Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 220953
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
353 AM CST THU JAN 22 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 353 AM CST THU JAN 22 2015

TRANQUIL WEATHER DURING THE PERIOD WITH CLOUDS BEING THE MAIN
FORECAST PROBLEM AS HIGH PRESSURE TRIES TO BUILD IN FROM THE
DAKOTAS. GOES FOG IMAGERY SHOWING WIDESPREAD CLOUDS OVER IA/WI AND
ERN DAKOTAS/NEB. SOME CLEARING IS OUT THERE ACROSS WRN MN BUT
THIS HAS STRUGGLED TO MAKE MUCH PROGRESS OVER THE PAST HOURS.
DAKOTAS/NEBRASKA CLOUD IS NOW MOVING EAST AND RIGHT IN THE HEART
OF THE SURFACE HIGH PRESSURE RIDGE AXIS FROM KINL-KLBF.

LOW-LEVEL RIDGE AXIS WILL SHIFT THROUGH AND TO THE SOUTHEAST TODAY
RAPIDLY BACKING THE FLOW TO W/SW BY AFTERNOON...CONTINUING TO
BRING THE DAKOTAS CLOUD TOWARD THE AREA. SO...IT APPEARS SOME
BREAKS WILL WORK IN...BUT ALSO MORE CLOUD. 925MB FLOW FROM THE
W/SW INCREASING TO 40 KTS TONIGHT SHOULD KEEP THE CLOUDS MOVING
NORTHEAST AND PROVIDE AN INCREASING PROBABILITY OF CLEARING FROM
THE SW. SO...HAVE TRENDED SOME SLOW PARTIAL CLEARING FROM THE WEST
TODAY...AND SOUTHWEST OVERNIGHT /PER BROAD 22.03Z SREF AND MESO
MODEL CEILING FORECAST TRENDS/. TEMPERATURES WILL COOL THIS
EVENING IF CLEARING IS PRESENT BUT INCREASING WIND FLOW SHOULD
STOP THAT FALL AFTER MIDNIGHT. OVERALL HAVE INCREASED TEMPERATURES
A FEW DEGREES THROUGH SATURDAY.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 353 AM CST THU JAN 22 2015

GOES WATER VAPOR IMAGERY SHOWING ENERGY CRASHING ONTO CENTRAL BRITISH
COLUMBIA COAST AT 06Z WITH A MODERATE POTENTIAL VORTICITY ANOMALY
AND WEAK-MODERATE 500-300 MB QG CONVERGENCE FORCING FOR LIFT. THE
22.00Z DETERMINISTIC MODELS IN GOOD AGREEMENT ON THE FORCING
STRENGTH AND TRACK OF THESE DYNAMICS. THE MAIN LIFT FOR THIS
SHORTWAVE TROUGH TRAVELS NORTH OF LAKE SUPERIOR WITH SOME WEAK
FORCING TRAILING SOUTHWEST IN THE TROUGH...AFFECTING MAINLY
NORTHERN WISCONSIN. THE LIFT ARRIVES FRIDAY AFTERNOON AND WARM
ADVECTION IN THE LOW LEVELS BRINGS A WARM LAYER ABOVE 0C /1-2C/ IN
FROM THE WEST. SATURATION APPEARS TO BE TOP-DOWN WITH THIS LIFT
AND LOW-LEVEL CLOUD SHOULD BE NORTH OF THE AREA...THUS DRIZZLE OR
FREEZING DRIZZLE HAVE BEEN REMOVED FROM THE FORECAST. THE WARM
LAYER OF 1-2C WILL QUICKLY /1-2 HOURS/ DIABATICALLY COOL...SO SOME
SLEET IS POSSIBLE AT FIRST SHOULD PRECIPITATION REACH THE SURFACE...THEN
RAIN/SNOW DEPENDING ON LOW-LEVEL TEMPERATURES. SHOULD BE A LOW/NO QPF
EVENT AND HAVE MINIMAL/NO IMPACT. HIGHEST PRECIPITATION CHANCES
/40 PERCENT/ ARE FOUND ACROSS NORTH CENTRAL WI FRIDAY
AFTERNOON...DECREASING SOUTHWESTWARD TO ONLY 20 PERCENT OVER SERN
MN WHERE LOW-LEVELS APPEAR VERY DRY PER 22.00Z GFS/NAM SOUNDINGS.
GFS SEEMS A BIT TOO SATURATED GIVEN THE LIFT/FORCING MAGNITUDE
AND PREFER HOW THE NAM IS HANDLING THE CLOUD PHYSICS OF THIS
EVENT /DRIER LOW-LEVELS AND MORE SUB-CLOUD SUBLIMATION FURTHER
SOUTHWEST/.

