SPC AC 241729
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 PM CDT FRI APR 24 2009
VALID 251200Z - 261200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
PLAINS...CNTRL PLAINS....MID-MS VALLEY...LOWER OH VALLEY AND LOWER
MICHIGAN...
...SRN AND CNTRL PLAINS...
AN UPPER-LEVEL TROUGH OVER THE SW DESERTS TONIGHT WILL MOVE INTO THE
FOUR CORNERS REGION SATURDAY AS SOUTHWEST FLOW REMAINS IN PLACE
ACROSS THE SRN AND CNTRL PLAINS. A BROAD LOW-LEVEL JET WILL CONTINUE
MOISTURE ADVECTION ACROSS THE SRN AND CNTRL PLAINS AS A COLD FRONT
ADVANCES SEWD INTO WRN OK...THE TX PANHANDLE AND SE KS BY LATE
AFTERNOON. AHEAD OF THE FRONT...SFC DEWPOINTS SHOULD BE IN THE LOWER
TO MID 60S F ALLOWING FOR MODERATE INSTABILITY ALONG AN AXIS FROM NW
TX NNEWD INTO WRN OK AND SRN KS. ALTHOUGH MODEL FORECAST SCENARIOS
ARE SLIGHTLY DIFFERENT...THE MODELS GENERALLY AGREE THAT ISOLATED TO
SCATTERED THUNDERSTORMS WILL INITIATE ALONG THE INSTABILITY AXIS
LATE SATURDAY AFTERNOON.
FORECAST SOUNDINGS ACROSS THE SRN PART OF THE SLIGHT RISK AREA AT
00Z SUNDAY SHOW MODERATE TO STRONG VERTICAL SHEAR PROFILES
ASSOCIATED WITH THE EXIT REGION OF A MID-LEVEL JET EJECTING NEWD OUT
OF THE BASE OF THE FOUR CORNERS UPPER-LEVEL TROUGH. THIS ALONG WITH
STEEP MID-LEVEL LAPSE RATES SHOULD SUPPORT A THREAT FOR SUPERCELLS
WITH LARGE HAIL. ATTM...THE BEST COMBINATION OF VERTICAL
SHEAR...INSTABILITY AND LAPSE RATES SHOULD BE IN NW OK AND THE ERN
TX PANHANDLE WHERE SUPERCELLS MAY BE CAPABLE OF PRODUCING VERY LARGE
HAIL. MODEL FORECASTS ALSO SHOW A PRONOUNCED LOW-LEVEL JET ACROSS
WRN OK WHICH WILL CREATE FAVORABLE BOUNDARY LAYER SHEAR CONDITIONS
FOR AN ISOLATED TORNADO THREAT SATURDAY EVENING. INSTABILITY AND
VERTICAL SHEAR IS FORECAST TO BE SLIGHTLY WEAKER NEWD ALONG THE
FRONT INTO SE KS AND NW MO SUGGESTING THE SEVERE THREAT WILL BE MORE
ISOLATED THERE.
...LOWER OH VALLEY/LOWER MICHIGAN...
SOUTHWEST FLOW WILL BE IN PLACE SATURDAY FROM THE CNTRL PLAINS INTO
THE UPPER MIDWEST AS AN UPPER-LEVEL TROUGH MOVES NEWD ACROSS THE NRN
GREAT LAKES. IN THE WAKE OF THE SYSTEM...A COLD FRONT SHOULD MOVE
SEWD ACROSS LOWER MI...IL AND NRN MO DURING THE DAY. SCATTERED
THUNDERSTORMS ARE FORECAST TO DEVELOP ALONG THE BOUNDARY DURING THE
LATE AFTERNOON WITH SEVERAL CLUSTERS OR A SMALL MCS PERSISTING INTO
THE LATE EVENING.
FORECAST SOUNDINGS ACROSS THE REGION LATE SATURDAY AFTERNOON SUGGEST
STRONG VERTICAL SHEAR WILL BE IN PLACE ACROSS LOWER MI IN THE RIGHT
ENTRANCE REGION OF AN EXITING MID-LEVEL JET. FURTHER SOUTHWEST
ACROSS NRN IL AND NRN MO...MODERATE VERTICAL SHEAR IS FORECAST WITH
INSTABILITY INCREASING DURING THE DAY. THE AMOUNT OF VERTICAL SHEAR
AND INSTABILITY SHOULD SUPPORT AN ISOLATED SEVERE STORMS CAPABLE OF
WIND DAMAGE AND HAIL. FORECAST SOUNDINGS ALSO SUGGEST LOW-LEVEL WIND
PROFILES WILL BE VEERED AND UNIDIRECTIONAL ACROSS NCNTRL IL AND
LOWER MI WHICH MAY HELP ACCELERATE DOWNDRAFTS SUSTAINING THE WIND
DAMAGE POTENTIAL INTO THE MID TO LATE EVENING.
...SRN AND CNTRL APPALACHIANS...
A BROAD UPPER-LEVEL RIDGE IS FORECAST ACROSS THE ERN SEABOARD
SATURDAY WHERE SLY FLOW SHOULD REMAIN PLACE ON THE WEST SIDE OF THE
RIDGE. MODEL FORECASTS ARE IN AGREEMENT...DEVELOPING MODERATE
INSTABILITY FROM THE MID-ATLANTIC SSWWD INTO CNTRL NC WHERE SFC
DEWPOINTS SHOULD RANGE FROM 55 TO 60 F. THE GFS INITIATES ISOLATED
TO SCATTERED THUNDERSTORMS ON THE WRN SIDE OF THE INSTABILITY AXIS
SATURDAY AFTERNOON IN THE SRN AND CNTRL APPALACHIANS PRIMARILY DUE
TO SFC HEATING. FORECAST SOUNDINGS AT 21Z ACROSS THIS AREA SUGGEST
DIRECTIONAL SHEAR AND INSTABILITY WILL BE SUFFICIENT FOR A FEW
MARGINALLY SEVERE STORMS. MID-LEVEL LAPSE RATES WILL CONTINUE TO BE
VERY STEEP SUGGESTING HAIL WILL BE THE PRIMARY THREAT.
..BROYLES.. 04/24/2009
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