Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 260231
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
831 PM CST SUN JAN 25 2015

.UPDATE...
ISSUED AT 831 PM CST SUN JAN 25 2015

AFTER MUCH DELIBERATION...HAVE DECIDED TO ISSUE THE WINTER
WEATHER ADVISORY FOR SOME OF THE FORECAST AREA. THE COUNTIES ALONG
THE MISSISSIPPI RIVER HAVE THE HIGHEST CONFIDENCE OF SEEING A
COUPLE HUNDREDTHS OF FREEZING DRIZZLE AS THE SNOW ENDS...WHILE IN
TAYLOR/CLARK COUNTIES THE POTENTIAL EXISTS FOR A LITTLE MORE SNOW
TO FALL THAN WHATS EVEN CURRENTLY FORECAST. THATS BECAUSE THE
RAP CONTINUES TO SHOW 7 C/KM LAPSE RATES MARCHING THROUGH WESTERN
WISCONSIN MONDAY MORNING...WHICH SHOULD ADD SOME CONVECTIVE
ENHANCEMENT TO THE SNOWFALL. THE EXPERIMENTAL HRRR AT BOULDER ALSO
SHOWS THIS CONVECTIVE ENHANCEMENT...EVEN INTO SOUTHEAST MN AND
INTO THE LSE AREA...RIGHT AT MORNING COMMUTE TIME.

ALTHOUGH SNOWFALL AMOUNTS WILL NOT REACH ADVISORY CRITERIA
ALONE...THE COMBINATION OF THE SNOW AND FREEZING DRIZZLE SHOULD
MAKE FOR A MESS ON ROADWAYS...ESPECIALLY THOSE LEFT UNTREATED.
ADDITIONALLY...HAVING THIS PRECIPITATION COME THROUGH AT MORNING
COMMUTE TIME IS ALSO A PROBLEM. THESE ARE THE MAIN REASONS WHY THE
ADVISORY HAS BEEN ISSUED.

UPDATE ISSUED AT 541 PM CST SUN JAN 25 2015

FOLLOWING THE SITUATION CLOSELY FOR MONDAY AS A WINTER WEATHER
ADVISORY MAY BE REQUIRED.

GOOD MODEL CONSENSUS EXISTS BETWEEN THE 25.15Z SREF...25.18Z
NAM/GFS AND 25.21Z RAP FOR SNOW TO MOVE INTO THE REGION VERY LATE
TONIGHT INTO MONDAY MORNING. GOOD DYNAMICAL SUPPORT IN THE MORNING
WITH A SHORTWAVE COMING THROUGH AS WELL AS HAVING THE LEFT EXIT
REGION OF AN UPPER LEVEL JET SITUATED OVERHEAD. ADDITIONALLY...THE
APPROACH OF A WARM FRONT WILL PROVIDE LOW LEVEL LIFT. THE CONCERN
BECOMES WHEN THE SHORTWAVE AND LEFT EXIT REGION LEAVE THE AREA BY
LATE MORNING...CAUSING MID-LEVEL DRYING AND THUS LOSS OF ICE IN
THE CLOUDS. MEANWHILE...WE STILL HAVE THAT WARM FRONT COMING INTO
THE REGION FROM NEAR I-35 TO PROVIDE THAT LOW LEVEL LIFT. THUS IT
APPEARS LIKELY WE SHOULD SEE SOME FREEZING DRIZZLE BY MID-LATE
MORNING...ESPECIALLY ALONG THE MISSISSIPPI RIVER COUNTIES.

ONE BENEFIT IS THAT SNOW IS STARTING OUT FIRST...WHICH SHOULD
MINIMIZE THE IMPACT OF THE FREEZING DRIZZLE ON TRAVEL.
HOWEVER...IF ROADS DO NOT GET TREATED...THEY COULD EASILY BE
SLIPPERY DUE TO THE COMBINATION OF SNOW AND FREEZING DRIZZLE.
ADDITIONALLY...THERE COULD BE ISSUES WITH THE SNOW COMING IN AT
COMMUTE TIME. SO BOTH SOME PROS AND CONS FOR A WINTER WEATHER
ADVISORY.

ANOTHER CONCERN IS THAT THE WARM FRONT MAY NOT MAKE IT FARTHER
EAST THAN A ROCHESTER TO OELWEIN LINE...KEEPING THE MISSISSIPPI
RIVER COUNTIES AT OR BELOW FREEZING THROUGH THE AFTERNOON...WHICH
WOULD BE COLDER THAN OUR CURRENT FORECAST. ALTHOUGH THE LOW LEVEL
LIFT IS PROGGED TO WEAKEN IN THE AFTERNOON...THERE IS PLENTY TO
KEEP SOME DRIZZLE GOING...WHICH COULD THEN FREEZE IF OUR
TEMPERATURES STAY COLD. ON THE OTHER HAND...DAYLIGHT THROUGH THE
CLOUDS MAY HEAT UP ROADS ENOUGH TO PREVENT ICING. NEEDLESS TO
SAY...PLENTY OF UNCERTAINTIES.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 257 PM CST SUN JAN 25 2015

CHALLENGES CONCERN PRECIPITATION CHANCES/AMOUNTS/TYPE LATE TONIGHT
THROUGH MONDAY WITH THE NEXT CANADIAN TROUGH MOVING THROUGH
NORTHWEST FLOW ALOFT. 25.12Z MODEL SUITE IN GOOD OVERALL AGREEMENT
WITH PRECIPITATION PLACEMENT...BUT DIFFER SLIGHTLY ON AMOUNTS...
ESPECIALLY EAST OF THE MS RIVER VALLEY. WILL USE A BLENDED
SOLUTION OF THE 25.12Z GFS/NAM/ECMWF/GEM WITH ADDITIONAL SUPPORT
FROM THE LATEST SUITE OF HIGH-RESOLUTION MODEL GUIDANCE.

THIS EVENING WILL BE PARTLY TO MOSTLY CLOUDY AND COOL WITH
TEMPERATURES DROPPING INTO THE LOWER TEENS TO LOWER 20S.
PRECIPITATION WILL HOLD OFF UNTIL AFTER MIDNIGHT WHEN AN 850 HPA
TROUGH OVER CENTRAL MANITOBA/EASTERN DAKOTAS MOVES ACROSS MN AND
INTO THE UPPER MS RIVER VALLEY. MODEST MID-LEVEL WARM AIR
ADVECTION/ISENTROPIC LIFT AND QG CONVERGENCE ALONG FRONTAL
BOUNDARY WILL SLIDE FROM WEST TO EAST ACROSS THE FORECAST AREA
MONDAY MORNING. INITIAL THERMAL/MOISTURE PROFILES ARE COLD ENOUGH
AND SATURATED TO AROUND 500 HPA FOR ALL SNOW. HOWEVER...AS DAY
PROGRESSES...ICE LOSS OCCURS AS 700 TO 500 HPA LAYER DRYS OUT.
WITH SUB-FREEZING BOUNDARY LAYER TEMPERATURES...EXPECT SNOW TO
TRANSITION TO FREEZING DRIZZLE FROM WEST TO EAST THROUGH THE DAY.
SNOW ACCUMULATION WILL BE GREATEST ALONG AND EAST OF A LINE FROM
EAU CLAIRE TO BLACK RIVER FALLS TO PLATTEVILLE WITH 1 TO 2 INCHES.
FARTHER WEST TO THE MS RIVER...A QUICKER CHANGE OVER TO DRIZZLE
WILL KEEP SNOW AMOUNTS GENERALLY IN THE HALF INCH TO AN INCH
RANGE. SNOW WEST OF THE RIVER WILL BE A TRACE TO HALF INCH.

A THIN GLAZE OF ICE FROM FREEZING DRIZZLE IS POSSIBLE MONDAY
MORNING...ESPECIALLY ALONG AND EAST OF THE MS RIVER VALLEY...BUT
BECAUSE THERE IS LIKELY TO BE A SHARP CUT-OFF BETWEEN THE STRONGEST
FORCING/BACK EDGE OF PRECIPITATION AND WHEN ICE LOSS OCCURS...
CONFIDENCE NOT HIGH ENOUGH AT THIS TIME TO HOIST AN ADVISORY.
IMPACTS TO THE MORNING COMMUTE A POSSIBILITY AND CERTAINLY
SOMETHING TO KEEP A CLOSE EYE ON THIS EVENING AND OVERNIGHT. IF
ICE ACCUMULATION DOES HAPPEN...IT SHOULD QUICKLY MELT AS
TEMPERATURES RISE TO ABOVE FREEZING FOR ALL AREAS EXCEPT THE FAR
EAST BEHIND THE WARM FRONT.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 257 PM CST SUN JAN 25 2015

LINGERING LIGHT SNOW/FREEZING DRIZZLE WILL PUSH EAST MONDAY NIGHT
WITH DRY CONDITIONS THROUGH TUESDAY AS SURFACE HIGH PRESSURE
BUILDS ACROSS THE REGION. SHOULD SEE SOME SUN BY LATE TUESDAY WITH
TEMPERATURES RISING INTO THE LOWER TO MID 30S.

WEDNESDAY WILL BE DRY AND POTENTIALLY QUITE WARM AS LOW PRESSURE
DRIFTS ACROSS THE REGION AND KEEPS MOST OF THE FORECAST AREA
WITHIN THE WARM SECTOR. PRECIPITATION WILL REMAIN TO THE NORTH
WITH 850 HPA TEMPERATURES ACROSS THE UPPER MS RIVER VALLEY FROM
+2 TO +5 C. CLOUD COVER COULD LIMIT TEMPERATURE RISE...BUT LOWER
40S A REAL POSSIBILITY...ESPECIALLY ACROSS NORTHEAST IA INTO
SOUTHWEST WI. PRECIPITATION CHANCES INCREASE WEDNESDAY NIGHT INTO
THURSDAY AS MID-LEVEL WAVE WRAPS-UP ACROSS WI.

LATE THURSDAY THROUGH SUNDAY...NORTHWEST FLOW ALOFT PERSISTS
ALLOWING A SERIES OF WEAK WAVES TO TRANSLATE ACROSS THE UPPER
MIDWEST. THE STRONGEST OF THESE IMPACTS THE REGION FRIDAY NIGHT
INTO SATURDAY WITH A 20-30 PERCENT CHANCE OF LIGHT SNOW.
TEMPERATURES FOR THE LATTER HALF OF THE WEEK INTO NEXT WEEKEND
WILL DROP SLIGHTLY EACH DAY AS AN ARCTIC TROUGH DROPS SOUTH ACROSS
EASTERN CANADA AND INTO THE EASTERN CONUS. HIGHS IN THE UPPER 20S
TO LOWER 30S ON THURSDAY WILL DROP INTO THE MID TEENS TO LOWER 20S
BY SUNDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 541 PM CST SUN JAN 25 2015

THE LOW STRATUS HAS CLEARED LSE BUT REMAINS STUCK FROM RST TO
I-35. WITH THE WIND FIELD BECOMING LIGHT...THE MVFR STRATUS AT
RST SHOULD PERSIST THROUGH THE EVENING WHILE LSE STAYS VFR.
DURING THE OVERNIGHT HOURS...THE APPROACH OF A LOW PRESSURE SYSTEM
FROM NORTHERN MN WILL TURN THE WINDS SOUTH TO SOUTHWEST...BRINGING
THE STRATUS NEAR I-35 BACK INTO LSE AROUND 09Z. ADDITIONALLY...WE
SHOULD SEE SNOW MOVE SOUTHEAST INTO THE TAF SITES BETWEEN
11-12Z...WITH THAT MOISTURE HELPING TO LOWER CEILINGS AND
VISIBILITIES TO IFR...OR POSSIBLY LIFR AT RST. AROUND 13Z AT RST
AND 16Z AT LSE...DRYING COMING IN AROUND 10000 FT WILL HELP SCOUR
OUT THE ICE IN THE CLOUDS...CAUSING THE SNOW TO TRANSITION TO
FREEZING DRIZZLE. THIS FREEZING DRIZZLE SHOULD END AT RST AROUND
15Z. HOWEVER...AT LSE...THE FREEZING DRIZZLE COULD PERSIST
THROUGH THE AFTERNOON WITH THE ICING PART ENDING AROUND 19Z AS
TEMPERATURES CLIMB ABOVE FREEZING. VISIBILITIES LOOK TO QUICKLY
IMPROVE TO MVFR AROUND LATE MORNING AS PRECIPITATION WEAKENS...BUT
CEILINGS ARE LIKELY TO STAY DOWN UNTIL LATE AFTERNOON AS MIXING
INCREASES.

ANY ICE ACCUMULATION WOULD BE A GLAZE AT MOST...WITH SNOW TOTALS
LESS THAN 1 INCH.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER WEATHER ADVISORY FROM 5 AM TO NOON CST MONDAY FOR WIZ017-
     029-032>034-041-042-053.

MN...WINTER WEATHER ADVISORY FROM 5 AM TO NOON CST MONDAY FOR MNZ079-
     088-096.

IA...NONE.
&&

$$

UPDATE...AJ
SHORT TERM...ROGERS
LONG TERM...ROGERS
AVIATION...AJ


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