Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 211801
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1201 PM CST WED JAN 21 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 349 AM CST WED JAN 21 2015

SNOW WILL GRADUALLY TAPER OFF TODAY AS SUBSIDENCE AND HIGH
PRESSURE BUILDS IN LATER TONIGHT. THIS WILL SET THE STAGE FOR
COLDER TEMPERATURES BY THURSDAY MORNING...ESPECIALLY IF SKIES
CLEAR OUT AS CURRENTLY FORECAST.

EARLY MORNING WATER VAPOR IMAGERY OVERLAID WITH 500MB HEIGHTS AND
WINDS IDENTIFIED TWO AREAS OF ENHANCED VORTICITY. THE FIRST WAS
CENTERED OVER THE MN/WI/IA BORDER...AND WAS RESPONSIBLE FOR THE
LIGHT SNOW FROM YESTERDAY. THE SECOND IS AN OPEN AVE ACROSS THE
DAKOTAS...AND SHOULD ALLOW A FEW SNOW SHOWERS TO PERSIST ACROSS THE
SOUTHEAST PORTION OF THE FORECAST AREA...IN PARTICULAR THE MINNESOTA
RIVER VALLEY. HOWEVER...THIS AREA OF VORTICITY WILL WEAKEN AS IT
GETS STRUNG OUT BY THE SPEEDMAX TO THE SOUTH...WHILE AN UPPER LEVEL
RIDGE BREAK OVERHEAD.

500MB HEIGHT RISES WILL PROMOTE SUBSIDENCE AND SURFACE HIGH PRESSURE
ACROSS THE UPPER MIDWEST LATER TONIGHT...WHICH WILL BRING A FINITE
END TO THE LIGHT SNOW/FLURRIES. FORECAST SOUNDINGS DRY OUT
CONSIDERABLY...AND DEPENDING ON THE RESIDUAL BOUNDARY LAYER MOISTURE
SHOULD SEE CLEARING SKIES AFTER MIDNIGHT ACROSS THE NORTHWEST. THE
UNCERTAINTY IN THE TIMING/AMOUNT OF CLEARING YIELDS LITTLE
CONFIDENCE IN THE LOW TEMPERATURES...AS COULD SEE TEMPS DROP SEVERAL
DEGREES INTO THE SINGLE DIGITS BEFORE SUNRISE UNDER CLEAR...CALM
CONDITIONS. HOWEVER...WARM AIR ADVECTION WILL BE ON THE DOORSTEP
FROM UPSTREAM SUBSIDENCE/CHINOOK WINDS.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 349 AM CST WED JAN 21 2015

THE LONG TERM WILL FEATURE CONTINUED ABOVE NORMAL TEMPERATURES
ALONG WITH A DECENT CHANCE FOR A PLOWABLE SNOWFALL EVENT DURING
THE LAST HALF OF THE WEEKEND.

THE LARGE SCALE PATTERN WILL FEATURE UPPER RIDGING NOSING INTO THE
PACIFIC NORTHWEST...WHICH WILL BE CONDUCIVE TO A PARADE OF WEAK
RIDGE-TOPPING SHORTWAVES DIVING ACROSS THE CENTRAL CONUS DURING
THE PERIOD.

ONE SUCH WAVE SCRAPES THE EASTERN PART OF THE AREA ON FRIDAY.
MOISTURE AND FORCING SOURCES ARE LIMITED...SO HAVE ONLY INCLUDED A
20 POP. THE ONE UNFORTUNATE REALITY IS THAT THE MILD AIR IN PLACE
WILL MEAN THE PRECIP TYPE WOULD BE A MIX OF RAIN...SNOW...AND
POSSIBLY EVEN SLEET.

A MUCH STRONGER WAVE IS FORECAST TO CLIP THE REGION ON SATURDAY
NIGHT AND SUNDAY. THIS SYSTEM IS FORECAST TO BE ACCOMPANIED BY
STRONG PV ADVECTION...700-600MB FORCING AND DEEP MOISTURE. A
MODERATE BAND OF SNOWFALL STILL LOOKS TO BLOSSOM OVER THE FORECAST
AREA ON SATURDAY NIGHT AND SUNDAY. WHILE THE AMPLITUDE/SPATIAL
DETAILS ARE NOT ENTIRELY CERTAIN AT THIS POINT...IT STILL LOOKS
LIKE A SWATH OF 0.20 TO 0.30 QPF IS POSSIBLE OVER THE AREA...WHICH
WOULD TRANSLATE TO 2 TO 4 INCHES.

THE NEXT WAVE IS FORECAST TO TOP THE RIDGE ON TUESDAY AND DROP
ACROSS THE FORECAST AREA. IT PRIMARILY LOOKS TO CLIP THE EASTERN
FRINGES OF THE AREA...SO HAVE RESTRICTED THE 20 POPS TO WEST
CENTRAL WI.

HIGH TEMPERATURES THROUGH THE PERIOD PRIMARILY RANGE FROM THE
UPPER 20S TO UPPER 30S FOR HIGHS...AND THE MID TEENS TO MID 20S
FOR LOWS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1144 AM CST WED JAN 21 2015

MAIN ISSUE THIS TAF PERIOD WAS WHEN TO BRING THROUGH CLEARING
TONIGHT/THU MORNING. BELIEVE THE NAM IS WAY TO OVERDONE ON LOW
LEVEL MOISTURE AND BELIEVE AS THE SFC RIDGE WORKS THROUGH...IT
WILL BRING CLEARING SKIES WITH IT. FOR TIMING...THE HRRR SUGGESTS
THAT THE GFSLAMP IS A BIT TOO AGGRESSIVE WITH ITS CLEARING...SO
WENT SLOWER WITH CIG IMPROVEMENTS THAN WHAT THE LAMP HAS. BASED
ON OBS UPSTREAM...CONDS WILL LIKELY DETERIORATE AS SITES GET INTO
THE BACK EDGE OF THE STRATUS...SO TRENDED TAFS BACK TO IFR/LOW END
MVFR BEFORE CLEARING THEM OUT. ALTHOUGH NO ACCUMULATIONS ARE
EXPECTED...EAU WILL SEE -SN CONTINUE FOR NO MORE THAN A COUPLE OF
HOURS...WHILE ANOTHER AREA OF SNOW IN WC MN MAY BRUSH RWF THIS
AFTERNOON.

KMSP...WE WILL BE MAINTAINING THE STRATUS...LIKELY THROUGH THE
WHOLE NIGHT. STILL SEE NO REASON WHY CIGS WILL NOT IMPROVE TO
ABOVE 017 THIS AFTERNOON...BUT THE LARGE BANK OF IFR CONDS ACROSS
NRN MN PUSHED ME TO BRINGING CIGS BACK UNDER 017 TONIGHT. WILL
HAVE TO WATCH TRENDS...BUT COULD SEE MSP DEALING WITH IFR CIGS
AGAIN THU MORNING. EXPECT STRATUS TO CLEAR OUT BY 15Z AT THE
LATEST...AND ONCE IT DOES ITS MAINLY CLEAR SKIES WITH SW WINDS
FOR THE REST OF THE TAF PERIOD.

/OUTLOOK FOR KMSP/
FRI...MVFR CIGS IN AFTN. WIND SW AT 10 KTS.
SAT...VFR. CHC IFR/MVFR -SN LATE. WINDS NW 5-10 KTS.
SUN...IFR/MVFR. CHC MORNING -SN. WINDS NE 5-10 KTS.

&&

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

$$

SHORT TERM...JRB
LONG TERM...LS
AVIATION...MPG



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