Areal Flood Warning 25, NWS Twin Cities, MN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
131 PM CDT THU SEP 23 2010

.DISCUSSION...
MAIN FORECAST CONCERNS ARE ONGOING RAIN AND EXACERBATION OF THE
EXISTING FLOODING. SEVERE WEATHER THREAT IS ALSO A CONCERN FOR
THIS AFTERNOON INTO EARLY EVENING WITH LOW CAPE/HIGH SHEAR
ENVIRONMENT MOVING THROUGH THE AREA AS THE SURFACE LOW AND UPPER
WAVE MOVE THROUGH. LIMITED TIME TO GO INTO TOO MANY DETAILS ON THE
FORECAST GIVEN VARIOUS ISSUES BEING MONITORED. UTILIZED A BLEND OF
THE HRRR AND RUC FOR THE SHORT TERM ISSUES... THEN TRENDED TOWARD
THE GFS FOR THE NEXT FEW DAYS... BEFORE GOING TOWARD A GFS/ECMWF
BLEND FOR THE LATER PERIODS.

HIGH DEWPOINTS AHEAD OF THE SURFACE LOW ARE RACING INTO THE AREA
AT THE CURRENT TIME. 0-1KM SHEAR VALUES LOOK TO INCREASE TO ABOVE
40KT OVER THE SOUTHERN PORTION OF THE AREA OVER THE NEXT FEW HOURS
AS MLCAPE VALUES CLIMB INTO THE 100-300 J/KG RANGE. THIS LOW
CAPE/HIGH SHEAR ENVIRONMENT COULD LEAD TO THE DEVELOPMENT OF SOME
LOW TOPPED SUPERCELLS SIMILAR TO WHAT MIGHT BE SEEN IN A TROPICAL
CYCLONE ENVIRONMENT... WITH MINIMAL LIGHTNING BUT SOME THREAT FOR
SHORT-LIVED WEAK TORNADOES AS THE LOW LEVEL SHEAR AND VORTICITY
MAXIMA MOVE ACROSS THE AREA IN CONCERT WITH THE SLIGHT BOOST IN
CAPE. WILL NEED TO KEEP ON TOP OF TRENDS IN LOW LEVEL REFLECTIVITY
AND STORM RELATIVE VELOCITY DATA THROUGH THE AFTERNOON INTO EARLY
EVENING FROM SOUTH CENTRAL MINNESOTA INTO WEST CENTRAL
WISCONSIN... SINCE SHORT-LIVED VELOCITY COUPLETS COULD LEAD TO THE
AFOREMENTIONED BRIEF TORNADOES. IN ADDITION... WITH SO MUCH WIND
JUST OFF THE DECK... ANY OF THE HEALTHIER SHRA/TSRA COULD LEAD TO
DAMAGING WIND GUSTS... PARTICULARLY IF WE CAN GET A LINE MODE TO
DEVELOP ALONG/AHEAD OF THE COLD FRONT. RECENT RADAR TRENDS SUGGEST
THIS MAY BE OCCURRING TO THE SOUTHWEST OF US AT THE CURRENT
TIME... SO WILL NEED TO KEEP MONITORING THIS FOR THE POSSIBLE WIND
THREAT. EMBEDDED HEAVY RAIN WILL CONTINUE TO WORK ACROSS THE AREA
THROUGH EARLY EVENING UNTIL MID LEVEL DRYING TAKES PLACE AND
SQUASHES MOST OF THE PCPN. HOWEVER... IT APPEARS MOST OF THE
HEAVIEST WIDESPREAD RAIN THE REMAINDER OF THIS EVENING SHOULD
GENERALLY BE NORTH OF WHERE THE HEAVIEST HAS OCCURRED THUS FAR...
SO WE HOPEFULLY WON/T SEE TOO MUCH ADDITIONAL AGGRAVATION OF THE
ALREADY TENUOUS FLOOD CONDITIONS IN PLACE ACROSS THE SOUTHERN AND
SOUTHEASTERN PART OF THE AREA.

