Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 282340
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
540 PM CST SAT FEB 28 2015

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 351 PM CST SAT FEB 28 2015

AT 3 PM...A SHORT WAVE TROUGH WAS PRODUCING SNOW ACROSS MISSOURI
AND CENTRAL ILLINOIS. MEANWHILE FURTHER TO THE NORTHWEST A COLD
FRONT WAS LOCATED ACROSS THE EASTERN DAKOTAS. IN BETWEEN THESE TWO
SYSTEMS...A SHORT WAVE RIDGE HAS KEPT SKIES MOSTLY SUNNY TO PARTLY
CLOUDY THIS AFTERNOON. WITH SUNSHINE...TEMPERATURES HAVE WARMED
INTO 10 TO 20 DEGREE RANGE. THE WARMEST TEMPERATURE WERE FOUND IN
THE FORESTED AREAS OF CENTRAL WISCONSIN. THIS IS DUE TO A LOWER
ALBEDO. FORESTED AREAS HAVE AN ALBEDO OF BETWEEN 0.10 AND 0.18.
COMPARED TO THE SNOW COVERED AREAS WHICH HAVE AN ALBEDO BETWEEN
0.2 AND 0.4 /DIRTY SNOW/.

FOR TONIGHT AND SUNDAY MORNING...THE SOUTHERN STREAM SHORT WAVE
WILL MOVE QUICKLY THROUGH THE SOUTHERN GREAT LAKES. WITH OUR AREA
BEING IN THE LEFT ENTRANCE REGION OF A 140 KNOT JET...WE ARE
SEEING SUBSIDENCE SOUTH OF INTERSTATE 90. THIS WILL KEEP THIS AREA
DRY THIS EVENING. DURING THE OVERNIGHT AND SUNDAY MORNING...THE
NORTHERN STREAM SYSTEM WILL MOVE QUICKLY ACROSS NORTHERN MINNESOTA
AND NORTHERN WISCONSIN. THIS SYSTEM WILL SATURATE THE AIR MASS
BELOW 800 MB ACROSS MUCH OF THE AREA. THE BEST SYNOPTIC AND
ISENTROPIC LIFT REMAINS NORTH OF INTERSTATE 94...SO KEPT A
20 PERCENT CHANCE OF SNOW GOING IN THIS AREA. ELSEWHERE THE LIFT
LOOKS RATHER MARGINAL...SO JUST WENT WITH FLURRIES.

ON SUNDAY AFTERNOON...ANOTHER NORTHERN SHORT WAVE MOVES THROUGH
THE REGION. MUCH OF THE LIFT ASSOCIATED WITH THIS SYSTEM IS
LOCATED BELOW THE MOISTURE...SO WENT WITH A DRY FORECAST DURING
THAT TIME FRAME.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 351 PM CST SAT FEB 28 2015

THE MONDAY NIGHT INTO TUESDAY TIME PERIOD CONTINUES TO BE ONE OF
GREATEST CONCERN FOR THIS TIME PERIOD. THE GFS AND GEM CONTINUE TO
BE THE FASTEST WITH SHORT WAVE MOVING THROUGH THE CENTRAL PLAINS.
THIS RESULTS IN QUICKER WARM AIR ADVECTION AND MODERATE 850 MB
MOISTURE TRANSPORT INTO THE AREA. MEANWHILE BOTH THE NAM AND ECMWF
ARE A BIT SLOWER WITH SHORT WAVE...THUS...THE DRY AIR MASS ACROSS
THE REGION IS MUCH SLOWER AT SATURATING. WHILE THERE ARE
DIFFERENCES ON WHEN WE WILL SATURATE...ALL OF THE DETERMINISTIC
MODELS HAVE VERY SIMILAR TIMING ON WHEN THE MAIN SHORT WAVE WILL
MOVE EAST THROUGH AREA. WITH A LONGER DURATION...IT MAKES SENSE
WHY THE GFS AND GEM HAVE HIGHER AMOUNTS OF QPF THAN THE NAM AND
ECMWF. WITH THE SOUNDINGS CONTINUING TO SHOW LESS THAN 100 MB
OF THE THERMAL PROFILE BETWEEN 750 AND 500 MB IN THE DENDRITIC
GROWTH ZONE...STILL THINKING THAT THE SNOW TO LIQUID RATIOS WILL
BE MAINLY IN 10-15 TO 1 RANGE.

