Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 060925
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
325 AM CST FRI MAR 6 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 325 AM CST FRI MAR 6 2015

CHALLENGES INCLUDE LOW PRECIPITATION CHANCES TONIGHT THROUGH THE
WEEKEND AND TEMPERATURES FOR THE ENTIRE SEVEN-DAY FORECAST PERIOD.
06.00Z MODEL SUITE IN GOOD OVERALL AGREEMENT WITH TIMING OF WEAK
SHORT-WAVES IN BROADER NORTHWEST FLOW ALOFT...BUT THERE EXIST SOME
SIGNIFICANT DIFFERENCES IN THE THERMAL PROFILES...ESPECIALLY
BETWEEN THE LATEST GFS/ECMWF. FOR THIS...WILL LEAN HEAVILY ON A
BLENDED SOLUTION FOR TEMPERATURES...BUT FAVOR THE WARMER SIDE OF
THE ENVELOPE GIVEN GFS/ECMWF ENSEMBLE GUIDANCE.

FOR TODAY...A DRY SURFACE TROUGH CURRENTLY ACROSS NORTHEAST ND/
NORTHWEST MN WILL SWING ACROSS THE UPPER MS RIVER VALLEY. PRIMARY
IMPACT WILL BE SOME MID-HIGH LEVEL CLOUDS AND A WIND SHIFT FROM
SOUTH TO WEST. CLOUD COVER AHEAD OF THE TROUGH WILL QUICKLY PUSH
EAST THIS MORNING WITH PARTLY TO MOSTLY SUNNY SKIES IN ITS WAKE.
24 HOUR TEMPERATURE CHANGE AT 925 HPA BY 07.00Z OF 10 TO 15
DEGREES CELSIUS WILL RESULT IN AFTERNOON HIGHS TODAY SOARING INTO
THE 30S.

A SECONDARY TROUGH WILL DROP SOUTH TONIGHT...BRINGING WITH IT A
SLIGHTLY BETTER CHANCE FOR SOME LIGHT SNOW. BEST LIFT COINCIDES
WITH WARM AIR ADVECTION MAINLY ACROSS EAST CENTRAL MN INTO
NORTHWEST AND WEST-CENTRAL WI. ANY ACCUMULATION WILL BE VERY LIGHT
WITH A TENTH OR TWO OF AN INCH POSSIBLE. ALL OTHER AREAS WILL
REMAIN DRY. TEMPERATURES TONIGHT WILL DROP INTO THE UPPER TEENS TO
LOWER 20S.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 325 AM CST FRI MAR 6 2015

COLD FRONT DROPS SOUTH LATE FRIDAY NIGHT INTO SATURDAY MORNING
WITH DEPARTING WAVE ALOFT. POST FRONTAL AIR MASS IS QUITE A BIT
COLDER WITH THE GFS COMPARED TO THE ECMWF...BUT WILL LEAN TOWARD
THE WARMER GUIDANCE BRINGING AFTERNOON HIGHS INTO THE MID 30S TO
NEAR 40 DEGREES IN SOME SPOTS. OTHERWISE SATURDAY WILL BE DRY WITH
A QUICK-MOVING SURFACE HIGH PASSING THROUGH THE REGION.

SATURDAY NIGHT INTO SUNDAY MORNING WILL SEE THE BEST CHANCE FOR
PRECIPITATION IN THE NEXT 7 DAYS...BUT OCCURRENCE IS STILL FAR
FROM CERTAIN. 06.00Z ECMWF/GEM BRING A QUICK TENTH OF AN INCH
LIQUID QPF MAINLY ACROSS THE SOUTHERN HALF OF THE FORECAST AREA
WHEREAS THE GFS/NAM ARE MAINLY DRY. ALL MODELS SHOWING THE RIGHT
ENTRANCE REGION OF A 500 TO 300 HPA JET OVERHEAD...BUT INTERNATIONAL
MODELS SHOWING A BIT MORE MOISTURE AND MID-LEVEL FORCING ALONG
WARM AIR ADVECTION TONGUE. ADJUSTED SOME TIMING...BUT OTHERWISE
MAINTAINED CHANCE POPS FOR NOW.

