Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 261148
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
548 AM CST FRI DEC 26 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 340 AM CST FRI DEC 26 2014

MAIN ITEM OF CONCERN IN THE SHORT TERM IS WHAT IS LOOKING INCREASING
LIKELY TO BE A 3 TO 5 INCH BAND OF SNOW TONIGHT FROM SW/SC MN INTO
WC WI. IS SOME CONCERN THAT A NARROW STRIP WITHIN THIS BAND COULD
SEE TOTALS MORE IN THE 5-7 INCH RANGE. GIVEN THE THREAT OF NEAR
WARNING TYPE SNOW TOTALS ALONG WITH MODERATE TO HIGH CONFIDENCE IN
THE BAND OF 3 TO 5 INCHES OF SNOW OCCURRING...WE DECIDED TO HOIST A
WINTER WEATHER ADVY FOR TONIGHT FOR ABOUT THE SE HALF OF THE MPX CWA.

WATER VAPOR IMAGERY SHOWS TWO FEATURES OF INTEREST IN THE SHORT
TERM. A CLOSED LOW DOWN IN THE 4 CORNERS REGION AND A NRN STREAM
SHORTWAVE WORKING SOUTHEAST INTO NRN MONTANA. THESE TWO FEATURES
WILL PHASE OVER THE PLAINS TONIGHT. THE 4 CORNERS WAVE WILL BE THE
DOMINATE PLAYER FOR PRECIP...THOUGH IT WILL BE LOSING ITS
AMPLIFICATION AS IT MERGES WITH THE NRN STREAM WAVE. AS THE PREVIOUS
LONG TERM DISCUSSION WENT OVER...CONVERGENCE BETWEEN THESE TWO WAVES
TONIGHT WILL RESULT IN A PRETTY SHARP GRADIENT ON THE NW SIDE OF THE
SNOW BAND...WITH AREAS NW OF A GRANITE FALLS TO LITTLE FALLS LINE
LIKELY SEEING NOTHING TONIGHT.

AT THE SFC...THERE IS A LEE SIDE LOW OVER ERN NEW MEXICO...WITH A
STATIONARY BOUNDARY EXTENDING ACROSS THE TX PANHANDLE UP INTO THE SE
TIP OF MN AND THE WRN U.P. OF MICHIGAN. ALSO OF IMPORTANCE THIS
MORNING IS THAT WE ARE ACTUALLY SEEING COLD AIR SPILLING SOUTH
BEHIND THIS BOUNDARY...WITH MOST LOCATION IN SASKATCHEWAN CURRENTLY
BELOW ZERO F. AS THE 4 CORNERS WAVE EJECTS NE...MODELS ARE IN GOOD
AGREEMENT IN A 1015 MB OR LOWER SFC LOW DEVELOPING OVER NRN MO
TONIGHT THAT WILL HEAD OFF INTO THE STRAITS OF MACKINAC BY SAT
AFTERNOON. THIS LOW WILL BE PULLING IN THE POLAR AIR ACROSS SRN
CANADA...WHICH WILL ALLOW FOR A HEALTHY DEFORMATION BAND OF SNOW TO
DEVELOP TO THE NW OF THE SFC LOW...WHICH WILL BE AIDED BY A TROWAL
THAT WILL BE WORKING IN ON THE COOL SIDE OF A 100+KT SWRLY MID LEVEL
JET STREAK THAT WILL BE WORKING ACROSS ERN IOWA TONIGHT.

