SPC AC 311959
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0259 PM CDT SAT MAY 31 2008
VALID 312000Z - 011200Z
...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF VA...MD AND SRN
NJ...
...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF SRN KS AND NRN
OK...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
PLAINS...MID MS VALLEY AND ERN SEABOARD...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE UPPER MS
VALLEY...
...MID-ATLANTIC...
WATER VAPOR SHOWS AN UPPER-LEVEL TROUGH OVER THE OH VALLEY WITH A
DRYSLOT ADVANCING EWD ACROSS THE CNTRL APPALACHIAN MTNS. THIS
FEATURE WILL CONTINUE EWD INCREASING LARGE-SCALE ASCENT ACROSS THE
REGION THIS AFTERNOON. MODERATE INSTABILITY HAS DEVELOPED SOUTH OF
AN MCS ONGOING ACROSS NRN VA...MD AND DE WITH RUC OBJECTIVE GUIDANCE
SUGGESTING MLCAPE VALUES RANGE FROM 2000 TO 3000 J/KG FROM ERN VA
SSWWD INTO ERN NC. INCREASING INSTABILITY...ASCENT AND LOW-LEVEL
CONVERGENCE ALONG A SFC TROUGH EAST OF THE APPALACHIANS SHOULD
RESULT IN NUMEROUS THUNDERSTORMS BY LATE AFTERNOON ACROSS THE WARM
SECTOR. FORECAST SOUNDINGS AND WSR-88D VWPS SHOW ABOUT 40 KT OF
VERTICAL SHEAR WHICH SHOULD BE SUFFICIENT FOR SEVERE MULTICELL LINE
SEGMENTS AND A FEW SUPERCELLS. IN ADDITION...RUC OBJECTIVE GUIDANCE
SHOWS A BROAD ILL-DEFINED 25 TO 35 KT LOW-LEVEL JET ACROSS THE
REGION AND FLOW HAS INCREASED IN THE ATLANTIC COASTAL PLAINS OVER
THE LAST 2 TO 3 HOURS. THIS COMBINED WITH STEEPENING LOW-LEVEL LAPSE
RATES SHOULD BE FAVORABLE FOR WIND DAMAGE AS SEVERAL LINE SEGMENTS
DEVELOP AND ORGANIZE LATE THIS AFTERNOON INTO EARLY THIS EVENING. A
FEW TORNADOES MAY ALSO OCCUR WITH SUPERCELLS WHERE THE COMBINATION
OF LOW-LEVEL SHEAR AND INSTABILITY IS MAXIMIZED. THE SEVERE THREAT
SHOULD GRADUALLY EXPAND SWWD INTO THE CAROLINAS ALTHOUGH CONVECTIVE
COVERAGE SHOULD BE LESS DUE TO DRYER MID-LEVEL AIR AND WEAKER
LARGE-SCALE ASCENT.
FURTHER NORTH ACROSS PA...NJ AND NY...INSTABILITY REMAINS WEAK WITH
RUC DATA SUGGESTING MLCAPE VALUES ARE ONLY IN THE 250 TO 500 J/KG
RANGE. EVEN SO...STRONG LARGE-SCALE ASCENT ASSOCIATED WITH THE
APPROACHING UPPER-LEVEL TROUGH AND SFC HEATING WILL SUPPORT
CONTINUED DEVELOPMENT OF SCATTERED THUNDERSTORMS THIS AFTERNOON. THE
AREA IS LOCATED JUST NORTH OF A BROAD 50 TO 60 KT MID-LEVEL JET AND
THE STRONG VERTICAL SHEAR ASSOCIATED WITH THIS FEATURE WILL BE
SUFFICIENT FOR A FEW SUPERCELLS ALONG WITH SEVERE MULTICELL LINE
SEGMENTS. WIND DAMAGE AND HAIL WILL LIKELY BE THE PRIMARY THREATS
WITH THE ACTIVITY.
...SRN PLAINS/OZARK REGION/CNTRL HIGH PLAINS...
A SMALL CLUSTER OF THUNDERSTORMS IS ONGOING IN THE WRN OZARKS AND IS
ASSOCIATED WITH A SHORTWAVE TROUGH EVIDENT ON WATER VAPOR IMAGERY.
