Area Forecast Discussion
Issued by NWS Twin Cities, MN

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FXUS63 KMPX 061148
AFDMPX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN
548 AM CST SAT FEB 6 2016

.UPDATE...
ISSUED AT 527 AM CST SAT FEB 6 2016

UPDATED TO INCLUDE 12Z AVIATION DISCUSSION BELOW.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 500 AM CST SAT FEB 6 2016

THE FOCUS OF THIS FORECAST WAS THE INCREASING POTENTIAL FOR A
GROUND BLIZZARDS SUNDAY AFTERNOON THROUGH MONDAY. AS IS USUALLY
THE CASE...SEVERITY HINGES ON BOTH SNOWFALL AND THE SNOWPACK...BUT
CONFIDENCE IS INCREASING THAT IMPACTS WILL BE HIGH...IN THE FORM
OF CLOSED ROADS ACROSS MUCH OF WESTERN AND SOUTHERN MN. FOR THAT
REASON EXPANDED THE BLIZZARD WATCH A FEW COUNTIES EAST.

EARLY MORNING WATER VAPOR IMAGERY TOGETHER WITH GFS 500MB HEIGHTS
AND WINDS SHOWED LOW AMPLITUDE ZONAL FLOW UPSTREAM OF THE
MIDWEST THROUGH THE GULF OF ALASKA. WITHIN THIS PATTERN WAS A
POTENT PV ANOMALY ACROSS THE IDAHO PANHANDLE. OVER THE NEXT 24
HOURS...THIS OPEN WAVE WILL TAKE ON A NEGATIVE TILT AND BECOME A
CUTOFF UPPER LEVEL LOW. THE SURFACE REFLECTION WILL TRACK ALONG
THE INTERNATIONAL BORDER TOWARD NORTHERN MINNESOTA SETTING THE
STAGE FOR COLD AIR ADVECTION AND STRONG WINDS ACROSS THE RED RIVER
AND MINNESOTA RIVER VALLEYS. THESE TYPES OF SETUPS FAVOR BOUNDARY
LAYER MIXING...STRONG WINDS...AND BLIZZARD CONDITIONS DEPENDING ON
THE SNOWPACK.

THE DETERRENTS FOR ACHIEVING A HIGH END BLIZZARD WITH THIS EVENT
ARE FEW. FIRST OF ALL...THE WARM SECTOR AHEAD OF THE COLD FRONT
WILL RAISE TEMPS INTO THE MID 30S ACROSS THE REGION. THIS WILL
SLIGHTLY MODIFY THE SNOWPACK...BUT OFTEN THE DEGREE OF MELTING IS
OVER ESTIMATED. FOR EXAMPLE...JANUARY 29 2008 SURFACE TEMPS WARMED
NEAR 40 WITH DEWPOINTS IN THE MID 30S AND RAIN ACROSS SOUTHERN
MN...YET AFTER THE COLD FRONT MOVED THROUGH WITH 40-50 MPH WINDS
AND A BAND OF LIGHT SNOW DEVELOPED. ALBERT LEA WAS LESS THAN 1/4
MI FOR 7 CONSECUTIVE HOURS AND I-90 WAS CLOSED. JANUARY 25 2010
TEMPS STARTED IN THE MID 30S ACROSS IOWA...BUT WINDS INCREASED
CAUSING BLOWING SNOW AND WHITEOUT CONDITIONS...CLOSING MOST ROADS
ACROSS THE STATE.

ANOTHER LIMITING FACTOR IS THE FACT THAT COLD AIR ADVECTION IS NOT
AS STRONG AS IN OTHER CASES...AND WHAT THAT MEANS IS THAT THE
FORECAST WINDS OF 50+ KTS OFF THE BUFKIT SOUNDINGS MAY NOT TRULY BE
REALIZED. ESPECIALLY EARLY ON IN THE EVENT WHEN THE HIGHER WINDS
ARE SOMEWHAT INFLATED BY THE INSTABILITY THAT DEVELOPS IN THE
SOUNDING. WITH THAT SAID...GUSTS OF 40+ KTS SEEM VERY REALISTIC...
AND THE DURATION IS ALSO CONCERNING. FOR THE REASON...EXPECTED THE
BLIZZARD WATCH EASTWARD AND EXTENDED THE TIME TO 18Z MONDAY. IN
REALITY...COULD SEE BLIZZARD CONDITIONS ANOTHER TIER EASTWARD OF
COUNTIES...BUT WILL LET THE DAY SHIFT HANDLE THIS SINCE THE EVENT
IS STILL OVER A COUPLE DAYS OUT.

THE TAKEAWAY IS THIS...FORECAST SOUNDINGS SHOW THE BEST UTILITY
WHEN TRYING TO DIAGNOSE AND PREDICT A GROUND BLIZZARD. THE
SOUNDINGS OFF BOTH THE NAM AND GFS SHOW OVER 50+ KT GUSTS...BUT
THINK THAT A MORE REALISTIC VALUE WILL BE 40 TO 45 KT GUSTS. THIS
IS THE UPPER END WHEN COMPARED TO SOUNDINGS FROM PAST GROUND
BLIZZARDS. THERE SHOULD BE PLENTY OF FRESH SNOW FROM THE WINTER
STORM EARLIER THIS WEEK. ITS VERY UNLIKELY THAT THE SNOWPACK WILL
MELT ENOUGH TO SUSTAIN ITSELF WITH THESE EXPECTED WINDS...NOT TO
MENTION ADDITIONAL FALLING SNOW OF AN INCH OR TWO AS THE THERMAL
PROFILE SATURATES IN THE DENDRITIC GROWTH ZONE. IF THE NUMERICAL
MODELS REMAINS ON TRACK...A SIGNIFICANT GROUND BLIZZARD SHOULD
COME TO FRUITION SUNDAY INTO

