Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 230932
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
332 AM CST TUE DEC 23 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 332 AM CST TUE DEC 23 2014

THE MAIN FOCUS CONTINUES TO BE ON THE SNOW THAT WILL FALL THIS
MORNING AND WITH HOW MUCH WILL ACCUMULATE. HAVE HAD GROWING
CONCERNS OVER THIS SHIFT THAT WE DID NOT HAVE ENOUGH IN THE
FORECAST IN PORTIONS OF SOUTHEAST MINNESOTA AND NORTH CENTRAL
IOWA...SO HAVE BEEFED THEM UP TO THE POINT WHERE AN ADVISORY IS
NEEDED FOR THIS AREA.

CURRENTLY...THE WELL ADVERTISED MAIN BAND OF PRECIPITATION IS NOW
MOVING INTO SOUTHERN WISCONSIN AND NORTHEAST IOWA AHEAD OF A
STRENGTHENING MID LEVEL SHORT WAVE TROUGH ALONG THE EASTERN EDGE
OF THE MAIN CLOSED LOW WHICH IS CURRENTLY CENTERED OVER OMAHA. AN
ELONGATED WEST TO EAST ORIENTED SURFACE LOW SPANS IOWA WITH THE
CENTER OF IT OVER DES MOINES. WITH TEMPERATURES ISOTHERMAL FROM
THE SURFACE UP THROUGH THE WARM LAYER...THE CHANGE OVER
TEMPERATURE FROM RAIN TO SNOW IS BEING DRIVEN BY SURFACE
TEMPERATURES WITH 34 DEGREES APPEARING TO BE THE MAGIC NUMBER FOR
THE CHANGE OVER TO OCCUR.

BASED ON THE TEMPERATURE FORECAST THROUGH THIS MORNING...MUCH OF
SOUTHEAST MINNESOTA...NORTH CENTRAL IOWA AND NORTH CENTRAL
WISCONSIN STAY BELOW 34F AS THE HEAVIEST PRECIPITATION MOVES
THROUGH. DEEP LIFT WILL ACCOMPANY THE CLOSED MID LEVEL LOW AND
SURFACE LOW AS IT PROPAGATES NORTHEASTWARD INTO SOUTHERN WISCONSIN
THIS MORNING. THIS TRACK PUTS THE DEFORMATION BAND ACROSS
SOUTHEAST MINNESOTA/NORTH CENTRAL WISCONSIN WITH IT PIVOTING RIGHT
OVER SOUTHEAST MINNESOTA THROUGH THE MORNING. THE DEEP LIFT FROM
THE CLOSED MID LEVEL LOW WILL LIKELY CAUSE SOME INTENSE PERIODS OF
SNOWFALL THIS MORNING WITH SOME 1 INCH PER HOUR RATES POSSIBLE IN
THE MAIN BAND. HOURLY PRECIPITATION RATES HAVE GENERALLY BEEN IN
THE 0.10 TO 0.25 INCH RANGE ACROSS IOWA AND EXPECT SIMILAR AMOUNTS
AS THIS BAND MOVES INTO THE REGION WITH QPF TOTALS OF 0.30 TO 0.50
INCHES FOR THIS EVENT. GENERALLY WENT WITH SNOW RATIOS OF
8:1...WHICH ENDS UP PUTTING DOWN A BAND OF 3 TO 5 INCHES FROM
NORTH CENTRAL IOWA (MITCHELL COUNTY) RUNNING THROUGH SOUTHEAST
MINNESOTA AND NORTH CENTRAL WISCONSIN. BASED ON THIS AND THE
IMPACT IT COULD HAVE ON THIS MORNINGS COMMUTE...PARTICULARLY IN
ROCHESTER...PLAN TO EXPAND THE WINTER WEATHER ADVISORY FOR THIS
AREA WHERE THE 3 TO 5 INCHES IS EXPECTED. THE MAIN IMPACT QUESTION
IS WITH WHETHER THE SNOW WILL ACCUMULATE ON THE ROADS DUE TO THE
AT OR ABOVE FREEZING TEMPERATURES...BUT REPORTS/SNOW PLOW CAMS
FROM CENTRAL IOWA SHOW THAT THE SNOW IS IN FACT ACCUMULATING ON
ROADS.