IT STILL APPEARS SATURDAY NIGHT AND SUNDAY /MORNING/ WILL HAVE A
MODERATE CHANCE OF ACCUMULATING SNOW IN THE REGION. THIS
SHORTWAVE TROUGH ENERGY WAS LOCATED NEAR 170W/30N IN THE BASE OF
THE ENERGETIC AND DEEP PACIFIC LONGWAVE TROUGH. THE DETERMINISTIC
MODELS AND LATEST SREF RUNS ARE ALL PAINTING THE SAME PICTURE...A
MODERATELY FORCED SYSTEM AND SURFACE CYCLONE MOVING THROUGH DURING
THIS PERIOD WITH ACCUMULATING SNOW IN THE 1-3 INCH RANGE.
HOWEVER...THE ENVELOPE FOR THIS SNOW AXIS AND LOW TRACK EXTEND
FROM THE MI U.P. /CANADIAN GLOBAL/ TO I-35 IN MINNESOTA
/ECMWF...NAM/. SO...WITH THE SHORTWAVE TROUGH OVER THE MIDDLE
OCEAN AND IT BEING 3 DAYS PRIOR TO ARRIVAL...WILL STEP SLOWLY INTO
THIS ONE. HAVE INCREASED PRECIPITATION CHANCES INTO THE 55 PERCENT
RANGE ACROSS NORTHCENTRAL WI...LOWER ELSEWHERE...AND FORECAST A
BROAD AREA OF 1-2 INCHES SATURDAY NIGHT. NOT CONFIDENT ENOUGH TO
DETAIL TIMING ON THIS FORECAST YET. FORCING AND LIFT CONSENSUS IN
THE MODELS IS PRETTY IMPRESSIVE AND FRONTOGENESIS/INSTABILITY IS
AS WELL...SO IF THESE PLAYERS COME TOGETHER...IT COULD BE HIGHER
SNOW AMOUNTS TOWARD AN ADVISORY LEVEL.

MONDAY-WEDNESDAY...RIGHT NOW IT APPEARS TO BE A BENIGN WEATHER
PATTERN WITH SOME SMALL SNOW CHANCES...AND TEMPERATURES REMAINING
ABOVE NORMAL. USED THE BLEND OF DETERMINISTIC MODELS FOR THIS
PERIOD.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1137 PM CST WED JAN 21 2015

MAIN ISSUE REVOLVES AROUND THE CURRENT MVFR STRATUS IN PLACE. THIS
STRATUS EXTENDS INTO CENTRAL MN...AND WITH A NORTHWEST
FLOW...EXPECT THE MVFR CEILINGS TO HOLD AT LEAST THROUGH THE
MORNING. AROUND MID-DAY...A SURFACE HIGH PRESSURE RIDGE OVER
NORTHWEST MN WILL CROSS THE TAF SITES...BRINGING CLEARING IN. DO
HAVE SOME CONCERN THAT AS WINDS SWING AROUND TO THE SOUTHWEST IN
THE AFTERNOON...SOME OF THE LOW CLOUDS IN EASTERN SOUTH DAKOTA AND
NEBRASKA COULD MOVE INTO THE TAF SITES. HOWEVER...WILL BANK ON
DAYTIME HEATING AND CONTINUED DRY AIR COMING IN FROM THE WESTERN
DAKOTAS TO HELP QUELL THAT CONCERN. SKIES SHOULD THEN BE CLEAR FOR
THE EVENING AHEAD OF THE NEXT LOW PRESSURE SYSTEM TRACKING ALONG
THE CANADIAN BORDER. SOUTHWEST WINDS DURING THE EVENING SHOULD
PICK UP...ESPECIALLY AT RST...TOWARDS 15 KT.


&&

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

$$

SHORT TERM...BAUMGARDT
LONG TERM...BAUMGARDT
AVIATION...AJ



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