SPC AC 171707
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1207 PM CDT WED OCT 17 2007
VALID 181200Z - 191200Z
...THERE IS A MDT RISK OF SVR TSTMS FROM THE OH RIVER IN NRN
KY...NWD INTO SERN WI AND LOWER MI...
...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MDT RISK FROM
THE CNTRL GULF COAST TO THE ERN U.P. OF MI...
...SYNOPSIS...
DEEPENING OF CENTRAL U.S. LOW PRESSURE SYSTEM DURING THE DAY1/DAY2
TIME PERIOD WILL ENHANCE THE PROSPECT FOR POTENTIALLY SIGNIFICANT
SEVERE WEATHER ALONG AND JUST EAST OF THE MS VALLEY
REGION...ESPECIALLY THAT REGION FROM IL/IND NWD INTO SERN WI/SWRN
LOWER MI THURSDAY. DAMAGING WINDS AND TORNADOES APPEAR TO BE THE
MAIN SEVERE WEATHER THREATS ACROSS THE MODERATE RISK AREA.
...MID MS/OH VALLEY...GREAT LAKES...
EARLY MORNING MODEL GUIDANCE CONTINUES EARLIER TRENDS OF DEEPENING
CNTRL PLAINS SFC CYCLONE LATE DAY1 OVER ERN NEB. SFC LOW SHOULD
LIFT FROM NEAR OMA NEWD INTO NWRN WI BY 18/12Z AS COLD FRONT SWEEPS
ACROSS THE MS VALLEY. INTENSE MID LEVEL HEIGHT FALLS...ON THE ORDER
OF 150-180M...AND ASSOCIATED LARGE SCALE ASCENT WILL SPREAD FROM
IA/IL NEWD INTO THE GREAT LAKES DURING THE DAYLIGHT HOURS AS SPEED
MAX TRANSLATES FROM SRN MO INTO LOWER MI. NEEDLESS TO
SAY...VERTICAL SHEAR PROFILES WILL BECOME QUITE FAVORABLE FOR
ORGANIZED...FAST-MOVING SEVERE THUNDERSTORMS.
LATEST THINKING IS SEVERE THUNDERSTORMS WILL BE ONGOING AT THE
BEGINNING OF THE PERIOD ARCING AHEAD OF THE FRONT FROM IA...IL INTO
WRN KY. FORECAST SOUNDINGS ACROSS THIS REGION SUGGEST CONVECTIVE
UPDRAFTS WILL BE MODULATED BY INTENSE SHEAR/FORCING WITHIN A WEAK
LAPSE RATE/INSTABILITY ENVIRONMENT. MEAN STORM FLOW AROUND 50KT
SUGGEST ORGANIZED BOW-TYPE STRUCTURES COULD EASILY ACCELERATE BEYOND
THESE SPEEDS PRODUCING POTENTIALLY DESTRUCTIVE DAMAGING WINDS. ANY
HEATING AHEAD OF THIS LINE WILL ONLY SERVE TO AID UPDRAFT POTENTIAL
AS THUNDERSTORMS SPREAD/DEVELOP NEWD TOWARD SRN WI/WRN IND/SWRN
LOWER MI BY NOON. IT/S NOT ENTIRELY CLEAR WHETHER DISCRETE
STRUCTURES THAT EVOLVE LATER IN THE AFTERNOON ALONG ADVANCING WIND
SHIFT WILL REMAIN ISOLATED OR EVOLVE INTO MORE NUMEROUS
CLUSTERS/LINE SEGMENTS. REGARDLESS...EMBEDDED SUPERCELLS MAY
PRODUCE TORNADOES IN ADDITION TO DAMAGING WINDS.
...GULF STATES...
WITH INTENSE LARGE SCALE FORCING EXPECTED TO SHIFT WELL NORTH OF THE
GULF STATES...BROAD BUT POTENTIALLY SIGNIFICANT LOW LEVEL WARM
ADVECTION WILL GRADUALLY INCREASE DURING THE OVERNIGHT HOURS ACROSS
PORTIONS OF AL INTO GA. THIS INCREASE IN WARM ADVECTION WILL BE DUE
MOSTLY TO SWLY LLJ THAT SHOULD EVOLVE WELL AHEAD OF MAIN UPPER
TROUGH AXIS. THERMODYNAMIC PROFILES ACROSS THIS REGION WILL PROVE
QUITE MOIST WITH PRECIPITABLE WATER VALUES LIKELY IN EXCESS OF 2
INCHES. WITH SFC DEW POINTS EXPECTED TO RISE INTO THE LOWER-MID
70S...ENHANCED LOW-MID LEVEL SHEAR WILL CREATE A FAVORABLE
ENVIRONMENT FOR STORM ROTATION. WEAK LAPSE RATES WILL NEGATE
UPDRAFT STRENGTH...BUT ISOLATED SUPERCELLS NONETHELESS MAY
OCCUR...ESPECIALLY DURING THE OVERNIGHT HOURS. ISOLATED TORNADOES
AND DAMAGING WINDS ARE THE PRIMARY SEVERE THREATS.
..DARROW.. 10/17/2007
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0800Z
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