Tornado Alley (PROG)

[F6]

dbleagl, and all -- heads up in Madison:

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    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 
     
    $$

http://www.spc.noaa.gov/products/outlook/pwo.html [will update]

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    SPC 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.

Categorical


Tornado

Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.

Hail

Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.

Wind


http://www.spc.noaa.gov/products/outlook/day1otlk.html [graphics won't update until 1300Z tomorrow morning; updates due at 1630Z, 2000Z and 0100Z (4/11) later today; use this link to see the later updated Day 1 Convective Outlooks]

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source for the above and for later watches and mesoscale discussions (and etc.): NOAA Storm Prediction Center, http://www.spc.noaa.gov/

best source for (the locally-issued) warnings and severe weather statements: College of DuPage Meteorology
Severe Weather and Flash Flood Warnings, http://kamala.cod.edu/svr/