Hail and Damaging Winds in Minnesota, May 23, 2012

AREA FORECAST DISCUSSION...UPDATED FOR 12Z TAFS
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
639 AM CDT WED MAY 23 2012

.DISCUSSION...

OVERVIEW...HIGH ENOUGH CONFIDENCE TO GO WITH A FLASH FLOOD WATCH
FOR PORTIONS OF THE FORECAST AREA TONIGHT. TRIED TO POSITION THE
WATCH IN A LOCATION WITH THE BEST OVERLAP BETWEEN EXPECTED RAINFALL
AND WET ANTECEDENT CONDITIONS OVER THE PAST SEVEN DAYS. THINK THE
SEVERE WEATHER THREAT IS SOMEWHAT MARGINAL AND SHOULD BE CONFINED
TO THIS AFTERNOON AND EVENING. THE BIGGEST HAZARD TONIGHT SHOULD
BE THE THREAT FOR LOCALIZED...ALBEIT GENERALLY MINOR...FLOODING.

ALREADY PLENTY OF CONVECTIVE ACTIVITY BACK NEAR THE COLD FRONT IN
EASTERN SOUTH DAKOTA. IN ADDITION TO STRONG 925-850MB MOISTURE
TRANSPORT...WARM AIR ADVECTION...AND WEAK ELEVATED INSTABILITY IN
CENTRAL/NORTHERN MN WITH THE PRE-FRONTAL SHOWERS/STORMS.
EVERYTHING STILL LOOKS ON TRACK FOR A SIGNIFICANT PRECIP EVENT
OVER THE NEXT 24-36 HOURS. PWATS ALREADY TOOK ANOTHER JUMP WITH
THE 23.00Z SOUNDING HERE AT MPX...GOING FROM 0.77" TO 0.89". WILL
CERTAINTY SEE THAT NUMBER CLIMB TODAY AS WELL AS A NUMBER OF OTHER
HEAVY RAIN INGREDIENTS. THE BIGGEST NOTICEABLE CHANGE IN THE
GUIDANCE FROM YESTERDAY IS A SLIGHT EASTWARD SHIFT IN THE AXIS OF
HEAVY RAIN. 23.00Z NAM NOW SHOWING GOOD OVERLAP IN THE 925-850MB
MOISTURE FLUX CONVERGENCE AND 600-700MB FGEN ROUGHLY ALONG AN AXIS
FROM SPRINGFIELD/NEW ULM...TO THE WEST TWIN CITIES METRO...TO
CAMBRIDGE. GOOD COUPLED JET STRUCTURE SHOULD BE MORE THAN
SUFFICIENT IN VACATING THE AIR ALOFT AND PROMOTING STRONG VERTICAL
MOTION. GEM-REG/EC/NAM/GFS...SHOW A RANGE OF 0.50-4.00" ACROSS
PARTS OF THE FORECAST AREA BY FRIDAY MORNING. WRF-ARW/NMM
SIMULATED REFLECTIVITY DEPICTS SEVERAL BANDS OF MULTI-CELLULAR
CONVECTION WITH EMBEDDED SEGMENTS OF ORGANIZED STRONGER
CONVECTION.

