Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 211116
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
516 AM CST WED JAN 21 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 215 AM CST WED JAN 21 2015

CURRENTLY AS OF 08Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED UPPER RIDGING OVER THE EAST PACIFIC INTO SOUTHWEST CANADA...
AN UPPER LOW TRAVERSING THE SOUTHERN FORECAST AREA...AND TROUGHING
OVER EASTERN CANADA. WEAK MID LEVEL FRONTOGENESIS COMBINED WITH
ABOUT 0.4 OF AN INCH OF PRECIPITABLE WATER PER 00Z RAOB DATA HAS
ALLOWED LIGHT SNOW TO PERSIST ACROSS LOCATIONS MAINLY
ALONG/SOUTHWEST OF I-94. THE AIRMASS ACROSS THE FORECAST AREA WAS
ALSO RELATIVELY WARM...NOTED BY AIR TEMPERATURES FROM THE LOW 20S TO
LOW 30S AND 850MB TEMPS OF -6 TO -8C. THESE READINGS HAVE KEPT SNOW
TO WATER RATIOS DOWN IN THAT 10-15 TO 1 RANGE...LIMITING
ACCUMULATIONS TO MOSTLY AT 1.5 INCHES OR LESS.

EXPECT THE SNOW TO BE ON A WANING TREND TODAY. THIS IS IN RESPONSE
TO THE UPPER LOW SHIFTING OFF TO THE EAST INTO LOWER MICHIGAN...
PRODUCING MID LEVEL SUBSIDENCE IN ITS WAKE...AS WELL AS THE MID-
LEVEL FRONTOGENESIS FALLING APART. IN FACT...MUCH OF THE SNOW COULD
BE DONE BY 18Z...BUT KEPT SOME 20 PERCENT CHANCES GOING THROUGH THE
AFTERNOON PER SOME HIGH RESOLUTION MODEL GUIDANCE KEEPING SOME VERY
LIGHT SNOW OR FLURRIES GOING. WITH THE WEAKENING FORCING THROUGHOUT
THE DAY...ANY ADDITIONAL ACCUMULATION SHOULD BE LESS THAN 1 INCH.
NEVERTHELESS...A SLIPPERY MORNING COMMUTE IS POSSIBLE FOR THOSE
ROADS THAT ARE NOT PLOWED OR TREATED.

ALTHOUGH THE SNOW IS TAPERING OFF...CLOUD COVER IS LIKELY TO HANG
AROUND THROUGH TONIGHT...DUE TO THE MID-LEVEL SUBSIDENCE TRAPPING
MOISTURE AND CYCLONIC LOW LEVEL FLOW. THESE CLOUDS WILL HAMPER
TEMPERATURES FROM CLIMBING MUCH...LIKELY AT MOST TO THOSE OF
YESTERDAY. A LITTLE BIT OF COLD ADVECTION IS PROGGED TONIGHT AS
925MB TEMPS FALL FROM -4 TO -6C AT 00Z TO -6 TO -8C AT 12Z. THIS
COOLING SHOULD ALLOW TEMPERATURES TO DIP INTO THE MID TEENS TO MID
20S DESPITE THE CLOUD COVER.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 215 AM CST WED JAN 21 2015

A PIECE OF THE UPPER RIDGING OVER SOUTHWEST CANADA IS PROGGED TO
MOVE INTO THE REGION FOR THURSDAY INTO THURSDAY NIGHT. THIS RIDGING
ALOFT COMBINED WITH A SURFACE RIDGE DROPPING SOUTH THROUGH THE
REGION SHOULD HELP IN CLEARING THE SKIES OUT ON THURSDAY. THE
CLEARING LOOKS TEMPORARY AS WARM ADVECTION MID CLOUDS RETURN LATE
THURSDAY NIGHT. ALTHOUGH 925MB TEMPS ARE A BIT COLDER ON THURSDAY
COMPARED TO TODAY...MORE SUNSHINE SHOULD HELP PRODUCE SIMILAR
READINGS AGAIN. TEMPERATURES COULD TANK A BIT EARLY IN THE EVENING
BEFORE INCREASING WINDS CAUSE READINGS TO RISE...PARTICULARLY
ALONG AND WEST OF THE MISSISSIPPI RIVER. GUIDANCE LOWS IN THE MID
TEENS TO MID 20S SEEM REASONABLE.

