Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 041059
AFDMPX

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

.UPDATED FOR 12Z AVIATION DISCUSSION...
ISSUED AT 558 AM CDT FRI SEP 4 2015

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 249 AM CDT FRI SEP 4 2015

SEASONABLY HOT AND HUMID AIR WILL CONTINUE ACROSS THE REGION...AND
THE 1.31 PWAT MEASURED FROM THE 04.00 MPX RAOB WILL INCREASE TO
NEAR 1.75 INCHES BY 00Z THIS EVENING. THATS CLOSE TO THE ALL TIME
RECORD OF 1.72 PER SPC SOUNDING CLIMATOLOGY PAGE.

EXPECT ANOTHER DRY DAY TODAY FOR MOST LOCATIONS...BUT CHANCES FOR
STORMS WILL INCREASE THIS AFTERNOON ACROSS THE WEST AS AN UPPER
LEVEL WAVE CURRENTLY OVER WESTERN NEBRASKA LIFTS NORTHWARD INTO
THE DAKOTAS. THE QUESTION IS WHETHER OR NOT THIS WAVE WILL BE
ABLE TO GENERATE ENOUGH VERTICAL MOTION TO BREAK THROUGH THE CAP
AND TAP INTO THE 2500 TO 3000 J/KG THAT IS FORECAST TO BE IN PLACE
ACROSS THE REGION.

THESE SHORTWAVES OF TROPICAL ORIGIN SEEM TO BE PRETTY EFFICIENT AT
GENERATING CONVECTION...SO HAVE INCREASED POPS TONIGHT ACROSS
THE EASTERN PORTION OF THE FORECAST AREA. THE 04.00 NCAR ENSEMBLE
IS IN VERY GOOD AGREEMENT WITH CONVECTION DEVELOPING OVERNIGHT
ACROSS EASTERN MN AND MOVING INTO WESTERN WI. THE WRF NMM/ARW ARE
A COUPLE HOURS QUICKER...BUT ALSO SHOW THIS SCENARIO UNFOLDING.
THE REASON FOR RELATIVELY LOW POPS STEMS FROM TIMING
UNCERTAINTY...NOT SO MUCH ACTUAL DEVELOPMENT/PLACEMENT. THEREFORE
AS MODELS BECOME INTO BETTER AGREEMENT HAVE A FEELING THAT POPS
WILL ALSO INCREASE ACROSS THE FORECAST AREA AS IT BECOMES MORE
CLEAR WHEN STORMS WILL DEVELOP. GIVEN THE AFOREMENTIONED MOIST
STATE OF THE ATMOSPHERE...TOGETHER WITH THE WARM CLOUD
DEPTH...ANTICIPATE RAINFALL RATES IN EXCESS OF 3 INCHES PER HOUR.
IN SHORT HEAVY RAIN AND FLOODING WILL BE THE MAIN ISSUE IF
TRAINING THUNDERSTORMS DEVELOP.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 249 AM CDT FRI SEP 4 2015

