST SOUNDINGS IN THE 600-800 MB LAYER MAY TEND TO
LIMIT UPDRAFT STRENGTH. ISOLATED STRONG WIND GUSTS SHOULD BE THE
PRIMARY THREAT.

..PETERS/GRAMS.. 05/03/2011

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