FAVORED THIS FORECAST CLOSELY TO THE 26.00 GFS. WHEN COMPARING QPF
SWATHS OF VARIOUS PIECES OF GUIDANCE THROUGH 00Z TO THE RAP...THE
GFS QPF WAS PRETTY MUCH LAID DOWN RIGHT ON TOP OF WHAT THE RAP
HAS...SO FELT CONFIDENT IN RIDING THAT FORECAST FORWARD. CONFIDENCE
IN THIS COURSE WAS FURTHER BOOSTED BY THE 26.06 NAM...WHICH SHIFTED
A BIT SE FROM ITS 26.00 RUN TO MORE OR LESS FALL IN LINE WITH THE
26.00 GFS. THE GFS SHOWS THE TROP FOLD GETTING DOWN BELOW 450
MB...SO THIS WILL HELP FORCE A RATHER INTENSE DEFORMATION BAND OF
PRECIP JUST TO THE NW OF ITS PATH. QPF FROM THE GFS GETS UP INTO THE
0.3-0.35 RANGE...BUT THE NAM12 ALONG WITH OTHER HIGHER RES MODELS
SHOW STORM TOTAL QPFS CLIMBING OVER 0.4. FOR SNOW RATIOS...ROEBBER
RATIO PROBABILITIES FOR TONIGHT WERE SPLIT PRETTY EVENLY BETWEEN THE
AVERAGE AND LIGHT BINS...WHICH WOULD SUPPORT RATIOS BEING UP IN THE
14-15:1 RANGE. 0.3" OF QPF WITH THESE RATIOS WOULD PUSH SNOW TOTALS
UP TO A LITTLE OVER 4 INCHES...BUT IF WE SEE QPF UP CLOSER TO 0.45
LIKE THE NAM HAS...THEN YOU ARE TALKING ABOUT SNOW TOTALS MORE IN
THE BALLPARK OF 6". LOOKING AT BUFR SOUNDINGS...LAPSE RATES ATOP THE
H8-H7 FGEN LAYER ARE UP AROUND 7 DEG C PER KM...SO WE SHOULD SEE
A WEAKLY STABLE ENVIRONMENT ATOP THE FGEN...WHICH WOULD FAVOR THE
DEVELOPMENT OF SOME CSI TYPE BANDING...AND SUPPORT THE HIGHER QPF
AMOUNTS THE HI-RES MODELS ARE HINTING AT. CURRENT EXPECTATIONS ARE
FOR A BAND OF 3+" TO FALL BETWEEN PLYMOUTH TO THE NORTH AND
ROCHESTER TO THE SOUTH WITH THE POTENTIAL FOR NOT MUCH MORE THAN A
20-30 MILE WIDE BAND OF 5-7" TO FALL WITHIN THIS BAND. AT THE
MOMENT...THE HIGHEST LIKELIHOOD FOR TOTALS LIKE THAT LOOKS TO
CENTERED NEAR A ST. JAMES/RED WING/CHIP FALLS LINE.

FOR THE REST OF THE FORECAST...TEMPERATURES WILL REMAIN STEADY
THROUGH THE DAY TODAY AS CLOUD COVER AND WEAK CAA HELP KEEP TEMPS
PARKED AT WHERE THEY CURRENTLY ARE UNTIL THE SFC LOW GETS GOING OVER
MO TONIGHT...WHICH WILL FINALLY HELP PULL COLDER AIR THIS DIRECTION.
WINDS WILL ALSO BE REMAINING OUT OF THE NORTH...BUT SPEEDS WILL
REMAIN UNDER 15MPH...SO NOT WORRIED ABOUT THERE BEING BLOWING AND
DRIFTING ISSUES WITH TONIGHTS SNOW.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 340 AM CST FRI DEC 26 2014

THE MOST NOTABLE WEATHER OVER THE NEXT WEEK BLEEDS INTO THE
BEGINNING OF THE LONG TERM FORECAST PERIOD...AND THEN BENIGN BUT
COLDER WEATHER MARKS THE REMAINDER OF THE FORECAST.

SNOW WILL BE ONGOING AT THE START OF THE PERIOD SATURDAY
MORNING...ALTHOUGH IT SHOULD TAPER OFF RATHER EFFICIENTLY FROM
WEST TO EAST ON SATURDAY MORNING AS DRIER AIR ASSOCIATED WITH THE
INCOMING SURFACE RIDGE WORKS INTO THE REGION. AN ADDITIONAL
DUSTING /MN/ TO ONE INCH /WI/ APPEARS POSSIBLE AFTER DAYBREAK
SATURDAY...BRINGING STORM TOTAL AMOUNTS TO THE GENERAL 2 TO 5 INCH RANGE
IN THE ADVISORY AREA.

TEMPERATURES OVER THE WEEKEND WON/T STRAY TOO FAR FROM NORMAL
VALUES FOR LATE DECEMBER...WITH HIGHS MAINLY IN THE 20S.

BY MONDAY...HOWEVER...H85 TEMPS DECLINE TO AROUND -18C...AND EVEN
FURTHER FOR TUESDAY...TO AROUND -20C. THIS WILL TRANSLATE TO
HIGHS IN THE SINGLE DIGITS /F/ AREA-WIDE BY TUESDAY...WITH SUB-ZERO
LOWS. WITH WINDS STAYING UP IN THE 5-10KT RANGE MONDAY AND TUESDAY
NIGHTS...WIND CHILLS WILL NEED TO BE MONITORED FOR THE POTENTIAL
FOR AN ADVISORY...PARTICULARLY OVER WEST CENTRAL MN WHERE READINGS
ARE FORECAST TO DIP NEAR 25 BELOW.

