Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 030518
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1118 PM CST MON MAR 2 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY EVENING)
ISSUED AT 321 PM CST MON MAR 2 2015

AT 3 PM...A 1032 MB HIGH WAS CENTERED OVER INDIANA. THE WINDS HAVE
BECOME SOUTHERLY ACROSS THE AREA...AND THEY WILL INCREASE INTO THE
10 TO 20 MPH RANGE TONIGHT AS THE SURFACE PRESSURE GRADIENT
STEADILY INCREASES ACROSS THE REGION.

REGIONAL RADARS ARE ALREADY SHOWING RADAR ECHOES FROM AUSTIN
MINNESOTA NORTHWEST TO ABERDEEN SOUTH DAKOTA. THIS IS ASSOCIATED
WITH 500 TO 600 MB FRONTOGENESIS. HOWEVER THE AIR MASS BELOW
650 MB IS VERY DRY...THUS...NO PRECIPITATION IS REACHING THE
GROUND AT THIS TIME. 02.12Z MODELS ARE IN GENERAL AGREEMENT THAT
THIS BAND WILL MOVE NORTH INTO CENTRAL MINNESOTA AND NORTHERN
WISCONSIN TONIGHT AND GRADUALLY DEEPEN INTO THE THE 800 TO 500 MB
RANGE. IN ADDITION...SOUTHERLY WINDS WILL GRADUALLY MOISTEN. AS
THIS OCCURS...EXPECT LIGHT SNOW TO DEVELOP NORTH OF INTERSTATE 94
TOWARD MIDNIGHT AND THEN THIS BAND WILL PIVOT AND BECOME
ORIENTATED ALONG THE APPROACHING ARCTIC COLD FRONT.

AS THIS OCCURS A SHORT WAVE TROUGH EJECTING OUT OF THE SOUTHWEST
UNITED STATES AHEAD OF THE MAIN LONG WAVE TROUGH OVER THE NORTHERN
AND CENTRAL PLAINS...WILL APPROACH THE AREA FROM SOUTHERN AND
WESTERN IOWA. THE COMBINATION OF STRONG 925 MB AND 850 MB MOISTURE
TRANSPORT AND WARM AIR ADVECTION AND STRONG 280 K ISENTROPIC LIFT
WILL RESULT IN THE RAPID DEVELOPMENT OF A SNOW BAND ACROSS IOWA
BETWEEN 03.06Z AND 03.09Z. THIS SNOW BAND THEN WILL MOVE INTO
AREAS ALONG AND SOUTH OF INTERSTATE 90 BETWEEN 03.08Z AND 03.10Z
AND THE REMAINDER OF THE AREA BETWEEN 03.10Z AND 03.13Z. MESO
MODELS SUGGEST THAT THIS BAND WILL MOVE QUICKLY NORTHEAST ACROSS
THE AREA ON TUESDAY MORNING. AS A RESULT...THE SNOW MAY BE ONLY
LIMITED TO A 6 HOUR PERIOD. CURRENT FORECAST GRIDS ARE A BIT MORE
BROAD BRUSHED THAN THAT...SO MAY HAVE TO TWEAK THE TIMING OF SNOW
A BIT MORE. THE SNOW WILL THEN QUICKLY END ACROSS THE AREA AS THE
ARCTIC FRONT MOVES EAST ACROSS THE AREA DURING THE AFTERNOON. WITH
950 TO 900 MB LAPSE RATES BETWEEN 8 AND 10 C/KM...WE MAY SEE A
BRIEF PERIOD OF SNOW SHOWERS FOR AN HOUR OR TWO AFTER THE FRONT
PASSES. LIQUID TO SNOW RATIOS WILL RANGE FROM 10-15 TO 1. THE
HIGHEST RATIOS WILL BE NORTH OF INTERSTATE 94. TOTAL SNOW AMOUNTS
OF 1 TO 2 INCHES LOOK LIKELY ALONG AND SOUTH OF INTERSTATE
90...AND 2 TO 4 INCHES NORTH OF THIS INTERSTATE. THE HIGHEST
TOTALS LOOK TO BE NORTH OF INTERSTATE 94.

IN ADDITION TO THE SNOW...THE MODELS CONTINUE TO SHOW THAT A DRY
SLOT WILL MOVE INTO THE AREAS ALONG AND SOUTH OF INTERSTATE 94. IF
ANY PRECIPITATION IS LEFT DURING THIS TIME FRAME...THERE MAY BE A
BRIEF PERIOD OF FREEZING DRIZZLE. IN ADDITION...THE NAM SHOWS THAT
A 2C WARM LAYER BETWEEN 800 AND 700 MB WILL NOSE INTO FAYETTE AND
CLAYTON COUNTIES IN NORTHEAST IOWA...AND GRANT COUNTY IN SOUTHWEST
WISCONSIN. THIS MAY RESULT IN A BRIEF PERIOD OF FREEZING RAIN AND
SLEET AHEAD OF A DRY SLOT.

