SPC AC 100542
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1242 AM CDT MON AUG 10 2009
VALID 101200Z - 111200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE CNTRL HIGH PLAINS INTO
THE NERN STATES...
...SYNOPSIS...
SHORT WAVE TROUGH CURRENTLY OVER THE DAKOTAS WILL CONTINUE EWD TODAY
THROUGH THE GREAT LAKES REGION. AS THIS OCCURS...VORTICITY MAXIMUM
OVER THE MID MS VALLEY WILL BECOME ENTRAINED IN QUASI-ZONAL FLOW
REGIME OVER THE OH VALLEY WITH THIS FEATURE ACCELERATING EWD THROUGH
THE MID ATLANTIC STATES. UPSTREAM...A WEAK IMPULSE IS FORECAST TO
SHIFT EWD FROM THE CNTRL ROCKIES INTO CNTRL PLAINS.
AT THE SURFACE...SYNOPTIC COLD FRONT WILL SAG SEWD THROUGH THE GREAT
LAKES WITH TRAILING EXTENSION OF BOUNDARY STALLING OVER THE CNTRL
HIGH PLAINS. THE COLD FRONT AND PRE-EXISTING OUTFLOW BOUNDARIES ARE
EXPECTED TO SERVE AS THE PRIMARY FOCI FOR STRONG TO SEVERE STORM
DEVELOPMENT THIS AFTERNOON INTO TONIGHT.
...MID MS VALLEY INTO THE NERN STATES...
PRE-FRONTAL TSTM CLUSTERS ARE EXPECTED TO BE ONGOING AT THE ONSET OF
THE FORECAST PERIOD FROM PORTIONS OF THE GREAT LAKES AND OH VALLEY
INTO THE MID ATLANTIC STATES. THIS ACTIVITY MAY TEND TO DECREASE IN
COVERAGE THROUGH THE MORNING WITH THE DIURNAL WEAKENING OF NOCTURNAL
LLJ. HOWEVER...THE IMPACTS OF RESIDUAL CLOUD DEBRIS AND CONVECTIVE
OUTFLOW CAST CONSIDERABLE UNCERTAINTY ON THE TIMING AND LOCATION OF
SUBSEQUENT AFTERNOON STORM DEVELOPMENT.
CURRENT THINKING IS THAT PREFERRED ZONE OF INITIATION MAY BE
DISPLACED TO THE S OF COLD FRONT /AND STRONGER FORCING ASSOCIATED
WITH SHORT WAVE TROUGH/ OVER THE OH VALLEY ALONG COLLECTIVE OUTFLOW
BOUNDARY REMNANT FROM NOCTURNAL TSTMS. AIR MASS ALONG AND S OF THIS
BOUNDARY SHOULD REMAIN QUITE MOIST WITH DEWPOINTS OF 65-75
F...CONTRIBUTING TO MLCAPE APPROACHING 1500-2500 J/KG. BELT OF
MODEST /30-40 KT/ WLY MIDLEVEL FLOW WILL ATTEND SHORT WAVE TROUGH
THROUGH THE REGION WITH FORECAST HODOGRAPHS EXHIBITING DEEP WLY FLOW
WITH 30-40 KT OF DEEP-LAYER SHEAR. GIVEN SETUP WILL FAVOR STORM
MODES SIMILAR TO SUNDAY...FEATURING EMBEDDED BOWING STRUCTURES
CAPABLE OF DAMAGING WINDS AND PERHAPS SOME HAIL.
...CNTRL PLAINS...
A MOIST BOUNDARY LAYER /DEWPOINTS IN THE 50S TO LOWER 60S/ WILL BE
MAINTAINED N OF STATIONARY BOUNDARY WHERE DAYTIME HEATING AND ERN
EXTENSION OF EML WILL CONTRIBUTE TO A MODERATELY UNSTABLE AIR MASS
WITH MLCAPE RANGING FROM AROUND 1000 J/KG ALONG THE FRONT RANGE TO
2000-2500 J/KG OVER KS. THE COMBINATION OF FRONTAL CONVERGENCE AND
OROGRAPHIC FORCING /BOTH AUGMENTED BY PASSAGE OF WEAK MIDLEVEL WAVE/
ARE EXPECTED TO YIELD ISOLATED TO SCATTERED TSTM DEVELOPMENT BY
AFTERNOON OVER PARTS OF ERN CO INTO KS.
REGION WILL RESIDE ALONG TRAILING FRINGE OF HIGHER MOMENTUM
MID/HIGH-LEVEL FLOW FIELDS ACCOMPANYING GREAT LAKES IMPULSE. WHEN
COUPLED WITH ELY LOW-LEVEL WIND COMPONENT...VERTICAL SHEAR WILL BE
SUFFICIENT FOR ORGANIZED/ROTATING STORMS CAPABLE OF MAINLY HAIL AND
DAMAGING WINDS.
..MEAD/JEWELL.. 08/10/2009
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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