Flash Flooding and Flooding in Minnesota, September 22 to 27, 2010

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
258 PM CDT WED SEP 22 2010

.SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT

MAIN FORECAST CONCERNS THIS PACKAGE...CONVECTION AND HEAVY RAIN
POTENTIAL TONIGHT INTO THU NIGHT...SHRA CHANCE SAT INTO SAT NIGHT...
TEMPERATURES.

DATA ANALYSIS AT 18Z HAD LOW PRESSURE IN EASTERN CO/WY...WITH
STRONGEST 3HR PRESSURE FALLS OF 2-3MB OVER SOUTHEAST ND TO EASTERN
NEB. THIS AIDED BY A SHORTWAVE SEEN IN WV IMAGERY NEAR THE NEB/SD
BORDER...WHICH APPEARS BEST HANDLED BY THE NAM WHICH IS STILL TOO
FAR NORTH WITH IT. A DIFFUSE WARM FRONT EXTENDED FROM NEAR KSUX
SOUTHEAST ACROSS IA TO NORTHERN IL. UPPER LEVEL DYNAMICS/DIVERGENCE
WITH THE SHORTWAVE...INCREASING 925-850MB MOISTURE TRANSPORT ON NOSE
OF AN INCREASING LOW LEVEL JET AND INCREASING INSTABILITY IN THE
INFLOW AIRMASS FUELING A COMPLEX OF TSRA WEST OF THE FCST AREA EARLY
THIS AFTERNOON. FCST MODELS NOT DOING EXCEPTIONALLY WELL WITH THIS
COMPLEX EARLY THIS AFTERNOON...BUT FOR MOST OF THE LOCAL/REGIONAL
WRF MODELS.

22.12Z MODEL RUNS INITIALIZED QUITE WELL AND OFFER RATHER SIMILAR
SOLUTIONS FOR TONIGHT INTO SAT NIGHT. STILL SOME MESO-SCALE
DIFFERENCES WHERE THE WARM FRONT ENDS UP AND RESULTING AXIS OF
CONVECTION AND GREATEST THREAT OF HEAVY/EXCESSIVE RAINS...BUT LESS
SO THAT THE TUE RUNS. DPROG/DT OF 500MB HGTS AT 22.12Z SHOWED MODEL
RUNS OF 20.12Z AND 21.12Z VERIFIED RATHER WELL ACROSS NOAM/EASTERN
PAC WITH MODELS TRENDING TOWARD A COMPROMISE OF THEIR EARLIER RUNS.
TREND CONTINUES TOWARD A COMPROMISE OF EARLIER RUNS THRU 36HRS...
FAVORING THE STRONGER OF THE EARLIER RUNS AS THE TROUGH MOVES INTO
THE CENTRAL/NORTHERN PLAINS. BETTER CONSENSUS IN THE 36-60HR PERIOD
AS THE TROUGH CROSSES THE REGION...AGAIN TOWARD A COMPROMISE OF THE
EARLIER RUNS...ESPECIALLY ON THE TIMING. TREND IS STRONGER WITH THE
NEXT SHORTWAVE TROUGH DROPPING INTO THE NORTHERN PLAINS. BETTER
CONSENSUS IN THE 60-84HR TIME-FRAME FAVORS A STRONGER/SLOWER
SOLUTION WITH THE NORTHERN STREAM SHORTWAVE DROPPING INTO THE
REGION. ECMWF WITH THE BETTER RUN-TO-RUN CONSISTENCY IN THE 36-84HR
PERIOD. CHECK OF OBS VS. MODEL DATA AT 18Z SHOWED MODELS REASONABLE
WITH THE SFC MASS FIELDS ACROSS THE CENTRAL CONUS. PER WV IMAGERY...
MODELS STRUGGLING WITH THE SHORTWAVE AIDING THE CONVECTIVE COMPLEX
WEST OF THE FCST AREA...GEM/GFS APPEAR TOO FAR EAST..NAM TOO FAR
NORTHWEST. AGAIN...MOST MODELS EXCEPT A FEW OF THE LOCAL/REGIONAL
WRF MODELS STRUGGLING WITH THE SOUTHEAST SD/NORTHWEST IA/SOUTHWEST
MN CONVECTION THIS MORNING/EARLY THIS AFTERNOON. MOST WEAK/SLOW AND
APPEAR THEY WILL BE TOO FAR NORTH WITH THE PRECIP IN THE 18-00Z
TIME-FRAME. THAT SAID...GENERALLY FAVORED THE MODEL/ENSEMBLE
CONSENSUS...LEANING TOWARD THE MORE SOUTHERLY SOLUTIONS WITH THE
HEAVY RAIN TONIGHT INTO THU NIGHT. GIVEN THE DIFFERENCES...AND
SIGNIFICANT IMPACTS TO THE SENSIBLE WEATHER THE NEXT COUPLE DAYS...
SHORT-TERM FCST CONFIDENCE AVERAGE THIS CYCLE.

