Area Forecast Discussion
Issued by NWS Twin Cities, MN

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000
FXUS63 KMPX 261837
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
1237 PM CST FRI DEC 26 2014

.UPDATE...
ISSUED AT 1142 AM CST FRI DEC 26 2014

UPDATED TO INCLUDE 18Z AVIATION DISCUSSION BELOW.

&&

.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 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1142 AM CST FRI DEC 26 2014

ALL SITES EXPECTED TO LINGER IN THE LOWER-END MVFR RANGE FOR
CEILINGS THRU THIS AFTN THEN DROP INTO IFR RANGE THIS EVENING THRU
OVERNIGHT. BEST CHCS FOR -SN WILL BE ALONG AND EAST OF A KRWF-KMSP
LINE...SO THOSE TWO SITES PLUS THE TWO WI SITES ARE EXPCTED TO SEE
-SN DEVELOP SHORTLY AFTER 00Z...STARTING OUT WITH MVFR VSBY BUT
THEN DROPPING INTO IFR RANGE SHORTLY THEREAFTER FOR GENERALLY 4-6
HOURS. CONDS IMPROVE BEYOND 12Z TMRW MRNG. HAVE ONLY GONE DOWN TO
1SM FOR VSBY BUT GOING DOWN TO 1/2SM OR LOWER...ESP FOR KMSP-KRNH-
KEAU...CERTAINLY CANNOT BE RULED OUT. SAME AS HAVING CEILINGS /OR
VV/ DROPPING TO 500FT OR LOWER AT TIMES. WINDS WILL REMAIN
GENERALLY NLY THROUGHOUT THIS TAF SET...THEN BECOME MORE WNW BY
MIDDAY TMRW.

KMSP...CEILINGS TO REMAIN SUB-1700FT FOR THE START OF THE 26/18Z
TAF...BUT THERE IS A WINDOW OF TIME CEILINGS MAY NUDGE ABOVE THAT
LEVEL TO CLOSE TO 2 KFT. HOWEVER...AS -SN MOVES IN THIS EVENING...
CEILINGS DROP BACK DOWN AND MAY WELL HIT IFR LEVELS BY MIDNIGHT.
LITTLE TRICKY TO SEE HOW LONG THE IFR-VSBY -SN WILL LAST BUT HAVE
OPTED TO KEEP THE 6-HOURS-WORTH OF IFR CONDS ATTM. CONDS IMPROVE
AROUND DAYBREAK WITH MID-UPR RANGE MVFR CEILINGS VERY POSSIBLE SAT
AFTN.

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

&&

.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.

&&

$$

UPDATE...JPC
SHORT TERM...MPG
LONG TERM...LS
AVIATION...JPC





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