Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 140257
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
945 PM CDT SAT SEP 13 2014

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 344 PM CDT SAT SEP 13 2014

FOR TONIGHT...THE 13.12Z MODELS ARE IN GOOD AGREEMENT THAT AN 850
MB WARM FRONT...CURRENTLY OVER NORTHWEST MINNESOTA...WILL MOVE
EAST ACROSS THE AREA. 850 MB TEMPERATURES WARM BY 4C OVERNIGHT.
WITH THE BEST LIFT AND MOISTURE TRANSPORT NORTH OF THE AREA...TOOK
OUT THE SMALL PRECIPITATION CHANCES THAT WERE LOCATED ACROSS NORTH
CENTRAL WISCONSIN.

ON SUNDAY AFTERNOON...THE 13.12Z MODELS ARE IN GOOD AGREEMENT THAT
THERE WILL BE AN INCREASE IN THE 500 TO 700 MB FRONTOGENESIS AHEAD
OF A SHORT WAVE TROUGH MOVING OUT OF THE PLAINS. HOWEVER THE AIR
MASS BELOW 500 MB REMAINS PARCHED. DUE TO THIS REMOVED THE RAIN
CHANCES FOR THIS TIME PERIOD.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 344 PM CDT SAT SEP 13 2014

ON SUNDAY NIGHT...THE FRONTOGENESIS DEEPENS THROUGHOUT THE NIGHT.
IT STARTS OUT BETWEEN 700 AND 500 MB AND BY 06Z MONDAY IT EXTENDS
FROM 900 TO 500 MB. THIS IS A RESULT OF A SHORT WAVE TROUGH
APPROACHING THE REGION FROM THE PLAINS. AS THIS OCCURS AND THE
NOCTURNAL JET INCREASES...THE MOISTURE IN COLUMN PROGRESSIVELY
INCREASES. DUE TO THIS...WENT WITH INCREASING PRECIPITATION
CHANCES ALONG AND SOUTH OF THE INTERSTATE 90 CORRIDOR. WITH VERY
LITTLE INSTABILITY...JUST KEPT THE PRECIPITATION AS SHOWERS.

ON MONDAY...THE MODELS ARE IN GOOD AGREEMENT THAT A SHORT WAVE
TROUGH AND CANADIAN COLD FRONT WILL MOVE SOUTHEAST THROUGH THE
FORECAST AREA DURING THE MORNING. AS THIS OCCURS...THE
PRECIPITATION CHANCES WILL END FROM THE NORTHWEST.

ON MONDAY NIGHT AND TUESDAY MORNING...A 1024 MB CANADIAN HIGH
PRESSURE SYSTEM WILL MOVE SOUTH ACROSS THE AREA. WHILE THE GFS AND
GEM HAVE COLDER SURFACE TEMPERATURES /IN THE 30S/ ON THAT
MORNING...THE ECMWF/S 850 MB TEMPERATURES ARE 2C COLDER WITH LOW
TEMPERATURES MAINLY IN THE LOWER 40S. FROM LOOKING AT THE
SOUNDINGS...IT LOOKS LIKE ECMWF HAS SLIGHTLY A BIT MORE WIND BELOW
800 MB AND THIS KEEPS THE LOW LEVELS MIXED JUST ENOUGH TO PROVIDE
THE SLIGHTLY WARMER TEMPERATURES. WE WILL HAVE TO WATCH THIS
PERIOD CLOSELY...BECAUSE IF THE WINDS LIGHTEN ENOUGH THERE WOULD
BE THE POTENTIAL TO DECOUPLE AND THIS COULD RESULT IN SOME PATCHY
FROST. IN ADDITION...THE LIGHTER WINDS COULD RESULT IN SOME
VALLEY FOG. SINCE THE SOUNDINGS ONLY SHOW A VERY SHALLOW LAYER
MOISTURE AND THE WINDS ARE RUNNING AROUND 10 KNOTS BELOW
800 MB...DECIDED TO LEAVE THIS OUT OF THE FORECAST FOR NOW.

FROM THURSDAY NIGHT INTO SATURDAY...THE MODELS CONTINUE TO
DISAGREE ON THE SPEED OF A TROUGH MOVING OUT OF THE PLAINS. THE
GFS IS MUCH SLOWER AND DEEPER WITH THIS TROUGH...THUS IT KEEPS
THIS TIME PERIOD DRY FOR THE UPPER MISSISSIPPI RIVER VALLEY.
MEANWHILE THE ECMWF HAS A MUCH MORE SHALLOW TROUGH AND MORE
PROGRESSIVE FLOW...THUS...IT HAS PRECIPITATION ACROSS THE AREA FOR
THIS TIME PERIOD. THIS INCLUDES A MCS THAT MOVES FROM THE UPPER
MISSISSIPPI RIVER VALLEY INTO THE GREAT LAKES ON FRIDAY NIGHT AND
SATURDAY. WITH THE 13.00Z ECMWF SO SIMILAR TO THE 13.12Z GFS...
TRENDED THE FORECAST MORE TOWARD THEIR SOLUTIONS THAN THE 13.12Z
ECMWF.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SUNDAY TONIGHT)
ISSUED AT 945 PM CDT SAT SEP 13 2014

A BAND OF 5-6KFT CLOUDS HAS DEVELOPED TO THE WEST...IN A REGION OF
LOW LEVEL WARM AIR ADVECTION AND WEAK MOISTURE TRANSPORT...AND AHEAD
OF A SFC WARM FRONT. THESE CLOUDS SHOULD EXIT EAST BETWEEN 12-15Z
SAT...WITH SOME INCREASING HIGH LEVEL CLOUDS LATER IN THE
AFTERNOON...AHEAD OF AN APPROACHING UPPER LEVEL SHORTWAVE TROUGH.
COULD SEE SOME LIGHT RAIN OVERNIGHT SUNDAY AS THE TROUGH SWINGS
THROUGH...IN A REGION OF SLOPING FRONTOGENETIC FORCING/LOW LEVEL
WARMING. NAM AND GFS FAVOR THIS...EC LEANING TOWARD DRY FOR NOW.

&&

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

$$

SHORT TERM...BOYNE
LONG TERM....BOYNE
AVIATION.....RIECK



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