Areal Flood Advisory 49, NWS Twin Cities, MN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
942 PM CDT FRI AUG 5 2011

.UPDATE...

UPDATED TO INCLUDE RECENT CONVECTIVE ACTIVITY AND LATEST TRENDS
THROUGH THE OVERNIGHT HOURS.

&&

.DISCUSSION...

SEVERAL MESOSCALE CONVERGENCE BOUNDARIES APPEARING ON LAST FEW
IMAGES OF VISIBLE SATELLITE HAVE ALLOWED A NARROW BAND OF SLOW-
MOVING THUNDERSTORMS TO DEVELOP OVER CENTRAL PORTIONS OF THE MPX
CWFA. SFC OBSERVATIONS INDICATE PRIME LOW LEVEL CONVERGENCE WINDS
WITHIN A DEEPLY MOIST ENVIRONMENT /SFC DEWPOINTS IN THE UPR 60S
AND PWATS NEAR 1.5 INCHES/. TSTMS QUICKLY DEVELOPED AND SPOTTER
REPORTS INDICATE RAINFALL RATES IN THE 1.0-1.5 INCH/HR RANGE. AM
NOT EXPECTING ACTIVITY TO LAST MUCH INTO THE OVERNIGHT
HOURS...EVEN IF THAT LONG...MAINLY DUE TO THE LOSS OF DAYTIME
HEATING AND LOSS OF PRIME INSTABILITY. SPC ANALYSIS STILL PUTS
CAPES NEAR 1500 J/KG...LI NEAR -6 DEG C...AND DECENT MOISTURE
TRANSPORT FROM THE SE SO WOULD NOT BE SURPRISED TO SEE SOME AREAS
RECEIVE NEAR AN INCH OF RAIN OVER THE NEXT HOUR OR SO. HAVE
TWEAKED GRIDS TO SHOW A BAND OF 40-50 POPS OVER CENTRAL
MN INTO W CENTRAL WI...GENERALLY ALONG A LINE FROM MONTEVIDEO TO
OAK GROVE TO EAU CLAIRE...WITH POPS QUICKLY DROPPING OFF TO THE N
AND S. HAVE MAINTAINED 30-40 POPS NEAR THE IA BORDER DUE TO
SHOWERS DRIFTING E NEAR A WEAK STALLED SFC BOUNDARY.

WELL AFTER MIDNIGHT...WINDS ARE EXPECTED TO DROP TO NEAR CALM FOR
CENTRAL AND SOUTHEASTERN PORTIONS OF THE CWFA. WITH PRECIPITATION
EXPECTED TO END BY THE EARLY MORNING HOURS...GIVEN ENOUGH CLEARING
THERE MAY WELL BE AREAS OF FOG DEVELOPING. SREF PINS IT MAINLY
OVER FAR WRN AND FAR SERN PORTIONS OF THE CWFA...BUT WINDS DROP
OFF MOST IN SERN PORTIONS SO HAVE PLAYED CENTRAL THROUGH SERN
PORTIONS OF THE CWFA THAT COULD SEE FOG OVERNIGHT. THIS MAY ALSO
PLAY INTO TEMPERATURES BY KEEPING THEM HIGHER THAN FCST. HAVE
NUDGED UP TEMPS 1-2 DEGREES SE WHILE KEEPING MOST OTHER AREAS AS-
IS...BUT THIS MAY NEED TO BE ADJUSTED PER HOURLY TRENDS OVERNIGHT.

