SWODY1
SPC AC 280059
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0759 PM CDT SUN SEP 27 2009
VALID 280100Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE GREAT LAKES
REGION AND OH VALLEY...
...GREAT LAKES/OH VALLEY...
WATER VAPOR IMAGERY CURRENTLY SHOWS AN IMPRESSIVE UPPER-LEVEL TROUGH
DIGGING SEWD INTO THE UPPER MS VALLEY. THIS SYSTEM WILL CONTINUE
ESEWD INTO THE GREAT LAKES REGION TONIGHT AS AN 80 TO 100 KT
MID-LEVEL JET ROUNDS THE BASE OF THE TROUGH. THUNDERSTORMS ARE
ONGOING IN SLY FLOW ALONG A MOIST AXIS WHERE SFC DEWPOINTS ARE IN
THE MID TO UPPER 50S F. IN SPITE OF WEAK INSTABILITY...THUNDERSTORM
COVERAGE SHOULD EXPAND IN COVERAGE QUICKLY AS A BAND OF VERY STRONG
LARGE-SCALE ASCENT MOVES INTO THE REGION FROM THE WEST THIS EVENING.
THIS COMBINED WITH INCREASING BOUNDARY LAYER FLOW SHOULD HELP A
SQUALL-LINE TO ORGANIZE ALONG A FAST-MOVING COLD FRONT DURING THE
LATE EVENING. THE SQUALL-LINE IS EXPECTED TO CONTINUE EWD ACROSS ALL
OF SRN LOWER MI AND ACROSS PARTS OF IND AND OH TONIGHT.
THE LATEST WSR-88D VWP IN THE CHICAGO AREA SHOWS A VEERING WIND
PROFILE WITH HEIGHT BELOW 2 KM WITH 0-6 KM SHEAR OF 60-65 KT. THIS
SHOULD EASILY SUPPORT A SEVERE THREAT WITH THE MORE INTENSE CELLS IN
THE DEVELOPING LINE. A FEW ROTATING STORMS WILL BE POSSIBLE IN THE
LINE OR AHEAD OF THE LINE ACROSS THE WARM SECTOR ESPECIALLY AS THE
LOW-LEVEL JET INTENSIFIES AFTER MIDNIGHT. A MARGINAL TORNADO AND/OR
HAIL THREAT MAY DEVELOP IF A SUPERCELL CAN GET GOING. HOWEVER...THE
GREATEST THREAT SHOULD BE FOR DAMAGING WIND GUSTS WITH BOWING
LINE-SEGMENTS AS THE SQUALL-LINE MOVES INTO ERN LOWER MI...ERN IND
AND NW OH LATER TONIGHT. THE WIND DAMAGE THREAT SHOULD BE
INCREASINGLY MARGINAL SWD ACROSS KY AND TN WHERE LARGE-SCALE ASCENT
SHOULD BE WEAKER AND CONVECTIVE COVERAGE SHOULD BE LESS.
...SRN NEW ENGLAND...
AN UPPER-LEVEL TROUGH EVIDENT ON WATER VAPOR IMAGERY IN THE
MID-ATLANTIC REGION WILL MOVE INTO SRN NEW ENGLAND THIS EVENING.
AHEAD OF THE TROUGH...A LOW-LEVEL JET IS CURRENTLY ANALYZED NEAR
CAPE COD WITH SEVERAL THUNDERSTORMS LOCATED WEST OF THE JET IN SERN
NY AND WRN MA AND CT. THIS ACTIVITY SHOULD MOVE EWD ACROSS SRN NEW
ENGLAND THIS EVENING. THE 00Z SOUNDING IN BOSTON SHOWS 50 KT OF FLOW
JUST ABOVE THE SFC WHICH SHOULD SUPPORT A MARGINAL TORNADO THREAT
AND POTENTIAL FOR STRONG WIND GUSTS.
..BROYLES.. 09/28/2009
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