AS SPC MENTIONED...JUST NOT SURE WELL HAVE MUCH IN THE WAY OF
CONVECTION TRULY ROOTED IN THE BOUNDARY LAYER UNLESS YOU'RE
TALKING ABOUT AREAS RIGHT ALONG THE COLD FRONT. IF THAT'S THE
CASE...WHILE THE SHEAR PROFILE IS STRONG ENOUGH TO SUPPORT
ORGANIZED CONVECTION...THE TORNADO THREAT WOULD BE HIGHLY LIMITED.
NOT TO MENTION THE DRY FORECAST SOUNDING BELOW 5KFT THIS
AFTERNOON/EVENING AND MARGINAL DEWPOINTS. AT THIS POINT...IF I HAD
TO RANK THE HAZARDS IT WOULD BE IN THIS ORDER: 1. HEAVY RAIN 2.
HAIL 3. WINDS 4. TORNADO. IN TERMS OF HEAVY RAIN...THE COLD FRONT
HEAVY RAIN ARCHETYPE IS NOT AS PROLIFIC AT PRODUCING FLASH
FLOODING AS SAY A WARM FRONT SCENARIO...ESPECIALLY THIS EARLY IN
THE CONVECTIVE SEASON. WITH THAT BEING SAID...THE PARAMETERS
EXPECTED TO BE IN PLACE TONIGHT ARE CLOSE TO WHAT WE'VE SEEN IN
PREVIOUS HEAVY RAIN EVENTS IN THIS PART OF THE COUNTRY. WE'LL HAVE
850MB MIXING RATIOS BETWEEN 10-12G/KG...STRONG FGEN LINES UP
NICELY ON THE WESTERN EDGE OF THE INSTABILITY GRADIENT...WHICH IS
ALSO THE WESTERN EDGE OF THE THETA-E RIDGE. WITH FLASH
FLOODING...YOU EITHER NEED VERY HIGH RAINFALL RATES OR GOOD
RAINFALL RATES FOR A PROLONGED PERIOD OF TIME. GIVEN THE SLOW
EASTWARD TRANSLATION OF THE FRONT...WE ARE CLOSER IN LINE WITH THE
LATTER. NOT SURE THE RAIN RATES WILL BE TREMENDOUS...BUT SHOULD
HAVE VERY GOOD RATES DURING A 3-6 HOUR WINDOW TONIGHT.

ON THURSDAY...THE MID LEVEL SHORT-WAVE TROUGH WILL EJECT ACROSS
THE CENTRAL PLAINS TOWARD THE GREAT LAKES REGION. WERE LOOKING FOR
POST COLD FRONTAL CONVECTION IN FAR EASTERN MN AND WESTERN WI. THE
AMOUNT OF CLEARING AND ABILITY FOR STORMS TO BECOME SURFACE BASED
IS A BIG QUESTION. WONDERING IF WE DON'T JUST KEEP ELEVATED
CONVECTION GOING ALL THE WAY THROUGH THE DAY. CONVECTIVE
INHIBITION TIED TO WARM TEMPS ALOFT SHOULD BE CONFINED TO AREAS
SOUTH OF MN/WI. AXIS OF HEAVIEST RAINFALL CENTERED OVER WEST
CENTRAL WI THURSDAY AFTERNOON.

IN THE EXTENDED...LULL IN THE WEATHER ON FRIDAY BEFORE A WARM
FRONT RETURNS ON SATURDAY BRINGING THUNDERSTORMS AS IT MOVES
THROUGH AND ANOTHER SHOT OF WARMTH BY SUNDAY. MODEL GUIDANCE
CONTINUES TO SHOW AN EVOLUTION TOWARD FLATTER MEAN FLOW BY THE
FIRST HALF OF NEXT WEEK WITH A LEAST TWO PRONOUNCED SHORTWAVES

&&

.AVIATION... /12Z TAF ISSUANCE/

COLD FRONT WILL BE MAIN FOCUS AREA FOR REDEVELOPMENT OF
THUNDERSTORMS LATER TODAY AND TONIGHT. SFC RIDGE OVER CENTRAL GREAT
LAKES...WILL KEEP MUCH OF THE EASTERN SECTION OF OUR FORECAST AREA
DRY AND QUIET THROUGH THIS EVENING.  BEST MOISTURE CONVERGENCE AND
INSTABILITY WILL OCCUR OVER THE WESTERN SECTION OF MN TODAY AND
SLIDE EAST OVER CENTRAL MN TONIGHT. CURRENT FORECAST SEEM TO BE ON
TRACK...ONLY SOME MINOR ADJUSTMENTS IN TIMING WERE NEEDED AT THIS
FORECAST ISSUANCE. EXPECT WEATHER CONDITIONS TO DETERIORATE TO MVFR
OR LOWER DURING THE OVERNIGHT PERIOD AND THURSDAY MORNING.  MUCH OF
DAY TODAY...WILL HAVE VFR CONDITIONS POSSIBLY LOWER TO MVFR IN
THUNDERSTORMS. MODERATE TO STRONG WINDS JUST BELOW 2000 FEET AGL
THIS MORNING WITH WINDS 210 DEG AT 40 KNOTS AT KMPX. DAYTIME HEATING
SHOULD EVENTUALLY MIX THROUGH THE LAYER...THUS TAPPING WINDS CLOSE
TO SURFACE BY MID MORNING.

