Special Weather Statement, NWS Twin Cities, MN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
657 PM CDT THU AUG 13 2009

.DISCUSSION...

THE FORECAST CHALLENGES ARE TEMPS/DEW POINTS ALONG WITH THUNDERSTORM
CHANCES INTO THE WEEKEND.

PER SATELLITE AND RADAR...AN MCV REMAINING FROM EARLY MORNING
CONVECTION IN ERN SD CONTINUES TO TWIST EASTWARD ACROSS SRN MN
THIS AFTN. THIS IS FORECAST BY THE HIGH RES RUC AND NAM TO REMAIN
INTACT AS A MECHANISM FOR SHOWER AND THUNDERSTORM GENERATION
ACROSS SRN AND SERN MN INTO WRN WI INTO THIS EVENING. THIS IS
MAINLY DUE TO STEEP MID-LEVEL LAPSE RATES. THE MCV IS LOST SO TO
SAY UNDER THE UPPER LEVEL RIDGING ACROSS THE CTRL US...THUS WIND
SHEAR VALUES ARE VERY LOW. SO DESPITE A LARGE QUANTITY OF
INSTABILITY...STORMS SHOULD REMAIN FAIRLY PULSY AND SLOW MOVING.
SO LOCALLY HEAVY RAIN AND SOME VERY ISOLATED HALF INCH TO DIME
SIZE HAIL EXPECTED INTO TONIGHT AS MCV EVOLVES EAST. WITH SRLY
FLOW AND HIGH TDS...MIN TEMPS TO REMAIN BALMY TONIGHT WITH PARTS
OF THE TWIN CITIES NOT DROPPING BELOW 70F. FLOW SHOULD PREVENT ANY
APPRECIABLE FOG...BUT COULD BE SOME SHALLOW GROUND FOG IN THE
AREAS THAT CLEAR IMMEDIATELY BEFORE SUNRISE /ERN MN AND POSSIBLY
WRN WI/.

DEEP WARM AIR MASS TO MOVE INTO THE REGION ON FRIDAY FROM THE
SOUTHWEST. MOSTLY SUNNY CONDITIONS ARE EXPECTED IN THE MN PORTION
OF THE FORECAST AREA WITH SOME LINGERING CLOUDS AND POSSIBLY EVEN
A SHOWER OR TWO IN WRN WI. MIXING TO 850-875MB YIELDS HIGHS IN THE
LOWER 90S WITH SOME ISOLATED MID 90S. DEW POINTS ARE EXPECTED TO
ACTUALLY BE LOWER BY A FEW DEGREES ON FRI...WITH PRIMARILY 65-68.
THE RESULTING HEAT INDICES SHOULD BE IN THE MID 90S WITH SOME
ISOLATED UPPER 90S TO 100F POSSIBLE. THE GULF OF MEXICO WILL BE
MORE OPEN TO THE SRLY FETCH ON SATURDAY...HOWEVER MORE CLOUDS FROM
CONVECTION TO OUR WEST MAY LIMIT TEMPS BY A FEW DEGREES. THUS HEAT
INDICES ARE EXPECTED TO BE SLIGHTLY LOWER OR POSSIBLY THE SAME ON
SAT.

EVOLUTION OF THE WEEKEND SYSTEM IS IN FAIRLY GOOD AGREEMENT WITHIN
THE GFS AND ECMWF SOLUTIONS...WITH EARLY SIGNS ON THE NAM ALSO
FAIRLY SIMILAR. THE GFS AND ECWMF DIVERGE BY SUN NIGHT INTO MON
WITH WHETHER THE FRONT SLOWS AND HANGS OR NOT...WITH THE ECMWF
CONSISTENTLY TRENDING THAT IT WILL WHILE THE GFS THAT IT WILL NOT.
HAVE LEANED THE ECMWF ROUTE WITH REGARD TO THAT...DUE TO LARGE
HEIGHTS AND A WARM AIR MASS TO OUR SOUTH. AN INCREASING LOW LEVEL
JET THROUGH FRIDAY NIGHT AND SATURDAY SHOULD PRIMARILY FOCUS THE
MOIST ADVECTION TO THE WEST AND NORTH TOWARDS THE STRONGER
DYNAMICS. HAVE ONLY SMALL POPS IN THE WRN AND NRN FORECAST AREA
INCREASING SLOWLY THROUGH THAT TIME...NAMELY IF SOMETHING MORE
ORGANIZED WERE TO DEVELOP TO THE WNW AND PUSH INTO THAT AREA AS IT
FADES. A BETTER CHANCE FOR THAT ARRIVES SATURDAY NIGHT AS THE
UPPER LEVEL WAVE SHIFTS EAST INTO THE DAKOTAS. THE HEIGHT FALLS
OVERRIDE THE WARM SECTOR IMMEDIATELY AHEAD OF THE FRONT IN MN AND
WI ON SUNDAY AND SUNDAY NIGHT AND CONTINUE THE HIGHER POPS THEN.
SEVERE POTENTIAL SAT NIGHT INTO SUNDAY EXISTS JUST GIVEN THE
INSTABILITY AND A FAIRLY STRONG DYNAMIC SYSTEM FORECAST FOR MID-
AUGUST. ONE PROBLEM IS A BIT OF A SPLIT ADVERTISED BY THE NAM AND
ECMWF WHICH WOULD NOT BE AS CONDUCIVE FOR SEVERE.