THIS CLUSTER SHOULD CONTINUE EWD INTO THE MID-MS VALLEY SUSTAINED BY
A CENTER OF MODERATE INSTABILITY /MLCAPE VALUES OF 2000 TO 2500
J/KG/ OVER NE AR INDICATED BY RUC OBJECTIVE GUIDANCE. A BROAD 45 TO
55 KT MID-LEVEL JET IS ORIENTED WEST TO EAST ACROSS THE REGION AND
THIS SHOULD SUPPORT SUPERCELLS AND BOWING LINE SEGMENTS WITHIN THE
CLUSTER FOR SEVERAL MORE HOURS. ADDITIONAL THUNDERSTORMS SHOULD ALSO
INITIATE EWD ALONG AN AXIS OF LOW-LEVEL CONVERGENCE ACROSS WRN TN
AND WRN KY. DUE TO STEEP LOW-LEVEL LAPSE RATES...STRONG INSTABILITY
AND HIGH SFC DEWPOINTS IN THE LOWER 70S F...THE STORMS SHOULD HAVE A
WIND DAMAGE THREAT. SUPERCELLS WILL ALSO BE CAPABLE OF PRODUCING
LARGE HAIL.
FURTHER WEST ACROSS THE SRN PLAINS...OBJECTIVE GUIDANCE CURRENTLY
INDICATES A CAPPING INVERSION IN PLACE ACROSS THE REGION. SHORT-TERM
MODEL FORECASTS GRADUALLY WEAKEN THE CAP BY EARLY THIS EVENING WITH
SCATTERED TO NUMEROUS THUNDERSTORMS INITIATING ALONG AN AXIS OF
LOW-LEVEL CONVERGENCE IN NRN OK AND SRN KS. STRONG INSTABILITY
ALREADY EXISTS WITH MLCAPE VALUES IN THE 2500 TO 3500 J/KG MAINLY
ACROSS OK. THIS SHOULD FUEL AN MCS WHICH SHOULD TRACK ESEWD ALONG
THE INSTABILITY GRADIENT THIS EVENING.
CONCERNING THE SEVERE POTENTIAL...FORECAST SOUNDINGS ACROSS THE
MODERATE RISK AREA SHOW A FAVORABLE SHEAR ENVIRONMENT FOR SUPERCELLS
WITH SUBSTANTIAL VEERING BELOW 700 MB AND 50 KT OF FLOW AT 500 MB.
SUPERCELLS WILL BE CAPABLE OF PRODUCING VERY LARGE HAIL DUE TO A
PLUME OF STEEP MID-LEVEL LAPSE RATES EXTENDING NEWD FROM WEST TX
INTO NCNTRL OK. AS THE LOW-LEVEL JET INCREASES EARLY THIS
EVENING...LOW-LEVEL SHEAR WILL BECOME FAVORABLE FOR A FEW TORNADOES.
THE WIND DAMAGE THREAT APPEARS LIKELY TO BE THE GREATEST EWD ACROSS
THE OZARKS AS AN MCS BECOMES ORGANIZED LATE THIS EVENING INTO THE
OVERNIGHT PERIOD. THE STRONG INSTABILITY SHOULD ALLOW THE SEVERE
THREAT TO PERSIST THROUGH LATE IN THE PERIOD.
FURTHER NORTHWEST ACROSS ERN CO...THUNDERSTORMS SHOULD INITIATE IN
THE HIGHER TERRAIN. ALTHOUGH INSTABILITY WILL BE RELATIVELY
WEAK...STEEP MID-LEVEL LAPSE RATES AND STRONG VERTICAL SHEAR SHOULD
SUPPORT A THREAT FOR ISOLATED ROTATING STORMS WITH HAIL AND STRONG
GUSTY WINDS POSSIBLE.
...UPPER MS VALLEY...
NORTHWEST FLOW WILL BE IN PLACE THIS AFTERNOON ACROSS THE REGION AS
A SHORTWAVE TROUGH EVIDENT ON WATER VAPOR IMAGERY APPROACHES THE
REGION. INCREASING LARGE-SCALE ASCENT WITH THIS FEATURE AND SFC
HEATING SHOULD ALLOW STORM COVERAGE TO INCREASE LATE THIS AFTERNOON
MOVING SEWD ALONG A GRADIENT OF MODERATE INSTABILITY FROM WRN MN
INTO ERN IA AND SWRN WI. ALTHOUGH FORECAST SOUNDINGS SUGGEST THE
SHEAR ENVIRONMENT IS ON THE LOW SIDE FOR SUPERCELLS...COLD AIR ALOFT
AND STEEP MID-LEVEL LAPSE RATES SHOULD SUPPORT A THREAT FOR ISOLATED
LARGE HAIL. UNIDIRECTIONAL LOW-LEVEL WINDS AND STEEP LOW-LEVEL LAPSE
RATES MAY ALSO SUPPORT A THREAT FOR ISOLATED WIND DAMAGE WITH THE
STRONGER CELLS.
..BROYLES.. 05/31/2008
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