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Replies to post #136419 on Tornado Alley (PROG)
http://www.spc.noaa.gov/products/outlook/pwo.html [will update]ZCZC SPCPWOSPC ALL
WOUS40 KWNS 100913
IAZ000-ILZ000-MIZ000-MNZ000-WIZ000-101800-
PUBLIC SEVERE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0413 AM CDT SUN APR 10 2011
...SEVERE THUNDERSTORMS EXPECTED OVER PARTS OF THE UPPER MISSISSIPPI
VALLEY FROM MID TO LATE AFTERNOON THROUGH EARLY THIS EVENING...
THE NWS STORM PREDICTION CENTER IN NORMAN OK IS FORECASTING THE
DEVELOPMENT OF A FEW STRONG TORNADOES OVER PARTS OF THE UPPER
MISSISSIPPI VALLEY FROM THE MID-LATE AFTERNOON INTO THE EARLY
EVENING HOURS
THE AREAS MOST LIKELY TO EXPERIENCE THIS ACTIVITY INCLUDE
NORTHEASTERN IOWA
EXTREME NORTHWEST ILLINOIS
WESTERN UPPER MICHIGAN
SMALL PART OF EAST-CENTRAL AND SOUTHEAST MINNESOTA
MUCH OF WISCONSIN
ELSEWHERE...SEVERE STORMS ARE ALSO POSSIBLE FROM THE CENTRAL AND
UPPER GREAT LAKES REGION SOUTHWEST INTO THE EASTERN PARTS OF THE
CENTRAL AND SOUTHERN PLAINS.
...KEY WEATHER PLAYERS...
A POTENT STORM SYSTEM OVER THE CENTRAL AND SOUTHERN ROCKIES IS
EXPECTED TO MOVE EAST INTO THE GREAT LAKES...MIDWEST AND PLAINS
STATES THIS AFTERNOON AND TONIGHT. AHEAD OF THIS FEATURE...WARM AND
MOIST AIR WILL STREAM NORTHWARD AHEAD OF A COLD FRONT... RESULTING
IN SEASONABLY STRONG INSTABILITY NEEDED TO SUPPORT SEVERE
THUNDERSTORMS.
...TIMING...
THUNDERSTORMS OBSERVED DURING THE PRE-DAWN HOURS FROM THE UPPER
MISSISSIPPI RIVER VALLEY INTO THE CENTRAL GREAT LAKES REGION WILL
CONTINUE TO ADVANCE EAST-NORTHEAST THROUGH THE MORNING HOURS.
ATTENTION WILL THEN TURN TO A POTENTIALLY ACTIVE AFTERNOON AND
EVENING ACROSS THE UPPER MISSISSIPPI VALLEY REGION. AS MORNING
CLOUDS DISSOLVE...THE ATMOSPHERE WILL BECOME INCREASINGLY UNSTABLE.
SEVERE THUNDERSTORMS WILL LIKELY DEVELOP FROM NORTHWEST
WISCONSIN...EAST-CENTRAL/SOUTHEAST MINNESOTA AND NORTHEASTERN IOWA
IN THE 200-400 PM PERIOD. THE STORMS WILL THEN DEVELOP/MOVE
THROUGHOUT MUCH OF WISCONSIN...WESTERN UPPER MICHIGAN AND
NORTHWESTERN ILLINOIS THROUGH EARLY EVENING.
...IMPACTS...
MORNING THUNDERSTORMS COULD BRIEFLY ACHIEVE STRENGTH TO PRODUCE
LARGE HAIL...BUT HIGHER-IMPACT SEVERE WEATHER WILL BE ASSOCIATED
WITH AFTERNOON/EVENING STORMS.
THUNDERSTORMS THAT DEVELOP LATER TODAY WILL LIKELY GROW INTO
SUPERCELLS WITH THREATS FOR A FEW STRONG TORNADOES...PARTICULARLY
ACROSS THE MODERATE RISK AREA. ADDITIONALLY...VERY LARGE
HAIL...GREATER THAN HEN EGG SIZE...WILL BE LIKELY ALONG WITH
DAMAGING WIND GUSTS.
STATE AND LOCAL EMERGENCY MANAGERS ARE MONITORING THIS DEVELOPING
SITUATION. THOSE IN THE THREATENED AREA ARE URGED TO REVIEW SEVERE
WEATHER SAFETY RULES AND TO LISTEN TO RADIO...TELEVISION...AND NOAA
WEATHER RADIO FOR POSSIBLE WATCHES...WARNINGS...AND STATEMENTS LATER
TODAY.
