Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 050345
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1045 PM CDT FRI SEP 4 2015

.SHORT TERM...(THIS EVENING AND SATURDAY)
ISSUED AT 117 PM CDT FRI SEP 4 2015

ALTHOUGH WE HAVE PLENTY OF INSTABILITY IN PLACE TODAY WITH
DEWPOINTS IN THE LOW/MID 70S...SHEAR/FORCING ARE CURRENTLY
LACKING. HOWEVER...A SHORTWAVE PUSHING IN FROM THE DAKOTAS SHOULD
HELP DRIVE AT LEAST LIGHT SHOWERS INTO WEST/NORTH CENTRAL MN THIS
AFTERNOON AND EVENING. SEEMINGLY BETTER CHANCES ARRIVE TONIGHT AS
A 30-40KT LLJ DEVELOPS AND A WEAK PV ADVECTION SIGNATURE MOVES
OVERHEAD. THESE MECHANISMS ARE SOMEWHAT DISJOINTED HOWEVER...AND
CAMS MODELS ARE MORE DRY THAN WET. THEREFORE CONFIDENCE IS RATHER
LOW...SO HAVE MAINTAINED 20-30 POPS. LOW TEMPS WILL REMAIN QUITE
MILD GIVEN THE ELEVATED DEWPOINTS AND CLOUD COVER. ANTICIPATE LOWS
SIMILAR TO THURSDAY NIGHT...RANGING FROM THE UPPER 60S TO MID 70S.

AN EVEN WARMER AND MORE HUMID DAY IS EXPECTED FOR SATURDAY...WITH
LITTLE TO NO CHANGE IN DEWPOINTS OR WINDS...AND EVEN SLIGHTLY
WARMER TEMPS NOSING INTO EAST/SOUTH CENTRAL MN. WILL HAVE SOME
AREAS NEARING HEAT ADVISORY CRITERIA...PARTICULARLY THE TWIN
CITIES METRO AREA WHERE HEAT INDICES ARE FORECAST IN THE MID 90S.
INSTABILITY WILL REMAIN HIGH...WITH EVEN GREATER PWAT VALUES
APPROACHING 2 INCHES. HAVE MAINTAINED 20-30 POPS FOR THE
AFTERNOON HOURS...BUT HIGHER CHANCES WILL ARRIVE ON SATURDAY
EVENING AS A STRONGER MID LEVEL SHORTWAVE APPROACHES.

.LONG TERM...(SATURDAY NIGHT THROUGH FRIDAY)
ISSUED AT 317 PM CDT FRI SEP 4 2015

AS A SURFACE LOW DEEPENS OVER THE DAKOTAS AND MOVES INTO MANITOBA
FROM SATURDAY NIGHT INTO SUNDAY...VERY MOIST AIR WILL CONTINUE TO BE
PUMPED NORTHWARD FROM THE GULF OF MEXICO INTO THE UPPER MIDWEST.
THIS MOIST SOUTHERLY FLOW WILL PRODUCE UNSEASONABLY HIGH PWAT VALUES
IN OUR AREA DURING THIS TIME...WITH THE NAM AND GFS BOTH SHOWING A
BAND OF GREATER THAN 2 INCH PWAT VALUES FROM SOUTHWEST MN THROUGH
THE TWIN CITIES AREA INTO WESTERN WISCONSIN FROM SATURDAY NIGHT
THROUGH SUNDAY NIGHT. WITH THE SPC SOUNDING CLIMATOLOGY SHOWING PWAT
RECORDS OF 1.71 INCHES ON 12Z SUNDAY MORNING AND 1.81 INCHES ON 00Z
SUNDAY EVENING...IT IS CERTAINLY POSSIBLE THAT BOTH OF THESE RECORDS
COULD BE BROKEN. SURFACE DEWPOINTS IN THE LOWER 70S WILL BE
WIDESPREAD...AND A SLOW-MOVING COLD FRONT TO THE SOUTH AND EAST OF
THE AFOREMENTIONED LOW WILL PROVIDE FORCING AS IT MOVES EASTWARD
THROUGH OUR AREA.  INSTABILITY IS ALSO EXPECTED TO BE FAIRLY
IMPRESSIVE...WITH CAPE VALUES LIKELY EXCEEDING 2000 J/KG AT TIMES.
AS A RESULT OF THIS SETUP...PERIODS OF SCATTERED THUNDERSTORMS WITH
THE POTENTIAL TO PRODUCE HEAVY RAIN ARE EXPECTED FROM SATURDAY NIGHT
THROUGH SUNDAY NIGHT.

