SWODY1
SPC AC 250543
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1243 AM CDT FRI SEP 25 2009
VALID 251200Z - 261200Z
...NO SVR TSTM AREAS FORECAST...
...SYNOPSIS...
MODEL CONSENSUS IS THAT UPPER LOW OVER THE CNTRL U.S. WILL FINALLY
BEGIN TO TRANSITION INTO AN OPEN WAVE AND EJECT ENEWD TOWARD INTO
THE MID MS VALLEY REGION IN RESPONSE TO A STRONG IMPULSE MOVING INTO
SWRN CANADA. VORT MAX NOW LOCATED OVER NEB WILL ROTATE AROUND WRN
PERIPHERY OF UPPER LOW INTO ERN CO BEFORE TURNING SEWD INTO WRN KS
FRIDAY AFTERNOON. THIS FEATURE WILL BE ACCOMPANIED BY A LOW LEVEL
CONVERGENCE BOUNDARY THAT WILL BE THE FOCUS FOR ADDITIONAL
THUNDERSTORM DEVELOPMENT ACROSS KS.
...KS THROUGH NWRN OK...
SURFACE AND UPPER AIR DATA FROM THURSDAY EVENING INDICATE THE RICHER
LOW LEVEL MOISTURE IS CONFINED TO SRN TX...THE LOWER MS VALLEY AND
SERN STATES. OWING TO THE EQUIVALENT BAROTROPIC NATURE OF THE UPPER
LOW...RESPONSE IN THE LOWER LEVELS WILL LIKELY REMAIN WEAK WITH
LIMITED MOISTURE RETURN. SUFFICIENT DIABATIC WARMING IS EXPECTED TO
DESTABILIZE THE ATMOSPHERE WITH UPPER 40S DEWPOINTS CHARACTERISTIC
OF THE WELL MIXED BOUNDARY LAYER. DIABATIC HEATING AND COLD AIR
ALOFT WITH -15C TO -18C AT 500 MB WILL RESULT IN STEEP LAPSE
RATES...BUT MODEST LOW LEVEL MOISTURE WILL LIMIT MLCAPE TO AOB 500
J/KG. THUNDERSTORMS ARE EXPECTED TO INCREASE IN COVERAGE ALONG AND
JUST AHEAD OF SURFACE BOUNDARY WITHIN ZONE OF DEEPER LIFT ASSOCIATED
WITH VORT MAX ROTATING SEWD THROUGH ERN CO AND WRN KS. MID LEVEL JET
ATTENDING THE VORT MAX MAY RESULT IN SUFFICIENT /30-40 KT/ BULK
SHEAR FOR SOME UPDRAFTS TO DEVELOP ROTATION...WHICH IN CONJUNCTION
WITH THE STEEP LAPSE RATES WILL CONTRIBUTE TO A THREAT FOR ISOLATED
LARGE HAIL. AN ISOLATED BRIEF TORNADO OR TWO CANNOT BE RULED OUT
WITHIN THIS ENVIRONMENT. STORMS WILL LIKELY WEAKEN DURING THE EARLY
EVENING WITH THE ONSET OF NOCTURNAL COOLING. THE EXPECTED MARGINAL
INSTABILITY COULD POSE A LIMITING FACTOR FOR A MORE ROBUST SEVERE
THREAT...AND WILL THEREFORE MAINTAIN LOW SEVERE PROBABILITIES.
HOWEVER...THIS AREA WILL CONTINUE TO BE MONITORED FOR A POSSIBLE
SLIGHT RISK IN LATER OUTLOOKS.
...LOWER MS VALLEY THROUGH TN VALLEY AND SRN OH VALLEY...
WIDELY SCATTERED TO SCATTERED THUNDERSTORMS ARE EXPECTED TO
REDEVELOP FRIDAY WITHIN THE MOIST BUT WEAKLY CAPPED WARM SECTOR OVER
THE SERN STATES. STRONGER FLOW ALOFT ASSOCIATED WITH THE UPPER LOW
WILL REMAIN WEST OF THE MOIST AXIS DURING THE DAY AND THIS WILL TEND
TO LIMIT ANY POTENTIAL FOR ORGANIZED SEVERE STORMS.
HOWEVER...AS THE UPPER LOW BEGINS TO TRANSITION TO AN OPEN WAVE AND
SHIFT EAST OVERNIGHT...STRONGER UPPER FLOW WILL BEGIN TO INTERCEPT
THE WRN PERIPHERY OF THE MOIST SECTOR. MODELS INDICATE THAT
CONVECTION WILL LIKELY INCREASE LATE FRIDAY NIGHT AS IMPULSE
ROTATING THROUGH BASE OF UPPER TROUGH OVERTAKES THE MOIST AXIS.
THERE IS SOME CONCERN THAT BULK SHEAR MAY BECOME SUFFICIENT FOR A
FEW STORMS TO DEVELOP UPDRAFT ROTATION WITH BOWING SEGMENTS.
HOWEVER...LIMITED LOW LEVEL RESPONSE WITH WEAK FLOW THROUGH 700
MB...WEAK LAPSE RATES AND A STABLE SURFACE LAYER WILL PROBABLY SERVE
AS LIMITING FACTORS FOR AN ORGANIZED SEVERE THREAT.
..DIAL/SMITH.. 09/25/2009
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