HAVE LEANED TOWARDS THE ECMWF AND SLOWER GFS ENSEMBLE IN THE LONG
RANGE. THIS KEEPS THE AREA A BIT WARMER /NEAR NORMAL/ AND IN
PROXIMITY OF THE FRONTAL BOUNDARY ON MON AND TUES. MIDWEEK SYSTEM
ADVERTISED TO BE THE BEGINNING OF A LONG WAVE PATTERN SHIFT TO
TROUGH EAST AND RIDGE WEST...FAMILIAR OF MUCH OF THIS SUMMER. THIS
WOULD TREND TOWARDS A SLIGHTLY COOLER THAN NORMAL WEEK TWO.

&&

.AVIATION.../00Z TAF ISSUANCE/

MID LEVEL WAVE THIS EVENING SPINNING ACROSS SE MN HAS BROUGHT
SHOWERS AND THUNDERSTORMS TO MAINLY SOUTH OF TAF SITES. CURRENT
RADAR TRENDS WOULD INDICATE THAT RAINS ARE DOWN FOR ALL BUT
EAU...WHO WILL HAVE THE WORST CONDITIONS MOVE OVHD FOR THE FIRST
COUPLE OF HOURS. HAVE ONLY SEEN OCCASIONAL 5SM VSBYS WITH VFR CIGS
TO THE SW OF EAU WITH THIS RAIN...AND EXPECT THE SAME TO HAPPEN
THERE. THIS WAVE IS PROGGED TO STALL OUT OVER SRN WI DURING THE
DAY TOMORROW...BUT MODELS IN GOOD AGREEMENT ON KEEPING BRUNT OF
MOISTURE SE OF TERMINALS...SO NOT ANTICIPATING ANY MORE PRECIP
THIS TAF PERIOD ONCE THE CURRENT SHRA/TSRA ACTIVITY DISSIPATES.
HAVE HAD FOG ISSUES THE LAST SEVERAL MORNINGS...AND WILL HAVE TO
WATCH AGAIN TONIGHT. FEEL MOST AIRPORTS WILL BE FINE TONIGHT...AS
WINDS IN THE BL ARE PROGGED TO STAY ABOVE 10 KTS ALL NIGHT...
HELPING TO KEEP THINGS MIXED. WITH MOIST SE WIND EXPECTED TO
PERSIST THROUGH THE NIGHT AT AXN AND RUC SHOWING LOW LEVELS OF
SOUNDING BEING MOIST BY 09Z...FEEL CONFIDENT ENOUGH IN FOG/STRATUS
DEVELOPING AT AXN TO KEEP TEMPO 3/4SM GROUP GOING. FOR
FRIDAY...MODELS BRING NICE NOSE OF WARM AIR IN ALOFT...HELPING
KEEP THINGS VFR...WITH VERY LITTLE CLOUD COVER EXPECTED. WILL SEE
PRESSURE GRADIENT TIGHTEN UP AND SHOULD HAVE NO TROUBLE MIXING
DOWN 20 TO 25KT GUSTS BY THE AFTERNOON. DIRECTIONS WILL BE
PRIMARILY SE OVERNIGHT...BEFORE TURNING TO JUST WEST OF SOUTH
DURING THE DAY FRIDAY.

&&

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

MTF/MPG

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
649 PM CDT THU AUG 13 2009

MNZ041>045-047>070-073>078-082>085-091>093-WIZ014>016-023>028-
150000-
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-
649 PM CDT THU AUG 13 2009

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

.DAY ONE...TONIGHT

A FEW THUNDERSTORMS WILL OCCUR TONIGHT ACROSS WEST CENTRAL
WISCONSIN AND SOUTHEAST MINNESOTA. THE STORMS ARE NOT EXPECTED TO
BE SEVERE.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY

HEAT INDEX VALUES WILL BE IN THE MID 90S IN PORTIONS OF CENTRAL
AND SOUTHERN MINNESOTA FRIDAY AFTERNOON. SOME COMMUNITIES COULD
APPROACH 100 DEGREES FOR AN HOUR OR TWO.

THUNDERSTORMS CHANCES WILL BE FOUND IN WESTERN MINNESOTA LATE
FRIDAY NIGHT AND GRADUALLY SPREAD EAST ACROSS THE REMAINDER OF
THE OUTLOOK AREA THROUGH THE WEEKEND. MOST OF ANY ACTIVITY
THROUGH SATURDAY SHOULD REMAIN BELOW SEVERE LIMITS. HOWEVER...DUE
TO THE APPROACH OF A STRONG LOW PRESSURE SYSTEM ON SATURDAY NIGHT
INTO SUNDAY...SEVERE THUNDERSTORMS ARE POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTER ACTIVATION WILL NOT BE NEEDED TONIGHT.

RAH

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