Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 251546
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
946 AM CST THU DEC 25 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 342 AM CST THU DEC 25 2014

THE MAIN FOCUS FOR TODAY IS WITH THE CLOUD COVER/TEMPERATURES
FOLLOWED BY THE CHANCES FOR DRIZZLE/FREEZING DRIZZLE TONIGHT.

CURRENTLY...A SURFACE RIDGE OF HIGH PRESSURE IS ALIGNED ALONG THE
MISSISSIPPI RIVER AND DRIFTING EASTWARD AS A BROAD AREA OF LOW
PRESSURE DEVELOPS IN THE PLAINS. FURTHER ALOFT...THE MID LEVEL
FLOW IS FLATTENING OUT ACROSS THE NORTHERN PLAINS/UPPER
MISSISSIPPI RIVER VALLEY AS A TROUGH DIGS ACROSS THE ROCKIES. A
LOW LEVEL STRATUS DECK IS PRODUCING SOME SCATTERED FLURRIES DUE TO
THE TOP OF THE SATURATED LAYER/CLOUD DECK BEING AROUND -10C
ACCORDING TO IR SATELLITE. THIS IS COLDER THAN WHAT LOCAL SHORT
TERM SOUNDINGS SUGGEST IS OCCURRING. IR SATELLITE/OBS ACTUALLY
SHOW THE WESTERN EDGE OF IT RAPIDLY CLEARING IN ACROSS CENTRAL
IOWA/SOUTHWEST MINNESOTA AND IS TIMED TO BE MOVING THROUGH THE
REGION THIS MORNING INTO EARLY AFTERNOON WITH EROSION OCCURRING
FROM SOUTHWEST TO NORTHEAST. HOWEVER...HIGH LEVEL CLOUD COVER IS
QUICK ON ITS HEELS AND WILL LIMIT THE POTENTIAL OF SEEING ANY
SUNLIGHT UNLESS IT ENDS UP THINNING OUT AS IT APPROACHES. BASED
ON THE LOW CLOUDS CLEARING OUT...BUMPED UP FORECAST HIGH
TEMPERATURES A FEW DEGREES AS SURFACE WINDS COME AROUND TO THE
SOUTHWEST AND BRING SOME WARMER AIR INTO THE REGION.

GOING INTO TONIGHT THE QUESTION IS WITH WHETHER ANY
DRIZZLE/FREEZING DRIZZLE WILL OCCUR AS LOW LEVEL MOISTURE
TRANSPORT RAMPS UP INTO THE REGION. THE 25.00Z MODELS ARE ALL IN
AGREEMENT THAT A 30-40KT LOW LEVEL JET WILL DEVELOP ACROSS THE
SOUTHERN PLAINS THIS EVENING WITH IT NOSING NORTHEASTWARD AS THE
NIGHT PROGRESSES. FORECAST SOUNDINGS FROM THE NAM/GFS BOTH SHOW A
DEEPENING SATURATED LOW LEVEL LAYER WHICH IS NOT COLD ENOUGH TO
FORM ICE. THERE APPEARS TO BE SOME WEAK LIFT THANKS TO THE LLJ
NOSE/SURFACE BOUNDARY PROVIDING SOME CONVERGENCE. THE 25.00/06Z
NAM SURFACE REFLECTIVITY PANES SHOW THIS DRIZZLE DEVELOPING FROM
THE WEST OVERNIGHT...PARTICULARLY AFTER MIDNIGHT AND ALONG WHERE
THE CONVERGENCE IS IN THE SURFACE/LOW LEVELS. WITH THE SOUTHERLY
WINDS KEEPING THE WARMER AIR IN PLACE...THERE IS SOME QUESTION
ABOUT HOW COLD TEMPERATURES WILL BE AND WHETHER THE DRIZZLE WILL
BE FREEZING OR NOT. WILL HAVE TO MONITOR TRENDS...BUT WITH
TEMPERATURES AT OR JUST ABOVE FREEZING...EXPECT THAT THE IMPACT
WILL NOT BE THAT GREAT.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 342 AM CST THU DEC 25 2014

GOING INTO THIS WEEKEND ON INTO THE MIDDLE OF NEXT WEEK...THE
FOCUS IS ON THE POTENTIAL FOR AN ACCUMULATING SNOW FRIDAY NIGHT
INTO SATURDAY FOLLOWED BY THE DRASTICALLY COLDER AIR MASS THAT
WILL SETTLE IN BY MIDWEEK.

