SWODY1
SPC AC 272000
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0300 PM CDT SUN SEP 27 2009
VALID 272000Z - 281200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE UPPER GREAT LAKES
AND MIDWEST...
...GREAT LAKES/MIDWEST/OHIO VALLEY THROUGH TONIGHT...
MID AFTERNOON SURFACE ANALYSIS FEATURES A COLD FRONT STEADILY
ADVANCING EAST-SOUTHEASTWARD OVER THE UPPER MIDWEST...EXTENDING FROM
THE WESTERN LAKE SUPERIOR VICINITY TO CENTRAL IA/NORTHWEST MO AS OF
20Z. PRIOR DISCUSSED SCENARIO STILL GENERALLY HOLDS...WITH TSTMS
EXPECTED TO INCREASE ALONG THE FRONTAL ZONE LATE THIS
AFTERNOON/EARLY EVENING ACROSS THE UPPER PENINSULA OF MI AND WI TO
NORTHERN IL/LAKE MI VICINITY. FOR ADDITIONAL SHORT TERM
INFORMATION...REFERENCE MESOSCALE DISCUSSION 2037.
MODEST MOISTURE HAS TENDED TO MIX IN THE PREFRONTAL WARM SECTOR
ACROSS IL/WI...BUT A NARROW AXIS OF SOMEWHAT RICHER MOISTURE
CONTINUES TO STREAM NORTHWARD AHEAD OF THE FRONT /NEAR 60F SURFACE
DEWPOINTS/...ALONG/IMMEDIATELY WEST OF THE MIDDLE MS RIVER VALLEY AT
MID AFTERNOON. SEVERE TSTMS CAPABLE OF HAIL/WIND WILL BE THE PRIMARY
HAZARDS...WITH STORMS LIKELY TO ORGANIZE INTO A FAST MOVING
QUASI-LINEAR CONVECTIVE LINE LATER THIS EVENING AS THE SURFACE LOW
DEEPENS OVER THE UPPER GREAT LAKES AND THE SURFACE COLD FRONT
FURTHER ACCELERATES EASTWARD. EVEN WITH LIMITED NEAR SURFACE
BUOYANCY AND NOCTURNALLY INCREASING CINH...AT LEAST ISOLATED WIND
DAMAGE WILL BE POSSIBLE WELL THROUGH THE EVENING/PERHAPS OVERNIGHT
INTO LOWER MI/PORTIONS OF THE OH VALLEY.
..GUYER.. 09/27/2009
.PREV DISCUSSION... /ISSUED 1125 AM CDT SUN SEP 27 2009/
POWERFUL FALL TROUGH AND POLAR JET MAX DRIVING ESEWD ACROSS NRN
PLAINS THIS AFTERNOON TO UPPER LAKES AND OH VALLEY OVERNIGHT. IN
RESPONSE SURFACE LOW RAPIDLY DEEPENS OVER LS THIS AFTERNOON/EVENING
WITH THE ASSOCIATED STRONG COLD FRONT CURRENTLY UPR MS VALLEY MOVING
EWD TO A POSITION FROM WRN LWR MI SWWD TO MO BY THIS EVENING. BY
12Z MON FRONT WILL BE ENTERING WRN NY/PA TRAILING WSWWD TO ACROSS
SRN PLAINS.
...WI/MI/ERN IA/IL LATE THIS AFTERNOON AND EVENING...
WARM SECTOR PRECEDING FROPA WILL BE
MOISTENING/DESTABILIZING...HOWEVER WILL REMAINED CAPPED TO ANY
SURFACE BASED STORM DEVELOPMENT UNTIL LATER THIS AFTERNOON. STRONG
FRONTAL LIFT ALONG WITH LARGE SCALE ASCENT AND MID LEVEL COOLING
WILL LEAD TO THUNDERSTORM INITIATION BY MID AFTERNOON FROM THE UP OF
MI INTO NRN WI AND THEN PROGRESSIVELY FURTHER S ALONG FRONT INTO NRN
IL BY EVENING.
AS LAPSE RATES STEEPEN AND MID LEVELS COOL...HAIL WILL BE LIKELY
WITH STORM DEVELOPMENT MI/WI ALONG WITH INCREASING THREAT OF
DAMAGING WINDS AS FLOW INCREASES AT ALL LEVELS WITH APPROACH OF
VIGOROUS TROUGH.
WITH MLCAPES LESS THAN 1000 J/KG...AND PWAT GENERALLY LESS THAN AN
INCH IN THE WARM SECTOR...WILL MAINTAIN THE THREAT AS A SLGT HOWEVER
EXPAND IT N INTO THE MI UP WHERE IT NOW APPEARS AIR MASS SHOULD
DESTABILIZE PRIOR TO FROPA MORE THAN EARLIER EXPECTED.
...LOWER MI/IND/OH OVERNIGHT...
AS THE SURFACE COLD FRONT SWEEPS EASTWARD OVERNIGHT...AN
INCREASINGLY MOIST BOUNDARY LAYER WILL PROMOTE GREATER THUNDERSTORM
COVERAGE. A FAST-MOVING LINE OF SHOWERS AND THUNDERSTORMS APPEARS
POSSIBLE FROM IND/LOWER MI EASTWARD ACROSS PARTS OF OH TONIGHT WITH
THE POTENTIAL FOR LOCALLY DAMAGING WINDS. WEAK INSTABILITY
PARAMETERS WILL CONTINUE TO BE THE MAIN MITIGATING FACTOR TO LESSEN
THE RISK OF A MORE WIDESPREAD WIND EVENT.
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