Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 282000
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
200 PM CST SUN DEC 28 2014

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 200 PM CST SUN DEC 28 2014

CURRENTLY AS OF 20Z...WATER VAPOR LOOP AND RAP 500MB HEIGHT ANALYSIS
SHOWED A STRONG SHORTWAVE DROPPING SOUTH THROUGH THE NORTHWESTERN
U.S. AND BRITISH COLUMBIA...A COLLECTION OF WEAK SHORTWAVES OVER
WYOMING AND NEBRASKA AND AN UPPER LOW OVER NORTHERN ONTARIO. DESPITE
A MAINLY ZONAL FLOW COMING ACROSS THE FORECAST AREA...A COLD FRONT
WAS EVIDENT AT THE SURFACE DROPPING SOUTH INTO THE AREA. THIS FRONT
EXTENDED FROM NORTHERN LOWER MI TO LA CROSSE TO SIOUX CITY IA. LOW
CLOUDS WITH A FEW FLURRIES WERE EVIDENT IN A 100 MILE WIDTH ZONE
BEHIND THE FRONT...WHILE SKIES WERE MAINLY SUNNY AHEAD OF IT. 925MB
TEMPS OF -6 TO -10C AND SUN HAS ALLOWED TEMPERATURES TO MOSTLY CLIMB
INTO THE 20S WITH A FEW NEAR 30 READINGS IN FAR SOUTHWEST WISCONSIN.
COLDEST READINGS HAVE BEEN OVER THE NORTHWEST 1/3 OF THE AREA WITH
MORE SNOW AND BEING FIRST TO EXPERIENCE THE FROPA. MUCH COLDER AIR
TRYING TO SINK SOUTH BEHIND THE FRONT WITH 925MB TEMPS IN THE -15 TO
-20C RANGE OVER MUCH OF NORTH DAKOTA INTO NORTHERN MN.

THE MAIN FEATURE OF INTEREST FOR THE SHORT TERM IS THE COLLECTION OF
WEAK SHORTWAVES OVER WYOMING AND NEBRASKA. MODELS ARE IN GOOD
AGREEMENT BRINGING THESE SHORTWAVES ACROSS IOWA AND SOUTHERN
PORTIONS OF THE FORECAST AREA LATE TONIGHT INTO MONDAY MORNING. WITH
THESE SHORTWAVES COMES INCREASING MID LEVEL FRONTOGENESIS...MOSTLY
IN THE WAKE OF THE CURRENT COLD FRONT DROPPING SOUTH THROUGH THE
FORECAST AREA. PROBLEM IS THAT AT THE TIME OF THE BEST MID LEVEL
LIFT...THERE IS ENOUGH DRY AIR BELOW THE MID CLOUDS TO ABSORB MUCH
OF THE SNOW PRODUCTION. WHEN THAT DRY AIR MOSTLY SATURATES...THE
LIFT IS GONE. THEREFORE...A MENTION OF FLURRIES AS THE PREVIOUS
FORECAST HAD SEEMS REASONABLE. MOST 28.12Z GUIDANCE OF QPF CONTINUES
TO PRODUCE A DRY FORECAST TOO.

COLD ADVECTION BEHIND THE COLD FRONT PASSAGE WILL BE THE MAIN FACTOR
IN DROPPING TEMPERATURES TONIGHT...SINCE CLOUDS SHOULD BE IN PLACE
FOR MOST LOCATIONS. 925MB TEMPS FALL TO -10C SOUTH TO -15C NORTH...
WHICH SHOULD ALLOW TEMPERATURES TO DROP INTO THE SINGLE DIGITS NORTH
TO NEAR 20 SOUTH. THE COLDEST READINGS ARE EXPECTED IN TAYLOR/CLARK
COUNTIES WHERE SOME CLEARING IS POSSIBLE THIS EVENING BEFORE
MID/HIGH CLOUDS OVERSPREAD. FURTHER 925MB TEMP COOLING TAKES PLACE
ON MONDAY DUE TO PERSISTENT NORTHERLY FLOW. READINGS DROP TO -13C
SOUTH TO -17C NORTH...WHICH MEANS HIGHS WILL STRUGGLE TO CLIMB MUCH
THAN A FEW DEGREES ABOVE THE LOWS TONIGHT.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 200 PM CST SUN DEC 28 2014

THE MAIN STORY MONDAY NIGHT THROUGH TUESDAY NIGHT IS THE COLD. ALL
MODELS CONTINUE TO DROP A 1050-1060MB HIGH SOUTHWARD ALONG THE LEE
SIDE OF THE ROCKIES DURING THIS TIME...WITH COLD ADVECTION
DOWNSTREAM OF THE HIGH OVER THE FORECAST AREA. 925MB TEMPS FALL TO
-16 TO -19C BY 12Z TUESDAY AND TO AROUND -20C BY 06Z WEDNESDAY. MUCH
OF THE TIME PERIOD SHOULD BE MOSTLY CLEAR...OUTSIDE OF SOME PASSING
CLOUDS TUESDAY AFTERNOON AND EVENING ASSOCIATED WITH A SHORTWAVE
TROUGH OF ARCTIC ORIGIN MOVING THROUGH. THE SOUTHEAST HALF OF THE
FORECAST AREA WILL STAY WARMER DUE TO THE FACT OF NO SNOW ON THE
GROUND...BUT STILL EXPECT CHILLY READINGS...ESPECIALLY TUESDAY NIGHT
WITH THE COLDEST AIR IN PLACE. A PERSISTENT NORTHWEST BREEZE SHOULD
EXIST SINCE WE ARE NOT UNDER THE CENTER OF THE HIGH...THEREFORE...
WIND CHILLS BECOME A FACTOR. ADVISORIES ARE LIKELY TO BE NEEDED BOTH
NIGHTS...PARTICULARLY OVER NORTH CENTRAL WI AND POSSIBLY PORTIONS OF
SOUTHEAST MN AND NORTHEAST IA TOO.

