Flash Flood in Minnesota, September 30, 2007

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1059 PM CDT SUN SEP 30 2007

.AVIATION... /06Z TAFS/
UPR LOW HAS MOVED INTO CNTRL IA...AND WILL CONTINUE ITS EWRD
MOVEMENT. BACK EDGE OF LO CLD SHIELD IS EVIDENT FROM APPROX LXL TO
MVE. AXN SHUD REMAIN VFR THRU THE DURATION...WITH LO
CLDS/BR...RESULTING IN SOME IFR CIGS/MVFR VSBYS...GRADUALLY ERODING
FROM W TO E AS THE UPR LOW MOVES AWAY. EAU MAY HANG ONTO THIS WELL
INTO THE AFTN...WITH THE LATEST NAM PROGS SHOWING A LOT OF LO LVL
MSTR REMAINING. WINDS WL SHIFT TO A SERLY DIRN BY THE AFTN/EVE AS
THE TRAILING SFC RDG MOVES TO THE E. AXN/RWF/STC MAY SEE SOME HI
CLDS LATE IN THE VALID TAF PERIOD FROM THE NEXT STORM SYSTEM.

&&

.PREV DISCUSSION... /ISSUED 343 PM CDT SUN SEP 30 2007/
WET EVENING AHEAD AS STRONG UPPER LOW CIRCULATION SPINS OVER
CENTRAL NEBRASKA AND STEADILY MOVES EASTWARD. VISIBLE SATELLITE
SHOWS CLEARING OCCURRING ACROSS EASTERN NEBRASKA/WESTERN IOWA AND
POKING INTO SOUTHWEST MINNESOTA. RADAR LOOP SHOWS THE
DIVERGENCE/DIFFLUENCE IN THE ATMOSPHERE AHEAD OF THE UPPER LOW AND
THE 90 KT SPEED MAX NOSING INTO SOUTHERN MINNESOTA AS SHOWERS AND
ISOLATED THUNDERSTORMS DEVELOP OVER EAST CENTRAL MINNESOTA AND
WEST CENTRAL WISCONSIN AND RACE NORTHEASTWARD. DEFORMATION AXIS
EVIDENT ON RADAR MOSAIC WITH PRECIP ACTIVITY FROM THE WESTERN TIP
OF THE CWA SOUTH-SOUTHWEST INTO EASTERN NEBRASKA. THIS WILL PASS
ACROSS THE CWA THE REST OF THE AFTERNOON AND THIS EVENING BRINGING
BANDS OF MODERATE TO OCCASIONALLY HEAVY RAIN AND THUNDERSTORMS.
STEEP LAPSE RATES IN THE COLD POOL OF THE UPPER LOW MAY ALLOW FOR
SOME HAIL DEVELOPMENT IN THE STRONGEST UPDRAFTS WITH THESE STORMS.
NEXT CONCERN IS FOR ADDITIONAL DEVELOPMENT IN THE WARM AND
UNSTABLE AIR ACROSS EASTERN NEBRASKA AND WESTERN IOWA AHEAD OF SFC
LOW POSITIONED OVER EASTERN NEBRASKA. THIS ACTIVITY WILL RACE
NORTHEASTWARD TOWARDS THE EASTERN CWA LATE THIS AFTERNOON AND
EARLY THIS EVENING. WILL BE SMALL SEVERE THREAT ACROSS THE FAR
SOUTH NEAR THE IOWA BORDER EARLY THIS EVENING. SFC TROUGH AXIS AND
UPPER LOW CLEAR THE CWA LATE THIS EVENING ALLOWING DRIER AND
COOLER AIR TO FILL IN.

AFTERNOON WATER VAPOR IMAGERY SHOWS NEXT TROUGH TO BRING SHOWERS AND
THUNDERSTORMS TO THE AREA NOW DIGGING INTO THE PACIFIC NORTHWEST.
THIS TROUGH DE-AMPLIFIES AS IT CROSSES THE WESTERN CONUS AS FLOW
BECOMES ZONAL BEHIND IT. SFC LOW DEVELOPS OVER ALBERTA WITH A TROUGH
EXTENDING SOUTHWARD INTO THE SOUTHERN PLAINS BY MONDAY NIGHT. AREA
OF WARM ADVECTION NOSES INTO THE SOUTHWEST CWA LATE MONDAY NIGHT
WITH COOL FRONT QUICKLY ENTERING MINNESOTA TUESDAY MORNING JUST
AHEAD OF UPPER TROUGH. HAVE CONTINUED WITH HIGH CHANCE POPS TUESDAY.
FAST ZONAL FLOW WITH 100+ KT UPPER JET PUNCHING ACROSS THE NORTHERN
CONUS WILL HELP THE TROUGH QUICKLY EXIT SO HAVE TRIMMED POPS TUESDAY
EVENING. HIGH PRESSURE PASSES TO THE SOUTH WEDNESDAY WITH HINTS OF A
WEAK UPPER WAVE CROSSING WEDNESDAY NIGHT.