&&

.AVIATION.../00Z TAF ISSUANCE/

COMPLEX PERIOD AHEAD...WITH QUESTION MARKS SURROUNDING STRATUS/FOG
POTENTIAL TONIGHT...FOLLOWED BY TIMING OF THUNDERSTORMS ACROSS THE
MN TERMINALS AT THE END OF THE PERIOD. FOR TONIGHT...NOT EXPECTING
ANY CONVECTION TO IMPACT TERMINALS...WITH ACTIVITY OVER IA COMING
ABOUT AS FAR NORTH AS I-90...NRN MN ACTIVITY IS STRUGGLING TO HOLD
TOGETHER AS IT SLIDES SOUTH OF A STATIONARY BOUNDARY...WHILE
SEVERE CONVECTION OVER THE WRN DAKOTAS IS NOT IMPLICATED BY THE
LOCAL WRF TO POSSIBLY EVEN ENTER THE AXN AREA UNTIL AFTER 12Z.
ONCE AGAIN GFSLAMP IS HITTING FOG QUITE HARD TONIGHT...BUT THERE
ARE SIGNS FROM CURRENT OBS AND THE RUC 925 MB FORECAST ACROSS SRN
MN/NRN IA THAT WE MAY END UP WITH A BANK OF STRATUS WORKING NORTH
ACROSS MN TONIGHT. BASED ON THE RUC FORECAST...IF A STRATUS DECK
GETS GOING...IT WOULD MOST LIKELY FORM ACROSS SRN MN AND WORK
NORTH ACROSS MAINLY WRN MN...HAVE GONE WITH THIS IDEA FOR RWF. FOR
THE FOG...WENT CLOSE TO WHAT WAS OBSERVED LAST NIGHT FOR
STC/RNH/EAU. FOR THUNDER CHANCES OVER MN IN THE AFTERNOON...
FOLLOWED SREF PROBS FOR TIMING. AT THIS POINT...HAVE FAIRLY WIDE
WINDOWS OF CONVECTIVE POTENTIAL AT MN TERMINALS THAT CAN BE
NARROWED DOWN AS WE GET A BETTER HANDEL ON CONVECTION TONIGHT
IMPACTS WHERE/WHEN STORMS GET GOING EARLY SAT AFTERNOON ACROSS THE
ERN DAKOTAS.

KMSP...MAIN POINT OF CONTENTION FOR TONIGHT IS THE POSSIBILITY OF
SOME MVFR OR LOWER STRATUS TO MOVE IN BY THE MORNING. THE 18Z NAM
GIVES THE IDEA OF LOWER CLOUDS APPROACHING FROM THE SOUTH TOWARD
SUNRISE. CONFIDENCE LOW IN THIS OCCURRING AT THE TIME...BUT A
SMATTERING STATIONS OVER IA AND SW MN ALREADY SHOWING MVFR
CIGS...SO THIS IS A POSSIBILITY THAT CAN NOT BE RULED OUT. FOR
TIMING OF THUNDER IN THE AFTERNOON...IF ANYTHING THE 22Z START
TIME IS TOO EARLY AND MAY BE MORE LIKE THE 00Z TO 02Z TIME PERIOD
FOR CONVECTION...BUT HAVE A COUPLE OF MORE TAFS TO IRON OUT THE
TIMING.

&&

.PREV DISCUSSION...
/ISSUED 709 PM CDT FRI AUG 5 2011/
THE PROBLEM IN THE SHORT TERM ARE THUNDERSTORM CHANCES SATURDAY AND
SATURDAY NIGHT...AND THE POTENTIAL FOR SEVERE WEATHER DURING THIS
PERIOD. A LOW PRESSURE SYSTEM OVER THE NORTHERN ROCKIES...WILL TRACK
EAST INTO THE UPPER MIDWEST BY SATURDAY EVENING THEN LIFT NORTHEAST
OVER NORTHERN MN SATURDAY NIGHT. MEANWHILE...A SHORTWAVE TROUGH WILL
DEEPEN AS IT COMES ACROSS THE UPPER MIDWEST SATURDAY NIGHT AND
SUNDAY MORNING. THUNDERSTORMS ARE EXPECTED TO DEVELOP TONIGHT OVER
THE DAKOTAS...AND SPREAD EAST INTO THE WESTERN SECTION OF MN BY
DAYBREAK SATURDAY. MUCH OF OUR FORECAST AREA WILL BE UNDER A
FAVORABLE LEFT EXIT REGION OF UPPER LEVEL JET MAX. SO THE PRIMARY
SEVERE WEATHER THREAT WILL BE DAMAGING WINDS. ISOLATED TORNADOES ARE
POSSIBLE CLOSE TO TRIPLE POINT AND SURFACE LOW NORTH OF
INTERSTATE 94 OVER WEST CENTRAL MN. SATURDAY MORNING AND EARLY
AFTERNOON...MOST OF THE CONVECTION SHOULD START OFF AS ELEVATED
AHEAD OF WARM FRONT BOUNDARY OVER SOUTHERN MN. THERE STILL SOME
UNCERTAINTY WHERE THE GREATEST THREAT OF SEVERE WEATHER WILL
OCCUR.