SATURDAY AND SUNDAY...MAIN UPR LVL RIDGE AXIS WILL LOCATE ITSELF
OVER THE ERN SEABOARD COME SAT MRNG BUT A TRAILING SECONDARY RIDGE
WILL ALLOW FOR HIGH HEAT AND HUMIDITY TO REMAIN OVER THE AREA FOR
SATURDAY. HIGHS WILL AGAIN HIT THE MID-UPR 80S FOR THE ENTIRE CWFA
WITH DEWPOINTS IN THE LWR 70S DUE TO A CONTINUED DEEP PLUME OF
MOISTURE FROM THE DEEP SOUTH. THIS WILL CREATE HEAT INDEX VALUES
INTO THE MID 90S FOR MUCH OF THE AREA. RELATED TO THE MOISTURE
SURGE WILL BE PWATS INCRG TO ARND 1.75 INCHES...POSSIBLY AS HIGH
AS 2.0 INCHES. THIS WILL BE A LARGE FACTOR IN CONJUNCTION WITH A
SHORTWAVE DISTURBANCE RIDING ATOP THE SECONDARY RIDGE THRU THE
CENTRAL PLAINS ON INTO THE UPR MISS RIVER VALLEY SAT NIGHT INTO
SUN MRNG. THIS WILL HELP PROMOTE SCTD SHWRS/TSTMS STARTING IN WRN
MN DURG THE DAY ON SAT...GRADUALLY PUSHING EWD SAT NIGHT INTO SUN
WITH STEADILY INCRG COVERAGE. THE HIGH PWATS COMBINED WITH WEAK
STORM MOTIONS AND STORM TRAINING MAY WELL LEAD TO PERIODS OF HEAVY
RAIN...PARTICULARLY SAT NIGHT INTO SUN. THERE LOOKS TO BE MODEST
0-6KM SHEAR IN THE 25-30KT AREA WHICH...WITH PROFILES SHOWING
VEERING WITH HEIGHT...COULD PROMOTE ISOLD STRONG/SEVERE TSTMS SAT
NIGHT BUT THE POTENTIAL IS ONLY MARGINAL. A DEVELOPING CDFNT OVER
THE PLAINS SAT NIGHT INTO SUN MRNG...IN ADVANCE OF A CUTOFF LOW
SHIFTING NEWD INTO WRN CANADA...WILL STEADILY PUSH THRU THE REGION
SUN AND HELP PUSH THE PRECIPITATION OFF TO THE E LATE DAY SUN THRU
SUN NIGHT. IN ADDITION...THE INCREASED CLOUD/RAIN COMPLICATIONS ON
SUNDAY WILL MAKE FOR SLIGHTLY LOWER MAX TEMPS AND HEAT INDEX
VALUES /ALTHOUGH HEAT INDICES IN THE LWR 90S CANNOT BE RULED OUT
AT ALL/.

MONDAY THROUGH THURSDAY...WITH THE CDFNT E OF THE AREA BY MON
MRNG...MUCH COOLER/DRIER AND MORE STABLE AIR WILL MOVE INTO THE
AREA MON WITH THE ARRIVAL OF HIGH PRES. HOWEVER...THIS HIGH PRES
AIRMASS WILL BE SHORT-LIVED DUE TO PROGRESSIVE ZONAL FLOW ALOFT.
ANOTHER AREA OF LOW PRES LOOKS TO SKIRT THE REGION TO THE
SOUTH...SPREADING ISOLD/SCTD SHWRS AND TSTMS ACRS THE AREA...
MAINLY OVER SRN PORTIONS. THIS SYSTEM THEN EXITS TO THE E ON
TUE...FOLLOWED BY HIGH PRES THAT WILL LAST THROUGH THE MIDDLE OF
THE WEEK AND ALLOWING FOR A DRY FCST. AS ALLUDED TO ABOVE... MUCH
COOLER TEMPERATURES WILL TAKE HOLD OF THE REGION STARTING MON.
HIGHS WILL DROP BACK TO THE UPR 60S TO MID 70S WITH LOWS FALLING
TO THE UPR 50S TO MID 50S ALONG WITH MUCH LOWER HUMIDITY LEVELS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 558 AM CDT FRI SEP 4 2015

MORNING MVFR/IFR CONDITIONS WILL GIVE WAY TO VFR CONDITIONS THIS
AFTERNOON. THE MAIN CHANGE TO THE FORECAST WAS TO INTRODUCE VICINITY
SHOWERS (AND THUNDERSTORMS) THIS EVENING AND OVERNIGHT. SHORT TERM
GUIDANCE IS IN GOOD AGREEMENT THAT STORMS WILL DEVELOP OVER
MINNESOTA AND WISCONSIN...BUT THE TIMING VARIES...SO ONLY HAVE VCSH
AT THIS TIME.

KMSP...
THE TIMING OF THE PRECIP LATER TODAY VARIES FROM AS EARLY AS
00Z...TO AS LATE AS 06Z. EXPECT EMBEDDED THUNDER...WITH AREAS OF
HEAVY RAIN WHICH COULD BRING IFR CONDITIONS. WINDS WILL BE SOUTHEAST
THROUGHOUT.

/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...JRB
LONG TERM...JPC
AVIATION...JRB


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