SPC AC 241618
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1118 AM CDT THU JUL 24 2008
VALID 241630Z - 251200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE NRN AND
CENTRAL PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF NEW ENGLAND...
...THERE IS A SLGT RISK OF SVR TSTMS OVER S TX...
...SYNOPSIS...
UPPER TROUGH NERN U.S. WILL GRADUALLY FILL AND SHIFT NEWD ACROSS NEW
ENGLAND. UPSTREAM S/WV TROUGH MT MOVES ACROSS NRN PLAINS TONIGHT.
T.S. DOLLY CONTINUES TO WEAKEN AS IT CROSSES LOWER RIO GRANDE VALLEY
INTO NERN MEXICO.
...NERN U.S...
REF MCD 1891
WILL CONTINUE WITH A LOW END SLIGHT RISK AHEAD OF THE COLD FRONT
ACROSS NEW ENGLAND THRU THIS AFTERNOON. HOWEVER THE COMBINATION OF
CLOUDINESS...WEAK LAPSE RATES AND MERIDIONAL FLOW WILL LIMIT THE
THREAT. WITH THE STRONG SLY UNIDIRECTIONAL FLOW AND POTENTIALLY
MLCAPES FROM 500-800 J/KG IN WHAT AREAS OF HEATING CAN
DEVELOP...WIND DAMAGE WILL BE POSSIBLE. SHORT TERM THREAT WILL BE
ALONG THE N/S PRE-FRONTAL BAND OF CONVECTION NOW MOVING SLOWLY EWD
SRN NH TO RI...WITH AN ADDITIONAL CONCERN POSSIBLY DEVELOPING ALONG
AND AHEAD OF THE COLD FRONT. THE FRONT SHOULD MOVE FROM ITS CURRENT
POSITION OVER ERN NY ACROSS SLOWLY EWD ACROSS NEW ENGLAND OVERNIGHT.
ANY SEVERE WITH THE FRONT DEPENDENT ON HOW MUCH
HEATING/DESTABILIZATION CAN OCCUR.
THE WEAK UPPER LOW WRN NY WILL LIFT NEWD AND OPEN INTO A TROUGH.
WHILE SHEAR IS GENERALLY WEAK THIS AREA...THE COOL MID LEVEL TEMPS
AND LAPSE RATES NEAR 7C/KM ALONG WITH MLCAPES AOA 500 J/KG WILL
SUPPORT A MARGINAL HAIL AND DAMAGING WIND THREAT.
...CENTRAL U.S...
OVERNIGHT MCS ACTIVITY GRADUALLY WEAKENING ACROSS IA/MO THIS AM.
EFFECTIVE OUTFLOW BOUNDARIES WILL SET UP FOR THE AFTERNOON FROM
CENTRAL MO NWWD INTO ERN NEB. A WEAK COOL FRONT ACCOMPANYING THE MT
S/WV TROUGH WILL MOVE TO CENTRAL ND SWWD INTO NERN WY BY LATER THIS
AFTERNOON. MOISTURE AND INSTABILITY WILL BE MORE THAN SUFFICIENT
VICINITY OF BOTH OUTFLOW AND FRONTAL BOUNDARIES FOR STRONG/SEVERE
THUNDERSTORM DEVELOPMENT BY MID/LATE AFTERNOON. MLCAPES WILL RANGE
DOWNWARD FROM AROUND 3000 J/KG IN THE VERY MOIST AIRMASS VICINITY
OUTFLOW BOUNDARY NEB/IA/MO TO 1500 J/KG IN THE HIGH PLAINS FROM SERN
MT/ERN WY EWD.
THE STRONGER UPPER SUPPORT AND MID LEVEL WINDS WITH THE MT S/W
TROUGH WILL PASS TO THE NORTH OF THE MORE FAVORABLE THERMODYNAMIC
ENVIRONMENT. THUS SEVERE THUNDERSTORMS ARE EXPECTED TO BE FOCUSED
NEAR THE SURFACE BOUNDARIES AND THE MODE EXPECTED TO BE PRIMARILY
MULTICELLULAR WITH SHORT LIVED SUPERCELLS. SEVERE THREAT SHOULD BE
HIGHLY DIURNAL GIVEN THE LIMITED DEEP LAYER SHEAR AND WARM MID
LEVELS.
AS NOCTURNAL LLJ INCREASES STORM MODE WILL LIKELY EVOLVE INTO ONE OR
MORE MCS/S TONIGHT VICINITY MO VALLEY. SEVERE THREAT BY THAT TIME
SHOULD BE LIMITED TO STRONG WINDS DRIVEN BY ANY COLD POOL
DEVELOPMENT.
WEAK UPSLOPE DEVELOPS INTO SERN MT/ERN WY MAINTAINING SUFFICIENT LOW
LEVEL MOISTURE TO FUEL STRONG SEVERE THUNDERSTORMS OFF THE HIGHER
TERRAIN. WITH STEEP LAPSE RATES AND MLCAPES AOA 1500 ALONG WITH
30-40 KT OF SHEAR CONDITION WILL SUPPORT SUPERCELL DEVELOPMENT.
LARGE HAIL AND DAMAGING DOWNBURST WINDS WILL BE THE PRIMARY THREAT
WITH ANY TORNADO OCCURRENCE BEING ISOLATED AND BRIEF GIVEN EXPECTED
HIGH BASES AND MARGINAL UPPER SUPPORT.
...MN LATE THIS AFTN/EARLY EVE...
A NARROW AXIS OF MODERATE INSTABILITY /SBCAPE TO 1500 J PER KG/ WILL
DEVELOP WITH SFC HEATING TODAY ALONG OLD COLD/OCCLUDED FRONT IN MN.
LIGHT SLY FLOW AHEAD OF FRONT WILL BOOST SFC DEWPOINTS INTO THE MID
60S F. FORCING FOR ASCENT WILL BE WEAK...THUS EXPECT EXISTING WARM
NOSE TO PERSIST AROUND 700 MB. BUT CONVERGENCE AND HEATING MAY
SPARK A FEW STORMS ALONG THE BOUNDARY. GIVEN 35 KT WNWLY MID LVL
FLOW...SETUP COULD YIELD A CONDITIONAL THREAT FOR STORMS WITH ISOLD
DMGG WIND AND HAIL.
...S TX TODAY/TONIGHT...
REMNANTS OF TROPICAL STORM DOLLY FCST TO CONTINUE WNW INTO NE
MEXICO. SUFFICIENT SHEAR IN THE 0-1 KM LAYER LIKELY WILL PERSIST
N OF THE CENTER TO MAINTAIN A THREAT OF LOW LEVEL MESOCYCLONES
AND ISOLD TORNADOES. THIS THREAT SHOULD BE GREATEST ALONG THE OUTER
EDGE OF THE SYSTEM...WHERE HEATING WILL BE GREATEST AND WHERE ASCENT
MAY BE ENHANCED ALONG WEAK ARC OF CONFLUENCE EXTENDING N/NE FROM
CIRCULATION CENTER ALONG THE S TX CSTL PLN.
THE SVR THREAT SHOULD DIMINISH TONIGHT AS BOUNDARY LAYER COOLS AND
DOLLYS CIRCULATION WEAKENS.
..HALES/SMITH.. 07/24/2008
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