EYES WILL BE ON THE MID LEVEL TROUGH DIGGING ACROSS THE
SOUTHWESTERN US AND HOW IT WILL EJECT INTO THE UPPER MIDWEST.
PREVIOUS MODEL RUNS HAD THIS WAVE COMING THROUGH AS MAINLY AN OPEN
TROUGH/SURFACE LOW BUT THE 25.00Z TRENDS WITH THE NAM/GFS/ECMWF
ARE TO GO DEEPER. THE ECMWF IS THE DEEPEST/SLOWEST WITH THIS
FEATURE AND BRINGS THE HEAVIEST SNOW TOTALS...POSSIBLY ADVISORY
WORTHY...ALONG WITH IT. ALL THREE MODELS ARE SHOWING A BAND OF
HEAVIER SNOW OCCURRING IN THE DEFORMATION AREA OF THE TROUGH WHICH
RUNS FROM SOUTHEAST MINNESOTA INTO NORTH CENTRAL WISCONSIN. MOST
OF THE AREA SHOULD JUST SEE SNOW FROM THIS SYSTEM...BUT SOME
PORTIONS OF EASTERN IOWA AND SOUTHWEST WISCONSIN COULD BE WARM
ENOUGH TO CHANGE IT OVER TO RAIN. THE ECMWF TRENDS WILL HAVE TO BE
MONITORED BECAUSE IT WOULD SET US UP FOR SOME HIGHER SNOWFALL
TOTALS THAN CURRENTLY BEING FORECAST. WITH IT BEING A NEW
DIRECTION BEING TAKEN WITH THIS ONE MODEL...DECIDED IT WOULD BE
BEST TO JUST BLEND THAT SOLUTION WITH THE NAM/GFS IDEA TO COME UP
WITH SNOW ACCUMULATIONS OF 1 TO 3 INCHES. THE MAIN PERIOD TO WATCH
WILL BE SATURDAY MORNING AS THE ECMWF HAS AROUND 0.25 INCHES OF
QPF IN THAT PERIOD WHEN THE NAM/GFS ONLY HAS 0.01 INCHES OR SO.

BEYOND THIS SYSTEM IT LOOKS LIKE WE WILL HAVE AN EXTENDED PERIOD
OF HAVING A COLDER AIR MASS WHERE HIGHS ONLY GET INTO THE
TEENS...PARTICULARLY GOING INTO TUESDAY AND WEDNESDAY. PERHAPS THE
SILVER LINING HERE IS THAT WITH THIS COLD AIR AND A BROAD RIDGE OF
HIGH PRESSURE DROPPING DOWN ACROSS MUCH OF THE CENTRAL US...SKIES
SHOULD BE CLEAR WHICH WOULD BE WELCOME AFTER THIS EXTENDED PERIOD
OF OVERCAST CONDITIONS.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 946 AM CST THU DEC 25 2014

946 AM UPDATE...LAST FEW MODEL RUNS OF THE RAP AS WELL AS TRENDS
IN OBSERVATIONS IN SOUTHEAST MINNESOTA HAVE SHOWN THAT THE STRATUS
REMAINS STUCK. AS SUCH...HAVE WENT MORE PESSIMISTIC WITH THE
FORECASTS AND HAVE HELD LOW CEILINGS IN PLACE FOR THE NEXT 24
HOURS. DID ALLOW RST TO CLIMB TO MVFR THIS AFTERNOON AS DAYTIME
HEATING HELPS. ADDITIONALLY...THERE APPEARS THERE COULD BE A BRIEF
SCATTERING OF THE CLOUDS AT LSE BETWEEN 21-01Z...WHICH HAVE BEEN
HONORED WITH A TEMPO GROUP.

541 AM DISCUSSION...

CURRENTLY WATCHING BACK EDGE OF IFR/MVFR STRATUS ACROSS SOUTH
CENTRAL MN INTO EASTERN IA ERODING NORTHEASTWARD TOWARD THE
KRST/KLSE TAF SITES. EXPECTING KRST TO BREAK OUT OF STRATUS BY
15Z AND KLSE BY 17Z. AS THIS CLEARS OUT...LOOK FOR ALTOCUMULUS TO
SPREAD IN FROM THE WEST AHEAD OF A WEAK AREA OF LOW PRESSURE OVER
THE PLAINS. AS THIS LOW CLOSES IN ON THE REGION TONIGHT...PLAN ON
A RETURN OF MVFR STRATUS BETWEEN 03-05Z. KRST LOOKS TO DIP INTO
IFR AFTER 09Z. WITH THE RETURN OF THIS STRATUS AND WEAK
LIFT...EXPECTING PATCHY LIGHT FREEZING DRIZZLE TO DEVELOP AFTER
MIDNIGHT. FEEL THIS DRIZZLE WILL BE HIT AND MISS...SO OPTED NOT TO
INCLUDE IN THE BODY OF THE TAFS AT THIS POINT.


&&

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

$$

SHORT TERM...HALBACH
LONG TERM...HALBACH
AVIATION...DAS/AJ


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