IN THE SHORT TERM...LOW LEVEL JET/MOISTURE TRANSPORT CONTINUES TO
INCREASE INTO THE SHRA/TSRA COMPLEX WEST OF THE AREA THIS AFTERNOON/
EVENING...MOVING EAST/NORTHEAST AS THE SD/NEB SHORTWAVE TRACKS EAST-
NORTHEAST THRU THIS EVENING. WITH CONVECTION SOUTH/REMAINING SOUTH
OF MOST MODEL TRACKS...HAVE INCREASED RAIN CHANCES THIS EVENING TO
80-100 PERCENT OVER THE NORTHWEST HALF OF THE FCST AREA. WITH
STORMS IN KFSD AREA ALREADY HAVING A HISTORY OF HEAVY RAINS...PW
VALUES/MOISTURE TRANSPORT OF THE INFLOW AIRMASS INCREASING THRU THIS
EVENING...WARM CLOUD DEPTH OF AROUND 4.5KM FOR DEEP WARM-RAIN
PROCESS...EXPANDED FLOOD WATCH SOUTHWARD TO ALL OF SOUTHEAST MN TO
LSE AND MONROE COUNTIES IN WI...STARTING 00Z WEST OF THE MS RIVER.
SLIGHT RISK OF SEVERE STORMS THIS EVENING...WITH LARGE HAIL THE MAIN
THREAT. SEE SWODY1 FOR DETAILS. LEAD SHORTWAVE TRACKS NORTHEAST OF
THE AREA LATER TONIGHT...WITH PERHAPS A BREAK FROM THE DEEP
FORCING/LIFT INTO THU MORNING. WITH NEXT STRONG SHORTWAVE AND THE
SFC LOW HEADED TOWARD THE AREA THU...LOW LEVEL JET QUICKLY BACKS AND
REFOCUSES TO FUEL CONVECTION AHEAD OF THE LOW/SHORTWAVE. DEEP/
STRONG FORCING/LIFT WITH THIS SYSTEM OVER THE AREA FOR THU...WITH AN
AIRMASS WITH PW VALUES OF 2 INCHES OR MORE...SOME 250 PERCENT OF
NORMAL...TO ACT UPON. WARM CLOUD DEPTH REMAINS AROUND 4.5KM...WITH
RAINFALL RATES OF 2+ INCHES/HR POSSIBLE. ANY OF THIS RAIN ON TOP OF
RAIN THAT FALLS TONIGHT COULD AND WOULD LIKELY PRODUCE SIGNIFICANT
RUNOFF. HOWEVER...WHERE THE HEAVIEST RAIN IS LIKELY TO FALL REMAINS
IN QUESTION...DEPENDING ON WHERE THE IA/NORTHERN IL WARM FRONT ENDS
UP. ANY ONGOING CONVECTION TONIGHT/EARLY THU WILL PREVENT THIS
BOUNDARY FROM MOVING AS FAR NORTH AS MANY MODELS INDICATE...AND
WOULD MOVE THE HEAVY RAIN THREAT FURTHER SOUTH INTO THE FCST AREA.
FLOOD WATCH FOR ROUGHLY THE NORTHWEST HALF OF THE FCST AREA
CONTINUED THRU THU/THU NIGHT. SHRA/TSRA CHANCES OF 80-100 PERCENT
ACROSS THE NORTHWEST 2/3 OF THE FCST AREA THU. THE LOW TRACKS INTO
THE U.P OF MI BY 12Z FRI...DRAGGING THE TRAILING COLD FRONT ACROSS
THE FCST AREA ROUGHLY 02Z-07Z THU NIGHT...INTO THE UNSEASONABLY
MOIST AIRMASS. A LINE OF SHRA/TSRA EXPECTED TO ACCOMPANY THE FRONT
ACROSS THE AREA. DRYING/ SUBSIDENCE TO SPREAD ACROSS THE AREA LATER
THU NIGHT...WITH A RAPID DECREASE OF SHRA AND END OF TSRA ONCE IT
PASSES. WRAP AROUND 850-700MB MOISTURE AND MID LEVEL TROWAL ROTATE
ACROSS THE AREA FRI...WITH A LINGERING -SHRA CHANCE OVER MAINLY THE
NORTHEAST HALF OF THE FCST AREA FRI MORNING. WEAK RIDGE OF HIGH
PRESSURE FOR FRI NIGHT...WITH NEXT NORTHERN STREAM TROUGH ALREADY
DIGGING/AMPLIFYING TOWARD THE AREA FOR SAT/SAT NIGHT. WITH THE TREND
TOWARD A STRONGER MID LEVEL TROUGH TO MOVE ACROSS THE AREA SAT/SAT
NIGHT...RAISED/EXPANDED -SHRA CHANCE ACROSS THE FCST AREA FOR SAT
AFTERNOON AND ADDED A -SHRA CHANCE TO MOST OF THE FCST AREA FOR SAT
NIGHT.