SNOW AMOUNTS WILL BE MUCH MORE VARIABLE GOING INTO WEST CENTRAL
WISCONSIN WITH VALLEY LOCATIONS LIKELY STAYING MAINLY AS RAIN AS
THE BAND COMES IN WITH HIGHER TERRAIN SEEING MORE SNOW. FOR
EXAMPLE...HAVE ABOUT 2 AND A HALF INCHES FORECAST FOR THE HILL
TOPS AND LESS THAN A HALF INCH FOR THE RIVER VALLEY LOCATIONS
WHERE TEMPERATURES ARE FORECAST TO BE AROUND 36F.

SOME LIGHT SNOW IS EXPECTED TO LINGER INTO THE AFTERNOON
HOURS...BUT THE INTENSITY WILL GREATLY DIMINISH AS THE LOW/TROUGH
MOVE OFF TO THE NORTHEAST. SO...IT IS A POSSIBILITY THAT THE 00Z
END TIME OF THE ADVISORY IS A LITTLE LATE AND COULD BE CUT OFF
EARLY...PARTICULARLY IN THE AREA THAT IS GETTING THE EXTENSION
THIS MORNING. 23.00Z NAM/GFS SOUNDINGS THEN SHOW THE COLUMN LOSING
ICE THIS EVENING...SO THERE COULD BE A PERIOD OF FREEZING DRIZZLE
IF THERE IS ANY LIFT LEFT IN THE LOW LEVELS. WILL HAVE TO MONITOR
CONDITIONS AS THE DAY PROGRESSES.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 332 AM CST TUE DEC 23 2014

THE MAIN FOCUS FROM MID WEEK ONWARD IS WITH A SYSTEM THAT IS
EXPECTED TO MOVE INTO THE REGION FRIDAY.

CLOUD COVER LOOKS LIKE IT WILL HOLD ON FOR CHRISTMAS EVE/DAY AS
SOME HIGHER RH REMAINS UNDER THE SHALLOW INVERSION. THERE IS NOT
MUCH COLD AIR ADVECTION TAKING PLACE BEHIND THE TROUGH...SO
TEMPERATURES DO NOT TAKE MUCH OF A HIT GOING INTO THE HOLIDAY.

THE NEXT TROUGH MOVES IN ON FRIDAY AND CONTINUES TO TREND SLOWER
AND TO THE NORTH WITH THE PRECIPITATION ASSOCIATED WITH IT. THE
23.00Z GFS IS THE MOST BULLISH WITH PRECIPITATION DEVELOPING ALONG
THE SOUTHERN EXTENT OF THE SYSTEM WHILE THE 23.00Z IS THE DRIEST
WITH MOST OF THE SNOW FALLING TO THE NORTH OF THE REGION. STILL
HAVE SOME PRECIPITATION CHANCES IN THERE FOR FRIDAY FOR MUCH OF
THE AREA...BUT EXPECT THE TREND WILL BE TO GO DRIER THERE. ANOTHER
MID LEVEL SHORT WAVE TROUGH DIVES DOWN INTO THE REGION ON MONDAY
BUT APPEARS TO BE WEAKENING AS IT APPROACHES.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1129 PM CST MON DEC 22 2014

MVFR/IFR CONDITIONS TO PERSIST INTO TUESDAY AS A LOW PRESSURE
SYSTEM LIFTS UP INTO THE REGION. THE MAIN QUESTION WILL BE WITH
PRECIPITATION TYPE AS TEMPERATURES ARE RIGHT AROUND FREEZING. LSE
HAS A HIGHER CHANCE OF BEING MORE RAIN THAN RST...BUT COULD EASILY
CHANGE OVER ON TUESDAY MORNING. LOW CONDITIONS WILL LIKELY HANG ON
THROUGH TUESDAY NIGHT AND POSSIBLY INTO WEDNESDAY. WINDS WILL BE
SHIFTING FROM THE NORTHEAST TO THE NORTHWEST ON TUESDAY.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR WIZ017-
     029-032>034.

MN...WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR MNZ079-
     086>088-094-095.

IA...WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR IAZ008.

&&

$$

SHORT TERM...HALBACH
LONG TERM...HALBACH
AVIATION...HALBACH


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