THE BAROCLINIC ZONE TIGHTENS JUST SOUTH OF THE FORECAST AREA ON
MONDAY. COULD SEE SOME RESULTANT LIGHT SNOW AS FAR NORTH AS
SOUTHERN MINNESOTA. HAVE INCLUDED SLIGHT CHANCE POPS ALONG THE
INTERSTATE 90 CORRIDOR FOR MONDAY...WHERE UP TO ONE INCH APPEARS
POSSIBLE.

TEMPERATURES MODERATE SLIGHTLY DURING THE MIDDLE OF THE UPCOMING WEEK...WITH
HIGHS IN THE 20S BY THURSDAY. HOWEVER...AN ARCTIC FRONT IS
FORECAST TO PUSH ACROSS THE AREA BY FRIDAY...CAUSING TEMPERATURES
TO RETREAT BACK BELOW NORMAL. THIS CLIPPER-LIKE SYSTEM MAY BRING
ACCUMULATING SNOW TO THE AREA LATE NEXT WEEK. HAVE INCLUDED 20
POPS FOR THURSDAY...BUT TEMPORAL AND SPATIAL AGREEMENT BETWEEN THE
MODELS IS ADMITTEDLY NOT GREAT AT THIS POINT.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 526 AM CST FRI DEC 26 2014

TWO ISSUES THIS TAF PERIOD WILL BE THE HEIGHT OF THE STRATUS
TODAY...FOLLOWED BY THE TIMING OF A BAND OF SNOW TONIGHT. THE
STRATUS IS HERE TO STAY FOR TODAY...WITH IT MOVING BACK INTO EAU
BY 15Z. FOLLOWED HEIGHT TREND OF THE GFSLAMP...WHICH MORE OR LESS
HAS A DIURNAL INCREASE IN HEIGHTS. FOR SNOW TONIGHT...FOLLOWED THE
TIMING OF THE GFS ALONG WITH THE HI-RES NMM/ARW. CONFIDENCE IN
OCCURRENCE OF THE SNOW IS HIGH. MSP/EAU/RNH LOOK TO GET INTO THE
MAIN BAND...RWF WILL BE ON THE EDGE OF THE MAIN BAND...STC ON THE
EDGE OF JUST SNOW...WHILE AXN WILL REMAIN OUTSIDE OF SNOW. TAFS
MAY BE A BIT QUICK IN TIMING...BUT EXPECT MAIN SNOW BAND TO BE
IMPACTING MSP/RNH/EAU BY 6Z. SNOWFALL RATES LOOK TO BE IN THE 1/2
TO 3/4 INCH PER HOUR RANGE...WHICH WILL TRANSLATE INTO VIS
BOUNCING BETWEEN 3/4SM AND 1 1/2SM DURING THE HEAVIEST SNOW. SNOW
WILL QUICKLY TAPER OFF SHORTLY AFTER 12Z IN MN...WHILE THE NEXT
TAF GETS TO WORK THE END OF THE SNOW INTO THE WI TAFS.

KMSP...IFR CIGS WILL LIKELY LIFT THIS MORNING...COMING AS EARLY AS
14Z AND AS LATE AS 18Z. WITH CIGS BETWEEN 020 AND 030 NORTH OF THE
TWIN CITIES...DID ALLOW CIGS TO GO ABOVE 017 LATE THIS AFTERNOON
BEFORE THE SNOW ARRIVES AND BRINGS THINGS BACK DOWN. WOULD PUT THE
CONFIDENCE ON THE CIG FORECAST THIS AFTERNOON AT MEDIUM. CURRENT
FORECAST HAS 3 INCHES OF SNOW FOR MSP TONIGHT...THOUGH DEPENDING
ON WHERE EXACTLY THE SW-NE ORIENTED BAND OF SNOW SETS UP...IT
COULD BE AS LITTLE AS 2" OR AS MUCH AS 5". MAY BE A BIT QUICK ON
ARRIVAL OF SNOW...BUT FULLY EXPECT IFR VIS SNOW BY 6Z TONIGHT.
SATURDAY MORNING...WE SHOULD SEE A PRETTY RAPID DROP-OFF IN SNOW
BETWEEN 12Z AND 15Z...WITH VFR CONDS POSSIBLE BY THE END OF THIS
TAF PERIOD.

/OUTLOOK FOR KMSP/
SAT...BCMG VFR. WINDS NW 10 KTS.
SUN...CHC MVFR CIGS. WINDS S 5 KTS...BCMG E.
MON...VFR. WINDS N 10KTS.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
MN...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 9 AM CST
     SATURDAY FOR MNZ053-060>063-065>070-073>078-082>085-091>093.

WI...WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO NOON CST
     SATURDAY FOR WIZ014>016-023>028.

&&

$$

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






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