LOOK FOR SUBSIDENCE TO BEGIN WORKING IN TONIGHT... WITH GENERAL
IMPROVEMENT IN SRHA AND CLOUD COVER AS WE WORK THROUGH THE
OVERNIGHT AND THE DAY ON FRIDAY. LOOK FOR PCPN CHANCES TO RETURN
AGAIN LATE FRIDAY NIGHT AND PARTICULARLY ON SATURDAY INTO SATURDAY
EVENING AS A FAIRLY ROBUST SHORTWAVE ARRIVES ON NORTHWEST FLOW. DO
NOT EXPECT SIGNIFICANT PCPN AMOUNTS WITH THIS SYSTEM... BUT
FORCING LOOKS SUFFICIENT TO BRING A SWATH OF PCPN THROUGH THE AREA
AS IT MIGRATES ACROSS FROM NORTHWEST TO SOUTHEAST. ONCE THIS
SYSTEM GETS OUT OF THE AREA... WE SHOULD GENERALLY SEE A DRIER
NORTHWEST OR WESTERLY UPPER FLOW PREVAIL THROUGH THE MIDDLE OF THE
UPCOMING WEEK WITH GENERALLY DRY BUT SEASONABLY COOL WEATHER.
THERE IS SOME CHANCE FOR PCPN WITH ANOTHER NORTHWEST FLOW SHORTWAVE
ON MONDAY... AND AGAIN ON WEDNESDAY... BUT AT THIS TIME CHOSE TO
ONLY INCLUDE SOME LOW POPS OVER THE NORTHEAST ON WEDNESDAY SINCE
THAT FEATURE LOOKS TO BE A BIT MORE AMPLIFIED THAN THE FEATURE
PROGGED FOR MONDAY INTO MONDAY NIGHT. IN EITHER CASE... MOISTURE
RETURN WILL BE LIMITED... SO DO NOT EXPECT ANY SIGNIFICANT PCPN IF
THINGS DO MANAGE TO COME TOGETHER A BIT BETTER THAN CURRENTLY ADVERTISED.

&&

.AVIATION.../18Z TAF ISSUANCE/

SEVERAL FACTORS WILL CAUSE SIGNIFICANT AVIATION PROBLEMS FOR THE
NEXT 6 TO 12 HRS...OR UNTIL THE MAIN LOW AND ASSOCIATED AREA OF
TSRA/SHRA MOVES NORTHEAST OF THE FA. CURRENTLY SFC LOW IS ACROSS
SE SD...WHICH WILL MOVE QUICKLY TO THE NORTHEAST ACROSS
RWF/MSP/RNH BY 00Z. WNDS ALONG AND SOUTH OF THIS LOW WILL BE
GENERALLY FROM THE S/SE AND VSBYS/CEILINGS WILL LIKELY BE IN THE
MVFR/VFR RANGE UNTIL WNDS SHIFT TO THE SW/W. NORTH OF THE
LOW...WNDS WILL BE PREDOMINATELY E/NE WITH LOW
VSBYS/CEILINGS...ESPECIALLY FOR AXN/STC. THERE COULD BE A PERIOD
OF LOW END MVFR CEILINGS FOR STC/AXN DEPENDING UPON THE TRACK OF
THE LOW AND HOW MUCH MIXING IN THE LOW LEVELS DEVELOPS IN SHRA.
MAIN TSRA SHOULD BE S AND SE OF SFC LOW WHICH WILL BE MAINLY FOR
EAU. CBS ARE LIKELY FOR MSP/RNH DURING THE MID TO LATE AFTN
HRS...BUT TSRA IS NOT LIKELY AT THIS TIME. AFTER THE SFC LOW
MOVES NORTHEAST OF THE FA...EXPECT SHRA TO DECREASE ALONG WITH
INCREASING W/SW WNDS OVERNIGHT. KEPT CEILINGS IN THE IFR/MVFR
RANGE UNTIL MORE INFORMATION UPSTREAM DEVELOPS AS THE MAIN SYSTEM
MOVE AWAY.

