| Categorical Graphic |
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| Probabilistic Tornado Graphic |
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| Probabilistic Damaging Wind Graphic |
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| Probabilistic Large Hail Graphic |
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SPC AC 011239
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0739 AM CDT FRI MAY 01 2009
VALID 011300Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE SRN PLAINS NEWD INTO
THE MS/LOWER OH VALLEYS...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF VA/NC...
...SYNOPSIS...
UPPER TROUGH WILL AMPLIFY SLIGHTLY ACROSS THE UPPER MS VALLEY/ GREAT
LAKES REGION...WHILE THE SRN BRANCH...WITH 30-40 KT MID LEVEL FLOW
AND EMBEDDED SHORTWAVE TROUGHS...REMAINS ACROSS THE SRN CONUS. THE
UPPER TROUGH WILL AID IN PUSHING A COLD FRONT RAPIDLY EWD INTO THE
NERN STATES/OH VALLEY THROUGH THE PERIOD...BUT THE WLY FLOW ALOFT
WILL SLOW THE SWD PROGRESSION OF THE FRONT ACROSS THE MID MS VALLEY
AND SRN PLAINS. ALSO OF CONVECTIVE IMPORTANCE WILL BE A
DRYLINE...EXPECTED BY LATE AFTERNOON TO EXTEND FROM NEAR THE COLD
FRONT IN FAR SWRN OK/NWRN TX SWD INTO THE ERN EDWARDS PLATEAU.
...SRN PLAINS...
MODERATE INSTABILITY AND DEEP LAYER SHEAR AT 30-40 KT IS LIKELY TO
MAINTAIN INTENSE STORMS ACROSS PORTIONS OF OK AND WRN AR THIS
MORNING. THOUGH HAIL IS THE PRIMARY THREAT...IF COLD POOLS CAN
DEVELOP...THE THREAT FOR WIND DAMAGE WOULD INCREASE. REFERENCE WW
220.
AS THE AIR MASS WARMS SOUTH OF THE FRONT/OUTFLOW BOUNDARIES...THE
COMBINATION OF 65-70 DEGREE DEWPOINTS AND STEEP LAPSE RATES WILL
RESULT IN STRONG INSTABILITY. THOUGH NO REAL DISCERNABLE SHORTWAVE
TROUGH IS EVIDENT IN WV IMAGERY OR MODELS...WEAK CAPPING AND
CONVERGENCE ALONG FRONT/DRYLINE/MORNING CONVECTIVE OUTFLOW
BOUNDARIES SHOULD PROVIDE SUFFICIENT LIFT FOR STORMS TO DEVELOP
DURING THE AFTERNOON HOURS. MOST LIKELY AREA FOR INTENSE STORM
DEVELOPMENT WILL BE NEAR THE INTERSECTION OF THE COLD FRONT/DRYLINE.
GIVEN THAT THE ATMOSPHERE WILL BE VERY UNSTABLE... MLCAPES
APPROACHING 4000 J/KG...AND DEEP LAYER AT 30-40 KT... STORMS THAT
DEVELOP ARE LIKELY TO BECOME QUICKLY SEVERE AND EVOLVE INTO
SUPERCELLS. STEEP LAPSE RATES AND THE DEGREE OF INSTABILITY INDICATE
BASEBALL OR BIGGER HAIL IS POSSIBLE WITH THESE STORMS. ALSO...THE
MOIST BOUNDARY LAYER AND STRONGLY CURVED HODOGRAPHS IN THE LOWER 1-2
KM WOULD SUPPORT TORNADOES. THE STRONG INSTABILITY AND RESULTANT
COLD POOLS MAY RESULT IN AN MCS...WITH THE POTENTIAL FOR BOWS/LINE
SEGMENTS TO SHIFT EWD ACROSS FAR SRN OK/NRN TX OVERNIGHT. THE LACK
OF STRONGER DYNAMICAL FORCING AND THE UNCERTAINTY REGARDING COVERAGE
PRECLUDES A MODERATE RISK ISSUANCE ATTM.
OVERNIGHT...STRONG SHORTWAVE TROUGH IS FORECAST TO MOVE INTO NM
TONIGHT...INDUCING A 30-40 KT LOW LEVEL JET OVER THE SLOW MOVING
COLD FRONT. THIS WILL RESULT IN WIDESPREAD PRECIPITATION AND
ELEVATED THUNDERSTORMS TO DEVELOP ACROSS OK OVERNIGHT. MUCAPES NEAR
2000 J/KG AND EFFECTIVE SHEAR AT 40 KT WOULD FAVOR ELEVATED
SUPERCELL STRUCTURES WITH SEVERE HAIL THE PRIMARY THREAT.
...MID MS/TN AND LOWER OH VALLEYS...
A MOIST AND UNSTABLE AIR MASS WILL BE FAVORABLE FOR THUNDERSTORMS
FORMING ALONG/AHEAD OF THE FRONT THIS AFTERNOON AND EVENING. MLCAPES
FROM 1000-2000 J/KG AND DEEP LAYER SHEAR AT 30 KT INDICATES THAT
MULTICELL STORMS WITH ISOLATED HAIL AND WIND DAMAGE WOULD THE MAIN
THREATS...MAINLY BETWEEN 18Z AND 01Z.
..MID-ATLANTIC REGION...
AT EARLY MORNING...UPPER CIRCULATION WAS LOCATED IN FAR WRN WV...
WITH TRAILING TROUGH EXTENDING SWD TO NEAR THE TN/NC BORDER. A SMALL
LINE OF CONVECTION WAS ASSOCIATED WITH THIS FEATURE AND IS TO REACH
CENTRAL/ERN VA BY MID DAY. THOUGH MID LEVEL LAPSE RATES WILL BE WEAK
AND CLOUDS WILL BE SLOW TO CLEAR...TEMPERATURES WARMING INTO THE 70S
SHOULD YIELD MLCAPES AROUND 1000 J/KG. THIS INSTABILITY ALONG WITH
UNIDIRECTIONAL WLY WINDS AT 30-40 KT BETWEEN 850-300 MB SHOULD BE
SUFFICIENT FOR SPORADIC WIND DAMAGE WITH THE LINE...BEFORE EXITING
INTO THE ATLANTIC BY LATE AFTERNOON.
..IMY.. 05/01/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z