A DEEP UPPER TROUGH DIGS TOWARDS THE ALEUTIAN ISLANDS WEDNESDAY AND HELPS
TO FORCE THE DEVELOPMENT OF A LONGWAVE TROUGH AXIS ALONG THE WEST
COAST OF NORTH AMERICA THURSDAY. AS A RESULT THE ZONAL PATTERN OF
MID WEEK TURNS SOUTHWESTERLY OVER THE LOCAL AREA. SFC CYCOLGENESIS
TAKES PLACE IN THE LEE OF THE ROCKIES INTO FRIDAY AS WARM MOIST AIR
STREAMS INTO THE REGION. WARM ADVECTION SETS UP AHEAD OF THE SYSTEM
THURSDAY NIGHT OR FRIDAY MORNING BRINGING CHANCES FOR RAIN
DEVELOPMENT. WARM FRONT/INVERTED TROUGH SETS UP ACROSS THE EASTERN
DAKOTAS/WESTERN MINNESOTA FRIDAY WITH VERY STRONG MID LEVEL TEMP
GRADIENT. WILL LIKELY BE A LARGE SFC TEMP GRADIENT SETTING UP AS
WELL BUT THIS WILL BE DIFFICULT TO PIN DOWN. VERY WARM TEMPS ARE
EXPECTED ACROSS THE CENTRAL AND EASTERN CWA FRIDAY. THE UPPER TROUGH
PUSHES INTO THE DAKOTAS SATURDAY AND BRINGS THE SFC LOW NORTHEAST
DRAGGING A COLD FRONT ACROSS THE CWA. MANY DETAILS STILL NEED TO BE
FIGURED OUT SUCH AS THE EVOLUTION OF THE SFC LOW...ITS TRACK...AND
TIMING. RECENT RUNS SHOW HAVE TENDED TO SPEED THE SYSTEM UP WITH
FRONTAL PASSAGE OCCURRING SATURDAY. WOULD NOT BE SURPRISED TO SEE
EARLY MORNING HIGHS IN THE NORTHWEST WITH TEMPS FALLING DURING THE
DAY BUT AGAIN...THE DETAILS ARE YET TO BE CLEAR. ANOTHER BIG
QUESTION IS THE MAGNITUDE OF COLD AIR WITH THE SYSTEM. HAVE
DECREASED TEMPS BEHIND THE FRONT SATURDAY AND HIGHS SUNDAY. HIGHS
SEVERAL DEGREES BELOW NORMAL LOOK POSSIBLE BEHIND THE FRONT SATURDAY
AND AGAIN SUNDAY.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...NONE.
WI...NONE.
&&

KAT/MDB

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
342 PM CDT SUN SEP 30 2007

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
012045-
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-
342 PM CDT SUN SEP 30 2007

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS FAR SOUTHERN
MINNESOTA. SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP
ACROSS WESTERN IOWA OVER THE NEXT SEVERAL HOURS AND MOVE NORTHEAST
TOWARDS THE MINNESOTA/IOWA BORDER. THESE STORMS MAY PRODUCE LARGE
HAIL AND DAMAGING WINDS. OTHER THUNDERSTORMS WILL MOVE ACROSS
SOUTH CENTRAL MINNESOTA THIS AFTERNOON AND THIS EVENING AS AN
UPPER LEVEL LOW CROSSES THE AREA. ISOLATED LARGE HAIL MAY OCCUR
WITH THE STRONGEST OF THESE STORMS...ESPECIALLY SOUTH OF A
MONTEVIDEO TO HUTCHINSON TO TWIN CITIES LINE. HEAVY DOWNPOURS AND
REDUCED VISIBILITY WILL BE POSSIBLE IN ALL SHOWERS AND
THUNDERSTORMS THROUGH THE EVENING. BE ALERT FOR PONDING OF WATER ON
ROADWAYS SUCH AS UNDER OVERPASSES AND IN AREAS WHERE LEAVES MAY
CLOG SEWER INLETS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

ANOTHER LOW PRESSURE SYSTEM IS EXPECTED TO CROSS THE REGION ON
TUESDAY LEADING TO THUNDERSTORM CHANCES ONCE AGAIN.  THERE IS A
SLIGHT RISK SOME OF THESE THUNDERSTORMS MAY BE SEVERE.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION MAY BE NEEDED.

MDB

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
519 PM CDT SUN SEP 30 2007

MNZ064-073-302300-
REDWOOD-YELLOW MEDICINE-
519 PM CDT SUN SEP 30 2007

...SIGNIFICANT WEATHER ALERT FOR YELLOW MEDICINE AND REDWOOD
COUNTIES UNTIL 600 PM CDT...

AT 516 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR WAS TRACKING A
STRONG THUNDERSTORM NEAR MARSHALL...OR 11 MILES SOUTHEAST OF GHENT...
AND MOVING NORTHEAST AT 25 MPH.

SMALL HAIL IS EXPECTED WITH THIS STORM.

SOME LOCATIONS THAT MAY BE IMPACTED BY THIS STORM INCLUDE
VESTA...MILROY...AND LUCAN.

PEOPLE IN NORTHWESTERN REDWOOD AND SOUTHEASTERN YELLOW MEDICINE
COUNTIES...SHOULD MONITOR THE WEATHER SITUATION CLOSELY. LISTEN FOR
POSSIBLE WARNINGS AND BE PREPARED TO TAKE APPROPRIATE ACTION SHOULD
SEVERE WEATHER THREATEN.

KAT