WITH THE IMPRESSIVE INFLUX OF MOISTURE AND RELATIVELY SLOW STORM
MOTION EXPECTED...CANNOT RULE OUT SOME LOCALIZED FLASH FLOODING
THROUGH SUNDAY NIGHT.  IN ADDITION TO PRODUCING HEAVY RAIN...A FEW
OF THE STORMS MAY BECOME STRONG TO SEVERE DUE TO THE STRONG
INSTABILITY MENTIONED EARLIER.  SHEAR WILL INITIALLY BE FAIRLY WEAK
AND COULD LIMIT SEVERE POTENTIAL SATURDAY EVENING...BUT 0-6 KM BULK
SHEAR COULD INCREASE TO AT LEAST 20-30 KTS ON SUNDAY...WHICH SHOULD
BE SUFFICIENT FOR MULTICELLULAR DEVELOPMENT WHEN COMBINED WITH THE
AMPLE INSTABILITY.

AFTER HIGHS IN THE MID-UPPER 80S AND ACTIVE WEATHER OVER THE
WEEKEND...COOLER AND DRIER AIR IS EXPECTED NEXT WEEK AS THE COLD
FRONT MOVES TO OUR EAST ON MONDAY MORNING.  ONE EXCEPTION TO THE
GENERALLY DRY WEEK MAY BE TUESDAY ACROSS SOUTHERN MN...WHEN THERE IS
A CHANCE OF RAIN TO THE NORTH OF A WEAK LOW PRESSURE SYSTEM MOVING
THROUGH IOWA.  HIGHS ARE EXPECTED TO MAINLY BE IN THE 70S FROM
MONDAY THROUGH FRIDAY...WITH LOWS GENERALLY IN THE 50S.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1045 PM CDT FRI SEP 4 2015

SHRA/TSRA ARE FADING LATE THIS EVENING ACROSS EASTERN MN AND
CONFIDENCE ON NEW DEVELOPMENT IN WESTERN MN AFTER MIDNIGHT IS
WANING. HENCE...CONCERN IS CHANGING FROM ADDITIONAL SHRA/TSRA TO
ONE OF MVFR OR LOWER CEILINGS/VSBYS IN STRATUS AND FOG DUE TO THE
VERY MOIST LEVEL CONDITIONS. NOT TOTALLY SOLD ON THIS IDEA AS WELL
AS USUALLY ONE DOMINATES OVER THE OTHER. WITH SOME WIND TONIGHT
ACROSS THE MN TAF SITES...VSBY ISSUES DURING THE LATE NIGHT HOURS
MAY DOMINATE OVER CEILINGS. AN EXCEPTION IS KEAU WHERE LIGHT
WINDS WILL PREVAIL WITH LESS THAN MVFR CEILINGS AND VSBYS
DEVELOPING. THE NEXT SHRA/TSRA CHANCES RETURN TO KAXN SATURDAY
EVENING. SOUTHERLY WINDS WILL BE ON THE INCREASE SATURDAY
AFTERNOON WITH 12-18 KNOTS GUSTING TO 20-25 KNOTS.

KMSP...THE AIRFIELD MAY ESCAPE WITH ONLY A NARROW BAND OF LIGHT
SHOWERS PASSING THROUGH IN THE 06Z-07Z PERIOD.
THEREAFTER...THINKING HAS CHANGED TO A DRY FORECAST. SOME MVFR
VSBY EXPECTED TOWARDS DAYBREAK ALONG WITH A SMALL CHANCE FOR AN
MVFR CEILING. THE MOST SIGNIFICANT WIND REMAINS SATURDAY AFTERNOON
WITH SOUTH WINDS 15 KNOTS GUSTING 22 KNOTS.

/OUTLOOK FOR KMSP/
SUN...VFR WITH MVFR/TSRA LIKELY AT TIMES. WIND SW AT 15G20KT.
MON...MVFR/TSRA POSSIBLE EARLY. THEN VFR. WIND NE AT 5-10KT.
TUE...VFR. WIND NNW AT 10KT.

&&

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

$$

SHORT TERM...LS
LONG TERM...ADL
AVIATION...RAH



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