KMSP...THE MAIN CONCERN TODAY...THUNDERSTORM CHANCES FOR LATER
TODAY. BELIEVE SHOWERS AND THUNDERSTORMS SHOULD HOLD OFF UNTIL THIS
EVENING AT THE MAIN AIRPORT. EXPECT WIDESPREAD SHOWERS AND
THUNDERSTORMS BEFORE MIDNIGHT TONIGHT WITH WEATHER CONDITIONS
LOWERING TO MVFR OR LOWER IN HEAVY RAIN AND THUNDERSTORMS.

/OUTLOOK...
THURSDAY...CHANCE OF SHOWERS AND THUNDERSTORMS WITH MVFR
CONDITIONS EXPECTED. IFR CONDITIONS POSSIBLE.
THURSDAY NIGHT...MVFR CEILINGS POSSIBLE EARLY.
FRIDAY...VFR CONDITIONS EXPECTED.
FRIDAY NIGHT...MVFR CEILINGS POSSIBLE LATE.
SATURDAY...CHANCE OF SHOWERS AND THUNDERSTORMS WITH MVFR
CONDITIONS POSSIBLE.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...FLASH FLOOD WATCH FROM THIS EVENING THROUGH THURSDAY AFTERNOON
     FOR ANOKA-BENTON-BLUE EARTH-BROWN-CARVER-CHISAGO-DAKOTA-
     HENNEPIN-ISANTI-KANABEC-KANDIYOHI-LE SUEUR-MARTIN-MCLEOD-
     MEEKER-MILLE LACS-MORRISON-NICOLLET-RAMSEY-REDWOOD-RENVILLE-
     SCOTT-SHERBURNE-SIBLEY-STEARNS-WASHINGTON-WATONWAN-WRIGHT.

WI...NONE.
&&

CLF/JM

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
504 AM CDT WED MAY 23 2012

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
241015-
DOUGLAS-TODD-MORRISON-MILLE LACS-KANABEC-STEVENS-POPE-STEARNS-
BENTON-SHERBURNE-ISANTI-CHISAGO-LAC QUI PARLE-SWIFT-CHIPPEWA-
KANDIYOHI-MEEKER-WRIGHT-HENNEPIN-ANOKA-RAMSEY-WASHINGTON-
YELLOW MEDICINE-RENVILLE-MCLEOD-SIBLEY-CARVER-SCOTT-DAKOTA-
REDWOOD-BROWN-NICOLLET-LE SUEUR-RICE-GOODHUE-WATONWAN-BLUE EARTH-
WASECA-STEELE-MARTIN-FARIBAULT-FREEBORN-POLK-BARRON-RUSK-
ST. CROIX-PIERCE-DUNN-PEPIN-EAU CLAIRE-
504 AM CDT WED MAY 23 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL AND
SOUTHERN MINNESOTA... AND WEST CENTRAL WISCONSIN.

.DAY ONE...TODAY AND TONIGHT

WIDESPREAD SHOWERS AND THUNDERSTORMS ARE EXPECTED TODAY AND
THURSDAY. WHILE THERE IS A SLIGHT RISK FOR SEVERE WIND OR HAIL
THIS AFTERNOON AND EVENING...THE MAIN HAZARD DURING THIS TIME
WILL LIKELY BE HEAVY RAINFALL...WHICH COULD BE AS HIGHS AS THREE
INCHES IN SOME LOCATIONS. THE TORNADO THREAT IS LOW. AGAIN...THE
HEAVY RAINFALL TONIGHT COULD LEAD TO FLOODING IN BOTH RURAL AND
URBAN AREAS...GENERALLY MINOR FLOODING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

SEVERAL MORE ROUNDS OF THE THUNDERSTORMS ARE POSSIBLE THURSDAY AND
OVER THE WEEKEND.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING.