Extreme Cold in Minnesota, January 17 to 18, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND FORKS ND
317 PM CST THU JAN 17 2008

.SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...
ARCTIC AIR IS ON ITS WAY WITH THE PRIMARY COLD FRONT NOW DROPPING
INTO SRN SASK AND SET TO BLAST THRU THE RED RIVER VALLEY BY 06Z.
THE 12Z MODELS CONTINUE TO HANDLE THIS WELL...WITH THE GFS AGAIN
DISPLAYING THE COLDER...FAVORED THERMAL PROFILES. WE HAVE LITTLE
DOUBT ABOUT THE BREADTH OF THE ARCTIC AIRMASS WITH -25 C 850MB AIR
IN NRN CANADA AT 12Z. MORE PROBLEMATIC IS -SN CHANCES WITH THE
ARCTIC BOUNDARY. PWATS ARE 0.25 INCHES...BUT MOISTURE IS SHALLOW
ON PROG SOUNDINGS. THE 12Z NAM/GFS AND 18Z RUC ALL AGREE ON
DROPPING THE MAIN QG FORCING THRU THE HIGH PLAINS /WHERE -SN IS
FALLING NOW/ AND THUS CAA AND FRONTAL CONVERGENCE WILL BE ABOUT
ALL WE CAN BANK ON FOR -SN POTENTIAL. GIVEN RAPID DRYING UPSTREAM
AND LACK OF VIS BLO 1-2SM...WE WILL SLIDE BACK ON POPS TONIGHT EAST
OF A KDVL-KFAR-KDTL LINE. THIS MEANS THAT WIND CHILLS RATHER THAN
A COMBO OF THEM AND BLSN ARE THE PRIMARY DANGER WITH THIS EVENT.
AFTER MUCH DISCUSSION...WE WILL FAVOR WIND CHILL HEADLINES
/INCLUDING A WARNING/ INSTEAD OF THE EARLIER ISSUED WINTER WEATHER
ADVISORY. LIKELY TO BE EXTENSIONS ON THESE HEADLINES PAST 18Z
FRI...BUT FOR NOW WE WILL CHOOSE TO CAPTURE THE RAPID CHANGES
TONIGHT/FRI MORNING FIRST AND GIVE US SOME TIME TO DECIDE IF WINDS
WILL STAY UP ENOUGH BY FRI EVE TO SATISFY THE 10 MPH CRITERIA FOR
HEADLINES. BITTER COLD NO MATTER WHAT.

THE PRIMARY ISALLOBARIC WIND COMPONENT IN THE FORM OF 8MB/3 HOUR
PRESSURE RISES IS SET TO DROP SOUTH WELL WEST OF THE FA TONIGHT...
BUT STRONG CAA WILL DRIVE LOW LEVEL MOMENTUM TRANSFER BY 06Z WITH
MIXING TO 900MB IN THE WAKE OF THE ARCTIC FRONT. BOTH NAM/GFS PROG
SOUNDINGS SHOW 30KTS AT THE TOP OF THE MIXED LAYER...MATCHING
CLOSELY THE 925-900MB GEOSTROPHIC WINDS. AS THE PRIMARY SFC LOW
DROPS INTO EASTERN NE BY 12Z...LOW LVL FLOW TURNS NRLY IN THE VALLEY
AND THIS FAVORABLE LINKAGE WILL FOCUS GUSTS NEAR THAT TIME. 850MB
TEMPS FALL TO -27 C NORTH OF KGFK BY THAT TIME AND TEMPS THIS
MORNING IN NRN MB UNDER THIS AIRMASS WERE NEAR -20 F. WINDS WILL
OFFSET COOLING SOME...BUT GIVEN INCREASING DRAINAGE EFFECT INTO
THE VALLEY AND THE FACT THAT TEMPS TODAY FELL 5 DEG F SHORT OF
EXPECTATIONS...WE ARE CONFIDENT IN DROPPING THE NRN FA INTO THE
-15 TO -20 F RANGE BY MORNING. GIVEN THE WINDS...THIS GETS THE NRN
2/3RDS OF THE FA INTO WIND CHILL WARNING CRITERIA. KFAR-KPKD A
BIT MORE ON THE FENCE BUT FELT IT BEST TO INCLUDE THEM AS WELL
WITH THE HIGH IMPACT NATURE OF THE COLD.

MODEL RH PROGS ARE NOT HANDLING THE ARCTIC INTRUSION WELL...WITH
HIGH 925-850MB RH CONTINUING UNTIL 00Z SAT. UPSTREAM OBS CERTAINLY
SUPPORT CLEARING MUCH MORE RAPIDLY THAN THAT...AND WITH CAA AND
LOW LVL DRYING EXPECT RAPID CLEARING 12-18Z FRI. THIS MEANS WE
WILL START FRI EVE OUT WITH OPTIMUM RADIATIONAL COOLING
CONDITIONS. LITTLE CHANGE IN THE AIRMASS THRU THE WEEKEND WITH
1000-500MB THICKNESS VALUES BLO 500 DECAMETERS AND 850MB TEMPS NEAR
-25 C. THUS SFC WINDS WILL MEAN ALMOST EVERYTHING TO ACTUAL MINS.
CERTAINLY COULD GET CLOSE TO -30 F FRI NIGHT IN THE NORTH...BUT
BASED ON 12Z SFC WIND PROGS IT WOULD SEEM SAT NIGHT IS THE BETTER
CANDIDATE. EVEN WITH SUNSHINE DURING THE DAY...A 10-15 F TEMP RISE
WILL BE HARD TO COME BY. AS A RESULT...WE CUT MAX TEMPS SAT AND
ESPECIALLY SUN. THE ARCTIC INVERSION WILL ONLY CONTINUE TO
STRENGTHEN DURING THIS PERIOD AND THERE WILL BE NOTHING TO
DISLODGE IT FROM THE VALLEY. AGAIN...WIND CHILL HEADLINES WILL BE
NECESSARY ANY TIME THE WIND GETS TO 10 MPH OR BETTER. AT THE
PRESENT...IT WOULD SEEM AN ADVISORY WILL BE NEEDED FRI AFTERNOON
...AND QUITE POSSIBLY ANOTHER WARNING COME FRI EVE. LATER SHIFTS
WILL MONITOR THESE POSSIBILITIES CLOSELY.

.LONG TERM...MONDAY THROUGH THURSDAY...
LONG RANGE MODELS STILL STICKING TO THEIR GUNS WITH A CONTINUATION
OF VERY COLD AND DRY CONDITIONS. WILL KEEP STRONG ARCTIC FROPA
ACROSS FORECAST AREA TUESDAY NIGHT INTO EARLY WED FOLLOWED BY
ANOTHER REINFORCING SHOT OF VERY COLD AIR FOR THE MIDDLE AND
LATTER HALF OF NEXT WEEK. SOME HINT OF A PERIOD OF MODERATING
TEMPS ON THURSDAY AS ARCTIC HIGH SHIFTS TO THE SOUTH AND EAST
OF CWFA WHILE LEE SIDE TROUGH TAKES SHAPE OVER SASK/ALBERTA
PROVINCES. PROXIMITY TO ARCTIC HIGH SUGGESTS ANY PRECIPITATION
THREAT SHOULD STAY TO THE SOUTH AND EAST OF FORECAST AREA.

&&

.AVIATION...
POTENT S/W TRAVERSING CWFA TONIGHT INTO EARLY FRIDAY SHOULD
BRING A PERIOD OF SNOW SHOWERS/FLURRIES TO REGION. EXPECT
VFR CONDITIONS LATE THIS AFTERNOON INTO FIRST PART OF TNGT
TO GIVE WAY TO MVFR CAT FOR ALL THREE TAF SITES. COULD SEE
SOME POCKETS OF IFR CONDITIONS AS INCREASING NORTHWEST FLOW
INDUCES PATCHES OF REDUCED VSBY IN -SN. EXPECT CONDITIONS TO
SLOWLY SUBSIDE LATER FRIDAY INTO SATURDAY WITH RETURN TO VFR CAT
AS ARCTIC HIGH AND ANTICYCLONIC CURVATURE OVERSPREADS CWFA FROM
WEST TO EAST.

&&

.FGF WATCHES/WARNINGS/ADVISORIES...
ND...WIND CHILL ADVISORY FROM 9 PM THIS EVENING TO 12 PM CST FRIDAY
     FOR NDZ049-052-053.

     WIND CHILL WARNING FROM 9 PM THIS EVENING TO 12 PM CST FRIDAY
     FOR NDZ006>008-014>016-024-026>030-038-039-054.

MN...WIND CHILL ADVISORY FROM 9 PM THIS EVENING TO 12 PM CST FRIDAY
     FOR MNZ029>032-040.

     WIND CHILL WARNING FROM 9 PM THIS EVENING TO 12 PM CST FRIDAY
     FOR MNZ001>009-013>017-022>024-027-028.

&&

SCHULTZ/NG/BERG

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