FRIDAY LOOKS TO BE THE WARMEST...AND BREEZIEST...DAY OF THE WORK
WEEK. A SHORTWAVE IS PROGGED TO DROP THROUGH SOUTHEAST THROUGH
NORTHERN MN INTO NORTHERN WI...INCREASING THE PRESSURE GRADIENT
ACROSS THE AREA. 925MB SOUTHWEST WINDS IN THE 25-40 KT RANGE ARE
SUGGESTED BY THE 21.00Z GFS/ECMWF...BRINGING THE RESPECTIVE TEMPS UP
TO 0 TO -3C. MIXING MIGHT BE SOMEWHAT REDUCED BY MID CLOUD
COVER...BUT HIGHS SHOULD BE ABLE TO TOP OUT IN THE 30S TO POSSIBLY
LOW 40S. THESE READINGS SHOULD ALLOW FOR GUSTS IN THE 20-25 MPH
RANGE OVER HIGHER TERRAIN/EXPOSED LOCATIONS. ADDITIONALLY...
ISENTROPIC LIFT AHEAD OF THE SHORTWAVE COULD PRODUCE A LITTLE LIGHT
RAIN/SNOW/SLEET MIX...DUE TO THE PRESENCE OF A WARM LAYER AND
SURFACE TEMPERATURES ABOVE FREEZING. PRECIPITATION SHOULD MOSTLY BE
CONFINED TO NORTH OF I-90 AND LIGHT AT BEST DUE TO DRY LOW TO MID
LEVEL AIR. THE FAST MOVING NATURE OF THE SHORTWAVE WILL ALLOW ANY
PRECIPITATION TO END BY FRIDAY EVENING.

NEXT ITEM OF INTEREST IS A MORE POTENT SHORTWAVE TROUGH TAKING AIM
AT THE REGION FOR LATE SATURDAY NIGHT THROUGH SUNDAY. EXACT TRACK IS
A BIT UNCERTAIN...WITH THE 21.00Z GFS HEADING THROUGH WESTERN IA...
COMPARED TO RIGHT THROUGH LA CROSSE FROM THE 21.00Z ECMWF...AND
EASTERN WI IN THE 21.00Z CANADIAN. THE TRACK WILL BE IMPORTANT AS A
FRONTOGENETIC BAND OF SNOW IS LIKELY ALONG/EAST OF ITS TRACK...WHICH
COULD BE ADVISORY WORTHY. RIGHT NOW JUST HAVE TO BROAD BRUSH WITH 30-
50 PERCENT CHANCES AND WAIT UNTIL MODELS COME TOGETHER. WOULD NOT BE
SURPRISED THE FARTHER WEST TRACK OF THE 21.00Z GFS COMES TRUE...OR
EVEN A SOLUTION FARTHER WEST. IN GENERAL...THE SNOW LOOKS TO DEPART
THE AREA BY SUNDAY EVENING...BUT CHANCES CONTINUE INTO MONDAY AS YET
ANOTHER WEAK SHORTWAVE IS PROGGED TO DROP INTO THE REGION ON
NORTHERLY FLOW. FINALLY BY TUESDAY WE COULD BREAK OUT OF THE
PRECIPITATION.

IN GENERAL...MOST OF THE TEMPERATURES THROUGHOUT THE LONG TERM
PERIOD EXPECTED TO STAY ABOVE NORMAL...DUE TO THE ARCTIC AIR ONLY
DROPPING THROUGH SOUTHEAST CANADA AND A FLOW OF MOSTLY PACIFIC AIR
INTO THE REGION. THERE SHOULD BE SOME COOL DOWN...THOUGH...FOR
SUNDAY INTO EARLY NEXT WEEK AS THE UPPER FLOW BECOMES A BIT MORE
NORTHERLY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 515 AM CST WED JAN 21 2015

LOCAL AND REGIONAL RADARS INDICATING THE BACK EDGE OF THE SNOW WAS
STARTING TO WORK SLOWLY SOUTH ACROSS THE AREA. EXPECTING TO SEE
THE LAST OF THE HEAVIER SNOW MOVE PAST BOTH TAF SITES BEFORE 15Z
WITH SOME LINGERING LIGHT SNOW HANGING ON UNTIL LATE MORNING. WILL
START BOTH TAF SITES WITH IFR CONDITIONS AND THEN TAKE THE
VISIBILITY UP TO MVFR AS THE SNOW DIMINISHES AND EVENTUALLY TO VFR
BY THE MIDDLE OF THE AFTERNOON. DESPITE THE SNOW ENDING AND THE
WEAK SURFACE BOUNDARY MOVING SOUTH OF THE AREA...THE FLOW STILL
REMAINS VERY WEAK WHICH DOES NOT BODE WELL FOR GETTING RID OF THE
CLOUDS ANYTIME SOON. WILL KEEP THE CEILINGS IFR THROUGH THE PERIOD
AT KRST WITH KLSE ON THE EDGE OF IFR TO MVFR.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...NONE.
MN...NONE.
IA...NONE.
&&

$$

SHORT TERM...AJ
LONG TERM...AJ
AVIATION...04


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