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 500 AM CST SAT FEB 6 2016

THE PATTERN OF NW FLOW ALOFT WITH A TROF OVER THE ERN CONUS COAST
AND A RIDGE OVER THE WRN CONUS COAST WILL REMAIN STEADY THROUGHOUT
THE MIDDLE-TO-END OF NEXT WEEK. THIS WILL MITIGATE THE POTENTIAL
FOR ANY LARGE SYSTEMS TO MOVE THROUGH THE AREA...THUS A RATHER DRY
SEVERAL DAYS IS EXPECTED...ALONG WITH PROMOTING EFFECTIVE COLD AIR
ADVECTION OF ARCTIC AIR INTO THE REGION THROUGH AT LEAST THE END
OF THE WEEK. AT THE SFC...HIGH PRES WILL DROP IN FROM CENTRAL
CANADA TUE- THU...MAKING FOR GENERALLY COLD BUT PARTLY CLOUDY
CONDITIONS. A WEAK TROF OF LOW PRES...POTENTIALLY EVOLVING INTO A
CDFNT...WILL DROP THRU THE REGION THU NIGHT INTO FRI MRNG. THIS
LOOKS TO BE THE ONLY CHC FOR MEASURABLE PRECIP THROUGHOUT THE
EXTENDED PORTION OF THE FCST...AND CHCS ARE NO HIGHER THAN 20
PERCENT ATTM. TEMPERATURES ARE EXPECTED TO REMAIN BELOW NORMAL
THROUGHOUT THE PERIOD WITH HIGHS IN THE TEENS TO LWR 20S AND LOWS
IN THE SINGLE DIGITS ABOVE AND BELOW ZERO.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 535 AM CST SAT FEB 6 2016

LOW CLOUDS OVER ERN MN INTO WRN WI WILL SLOWLY ERODE OFF TO THE E
AS A WEAK UPPER LEVEL RIDGE APPROACHES THE REGION...HELPING SCOUR
OUT SOME OF THE LOW LEVEL MOISTURE ACROSS THE AREA. MID-HIGH LEVEL
CEILINGS WILL THEN PREVAIL FROM LATE THIS AFTN THROUGH THE
OVERNIGHT HOURS. AS THE LARGE STORM SYSTEM APPROACHES FROM THE
W...SOME -SN MAY TRY TO MAKE AN APPEARANCE CLOSE TO 12Z BUT
CHANCES ARE LOW /WITH CHANCES INCREASING AFTER DAYBREAK TUESDAY/.
CEILINGS WILL GRADUALLY LOWER OVERNIGHT THRU TMRW...POTENTIALLY
INTO MVFR RANGE FOR THE NWRN MN TAF SITES. THE OTHER MAIN CONCERN
WILL BE STRONG WINDS DEVELOPING LATE TONIGHT THRU TMRW...
PARTICULARLY IN THE LOWEST LEVELS OFF THE DECK. WHILE SFC
SUSTAINED WIND SPEEDS LINGER CLOSE TO 10 KTS...BUT SOMETIMES AS
HIGH AS 15...STRONG LOW LEVEL WINDS WILL DEVELOP. MODEL SOUNDINGS
AND BUFKIT PROFILES INDICATE WINDS INCRG TO ARND 40 KT AS WELL AS
HAVING A 40-60 DEGREE DIRECTIONAL DIFFERENCE FROM SFC WINDS...SO
HAVE OPTED TO INCLUDE LLWS MENTIONS AT ALL TAF SITES.

KMSP...ONCE THE MVFR CLOUDS ERODE TO THE E LATER THIS MRNG... WILL
LOOK FOR VFR CONDS TO PREVAIL THRU TMRW MRNG. NO PRECIP EXPECTED
WITHIN THE FIRST 24 HRS...BUT THEN CONFIDENCE DROPS AFTER 12Z TMRW
IN KEEPING A DRY FCST...PARTICULARLY AFTER 14Z-15Z. HAVE INCLUDED
A PROB30 MENTION IN THE 24-30 HR PORTION OF THIS TAF SINCE CHCS DO
INCRS LATE MRNG FOR HAVING THE -SN MOVE INTO THE AREA FROM THE N.
HAVE ALSO INCLUDED THE LLWS MENTION FOR KMSP AS SEVERAL MOS
GUIDANCE PLUS BUFKIT/MODEL SOUNDINGS SUPPORT THE THINKING.

/OUTLOOK FOR KMSP/
MON...CHC MVFR/IFR/-SN. WINDY. BLSN POSSIBLE. WIND NW 20G35KT.
TUE...VFR. WIND NW 10 KTS.
WED...VFR. WIND NW 5-10 KTS.

&&

.MPX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...BLIZZARD WATCH FROM SUNDAY MORNING THROUGH LATE SUNDAY NIGHT FOR
     MNZ041-047-048-055.

     BLIZZARD WATCH FROM SUNDAY AFTERNOON THROUGH MONDAY MORNING FOR
     MNZ054-056>058-064>067-073>076-082>084-091>093.

&&

$$

UPDATE...JPC
SHORT TERM...JRB
LONG TERM...JPC
AVIATION...JPC


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