SPC AC 270536
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1236 AM CDT THU AUG 27 2009
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN ND INTO NWRN MN...
...ERN ND THROUGH NWRN MN...
A SHORTWAVE TROUGH CURRENTLY MOVING THROUGH SRN ALBERTA IS IN THE
PROCESS OF CRESTING UPPER RIDGE AND WILL TURN SEWD...REACHING THE
NRN PLAINS AND UPPER MS VALLEY THURSDAY AFTERNOON AND EVENING
ACCOMPANIED BY A COLD FRONT. IN-SITU MOISTURE WITH BOUNDARY LAYER
DEWPOINTS IN THE LOW TO MID 50S WILL PERSIST IN PRE-FRONTAL WARM
SECTOR. A PLUME OF 7-8 C/KM 850-500 MB LAPSE RATES WILL ADVECT EWD
ABOVE THE WARM SECTOR...AND AS DIABATIC HEATING COMMENCES MLCAPE
FROM 500-1000 J/KG WILL BE POSSIBLE. OWING TO THE EWD ADVECTION OF
THE EML...THE ATMOSPHERE WILL LIKELY REMAIN CAPPED TO SURFACE BASED
STORMS MOST OF THE DAY. HOWEVER...INCREASING FORCING FOR ASCENT AND
THERMAL TROUGH ATTENDING THE SEWD ADVANCING IMPULSE MAY CONTRIBUTE
TO SUFFICIENT EROSION OF THE CAP FOR AT LEAST ISOLATED TO WIDELY
SCATTERED STORMS TO INITIATE IN FRONTAL ZONE BY LATE AFTERNOON. A
40+ KT MID LEVEL JET ACCOMPANYING THE SHORTWAVE TROUGH WILL RESULT
IN BULK SHEAR SUPPORTIVE OF UPDRAFT ROTATION...WHICH IN CONJUNCTION
WITH THE STEEP LAPSE RATES AND COOL TEMPERATURES ALOFT WILL SUPPORT
A THREAT FOR LARGE HAIL. ANY SEVERE THREAT WILL WANE TOWARD MID
EVENING AS THE BOUNDARY LAYER STABILIZES.
...SERN THROUGH N CNTRL TX...
THE ATMOSPHERE WILL LIKELY ONCE AGAIN BECOME MODERATELY UNSTABLE
ALONG MOIST AXIS ACROSS ERN TX. POTENTIAL WILL EXIST FOR STORMS TO
REDEVELOP ALONG AND SOUTH OF FRONT OR RESIDUAL OUTFLOW BOUNDARIES
DURING THE DAY. A FEW STORMS MAY BECOME CAPABLE OF PRODUCING
ISOLATED STRONG WIND GUSTS AND HAIL...BUT MODEST MID LEVEL LAPSE
RATES AND VERTICAL SHEAR WILL SERVE AS LIMITING FACTORS FOR A MORE
ROBUST SEVERE THREAT.
..DIAL/GARNER.. 08/27/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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