IN THE WAKE OF THE ARCTIC COLD FRONT...THE COMBINATION OF VERY
STEEP 950 TO 900 MB LAPSE RATES...STRONG SUBSIDENCE...AND STRONG
COLD AIR ADVECTION WILL PRODUCE STRONG WIND GUSTS ESPECIALLY
ACROSS NORTHEAST IOWA AND SOUTHEAST MINNESOTA FROM 03.21Z AND
04.03Z. BOTH THE NAM AND GFS SUGGEST THAT THE WINDS WILL GUST UP
TO 40 MPH. MEANWHILE THE ECMWF IS PRODUCING WIND GUSTS UP TO 45
MPH ACROSS NORTHEAST IOWA. THERE IS CURRENTLY ONE INCH OF
BLOWABLE SNOW ACROSS THIS AREA WITH ANOTHER 1 TO 3 INCHES OF
ADDITIONAL SNOW...SO THERE IS A CONCERN THAT WE MAY HAVE A BRIEF
GROUND BLIZZARD DURING THIS TIME FRAME. THIS IS ESPECIALLY THE
CASE...IF THE ECMWF WIND GUSTS VERIFY. HOWEVER WITH SOME QUESTIONS
ON WHETHER THE HEAVIER SNOW MAY LIMIT THE EXISTING SNOW FROM
BLOWING AND WHETHER A DRY SLOT AND MIXED PRECIPITATION MAY LIMIT
ADDITIONAL SNOW...IT WAS THE CONSENSUS TO JUST STAY WITH THE
WINTER WEATHER ADVISORY FOR NOW. THIS WOULD ALLOW US MORE TIME TO
EVALUATE THE AMOUNT OF NEW SNOW THAT MAY FALL AND WHETHER THE WIND
GUSTS WILL ACTUALLY BE THAT HIGH.

.LONG TERM...(TUESDAY OVERNIGHT THROUGH MONDAY)
ISSUED AT 321 PM CST MON MAR 2 2015

IN THE WAKE OF THE ARCTIC COLD FRONT...A VERY COLD AIR MASS WILL
MOVE INTO THE REGION. 850 MB TEMPERATURES RANGE FROM -22 TO -26C.
THIS WILL RESULT IN HIGH TEMPERATURES OF 5 TO 15F ON WEDNESDAY AND
THURSDAY AND LOW TEMPERATURES OF 5 TO -10 ON WEDNESDAY MORNING AND
-5 TO -15 ON THURSDAY MORNING. WIND CHILLS ON WEDNESDAY MORNING
WILL RANGE -15 TO -25 NORTH OF A CHARLES CITY IOWA TO NEILLSVILLE
WISCONSIN LINE AND FROM -15 TO -30 ACROSS THE ENTIRE ARE ON
THURSDAY MORNING. DUE TO THESE LOW WIND CHILLS...A WIND CHILL
ADVISORY MAY HAVE TO BE CONSIDERED FOR BOTH OF THESE TIME PERIODS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1118 PM CST MON MAR 2 2015

DRY AIR...LEADING TO VFR CEILINGS LATE THIS EVENING...IS BEING
WORKED ON BY WIDESPREAD LIFT NOW APPROACHING AHEAD OF SOUTHWEST
SHORT WAVE. SATURATION WILL CONTINUE WITH SHORT TERM MODEL GUIDANCE
SUGGESTING A SLIGHTLY LATER ONSET OF PRECIPITATION EARLY TUESDAY
MORNING. MVFR CONDITIONS COULD BECOME IFR FOR A TIME AFTER DAYBREAK
BUT AS QUICK AS SNOW MOVES IN...WILL EXIT AFTER A FEW HOURS DUE TO
SPEED OF WAVE AND ASSOCIATED UPPER JET.

AS SNOW WINDS DOWN...NORTHWEST SYSTEM WILL DROP IN WITH STRONG
FORECAST LOW LEVEL WINDS...ESPECIALLY ACROSS SOUTHERN MINNESOTA.
CONFIDENCE IN BLOWING SNOW IS ONLY MARGINAL BUT ENOUGH TO INCLUDE IN
KRST AS WINDS PEAK IN INTENSITY LATE TUESDAY AFTERNOON AND INTO THE
EVENING. AS VISIBILITIES INCREASE LATE IN FORECAST PERIOD...STILL
EXPECT CEILINGS TO LINGER WITH GENERAL IFR/MVFR CONDITIONS.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER WEATHER ADVISORY FROM 3 AM TO 9 PM CST TUESDAY FOR WIZ017-
     029-032>034-041>044-053>055-061.

MN...WINTER WEATHER ADVISORY FROM 3 AM TO 9 PM CST TUESDAY FOR MNZ079-
     086>088-094>096.

IA...WINTER WEATHER ADVISORY FROM 3 AM TO 9 PM CST TUESDAY FOR
     IAZ008>011-018-019-029-030.

&&

$$

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


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