SPC AC 030557
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT FRI JUL 03 2009
VALID 041200Z - 051200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER OH VALLEY INTO
THE SRN PLAINS...
...THERE IS A SLGT RISK OF SVR TSTMS OVER ERN PARTS OF WY AND CO...
...SYNOPSIS...
QUASI-STATIONARY UPPER LOW OVER THE LOWER GREAT LAKES IS FORECAST TO
PERSIST INTO SATURDAY...WITH AMPLITUDE OF THE ERN US LONG WAVE
DIMINISHING. THIS WILL RESULT IN BROAD WNWLY FLOW ALOFT ACROSS MUCH
OF THE US FROM THE NRN/CENTRAL INTERMOUNTAIN REGION TO THE ATLANTIC
COAST...DOWNSTREAM FROM AN UPPER RIDGE AXIS OVER THE INTERMOUNTAIN
WEST.
AT THE SURFACE...A LOW IS FORECAST TO MOVE ESEWD ACROSS THE MID MS
VALLEY TOWARD THE UPPER OH VALLEY BY THE END OF THE PERIOD...WITH A
TRAILING COLD FRONT MOVING SWD ACROSS THE OZARKS AND INTO THE SRN
PLAINS. A QUASI-STATIONARY FRONT WILL EXTEND EWD FROM THE LOW.
...MID MS VALLEY INTO THE OH VALLEY...
AN MCS IS EXPECTED TO BE ONGOING AT THE START OF THE PERIOD OVER
PARTS OF NRN MO...ERN IA AND NRN/CENTRAL IL. THE CONVECTIVE SYSTEM
WILL BE PRIMARILY ELEVATED TO THE NORTH OF THE SURFACE LOW AND
QUASI-STATIONARY FRONT...MAINTAINED BY STRONG LOW LEVEL CONVERGENCE
AND WARM ADVECTION LIFT NEAR THE NOSE OF A 50 KT SWLY LOW LEVEL JET.
GIVEN THE BACKGROUND 35-45 KT MID LEVEL WINDS AND RESULTANT STRONG
VERTICAL SHEAR...THERE IS POTENTIAL FOR A FEW SEVERE STORMS TO OCCUR
IN THE SRN PART OF THE MCS DURING THE MORNING...ALTHOUGH WEAK
INSTABILITY SHOULD LIMIT THE OVERALL SEVERE THREAT. STORMS MAY
INTENSIFY BY LATE MORNING/EARLY AFTERNOON AS STRONG DIURNAL HEATING
OCCURS ALONG THE SRN EDGE OF THE CONVECTIVE CLOUD SHIELD OVER PARTS
OF THE MID MS VALLEY AND UPPER OH VALLEY. CONTINUED FAVORABLE
LOW-LEVEL AND DEEP LAYER SHEAR WILL ENHANCE STORM ORGANIZATION AND
INTENSITY...AND MAY COMPENSATE FOR WEAK MID LEVEL LAPSE RATES ACROSS
THE AREA. DAMAGING WIND GUSTS AND HAIL WILL BE POSSIBLE WITH
STRONGER STORMS...WHICH SHOULD DIMINISH AFTER 03Z.
...SRN PLAINS INTO THE OZARKS...
AIR MASS IS EXPECTED TO UNDERGO SUBSTANTIAL DIURNAL HEATING AHEAD OF
THE ADVANCING COLD FRONT...AND WHEN COUPLED WITH SURFACE DEW POINTS
IN THE 60S TO LOW 70S...WILL RESULT IN MLCAPE OF 1000-2000 J/KG.
STRONG HEATING WILL GRADUALLY WEAKEN THE CAP DURING THE
AFTERNOON...AND LOW-LEVEL CONVERGENCE ALONG THE FRONT WILL PROMOTE
DEVELOPMENT OF SCATTERED THUNDERSTORMS. ALTHOUGH MID LEVEL
WINDS/DEEP LAYER SHEAR WILL BE MODEST AT BEST...LARGE
TEMPERATURE/DEW POINT SPREADS ASSOCIATED WITH A RELATIVELY DEEP
MIXED LAYER...AND DRIER AIR IN THE MID LEVELS WILL CONTRIBUTE TO
LARGE DCAPE VALUES INDICATIVE OF ENHANCED DOWNDRAFT INTENSITY AND
THREAT FOR DAMAGING WIND GUSTS. THERE WILL ALSO BE A THREAT FOR
LARGE HAIL WITH STRONGER CELLS. SEVERE THREAT IS EXPECTED TO SPREAD
SWD ALONG THE FRONT AND ASSOCIATED OUTFLOW BOUNDARIES THROUGH THE
EVENING HOURS.
...ERN PARTS OF WY AND CO...
WEAK UPSLOPE LOW LEVEL WINDS ARE FORECAST TO DEVELOP OVER THE ERN
SLOPES OF THE ROCKIES ON SATURDAY AS A WEAK SURFACE RIDGE MOVES INTO
PARTS OF SD AND NEB. THIS WILL MAINTAIN SURFACE DEW POINTS IN THE
LOW 50S...AND CONTRIBUTE TO AN UNSTABLE AFTERNOON ENVIRONMENT WITH
MLCAPE AROUND 1000-1500 J/KG. THUNDERSTORMS ARE LIKELY TO DEVELOP
OVER THE HIGHER TERRAIN DURING THE AFTERNOON AND MOVE EWD/ESEWD INTO
THE HIGH PLAINS WITHIN A BAND OF 25-35 KT MID LEVEL FLOW. DEEP
LAYER SHEAR WILL BE SUFFICIENT FOR ORGANIZED STORMS TO
DEVELOP...INCLUDING A FEW SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL
AND STRONG WIND GUSTS THROUGH THE EVENING HOURS.
..WEISS.. 07/03/2009
CLICK TO GET WUUS02 PTSDY2 PRODUCT
NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
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