GUIDANCE HIGHS/LOWS THRU THE PERIOD GENERALLY SIMILAR AND GENERALLY
FAVORED A COMPROMISE MOST PERIODS. WITH PLENTY OF CLOUDS/SHRA/TSRA
EXPECTED THU...TRENDED HIGHS A FEW DEGREES BELOW GUIDANCE VALUES
AND THIS MAY STILL NOT BE ENOUGH.

.LONG TERM...SUNDAY THROUGH WEDNESDAY

ALL MEDIUM RANGE MODELS HAVE TRENDED TOWARD THE STRONGER...OUTLIER
LOOKING SOLUTIONS SHOWN BY THE ECMWF THEN GFS OVER THE PAST COUPLE
DAYS OF RUNS. IN SPITE OF THE STRONG SHIFT IN THE 22.00 MEDIUM RANGE
MODELS WITH THE SAT/SAT NIGHT SYSTEM...SENSIBLE WEATHER FCST FOR
DAYS 4-7 SHOWS SURPRISING CONTINUITY FROM FCST 24HRS AGO. WITH THE
TREND OF ALL MODELS TOWARD A STRONGER UPPER LOW TO SINK SOUTH ACROSS
THE REGION OVER THE WEEKEND...BE OVER THE MID MS VALLEY MON...THEN
SLOWLY LIFT NORTHEAST TUE/WED...MODEL RUN-TO-RUN CONSISTENCY WITH
MOST 20.00Z AND 21.00Z RUNS ON THE POOR SIDE. HOWEVER...ECMWF DOES
SHOW SOME MODEST RUN-TO-RUN CONSISTENCY BY LATE TUE AND WED WITH
TROUGHING OVER THE EASTERN CONUS. WITH THE UPPER LOW SINKING INTO
THE MID MS VALLEY SUN...MODELS DO SHOW SOME CONSISTENCY FOR
SHORTWAVE RIDGING ALOFT OVER THE UPPER MIDWEST SUN INTO MON. SOME
BETTER CONSISTENCY FOR A NORTHERN STREAM SHORTWAVE TO DROP INTO THE
REGION LATE MON INTO TUE...WITH SHORTWAVE RIDGING RETURNING FOR
LATER TUE AND WED. GIVEN THE STRONG TRENDS/SHIFTS IN MODELS SAT/
SUN...LONG-TERM FCST CONFIDENCE AVERAGE AT BEST THIS CYCLE. LIKE
HPC...PREFERRED A SOLUTION WEIGHTED TOWARD ECMWF WHICH LOOKS TO BEST
REPRESENT A COMPROMISE SOLUTION. SHORTWAVE RIDGING ALOFT AND SFC
