Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 201127
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
527 AM CST SAT DEC 20 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 339 AM CST SAT DEC 20 2014

THE MAIN FOCUS TODAY INTO TONIGHT CONTINUES TO BE ON THE
PROBABILITIES OF SEEING SOME FREEZING DRIZZLE AND FLURRIES.

CURRENTLY IN WEAK SOUTHERLY FLOW IN THE LOW LEVELS WITH A RIDGE
OVER THE CENTRAL GREAT LAKES AND LOW PRESSURE OVER THE EASTERN
ROCKIES. A CLOSED MID LEVEL LOW IS DRIFTING EAST ACROSS SOUTHERN
MANITOBA/ONTARIO WHILE A SHORT WAVE TROUGH DIVES SOUTH OF IT INTO
IOWA. SOME WEAK LOW LEVEL WARM AIR ADVECTION HAS LEAD TO SOME
LOWER STRATUS TO FORM ALONG AND EAST OF THE INTERSTATE 35
CORRIDOR. THERE IS JUST ENOUGH LIFT THERE TO PRODUCE SOME DRIZZLE AND
WITH TEMPERATURES BELOW FREEZING THERE HAS BEEN SOME SPOTS THAT
HAVE REPORTED SOME LIGHT GLAZING ON ROADS AND OTHER EXTERNAL
SURFACES. THIS WAA APPEARS TO WEAKEN FOR A PERIOD TODAY BEFORE
STRENGTHENING AGAIN TONIGHT ACROSS NORTHEAST IOWA INTO SOUTHWEST
WISCONSIN. COULD SEE SOME MORE OF THE SAME WITH THE COLUMN NOT
HAVING ANY ICE PRESENT AND SURFACE TEMPERATURES BELOW FREEZING.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 339 AM CST SAT DEC 20 2014

QUITE THE MESSY PATTERN THROUGH THE WEEK WITH THURSDAY LOOKING THE
MOST LIKELY TO BE THE ONLY DRY ONE OF THE BUNCH. PRECIPITATION
SHOULD BECOME A BIT MORE WIDESPREAD...THOUGH STILL LIGHT...ON
SUNDAY AS A 700MB TROUGH INTERACTS WITH THE LOW LEVEL WARM AIR
ADVECTION. LIFT/MOISTURE LOOKS DEEP ENOUGH TO INTRODUCE SOME ICE
THOUGH IT ALSO BRINGS AN ABOVE FREEZING WARM LAYER IN AROUND 850MB
AS WELL. THEREFORE...PRECIPITATION TYPE IS A MESS FOR SUNDAY WITH
PERHAPS SOME FREEZING DRIZZLE TO START IN THE MORNING AS THE DRY
AIR BETWEEN 900-700MB IS TOO DEEP FOR SEEDER FEEDER TO WORK. AS
THE COLUMN STARTS TO SATURATE UNDER THE DEEPER LIFT IN THE
AFTERNOON...THE WARM LAYER MOVES IN WITH THE PRECIPITATION TYPE
LIKELY BEING SNOW OR SLEET INITIALLY. 20.00Z NAM/GFS SOUNDINGS
THEN INDICATE THAT AS THE PRECIPITATION FALLS THAT THE WARM LAYER
SHOULD COOL AGAIN WITH THE PRECIP TYPE CHANGING BACK TO SNOW. AS
THE WAVE THEN SHIFTS TO THE EAST SUNDAY NIGHT...IT APPEARS AS
THOUGH ICE IS LOST AND THAT THE PRECIPITATION TYPE THEN GOES BACK
TO BEING DRIZZLE.

WARMER AIR SHOULD THEN MOVE IN ON MONDAY AS A MORE POTENT TROUGH
DEVELOPS OVER THE DAKOTAS. THE 20.00Z NAM/ECMWF TRENDS APPEAR TO
BE PREFERRED OVER THE 20.00Z GFS WHICH IS MUCH FASTER WITH THE
CLOSED LOW. THE NAM/ECMWF SOLUTION BRINGS A BAND OF RAIN THROUGH
AND LIFTS IT TO THE NORTHEAST BY MONDAY EVENING WITH THE DRY SLOT
OF THE SYSTEM MOVING IN. THE GFS HAS THE SURFACE LOW MUCH FURTHER
SOUTH AS WELL AND WOULD KEEP PRECIP AROUND MUCH LONGER.
OVERALL...CONFIDENCE IN HOW THIS SYSTEM WILL PLAY OUT IS PRETTY
LOW AT THIS POINT.

COLDER AIR WILL MOVE IN BY MID WEEK WITH ANY PRECIPITATION
FALLING THROUGH THE REST OF THE WEEK EXPECTED TO BE SNOW. A SYSTEM
OF INTEREST IS WITH WHAT THE 20.00Z ECMWF IS SHOWING FOR THURSDAY
NIGHT THROUGH FRIDAY NIGHT. WHILE THE 20.00Z GFS ONLY HAS A WEAK
INVERTED TROUGH MOVING THROUGH THE ECMWF SHOWS A POTENT STORM
SYSTEM TRACKING THROUGH THE MID MISSISSIPPI RIVER VALLEY REGION
WITH A DEEPENING SURFACE LOW PROPAGATING FROM THE SOUTHERN PLAINS
THROUGH NORTHERN ILLINOIS ON TOWARD CENTRAL LAKE MICHIGAN. MODEL
CONSISTENCY HAS BEEN ALL OVER THE PLACE FOR THIS TIME FRAME...SO
WILL HAVE TO WAIT AND SEE WHAT LATER RUNS COME UP WITH.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 527 AM CST SAT DEC 20 2014

WEAK TROUGH OF LOW PRESSURE OVER NORTHEAST IA EARLY THIS MORNING
WILL PUSH EAST OF THE AREA BY LATER THIS MORNING. THIS IS EXPECTED
TO BRING AN END TO LIGHT SNOW/FREEZING DRIZZLE ACTIVITY AROUND THE
AREA. OTHERWISE...PLAN ON IFR CONDITIONS AT KRST TO IMPROVE INTO
MVFR RANGE BY 18Z WHILE MVFR CIGS ARE EXPECTED TO CONTINUE AT
KLSE. ANOTHER TROUGH OF LOW PRESSURE MOVES TOWARD THE REGION
TONIGHT FOR ANOTHER BOUT OF FZDZ. KEPT OUT OF THE BODY OF THE
KRST/KLSE TAFS FOR NOW AS BEST SATURATION FOR FZDZ POTENTIAL
REMAINS JUST SOUTH OF THE SITES THROUGH 12Z. APPEARS KLSE REMAINS
MVFR THROUGH TONIGHT WHILE KRST IS EXPECTED TO SLIP INTO IFR ONCE
AGAIN AFTER 06Z.

&&

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

$$

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


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