ANOTHER SHORTWAVE TROUGH WILL PUSH SOUTHEAST OVER CENTRAL CANADA AND
THE UPPER MIDWEST ON MONDAY. THIS WAVE SHOULD MOVE QUICKLY THROUGH
THE UPPER MIDWEST BY WEDNESDAY MORNING.

COOLER WEATHER REGIME WILL COMMENCE OVER THE UPPER MIDWEST AS
NORTHWEST AIRFLOW SETS UP ALOFT. 850 MB TEMPS COOL DOWN
SIGNIFICANTLY WITH DAYTIME HIGHS MAINLY IN THE 70S OCCURRING THE
LATTER HALF OF THE WORK WEEK.

&&

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

JPC/MPG

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1202 PM CDT FRI AUG 5 2011

MNZ041>045-047>050-054>058-064-061100-
DOUGLAS-TODD-MORRISON-MILLE LACS-KANABEC-STEVENS-POPE-STEARNS-
BENTON-LAC QUI PARLE-SWIFT-CHIPPEWA-KANDIYOHI-MEEKER-
YELLOW MEDICINE-
1202 PM CDT FRI AUG 5 2011

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED NON-SEVERE THUNDERSTORMS WILL BE POSSIBLE IN WEST
CENTRAL MINNESOTA LATE TONIGHT. ANY THUNDERSTORMS THAT DEVELOP
WILL BE CAPABLE OF PRODUCING HEAVY RAINFALL AND GUSTY WINDS.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MOST OF THE
OUTLOOK AREA ON SATURDAY AFTERNOON AND EVENING. THE MAIN HAZARD
WILL BE HAIL AND HIGH WINDS...ALONG WITH TORRENTIAL RAINFALL.

ANOTHER CHANCE OF THUNDERSTORMS ARE POSSIBLE MONDAY AND TUESDAY.
SEVERE WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION WILL NOT BE NEEDED THIS AFTERNOON OR
TONIGHT. HOWEVER...SPOTTER ACTIVATION MAY BE NEEDED SATURDAY
AFTERNOON AND EVENING.

MNZ069-070-074>078-082>085-091>093-WIZ024-026-061100-
SCOTT-DAKOTA-BROWN-NICOLLET-LE SUEUR-RICE-GOODHUE-WATONWAN-
BLUE EARTH-WASECA-STEELE-MARTIN-FARIBAULT-FREEBORN-PIERCE-PEPIN-
1202 PM CDT FRI AUG 5 2011

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

ISOLATED NON-SEVERE THUNDERSTORMS WILL BE POSSIBLE IN SOUTH
CENTRAL MINNESOTA THIS AFTERNOON AND EARLY EVENING.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MOST OF THE
OUTLOOK AREA ON SATURDAY AFTERNOON AND EVENING. THE MAIN HAZARD
WILL BE HAIL AND HIGH WINDS...ALONG WITH TORRENTIAL RAINFALL.

ANOTHER CHANCE OF THUNDERSTORMS ARE POSSIBLE MONDAY AND TUESDAY.
SEVERE WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION WILL NOT BE NEEDED THIS AFTERNOON OR
TONIGHT. HOWEVER...SPOTTER ACTIVATION MAY BE NEEDED SATURDAY
AFTERNOON AND EVENING.

MNZ051>053-059>063-065>068-073-WIZ014>016-023-025-027-028-061100-
SHERBURNE-ISANTI-CHISAGO-WRIGHT-HENNEPIN-ANOKA-RAMSEY-WASHINGTON-
RENVILLE-MCLEOD-SIBLEY-CARVER-REDWOOD-POLK-BARRON-RUSK-ST. CROIX-
DUNN-CHIPPEWA-EAU CLAIRE-
1202 PM CDT FRI AUG 5 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MINNESOTA...EAST CENTRAL MINNESOTA...SOUTHWEST MINNESOTA...
NORTHWEST WISCONSIN AND WEST CENTRAL WISCONSIN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MOST OF THE
OUTLOOK AREA ON SATURDAY AFTERNOON AND EVENING. THE MAIN HAZARD
WILL BE HAIL AND HIGH WINDS...ALONG WITH TORRENTIAL RAINFALL.

ANOTHER CHANCE OF THUNDERSTORMS ARE POSSIBLE MONDAY AND TUESDAY.
SEVERE WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION WILL NOT BE NEEDED THIS AFTERNOON OR
TONIGHT. HOWEVER...SPOTTER ACTIVATION MAY BE NEEDED SATURDAY
AFTERNOON AND EVENING.