HIGH PRESSURE ARE OVER THE REGION SUN/MON...FOR A CONTINUED DRY FCST
THESE DAYS. NORTHERN STREAM SHORTWAVE AND COLD FRONT FOR LATER
MON/MON NIGHT ARE SQUEEZED/WEAKENED AS THEY APPROACH AND THE MID MS
VALLEY LOW BEGINS TO LIFT NORTHEAST. CIRCULATION OF THIS SYSTEM MAY
IMPACT THE SOUTHEAST END OF THE FCST AREA AS IT PASSES MON NIGHT/
TUE. GIVEN LOW CONFIDENCE AND PLENTY OF MODEL UNCERTAINTY...WILL
LEAVE THESE PERIODS DRY AS WELL. SHORTWAVE RIDGING ALOFT AND HIGH
PRESSURE RETURN FOR WED. NUMERICAL TEMP GUIDANCE REASONABLY SIMILAR
THRU THE PERIOD AND LOOK GOOD...THOUGH DID FAVOR HPC GUIDANCE WHICH
INCORPORATED MORE OF THE ECMWF SOLUTION.

&&

.AVIATION...TONIGHT AND THURSDAY

CURRENTLY WATCHING A STRONG AREA OF LOW PRESSURE OVER THE CENTRAL
PLAINS LIFTING A WARM FRONT NORTHWARD INTO NORTHERN IA. STRONG
CONVECTION TAKING PLACE ALONG AND AHEAD OF THIS WARM FRONT AS LOW
LEVEL MOISTURE TRANSPORT INCREASES. THIS WILL CONTINUE TO FUEL
SHRA/TS ACTIVITY INTO THIS EVENING ACROSS SOUTHEAST MN/SOUTHWEST WI
INCLUDING THE KRST/KLSE TAF SITES. EXPECTING WIDESPREAD MVFR/IFR
CONDITION WITH ABUNDANT LOW LEVEL MOISTURE AND SHRA/TS ACTIVITY.
EXPECTING SHRA/TS ALONG WITH MVFR/IFR CONDITIONS TO REMAIN IN THE
VICINITY THROUGH THURSDAY MORNING AS THE WARM FRONT HANGS UP ALONG
THE I-90/94 CORRIDOR. THE COLD FRONT FROM THIS LOW PRESSURE SYSTEM
IS THEN EXPECTED TO SWEEP EASTWARD THROUGH THE AREA LATE THURSDAY
AFTERNOON/THURSDAY EVENING...FUELING MORE SHRA/TS ACTIVITY. LATER
SHIFTS WILL COVER THIS MORE IN DETAIL WITH SUBSEQUENT SETS OF
TAFS.