MSP...PERIODS OF SHRA/+SHRA THRU 22Z...WITH CEILINGS VARIABLE
BETWEEN 900 AND 2000 FEET. SFC WNDS WILL LIKELY BE FROM THE
E/SE...THEN MORE S/SW AS THE SFC LOW MOVES OVERHEAD. WNDS WILL
BECOME MORE SW/W OVERNIGHT AND INCREASE SIGNIFICANTLY WITH GUSTS
NEAR 30 KTS. KEPT CEILINGS NEAR 1000 FEET...BUT THIS IS HIGHLY
VARIABLE DUE TO THE PROXIMITY OF THE SFC LOW AND HOW MUCH MIXING
DEVELOPS IN THE NEXT 6 HRS.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...FLOOD WATCH THROUGH FRIDAY MORNING FOR ANOKA-BENTON-BLUE EARTH-
     BROWN-CARVER-CHIPPEWA-CHISAGO-DAKOTA-DOUGLAS-FARIBAULT-
     FREEBORN-GOODHUE-HENNEPIN-ISANTI-KANABEC-KANDIYOHI-LAC QUI
     PARLE-LE SUEUR-MARTIN-MCLEOD-MEEKER-MILLE LACS-MORRISON-
     NICOLLET-POPE-RAMSEY-REDWOOD-RENVILLE-RICE-SCOTT-SHERBURNE-
     SIBLEY-STEARNS-STEELE-STEVENS-SWIFT-TODD-WASECA-WASHINGTON-
     WATONWAN-WRIGHT-YELLOW MEDICINE.

WI...FLOOD WATCH THROUGH FRIDAY MORNING FOR BARRON-CHIPPEWA-DUNN-EAU
     CLAIRE-PEPIN-PIERCE-POLK-RUSK-ST. CROIX.

&&

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1226 PM CDT THU SEP 23 2010

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
241200-
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-
1226 PM CDT THU SEP 23 2010

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

AREAS OF HEAVY RAINFALL WILL CONTINUE ACROSS THE OUTLOOK AREA
THROUGH EARLY EVENING. WIDESPREAD FLOODING HAS BEEN REPORTED
ACROSS SOUTHERN MINNESOTA AND THAT WILL CONTINUE THROUGH THIS
AFTERNOON AND LIKELY INTO THE NIGHTTIME HOURS. THIS INCLUDES
RAPIDLY RISING RIVERS AND STREAMS.

IN ADDITION...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS
THROUGH EARLY EVENING ACROSS SOUTH CENTRAL AND EASTERN MINNESOTA
AND WEST CENTRAL WISCONSIN. SCATTERED THUNDERSTORMS WILL HAVE THE
POTENTIAL TO INCREASE IN COVERAGE LATER THIS AFTERNOON AS LOW
PRESSURE LIFTS NORTHEAST. SOME OF THESE MAY BECOME SEVERE...WITH
THE PRIMARY THREATS BEING ISOLATED DAMAGING WINDS AND BRIEF
TORNADOES.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

HEAVY RAINFALL EXPECTED FROM THE WEDNESDAY AND THURSDAY STORM
SYSTEM WILL LEAD TO RISES ON MANY LOCAL STREAMS AND RIVERS. THIS
MAY RESULT IN SEVERAL RIVERS REACHING OR EXCEEDING FLOOD
STAGE...ESPECIALLY ACROSS CENTRAL MINNESOTA INTO WEST CENTRAL
WISCONSIN...FROM LATER THIS WEEK INTO NEXT WEEK.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EARLY
EVENING ACROSS SOUTH CENTRAL AND EASTERN MINNESOTA AND WEST
CENTRAL WISCONSIN. IN ADDITION...REPORTS OF FLOODING OR RAINFALL
AMOUNTS ARE GREATLY APPRECIATED.

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