SWODY1
SPC AC 150602
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0102 AM CDT WED AUG 15 2007
VALID 151200Z - 161200Z
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE CNTRL AND
NRN PLAINS...UPPER MIDWEST AND UPPER MS VALLEY...
..WRN GREAT LAKES AND LOWER OH VALLEY...
WLY FLOW ALOFT WILL BE IN PLACE ACROSS THE REGION TODAY AS AN
UPPER-LEVEL TROUGH MOVES EWD ACROSS MANITOBA. A WEAK SFC LOW IS
FORECAST TO DEVELOP THIS AFTERNOON AND DRIFT EWD ACROSS SRN IA WITH
A LOW-LEVEL JET POSITIONED FROM ERN IA AND NRN IL NWD ACROSS WI INTO
UPPER MI. LOW-LEVEL CONVERGENCE NEAR THE SFC LOW AND INCREASING
LOW-LEVEL FLOW ASSOCIATED WITH THE LOW-LEVEL JET SHOULD SUPPORT THE
DEVELOPMENT OF SCATTERED THUNDERSTORMS. MCS DEVELOPMENT APPEARS
POSSIBLE ALONG THE WRN EDGE OF THE LOW-LEVEL JET THIS EVENING.
CONCERNING THE SEVERE POTENTIAL...THE NAM AND GFS SHOW THE STRONGEST
INSTABILITY LATE THIS AFTERNOON FROM SRN MN AND IA EXTENDING EWD
INTO NRN IL WHERE SFC DEWPOINTS WILL LIKELY BE IN THE LOWER TO MID
70S F. STRONG VERTICAL SHEAR WILL ALSO BE IN PLACE DUE TO ABOUT 20
KT OF SLY LOW-LEVEL FLOW AND 40 KT OF WLY MID-LEVEL FLOW SHOWN ON
FORECAST SOUNDINGS. THESE FACTORS COMBINED WITH STEEP MID-LEVEL
LAPSE RATES SHOULD BE FAVORABLE FOR ISOLATED SUPERCELLS WITH LARGE
HAIL. A POTENTIAL FOR WIND DAMAGE MAY ALSO EXIST WITH THE BETTER
ORGANIZED CONVECTIVE CLUSTERS. MODEL FORECASTS ARE IN GENERAL
AGREEMENT MOVING CONVECTION EWD ACROSS LAKE MICHIGAN INTO LOWER MI
DURING THE OVERNIGHT PERIOD. HOWEVER...INSTABILITY ACROSS THIS PART
OF THE OUTLOOK AREA WILL LIKELY BE MARGINAL FOR SEVERE STORMS.
..UPPER MIDWEST/NRN AND CNTRL PLAINS...
AN UPPER-LEVEL TROUGH OVER SRN CANADA EVIDENT ON WATER VAPOR IMAGERY
WILL AMPLIFY TODAY MOVING ACROSS MANITOBA INTO WRN ONTARIO THIS
EVENING. AT THE SFC...A COLD FRONT WILL MOVE SEWD ACROSS SD AND MN.
AHEAD OF THE BOUNDARY...MODERATE TO STRONG INSTABILITY WILL BE IN
PLACE BY AFTERNOON WHICH COMBINED WITH LOW-LEVEL CONVERGENCE ALONG
THE BOUNDARY SHOULD SUPPORT THE DEVELOPMENT OF SCATTERED
THUNDERSTORMS. THE GREATEST THUNDERSTORM COVERAGE SHOULD EXIST
ACROSS NRN AND CNTRL MN WHERE LARGE-SCALE ASCENT WILL BE STRONGER
DUE TO INFLUENCE OF THE UPPER-LEVEL TROUGH.
CONCERNING THE SHEAR ENVIRONMENT...A 90 KT MID-LEVEL JET ASSOCIATED
WITH THE UPPER-LEVEL TROUGH WILL MOVE EWD ACROSS SRN MANITOBA. THIS
FEATURE WILL CREATE STRONG VERTICAL SHEAR PROFILES ACROSS NERN
SD...CNTRL MN AND NRN MN. IN ADDITION...FORECAST SOUNDINGS ACROSS
THIS AREA THIS AFTERNOON SHOW 500 MB TEMPS OF -10 TO -12 C WHICH
COMBINED WITH THE SHEAR SHOULD BE FAVORABLE FOR A FEW ROTATING
STORMS WITH LARGE HAIL POTENTIAL. AN ISOLATED WIND DAMAGE THREAT MAY
ALSO DEVELOP DURING THE LATE AFTERNOON AS LAPSE RATES BECOME STEEP.
FURTHER SOUTHWEST ACROSS SERN SD AND NRN NEB...LARGE-SCALE ASCENT
WILL BE CONSIDERABLY WEAKER DUE TO LESS OF AN INFLUENCE FROM THE
UPPER-LEVEL TROUGH. AS A RESULT...STORM COVERAGE MAY REMAIN ISOLATED
ACROSS MUCH OF THE WRN PART OF THE SLIGHT RISK AREA. ALTHOUGH STRONG
INSTABILITY SHOULD AGAIN DEVELOP TODAY...VERTICAL SHEAR WILL ALSO BE
WEAKER THAN AREAS FURTHER NORTHEAST. FOR THIS REASON...MOST OF THE
STORMS WITH SEVERE POTENTIAL MAY REMAIN MULTICELLULAR. WIND DAMAGE
AND ISOLATED LARGE HAIL WILL BE POSSIBLE MAINLY NEAR PEAK HEATING
WHEN INSTABILITY AND LOW-LEVEL LAPSE RATES WILL BE MAXIMIZED.
..TEXAS COAST...
TROPICAL DEPRESSION FIVE IS FORECAST BY THE HURRICANE CENTER TO
APPROACH THE SRN TEXAS COAST TODAY. RAINBANDS FROM THE SYSTEM WILL
GRADUALLY SPREAD INLAND FROM LATE THIS AFTERNOON INTO THE OVERNIGHT
PERIOD. FORECAST SOUNDINGS ALONG THE TX COAST INCREASE LOW-LEVEL
SHEAR PROFILES THIS EVENING AND THIS MAY BE SUFFICIENT FOR A
MARGINAL TORNADO THREAT WITH STORMS THAT ROTATE.
.BROYLES/SCHNEIDER.. 08/15/2007
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