SPC AC 011723
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1223 PM CDT SAT AUG 01 2009
VALID 021200Z - 031200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE DELMARVA INTO
CNTRL/ERN CAROLINAS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF CNTRL/ERN SD INTO
SWRN/W-CNTRL MN...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF SRN ORE...
...SYNOPSIS...
LARGE-SCALE PATTERN WILL REMAIN UNCHANGED THROUGH THE
PERIOD...FEATURING LONGWAVE TROUGH --ANCHORED BY VORTEX OVER JAMES
BAY-- OVER CNTRL/ERN CANADA INTO THE SERN STATES...AND REX BLOCK
OVER THE ERN PACIFIC/WRN N AMERICA. WITHIN THIS BROADER-SCALE
REGIME...SHORT WAVE TROUGH INITIALLY FROM THE UPPER GREAT LAKES INTO
CNTRL/SRN APPALACHIANS WILL TRANSLATE NEWD THROUGH THE LOWER GREAT
LAKES...NEW ENGLAND AND THE MID ATLANTIC STATES. MEANWHILE...NEXT
UPSTREAM SHORT WAVE TROUGH WILL PROGRESS SEWD THROUGH THE NRN PLAINS
AND UPPER GREAT LAKES.
AT THE SURFACE...COLD FRONT ASSOCIATED WITH FORMER SHORT WAVE TROUGH
MENTIONED ABOVE WILL SHIFT EWD FROM THE LOWER GREAT LAKES AND
APPALACHIANS TOWARD THE ATLANTIC COAST. FARTHER W...COLD FRONT
ATTENDANT TO LATTER-MENTIONED IMPULSE WILL SURGE SEWD THROUGH THE
NRN PLAINS AND UPPER MS VALLEY. A PRE-FRONTAL TROUGH WILL PRECEDE
THIS COLD FRONT...EXTENDING SWWD FROM LOW PRESSURE OVER THE RED
RIVER VALLEY --OF ND/MN-- INTO THE CNTRL/SRN HIGH PLAINS.
...NEW ENGLAND INTO THE CNTRL/ERN CAROLINAS...
SCATTERED TO NUMEROUS TSTMS ARE EXPECTED TO DEVELOP ALONG/AHEAD OF
COLD FRONT SUN AS FORCING FOR ASCENT ASSOCIATED WITH MIGRATORY SHORT
WAVE TROUGH ACTS ON A MOIST/UNSTABLE AIR MASS. THE STRONGEST
FORCING FOR ASCENT AND VERTICAL SHEAR WILL SPREAD EWD/NEWD FROM THE
LOWER GREAT LAKES THROUGH NEW ENGLAND IN CONJUNCTION WITH PRIMARY
VORTICITY LOBE. HOWEVER...FORECAST SOUNDINGS INDICATE THAT LAPSE
RATES WILL REMAIN WEAK WHICH WILL LIMIT MLCAPE TO LESS THAN 1000
J/KG. NONETHELESS...THE MORE INTENSE STORMS WILL REMAIN CAPABLE OF
SOME MARGINALLY SEVERE HAIL AND/OR LOCALLY STRONG WIND GUSTS.
FARTHER S...A WARMER AND MORE MOIST BOUNDARY LAYER WILL CONTRIBUTE
TO POCKETS OF MODERATE INSTABILITY /MLCAPE OF 1000-1500 J PER KG/
AHEAD OF COLD FRONT BY AFTERNOON. VERTICAL SHEAR WILL CONCURRENTLY
STRENGTHEN WITH APPROACH OF SHORT WAVE TROUGH WITH ENVIRONMENT
BECOMING SUPPORTIVE OF ORGANIZED STORM CLUSTERS CAPABLE OF DAMAGING
WINDS AND HAIL ACROSS THE PIEDMONT AND COASTAL PLAIN INTO SUN
EVENING.
...NRN PLAINS INTO UPPER MIDWEST...
WHILE BOUNDARY LAYER MOISTURE WILL REMAIN SOMEWHAT LIMITED /I.E.
DEWPOINTS IN THE UPPER 40S TO 50S/ AHEAD OF COLD FRONT...LAPSE RATES
WILL STEEPEN...YIELDING MLCAPE OF 500-1000 J/KG BY AFTERNOON.
STRONG DYNAMIC FORCING FOR ASCENT AND 40-50 KT OF DEEP NWLY SHEAR
WILL SUPPORT THE DEVELOPMENT OF SCATTERED STRONG/SEVERE STORMS ALONG
SURFACE FRONT BY MID/LATE AFTERNOON. THE PRESENCE OF DEEPLY MIXED
BOUNDARY LAYER CONDITIONS AND STEEP MIDLEVEL LAPSE RATES WILL
PROMOTE HAIL AND LOCALLY DAMAGING WIND GUSTS WITH THE STRONGEST
STORMS THROUGH SUN EVENING.
SOME POTENTIAL FOR HAIL MAY CONTINUE INTO SUN NIGHT EWD INTO WI AS
ELEVATED STORMS INCREASE IN COVERAGE ALONG NOCTURNAL LLJ.
...SRN ORE/NRN CA...
STEEP LAPSE RATES...MODERATE CONVECTIVE INSTABILITY /MLCAPE OF
1000-1500 J PER KG/ AND 30-40 KT DEEP SELY SHEAR WILL BE SUPPORTIVE
OF A FEW ORGANIZED...DIURNAL STORMS WITHIN NERN QUADRANT OF
DEEP-LAYER LOW OFF THE CA COAST. THE MORE INTENSE STORMS WILL BE
CAPABLE OF DAMAGING WIND GUSTS AND HAIL INTO SUN NIGHT.
...CNTRL/SRN HIGH PLAINS...
EML/STEEP MIDLEVEL LAPSE RATES WILL BE ADVECTED EWD OVER THE HIGH
PLAINS IN ADVANCE OF SHORT WAVE TROUGH DIGGING SEWD THROUGH THE NRN
PLAINS. THIS PROCESS WILL OCCUR BENEATH A MOISTENING BOUNDARY LAYER
E OF SURFACE TROUGH WITH AIR MASS BECOMING MODERATELY UNSTABLE WITH
MLCAPE OF 1500-2000 J/KG. WEAK MIDLEVEL IMPULSE NOW OVER SRN ID IS
FORECAST TO TRANSLATE SEWD THROUGH CO INTO WRN KS SUN...PROVIDING
BACKGROUND FORCING FOR ISOLATED STORM DEVELOPMENT.
CURRENT MODEL GUIDANCE SUGGESTS THAT VERTICAL SHEAR WILL REMAIN ON
THE MARGINS OF THAT SUPPORTIVE OF ORGANIZED/ROTATING UPDRAFTS. ONLY
LOW SEVERE PROBABILITIES WILL BE MAINTAINED IN THIS
FORECAST...THOUGH AN UPGRADE TO SLIGHT RISK MAY BE REQUIRED FOR WRN
KS INTO THE OK/TX PNHDLS IN SUBSEQUENT DAY ONE OUTLOOKS.
..MEAD.. 08/01/2009
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
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