IF PRECIPITATION DOES OCCUR SUNDAY MORNING...IT WILL MOVE OUT
QUICKLY BY THE AFTERNOON WITH DRY CONDITIONS THEREAFTER AND
CONTINUING FOR THE REST OF WORK WEEK. CHALLENGE WILL BE DAILY
TEMPERATURES AS NORTHWEST FLOW ALOFT BEGINS TO FLATTEN LATE SUNDAY
INTO MONDAY...ALLOWING MUCH WARMER PACIFIC AIR MASS TO OOZE INTO
THE CENTRAL PLAINS. AT ISSUE IS THAT THE TEMPERATURE GRADIENT
BETWEEN THIS WARMER AIR AND COLDER CANADIAN AIR TO THE NORTH WILL
OSCILLATE SOMEWHERE NEAR THE FORECAST AREA. IN GENERAL...THE
06.00Z GFS KEEPS THE UPPER MS RIVER VALLEY ON THE COLD SIDE OF
THIS GRADIENT...WHEREAS THE ECMWF IS ON THE WARM SIDE PER 925 HPA
TEMPERATURES.

AS AN EXAMPLE...FORECAST HIGHS TUESDAY/WEDNESDAY AT LA CROSSE ARE
20 PLUS DEGREES APART BETWEEN THE COLDER GFS AND WARMER ECMWF.
MELTING SNOW COVER WILL ALSO HAVE A SIGNIFICANT IMPACT ON SURFACE
TEMPERATURES. AS NOTED ABOVE...SIDED WITH THE WARMER GUIDANCE
GIVEN SIMILARITIES TO BOTH THE GFS/ECMWF ENSEMBLES...BUT SOMETHING
THAT WILL NEED ADJUSTMENT THROUGH THIS WEEKEND AND INTO NEXT WEEK.
EITHER WAY...TEMPERATURES WILL BE NOTICEABLY WARMER COMPARED TO
THE PAST COUPLE DAYS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY EVENING)
ISSUED AT 1100 PM CST THU MAR 5 2015

A SFC HIGH WILL CONTINUE TO SLIP SOUTHEAST TONIGHT...WITH A
TIGHTENING PRESSURE GRADIENT REPLACING IT. WINDS WILL BE ON THE
INCREASE THROUGH THE OVERNIGHT AS A RESULT...AND SHOULD STAY BREEZY
THROUGH FRI MORNING. THE STRONGEST WINDS WILL LIKELY OCCUR IN THE 08-
14Z TIME FRAME. LLWS IS A CONCERN AS RAP/NAM12 BUFKIT SOUNDINGS
SUGGESTING 40+ KTS OF WIND BY 2 KFT ROUGHLY FROM 08-13Z. BIGGER
CONCERN FOR KLSE WHICH WILL HAVE A BIT LESS SFC WIND COMPARED TO
KRST.

THE NAM POINTS TO INCREASING NEAR SFC MOISTURE ON FRIDAY...WHICH
WOULD RESULT IN AT LEAST AN MVFR DECK OF CLOUDS. ITS LIKELY THE
RESULT OF ANTICIPATED SNOW MELT. THE GFS IS DRIER. NO EVIDENCE OF
THIS ON SATELLITE OR VIA SFC OBS...AND NOT MUCH FOR SNOW PACK IN THE
SOURCE REGION OF THE WIND /AT LEAST UNTIL YOU GET INTO NORTHERN IA/.
WILL STICK WITH VFR CLOUDS - IF ANY - FOR NOW. EXPECT AN INCREASING
MID/UPPER LEVEL DECK OF CLOUDS FRI NIGHT AS AN UPPER LEVEL SHORTWAVE
STARTS TO APPROACH THE REGION.

&&

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

$$

SHORT TERM...ROGERS
LONG TERM...ROGERS
AVIATION...RIECK


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