SWODY1
SPC AC 240121
DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0821 PM CDT WED JUL 23 2008
VALID 240100Z - 241200Z
...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE NRN AND CNTRL
PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF THE MID ATLANTIC
INTO THE NERN STATES...
...THERE IS A SLGT RISK OF SVR TSTMS OVER S TX...
CORRECTED FOR TX PORTION OF DISCUSSION
...NRN AND CNTRL PLAINS AREA...
ISOLATED STORMS HAVE DEVELOPED ALONG FRONTAL BOUNDARY FROM CNTRL ND
SWD THROUGH N CNTRL SD WHERE THE ATMOSPHERE HAS DESTABILIZED IN A
NARROW CORRIDOR WITH MLCAPE FROM 1500 TO 2000 J/KG. MID-UPPER LEVEL
TEMPERATURES ARE FAIRLY WARM WITH -6 C AT 500 MB WHICH IS LIMITING
700 TO 500 MB LAPSE RATES TO AOB 7 C/KM. HOWEVER...SELY LOW LEVEL
FLOW BENEATH A BELT OF 35-40 KT 500 MB WINDS ASSOCIATED WITH A
SHORTWAVE TROUGH MOVING EWD ALONG THE U.S./CANADIAN BORDER IS
RESULTING IN 40-50 KT BULK SHEAR SUPPORTIVE OF SUPERCELLS. LOW LEVEL
HODOGRAPHS WITH EFFECTIVE STORM RELATIVE HELICITY OF 150-200 M2/S2
WILL SUPPORT A SMALL WINDOW OF OPPORTUNITY FOR AN ISOLATED TORNADO
OR TWO BEFORE THE BOUNDARY LAYER DECOUPLES LATER THIS EVENING.
OTHERWISE...LARGE HAIL SHOULD BE THE PRIMARY THREAT.
OTHER STORMS THAT DEVELOPED OVER THE HIGH PLAINS CONTINUE ACROSS WRN
NEB AND SWRN SD WHERE THE ATMOSPHERE IS MODERATELY UNSTABLE AND
LAPSE RATES ARE STEEP. ISOLATED DAMAGING WIND AND LARGE HAIL APPEAR
TO BE THE PRIMARY THREATS WITH THIS ACTIVITY. STORMS ARE EXPECTED TO
DEVELOP FARTHER EWD ACROSS CNTRL AND ERN NEB AND SPREAD INTO SERN SD
AND WRN IA LATER TONIGHT AS DEVELOPING SLY LOW LEVEL JET ENHANCES
LIFT IN VICINITY OF NW-SE ORIENTED BAROCLINIC ZONE. THIS ACTIVITY
WILL POSE A THREAT FOR ISOLATED LARGE HAIL AND DAMAGING WIND.
...NERN STATES...
COLD FRONT EXTENDS FROM W CNTRL NY SSWWD TO ALONG THE APPALACHIANS.
A WARM FRONT EXTENDS FROM SRN NEW ENGLAND WWD TO CNTRL NY WHERE IT
INTERSECTS THE FRONT. THIS BOUNDARY MAY SHIFT SLOWLY NWD OVERNIGHT
WHILE THE COLD FRONT MOVES SLOWLY EWD. THE MOIST WARM SECTOR EAST OF
THE COLD FRONT REMAINS MARGINALLY TO MODERATELY UNSTABLE...BUT THE
ONGOING CONVECTION IS EXHAUSTING THE INSTABILITY. LATER TONIGHT THE
LOW LEVEL JET IS FORECAST TO STRENGTHEN TO IN EXCESS OF 50 KT FROM
ERN NY INTO SRN NEW ENGLAND WITHIN ZONE OF ASCENT AND HEIGHT FALLS
ASSOCIATED WITH A VORT MAX THAT WILL EJECT NEWD TOWARD THIS REGION
FROM BASE OF LARGER SCALE UPPER TROUGH. SIZE OF LOW LEVEL HODOGRAPHS
WILL INCREASE...AND THIS WILL MAINTAIN A THREAT FOR EMBEDDED
SUPERCELLS AND BOWING STRUCTURES CAPABLE OF PRODUCING ISOLATED
TORNADOES AND DAMAGING WIND DESPITE THE INCREASINGLY MARGINAL
INSTABILITY.
...CAROLINAS THROUGH MID ATLANTIC...
THREAT FOR ISOLATED DAMAGING WIND AND HAIL WILL PERSIST THROUGH 03Z
WITH LINE OF STORMS MOVING EWD FROM CNTRL NC NWD THROUGH CNTRL VA.
HOWEVER...INSTABILITY AXIS DOWNSTREAM FROM THIS ACTIVITY IS NARROW
DUE TO PREVIOUS WIDESPREAD CONVECTION WHICH HAS STABILIZED THE
BOUNDARY LAYER FROM ERN NC THROUGH ERN VA. THIS SUGGEST THE STORMS
SHOULD BEGIN A DECREASING TREND LATER THIS EVENING.
...S TX...
DOLLY IS CENTERED JUST NORTH OF BROWNSVILLE AND CONTINUES TO MOVE
SLOWLY WWD. SURFACE AND VWP DATA SHOW SUFFICIENT VERTICAL SHEAR FOR
LOW LEVEL MESOCYCLONES WITH STORMS DEVELOPING WITHIN OUTER BANDS
NORTH OF CENTER. THE PRIMARY LIMITING FACTOR HAS BEEN AND WILL
CONTINUE TO BE THE MARGINAL THERMODYNAMIC ENVIRONMENT.
...NRN ROCKIES THROUGH MT...
INCREASING LARGE SCALE ASCENT ASSOCIATED WITH A SHORTWAVE TROUGH
MOVING EWD THROUGH THE NRN ROCKIES WILL SUPPORT THUNDERSTORM
DEVELOPMENT THIS EVENING AND TONIGHT. LATEST OBSERVED DATA SHOW
INSTABILITY IS MARGINAL IN THIS REGION DUE TO LIMITED LOW LEVEL
MOISTURE WITH DEWPOINTS MOSTLY IN THE 40S. HOWEVER...STEEP LAPSE
RATES...INVERTED-V BOUNDARY LAYERS AND BULK SHEAR AROUND 40 KT WILL
SUPPORT A THREAT OF ISOLATED DAMAGING WIND AND HAIL WITH THE
STRONGER STORMS. THE MODEST INSTABILITY SUGGEST THE SEVERE EVENTS
SHOULD REMAIN TOO ISOLATED FOR A CATEGORICAL RISK...BUT WILL
MAINTAIN 5% SEVERE PROBABILITIES IN THIS REGION.
..DIAL.. 07/24/2008
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