..RACY/HART.. 04/10/2011
$$
CategoricalSPC AC 101123
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0623 AM CDT SUN APR 10 2011
VALID 101300Z - 111200Z
...THERE IS A MDT RISK OF SVR TSTMS THIS AFTERNOON AND EVENING OVER
PARTS OF SOUTHEAST MN...NORTHEAST IA...NORTHWEST IL...MUCH OF
WI...AND WESTERN UPPER MI...
...THERE IS A SLGT RISK OF SVR TSTMS FROM THE GREAT LAKES REGION
INTO CENTRAL TX...
...A LOCALIZED OUTBREAK OF SEVERE THUNDERSTORMS AND TORNADOES IS
POSSIBLE LATER TODAY OVER PORTIONS OF THE UPPER MS VALLEY AND
WESTERN GREAT LAKES REGION...
MORNING WATER VAPOR IMAGERY SHOWS A DEEP UPPER TROUGH OVER THE
WESTERN UNITED STATES. A 90-100 KNOT MID/UPPER LEVEL JET IS MOVING
ACROSS NM AND WILL NOSE INTO THE MIDWEST STATES THIS AFTERNOON.
RAPID SURFACE CYCLOGENESIS WILL ENSUE...WITH A DEEP LOW TRACKING
FROM NORTHWEST IA INTO WESTERN UPPER MI. STRONG AND INCREASING
SOUTHERLY LOW LEVEL WINDS IN THE WARM SECTOR OF THE LOW WILL DRAW
60S DEWPOINTS NORTHWARD AND YIELD A MODERATELY UNSTABLE AIR MASS AS
FAR NORTH AS A WARM FRONT LOCATED ROUGHLY ALONG THE SOUTHERN SHORES
OF LAKE SUPERIOR. THE AREA ALONG AND SOUTH OF THE WARM FRONT WILL
POSE THE GREATEST THREAT OF SIGNIFICANT SEVERE WEATHER LATER
TODAY...INCLUDING THE RISK OF DAMAGING TORNADOES.
CURRENT INDICATIONS ARE THAT MORNING CONVECTION OVER MN/WI WILL
RETREAT NORTHEASTWARD...WITH CONSIDERABLE SUNSHINE DEVELOPING ACROSS
THE REGION THROUGH EARLY AFTERNOON. A RATHER STRONG CAPPING
INVERSION WILL SUPPRESS NEW THUNDERSTORM DEVELOPMENT UNTIL MID-LATE
AFTERNOON AS THE EXIT REGION OF THE UPPER JET WEAKENS THE CAP NEAR
THE SURFACE LOW AND COLD FRONT OVER EASTERN MN/NORTHEAST IA. STORMS
IN THIS AREA ARE EXPECTED TO RAPIDLY BECOME SUPERCELLULAR WITH THE
THREAT OF VERY LARGE HAIL AND TORNADOES. CONVECTION SHOULD RACE
NORTHEASTWARD AT OVER 50 KNOTS ACROSS THE MODERATE RISK AREA DURING
THE AFTERNOON AND EARLY EVENING HOURS. FORECAST SOUNDINGS SHOW
EFFECTIVE HELICITY VALUES OF 250-400 MS/S2 AND VERY STRONG DEEP
LAYER VERTICAL SHEAR. THE COMBINATION OF WEAKENING
CAP...STRENGTHENING WIND FIELDS...AND ENHANCED SHEAR NEAR AND JUST
SOUTH OF THE WARM FRONT WILL POSE A RISK OF STRONG TORNADOES.
INTENSE ACTIVITY MAY SPREAD AS FAR EAST AS WESTERN UPPER MI BEFORE
ENCOUNTERING A MORE STABLE AIR MASS...WHERE WEAKENING IS EXPECTED.
VARIOUS MODEL SOLUTIONS LEND DOUBT REGARDING COVERAGE OF
THUNDERSTORMS WITH SOUTHWARD EXTENT. IT APPEARS LIKELY THAT AT
LEAST ISOLATED SEVERE/SUPERCELL THUNDERSTORMS WILL FORM AS FAR SOUTH
AS EASTERN IA AND NORTHWEST IL. HOWEVER...SOMEWHAT VEERED LOW LEVEL
FLOW APPEARS LIKELY TO DECREASE THE RISK OF SIGNIFICANT TORNADOES
COMPARED TO AREAS FARTHER NORTH OVER WI.
LATER THIS EVENING...MORE NUMEROUS THUNDERSTORMS ARE EXPECTED TO
DEVELOP ALONG THE COLD FRONT FROM MO INTO THE ARKLATEX REGION...AND
EVENTUALLY INTO TX OVERNIGHT. STRONG WINDS ALOFT AND MODERATE
INSTABILITY WILL HELP TO PROMOTE A RISK OF DAMAGING WINDS AND HAIL
IN THESE STORMS THROUGH MUCH OF THE NIGHT.
AI