&&

.HYDROLOGY...TONIGHT AND THURSDAY

A STRONG LOW PRESSURE SYSTEM AND SHORTWAVE TROUGH WILL MOVE INTO
THE CENTRAL PLAINS TONIGHT THEN INTO MN THU. A VERY HUMID AIRMASS
WILL BE IN PLACES AHEAD OF THIS LOW WITH SHRA/TSRA EXPECTED ACROSS
THE ENTIRE FORECAST AREA THROUGH THURSDAY NIGHT. PRECIPITABLE WATER
VALUES WILL INCREASE TO 200-250 PERCENT OF NORMAL...AND WITH THE
WARM CLOUD DEPTHS OVER 4KM...STRONG POTENTIAL EXISTS FOR TORRENTIAL
DOWNPOURS AND LOCALLY HEAVY RAINS. AT THIS TIME IT APPEARS THE
GREATEST THREAT FOR HEAVY RAIN WILL BE ALONG/NORTH OF A KAUM-KLSE-
TOMAH WI LINE. CONSENSUS OF FCST MODELS PRODUCE 2 TO AS MUCH AS 6
INCHES OF RAIN WITH THIS SYSTEM TONIGHT THRU THU EVENING. EXACTLY
WHERE THE HEAVIEST RAINS WILL FALL REMAINS IN QUESTION...DEPENDING
ON THE LOCATION OF A WARM FRONT AHEAD OF THE LOW...AND WHERE THE
SHRA/TSRA FIRST START. WITH THE FRONT NOT MOVING MUCH TODAY AND
SHRA/TSRA ALREADY SOUTH OF WHERE MOST FCST MODEL INDICATE...HAVE
EXPANDED FLOOD WATCH SOUTH TO INCLUDE ALL OF SOUTHEAST MN AND PARTS
OF WI NORTH OF KLSE-TOMAH. WITH CONVECTION HEADED INTO SOUTHEAST MN
ALREADY THIS EVENING...MOVED START TIME OF THE WATCH WEST OF THE MS
RIVER UP TO 00Z THIS EVENING...AND LEFT IT TO START EAST OF THE MS
RIVER AT 06Z TONIGHT. WATCH RUNS THRU 12Z FRI MORNING ALL AREAS.
THIS IS A POTENTIALLY VERY DANGEROUS FLOODING SITUATION.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...FLOOD WATCH FROM 1 AM CDT THURSDAY THROUGH FRIDAY MORNING FOR
     WIZ017-WIZ029-WIZ032-WIZ033-WIZ034-WIZ041-WIZ042.

MN...FLOOD WATCH FROM 7 PM CDT THIS EVENING THROUGH FRIDAY MORNING
     FOR MNZ079-MNZ086-MNZ087-MNZ088-MNZ094-MNZ095-MNZ096.

IA...NONE.
&&

SHORT/LONG TERM...RRS
HYDROLOGY.........RRS
AVIATION..........DAS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE LA CROSSE WI
1231 PM CDT WED SEP 22 2010

IAZ008>011-018-019-029-030-MNZ086>088-094>096-WIZ041>044-053>055-061-
231100-
ADAMS-ALLAMAKEE-CHICKASAW-CLAYTON-CRAWFORD-DODGE-FAYETTE-FILLMORE-
FLOYD-GRANT-HOUSTON-HOWARD-JUNEAU-LA CROSSE-MITCHELL-MONROE-MOWER-
OLMSTED-RICHLAND-VERNON-WINNESHIEK-WINONA-
1231 PM CDT WED SEP 22 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PARTS OF SOUTHEAST
MINNESOTA...NORTHEAST IOWA...AND SOUTHWEST AND CENTRAL WISCONSIN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A WARM FRONT EXTENDING EAST FROM A LOW PRESSURE SYSTEM OVER
EASTERN COLORADO WILL BE THE FOCUS FOR THUNDERSTORMS THIS
AFTERNOON AND INTO TONIGHT. THERE WILL BE ENOUGH INSTABILITY AND
FAVORABLE WIND PROFILES TO SUPPORT STRONG...TO POSSIBLY SEVERE
THUNDERSTORMS THIS EVENING. LARGE HAIL WOULD BE THE MAIN THREAT...
WITH DAMAGING WINDS AND ISOLATED TORNADOES ALSO POSSIBLE.

