SWODY1
SPC AC 270529
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1229 AM CDT SUN SEP 27 2009
VALID 271200Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE GREAT LAKES
AND OH VALLEY...
...WRN GREAT LAKES...
A POWERFUL UPPER-LEVEL TROUGH WILL AMPLIFY AND DIG SEWD INTO THE
UPPER MS VALLEY TODAY. AHEAD OF THE SYSTEM...A LOW-LEVEL JET WILL
STRENGTHEN...TRANSPORTING LOW-LEVEL MOISTURE QUICKLY NWD INTO THE
WRN GREAT LAKES REGION WITH SFC DEWPOINTS ACROSS THE UPPER-MS VALLEY
REACHING THE MID TO UPPER 50S F. AS SFC TEMPS HEAT UP TODAY AND
MODERATE INSTABILITY DEVELOPS ACROSS PARTS OF THE UPPER MS
VALLEY...SCATTERED SFC-BASED THUNDERSTORMS SHOULD INITIATE ALONG THE
INSTABILITY AXIS. ETA-KF FORECAST SOUNDINGS AT MID-AFTERNOON IN
WI...UPPER MI AND WRN LOWER MI SHOW STRONG VERTICAL SHEAR
PROFILES...STEEP LAPSE RATES IN THE 700 TO 500 MB LAYER AND RAPIDLY
COOLING AIR ALOFT DUE TO THE APPROACHING UPPER-LEVEL TROUGH. THIS
SHOULD BE FAVORABLE FOR HAIL WITH THE MORE INTENSE CELLS. ISOLATED
WIND DAMAGE WILL ALSO BE POSSIBLE ESPECIALLY IF A PERSISTENT
LINE-SEGMENT CAN ORGANIZE. LOW-LEVEL MOISTURE MAY BE ENHANCED OVER
THE WARM WATERS OF LAKE MICHIGAN AND THIS MAY HELP THE CONVECTION
WITH THE THREAT REACHING WRN LOWER MI DURING THE EARLY EVENING.
...GREAT LAKES/OH VALLEY...
AN IMPRESSIVE MID-LEVEL JET ASSOCIATED WITH A AMPLIFYING UPPER-LEVEL
TROUGH IN THE MS VALLEY WILL APPROACH THE REGION FROM THE WEST
TODAY. SCATTERED THUNDERSTORMS APPEAR LIKELY TO INITIATE IN THE EXIT
REGION OF THE JET EARLY THIS EVENING IN SE WI AND NRN IL AND MOVE
QUICKLY EWD ACROSS THE REGION WITH THE LEADING EDGE OF ASCENT. THE
STORMS SHOULD BECOME LINEAR ORGANIZING FROM NORTH TO SOUTH ALONG A
COLD FRONT MOVING INTO LOWER MI AND IND DURING THE LATE EVENING AND
INTO ERN LOWER MI AND WRN OH DURING THE OVERNIGHT PERIOD. FORECAST
SOUNDINGS TONIGHT SUGGEST INSTABILITY WILL REMAIN WEAK AHEAD OF THE
COLD FRONT AND THE LINE MAY NOT BE ACCOMPANIED WITH MUCH LIGHTNING
ESPECIALLY SWD ACROSS PARTS OF KY AND TN. HOWEVER...THE ENVIRONMENT
SHOULD BE CHARACTERIZED BY VERY STRONG ASCENT...50-60 KT OF VERTICAL
SHEAR AND 40-50 KT OF FLOW AT THE TOP OF THE BOUNDARY LAYER. THIS
SHOULD SUPPORT AN ISOLATED WIND DAMAGE THREAT WITH A FAST-MOVING
LINE OF STORMS AS THE COLD FRONT MOVES ACROSS THE SRN GREAT LAKES
REGION AND NRN OH VALLEY LATE TONIGHT.
...SRN NEW ENGLAND...
AN UPPER-LEVEL TROUGH WILL MOVE NEWD ALONG THE ERN SEABOARD TODAY.
AHEAD OF THE TROUGH...A LOW-LEVEL JET WILL TRANSPORT MOISTURE NWD
INTO SRN ENGLAND. AS SFC TEMPS WARM AND LARGE-SCALE ASCENT
INCREASES...THUNDERSTORMS APPEAR LIKELY TO DEVELOP IN THE CNTRL
APPALACHIAN MTNS AND MOVE ENEWD INTO SRN NEW ENGLAND LATE THIS
AFTERNOON INTO THE EARLY EVENING. ETA-KF FORECAST SOUNDINGS IN MA
AND CT AT 00Z SHOW 50 KT OF VERTICAL SEAR WITH 0-1 KM SHEAR AT 30
KT. THIS SHOULD OVERCOME THE WEAK INSTABILITY AND A FEW ROTATING
STORMS WILL BE POSSIBLE WITH A MARGINAL TORNADO AND/OR WIND DAMAGE
THREAT.
..BROYLES/SMITH.. 09/27/2009
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