THIS SYSTEM LOOKS RATHER SIMILAR STRUCTURALLY...HOWEVER...THERE
ARE SOME DIFFERENCES ON WHERE THE WARM FRONT IS LOCATED AND WHERE
THE DEFORMATION BAND WILL INITIALLY FORM AND HOW FAST IT WILL
PIVOT EAST THROUGH THE REGION. THIS WILL GREATLY AFFECT WHERE THE
HEAVIEST SNOW WILL ULTIMATELY FALL. DUE TO MODEL
RESOLUTION...THINKING THAT BOTH THE GFS AND ECMWF ARE NOT FOCUSED
ENOUGH ON WHERE THIS BANDED PRECIPITATION WILL OCCUR. IN
ADDITION...THERE IS SOME CONCERN THAT THUNDERSTORM ACTIVITY IN THE
MID MISSISSIPPI RIVER VALLEY MAY LIMIT THE NORTHWARD ADVANCE OF
MOISTURE INTO THE REGION. ANOTHER CONCERN IS THAT THE GFS IS
BRINGING WARM AIR INTO THE REGION WHICH MAY RESULT IN A WINTRY MIX
SOUTH OF INTESTATE 90. MEANWHILE THE OTHER MODELS HAVE THIS MIX
OCCURRING MORE TOWARD INTERSTATE 80. THERE ARE WAY TOO MANY
CONCERNS AT THIS TIME TO BE OVER SPECIFIC IN THE SNOW TOTAL
FORECAST. AS A RESULT...CONTINUED TO BROAD BRUSH THE 3 TO 6 INCH
SNOW TOTALS ACROSS THE AREA. IN SOME AREAS...THESE TOTALS MAY HAVE
TO BE ENHANCED AND IN OTHERS LOWERED...BUT WHERE EXACTLY IS STILL
IN QUESTION DUE TO THE WIDESPREAD SNOW AMOUNTS SHOWING UP IN THE
SPC SREF PLUMES.

FROM LATE TUESDAY AFTERNOON INTO TUESDAY NIGHT...THE MODELS
CONTINUE TO SHOW VERY STEEP LOW LEVEL LAPSE RATES DEVELOPING BELOW
850 MB. THIS WILL ALLOW THE WINDS TO GUST INTO THE 25 TO 35 KNOT
RANGE. THIS COULD RESULT IN CONSIDERABLE BLOWING SNOW ESPECIALLY
IN SOUTHEAST MINNESOTA AND NORTHEAST IOWA. HOWEVER THIS WILL BE
HIGHLY DEPENDENT ON HOW MUCH SNOW FALLS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 540 PM CST SAT FEB 28 2015

MAINLY MID LEVEL CEILINGS MOVING ACROSS AREA THIS EVENING...BETWEEN
SYSTEM TO THE SOUTH AND SHORT WAVE IN NORTHERN FLOW. CEILINGS IN VFR
RANGE FOR MOST PART BUT SOME LOWER LEVEL MOISTURE COULD ADVECT
NORTHWARD AHEAD OF NORTHERN WAVE...MAKING MVFR CONDITIONS AT TIMES
MAINLY OVERNIGHT. CONFIDENCE NOT GREAT IN THIS SCENARIO. THEN AS
SHORT WAVE PASSES SUNDAY...SHOULD SEE RETURN TO VFR AND EVEN
CLEARING AS NORTHWEST WINDS INCREASE POST FRONTAL.

&&

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

$$

SHORT TERM...BOYNE
LONG TERM...BOYNE
AVIATION...SHEA



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