SOME MODERATION TAKES PLACE WEDNESDAY INTO THURSDAY / NEW YEARS EVE
AND DAY / IN RESPONSE TO A POTENT SHORTWAVE TROUGH DIGGING INTO
NORTHERN ONTARIO AND LAKE SUPERIOR. HOWEVER...THIS MODERATION TAKES
PLACE AT THE EXPENSE OF HIGHER WINDS...WHICH MEANS A PERSISTENT WIND
CHILL FACTOR. FIRST...THE WESTERLY WINDS ADVECT DOWNSLOPED AIR OFF
THE ROCKIES TOWARDS THE FORECAST AREA...BOOSTING 925MB TEMPS TO
AROUND -14C BY 00Z THU AND -8 TO -10C BY 00Z FRI. THESE READINGS
SHOULD HELP BRING HIGHS BACK UP INTO THE TEENS ON WEDNESDAY AND
MOSTLY INTO THE 20S ON THURSDAY. NOW REGARDING THE WINDS...925MB
SPEEDS ARE PROGGED TO INCREASE TO THE 35 TO 45 KT RANGE AT 00Z THU
BEFORE RELAXING SOME FOR DURING THE DAY THURSDAY. WITH PLENTY OF SUN
ON WEDNESDAY...WE SHOULD SEE SOME GOOD MIXING OF THOSE WINDS. RIGHT
NOW IT APPEARS GUSTS MAY TOP OUT AROUND 30 KT...HIGHEST IN SOUTHEAST
MN...BUT WORTH MONITORING OVER THE NEXT FEW DAYS TO SEE IF THESE END
UP HIGHER. SOMETHING ELSE TO MONITOR ON THURSDAY IS POSSIBLE LIGHT
SNOW AS A COLD FRONT AND SHORTWAVE TROUGH DROP THROUGH THE NORTHERN
PORTION OF THE FORECAST AREA. HAVE ADDED SOME CHANCE POPS TO
LOCATIONS NORTH OF I-90.

FOR FRIDAY INTO SATURDAY...WE NEED TO WATCH CLOSELY THE EVOLUTION
AND TRACK OF AN UPPER LOW THAT COMES OUT OF THE SOUTHWESTERN U.S..
THIS UPPER LOW...FORMED BY THE CURRENT STRONG SHORTWAVE DIVING SOUTH
THROUGH THE NORTHWESTERN U.S....IS PRESENTLY PROGGED TO GET LIFTED
THROUGH MISSOURI AND INTO LOWER MI ON SATURDAY. SOME WARM ADVECTION
SNOW COULD BEGIN TO APPROACH THE REGION AS EARLY AS LATE FRIDAY WELL
DOWNSTREAM OF THIS UPPER LOW...OR FROM A FRONTOGENESIS BAND TRACKING
ACROSS THE NORTHERN U.S.. HOWEVER...FRIDAY NIGHT INTO SATURDAY SEEM
TO BE THE BETTER CHANCES IN SEEING A COLD CONVEYOR BELT BAND OF SNOW
TRACK ACROSS THE FORECAST AREA FROM THE UPPER LOW. IF THIS SYSTEM
TRACKS FARTHER NORTHWEST...MAY END UP WITH AN ADVISORY LEVEL SNOW.
NOTE THAT THE 28.12Z ECMWF/UKMET/CANADIAN PRESENT A MUCH SLOWER IDEA
WITH THE UPPER LOW...RESULTING IN A MUCH DRIER SCENARIO...THUS
PLENTY OF UNCERTAINTY AND ONLY 30-40 PERCENT PRECIPITATION CHANCES.

POST THE SATURDAY SYSTEM...A STRONG SURGE OF ARCTIC AIR LOOKS POISED
TO IMPACT THE REGION FOR SUNDAY INTO EARLY NEXT WEEK. IT COULD BE
NEARLY AS COLD AS THE JANUARY 5-7TH 2014 ARCTIC OUTBREAK...AND JUST
HAPPENS TO BE THE SAME DATES. THE 28.12Z MODEL CYCLE DEPICTS THE GFS
COLDER WHILE THE ECMWF WAS WARMER AND A BIT MORE DELAYED...WAITING
UNTIL MONDAY TO DRIVE THE COLD AIR IN. NEEDLESS TO SAY...STAY
TUNED.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1130 AM CST SUN DEC 28 2014

AVIATION WEATHER PRETTY GOOD TODAY BUT WATCHING BAND OF MVFR
CEILINGS SLOWLY PUSHING SOUTH WITH WEAK FRONT. THIS CLOUD BAND HAS
BEEN THINING A BIT BUT STILL EXPECTING IT TO TRACK SOUTH CLOSER TO
INTERSTATE 90 CORRIDOR THIS AFTERNOON. TIMING OF THAT SAME BAND
CLEARING OUT A BIT MORE TOUGH BUT GUIDANCE SUGGESTS EARLY MONDAY
MORNING WITH VFR CEILINGS REMAINING IN PLACE.


&&

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

$$

SHORT TERM...AJ
LONG TERM...AJ
AVIATION.....SHEA



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