Friday, May 29, 2009

DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 291725
SWODY2
SPC AC 291722

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1222 PM CDT FRI MAY 29 2009

VALID 301200Z - 311200Z

...THERE IS A SLGT RISK OF SVR TSTMS KY...MIDDLE TN...SW OH...SRN
IND...IL...NRN MO AND FAR NE KS...

...LOWER OH VALLEY/MID TO UPPER MS VALLEY...
AN UPPER-LEVEL TROUGH OVER THE CNTRL APPALACHIAN MTNS WILL REMAIN IN
PLACE TONIGHT AND SATURDAY AS A 60 TO 75 KT MID-LEVEL JET MOVES SEWD
INTO THE BASE OF THE TROUGH. AT THE SFC...A FRONTAL BOUNDARY SHOULD
BE LOCATED FROM NRN MO ESEWD ACROSS SRN IL INTO CNTRL KY SATURDAY.
GFS/NAM/NAMKF AND SREF MODEL FORECASTS ARE IN FAIRLY GOOD AGREEMENT
LATE SATURDAY MORNING WITH A CLUSTER OF THUNDERSTORMS LOCATED ACROSS
IL...SRN IND AND WRN KY IN THE RIGHT REAR QUADRANT OF THE MID-LEVEL
JET. CONVECTION WITH THIS FEATURE OR NEW STORMS THAT DEVELOP SOUTH
OF THE CLUSTER SHOULD MOVE SEWD ALONG THE BOUNDARY ACROSS CNTRL KY
DURING THE AFTERNOON. A CONSENSUS OF FORECAST SOUNDINGS IN CNTRL KY
AT 21Z SATURDAY SHOW MODERATE INSTABILITY WITH 40 TO 50 KT OF
VERTICAL SHEAR SUGGESTING THE ENVIRONMENT WILL BE FAVORABLE FOR A
SEVERE THREAT WITH THE CONVECTIVE CLUSTER. AT THIS TIME...CONVECTIVE
MODE REMAINS QUESTIONABLE. IF ISOLATED SUPERCELLS CAN
ORGANIZE...THEN LARGE HAIL AND A FEW TORNADOES WILL BE POSSIBLE. IF
LINE-SEGMENTS ARE FAVORED...THEN THE PREDOMINANT THREAT COULD BE
WIND DAMAGE. ANOTHER UNCERTAINTY IS THE TIMING OF THE CONVECTIVE
SYSTEM. IF THE TIMING IS LATER IN THE AFTERNOON WHEN INSTABILITY IS
MAXIMIZED...THEN THE SEVERE THREAT COULD BE MORE SUBSTANTIAL.

FURTHER WEST ACROSS NRN MO...MODEL FORECASTS DEVELOPS STRONG
INSTABILITY WITH MLCAPE VALUES RANGING FROM 2000 TO 3000 J/KG.
ALTHOUGH FORCING WILL BE WEAKER ALONG THE BOUNDARY IN NRN
MO...LOW-LEVEL CONVERGENCE AND SFC HEATING COULD HELP INITIATE A FEW
STORMS. THE STRONG INSTABILITY COUPLED WITH 30 TO 40 KT OF VERTICAL
SHEAR EVIDENT ON FORECAST SOUNDINGS SHOULD BE ADEQUATE FOR AN
ISOLATED SEVERE THREAT SATURDAY AFTERNOON.

...LOWER MICHIGAN...
AN UPPER-LEVEL LOW IS FORECAST TO MOVE SEWD ACROSS ONTARIO SATURDAY
AS A 70 TO 85 KT MID-LEVEL JET SOUTHWEST OF THE LOW MOVES INTO THE
WRN GREAT LAKES. AHEAD OF THIS FEATURE...A COLD FRONT WILL ADVANCE
SEWD ACROSS LOWER MICHIGAN DURING THE DAY WITH THE MODELS DEVELOPING
THUNDERSTORMS ALONG THE BOUNDARY. ALTHOUGH INSTABILITY SHOULD BE
RELATIVELY WEAK ACROSS LOWER MI SATURDAY AFTERNOON...FORECAST
SOUNDINGS SHOW ABOUT 50 KT OF VERTICAL SHEAR. THIS ALONG WITH COLD
AIR ALOFT /500 MB TEMPS AROUND -20 C/ SHOULD BE SUPPORTIVE OF HAIL
WITH THE STRONGER UPDRAFTS.

...SRN FL PENINSULA...
A COLD FRONT IS FORECAST TO MOVE SWD ACROSS THE FL PENINSULA
SATURDAY. THUNDERSTORMS SHOULD DEVELOP ALONG AND SOUTH OF THE
BOUNDARY DURING THE AFTERNOON MAINLY FROM LAKE OKEECHOBEE TO THE
SOUTH. WITH SFC DEWPOINTS IN THE LOWER TO MID 70S F...MODERATE TO
STRONG INSTABILITY SHOULD BE PRESENT. IN ADDITION...FORECAST
SOUNDINGS AT 21Z SATURDAY IN SRN FL SHOW ABOUT 30 KT OF VERTICAL
SHEAR. THIS COMBINED WITH 20 TO 25 KT OF WLY FLOW AT 850 MB COULD BE
ENOUGH FOR MARGINALLY SEVERE WIND GUSTS WITH THE STRONGER UPDRAFTS.

...NRN CA/SRN ORE/NW NV...
AN UPPER-LEVEL RIDGE WILL CONTINUE TO BE IN PLACE ACROSS THE NWRN
STATES. THUNDERSTORMS ARE FORECAST TO DEVELOP ON THE WRN SIDE OF THE
RIDGE IN THE SIERRAS AND IN THE CASCADES OF CNTRL ORE BY AFTERNOON
AS SFC TEMPS WARM. IN SPITE OF THE WEAK MID-LEVEL FLOW /20 KTS OR
LESS/...MODERATE INSTABILITY AND STEEP LAPSE RATES SHOULD BE ENOUGH
FOR A MARGINAL SEVERE THREAT NEAR PEAK HEATING.

..BROYLES.. 05/29/2009

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