IN ADDITION...AN UNUSUALLY MOIST AIR MASS IN THE ATMOSPHERE WILL
PROMOTE A HEAVY RAIN POTENTIAL. HIGH RAINFALL RATES WITH THE
STRONGEST STORMS COULD RESULT IN STREET AND OTHER URBAN FLOODING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH WEDNESDAY

THUNDERSTORMS WILL CONTINUE TO BE POSSIBLE ALONG AND NORTH OF THE
WARM FRONT THURSDAY. HEAVY RAIN WILL BE THE MAIN THREAT FROM THESE
STORMS...WITH LARGE HAIL OR DAMAGING WINDS NOT ANTICIPATED AT THIS
TIME. BY THURSDAY EVENING...A COLD FRONT TRACKING EAST OUT OF THE
PLAINS COULD SPAWN A LINE OF THUNDERSTORMS. THIS LINE WOULD HAVE A
GREATER THREAT OF LARGE HAIL AND DAMAGING WINDS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING AND COULD
ALSO BE NEEDED FOR THURSDAY EVENING. RAINFALL AND ANY FLOODING
REPORTS OVER THE NEXT COUPLE DAYS WOULD BE APPRECIATED.

.EMERGENCY MANAGEMENT COORDINATION...

A CONFERENCE CALL IS SCHEDULED AT 3 PM.

MNZ079-WIZ017-029-032>034-231100-
BUFFALO-CLARK-JACKSON-TAYLOR-TREMPEALEAU-WABASHA-
1231 PM CDT WED SEP 22 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PARTS OF SOUTHEAST MINNESOTA...
WESTERN AND NORTH CENTRAL WISCONSIN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

A WARM FRONT EXTENDING EAST FROM A LOW PRESSURE SYSTEM OVER
EASTERN COLORADO WILL BE THE FOCUS FOR THUNDERSTORMS LATE THIS
AFTERNOON AND INTO TONIGHT. THERE WILL BE ENOUGH INSTABILITY AND
FAVORABLE WIND PROFILES TO SUPPORT STRONG...TO POSSIBLY SEVERE
THUNDERSTORMS THIS EVENING. LARGE HAIL WOULD BE THE MAIN THREAT...
WITH DAMAGING WINDS AND ISOLATED TORNADOES ALSO POSSIBLE.

IN ADDITION...AN UNUSUALLY MOIST AIR MASS IN THE ATMOSPHERE WILL
PROMOTE A HEAVY RAIN POTENTIAL. HIGH RAINFALL RATES WITH THE
STRONGEST STORMS WILL RESULT IN PONDING OF WATER AND SIGNIFICANT
RISES ON AREA RIVERS AND STREAMS. CURRENTLY...LOCATIONS ALONG AND
NORTH OF A ZUMBRO FALLS MINNESOTA TO BLACK RIVER FALLS WISCONSIN LINE
LOOK TO BE AT THE HIGHEST RISK FOR HEAVY RAINFALL.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH WEDNESDAY

SHOWERS AND SCATTERED THUNDERSTORMS ARE LIKELY FOR THURSDAY AND
THURSDAY NIGHT...WITH HEAVY RAIN THE MAIN THREAT. TOTAL
RAINFALL FROM WEDNESDAY AND THURSDAY OF 2 TO 3 INCHES...WITH LOCALLY
HIGHER AMOUNTS...ARE POSSIBLE. THIS...ALONG WITH HIGH RAINFALL
RATES...WILL LEAD TO SIGNIFICANT RISES ON AREA STREAMS AND RIVERS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING AND COULD
ALSO BE NEEDED FOR THURSDAY EVENING. RAINFALL AND ANY FLOODING
REPORTS OVER THE NEXT COUPLE DAYS WOULD BE APPRECIATED.

.EMERGENCY MANAGEMENT COORDINATION...

A CONFERENCE CALL IS SCHEDULED AT 3 PM.

DTJ