Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 231603
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1003 AM CST MON FEB 23 2015

.UPDATE...
ISSUED AT 1003 AM CST MON FEB 23 2015

THE WIND CHILL ADVISORY HAS BEEN ALLOWED TO EXPIRE. LOOK FOR WIND
CHILLS TO GRADUALLY IMPROVE TO THE SINGLE DIGITS BELOW ZERO BY
EARLY THIS AFTERNOON.

&&

.SHORT TERM...(TODAY THROUGH WEDNESDAY)
ISSUED AT 307 AM CST MON FEB 23 2015

FOR THE MOST PART...THE WIND CHILL ADVISORY IS WORKING OUT THIS
MORNING. TEMPERATURES HAVE FALLEN INTO THE SINGLE DIGITS AND TEENS
BELOW ZERO WITH A NORTHWEST TO WEST WIND AT 5 TO 10 MPH WHICH IS
GIVING WIND CHILLS OF 20 BELOW OR COLDER. THE EXCEPTION TO THIS IS
IN THE VALLEYS AND NORMALLY MORE SHELTERED LOCATIONS WHERE THE
WINDS HAVE PRETTY MUCH GONE CALM SO THERE IS NOT MUCH OF
DIFFERENCE BETWEEN THE AIR TEMPERATURE AND WIND CHILL. STILL
EXPECTING A LITTLE MORE DROP IN AIR TEMPERATURES THIS MORNING TO
KEEP THE WIND CHILLS IN THE ADVISORY RANGE AND NO CHANGES PLANNED
TO ADVISORY.

THE 23.00Z MODELS CONTINUE TO SUGGEST A CHANCE FOR SOME LIGHT SNOW
ACROSS THE EASTERN SECTIONS OF THE AREA FOR LATE TONIGHT INTO
TUESDAY. THE MAIN UPPER LEVEL LOW IS STILL EXPECTED TO MOVE ACROSS
ONTARIO BETWEEN HUDSONS BAY AND THE GREAT LAKES WITH THE SHORT
WAVE TROUGH COMING ACROSS THE GREAT LAKES AND THE NORTHEAST
SECTIONS OF WISCONSIN. THIS KEEPS THE BEST PV ADVECTION IN THE
500-300 MB LAYER NORTHEAST OF THE FORECAST AREA BUT THERE SHOULD
STILL BE A PERIOD OF SOME WEAK TO MODERATE PV ADVECTION THAT COMES
ACROSS...ESPECIALLY IN THE INTERSTATE 94 CORRIDOR. THE QG
CONVERGENCE LOOKS TO BE WEAK TO MODERATE BUT DEEP EXTENDING
THROUGH THE 1000-300 MB COLUMN. SOME WEAK FRONTOGENESIS IN THE
850-500 MB LAYER SHOULD OCCUR WITH THE PASSAGE OF THE COLD FRONT
LATE TONIGHT INTO TUESDAY MORNING. THE NAM WOULD SUGGEST THAT UP
TO 5 UBAR/S OF UP GLIDE WILL COME ACROSS THE AREA LATE TONIGHT ON
THE 280K ISENTROPIC SURFACE. THIS FORCING IS EXPECTED TO BE
SUFFICIENT TO PRODUCE A PERIOD OF LIGHT SNOW LATE TONIGHT INTO
TUESDAY MORNING ALONG AND NORTHEAST OF INTERSTATE 94. QPF AMOUNTS
SHOULD BE PRETTY MINIMAL...BUT STILL ENOUGH TO SQUEEZE OUT A FEW
TENTHS OF ACCUMULATION AND WILL HAVE AROUND A 20 PERCENT CHANCE
ALONG THE MISSISSIPPI RIVER UP TO ABOUT 60 PERCENT NORTHEAST OF
INTERSTATE 94.

ANOTHER CHANCE FOR SOME LIGHT SNOW LOOKS LIKE IT MAY ARRIVE
WEDNESDAY...ALTHOUGH THERE ARE STILL PLENTY OF MODEL DIFFERENCES
WITH THIS SYSTEM. A SHORT WAVE TROUGH IS EXPECTED TO DROP OUT OF
WESTERN CANADA AND COME DOWN THROUGH THE MISSOURI RIVER VALLEY.
THE DIFFERENCES REVOLVE AROUND THE TRACK THE SHORT WAVE TROUGH
WILL EVENTUALLY TAKE. THE 23.00Z ECMWF AND GEM HAVE A MORE
NORTHEAST TRACK COMING ACROSS SOUTHWEST MINNESOTA AND CENTRAL IOWA
WHILE THE 23.00Z NAM AND GFS ARE FARTHER WEST WITH IT. THESE
DIFFERENCES THEN RESULT IN THE ECMWF AND GEM PRODUCING SOME LIGHT
SNOW OVER ABOUT THE SOUTHWEST QUARTER OF THE FORECAST AREA WHILE
THE NAM AND GFS REMAIN DRY. THIS SHORT WAVE TROUGH IS STILL WELL
OUT OVER THE NORTHERN PACIFIC AND NEEDS TO TOP THE RIDGE OVER
WESTERN CANADA AND WOULD NOT BE SURPRISED TO SEE A DIFFERENT
TRACK THAN WHAT ANY OF THE MODELS ARE CURRENTLY SHOWING. WILL ADD
IN A 20 TO 30 PERCENT CHANCE ACROSS THE SOUTHWEST SECTIONS AND
EXPECT THAT THIS FORECAST WILL NEED TO BE REFINED ONCE THE SHORT
WAVE TROUGH COMES ONSHORE AND GETS INTO THE RAOB NETWORK.

.LONG TERM...(WEDNESDAY NIGHT THROUGH SUNDAY)
ISSUED AT 307 AM CST MON FEB 23 2015

THE MODELS ARE SUGGESTING A PATTERN CHANGE MAY OCCUR DURING THIS
PERIOD. THE RIDGE CURRENTLY JUST OFF THE PACIFIC COAST IS SHOWN TO
GET PUSHED FARTHER WEST OUT INTO THE CENTRAL PACIFIC. THIS SHOULD
ALLOW ENERGY TOPPING THE RIDGE TO DIG OUT A TROUGH OVER THE
WESTERN CONUS WITH SOUTHWEST FLOW DEVELOPING ACROSS THE CENTRAL
PART OF THE COUNTRY. THE FIRST SHORT WAVE TROUGH TO COME OUT IN
THIS SOUTHWEST FLOW IS EXPECTED TO COME ACROSS MIDWEST SATURDAY
NIGHT AND SUNDAY. HOWEVER...MODELS TEND TO HAVE A BIAS IN BEING
TOO FAST WITH SOUTHWEST FLOW SYSTEMS...SO WOULD NOT BE SURPRISED
TO SEE SOME CHANGES IN THE TIMING AND POSITION OF THIS SYSTEM.
GIVEN ALL THIS...WILL STAY WITH THE MODEL CONSENSUS GRIDS AND SHOW
A SMALL CHANCE OF SOME SNOW SATURDAY AND THEN A 30 TO 50 PERCENT
CHANCE SATURDAY NIGHT AND SUNDAY. THIS SOUTHWEST FLOW SHOULD ALSO
ALLOW FOR SOME WARMER AIR TO COME IN. HIGHS IN THE SINGLE DIGITS
AND TEENS THURSDAY AND FRIDAY COULD WARM TO THE INTO THE MIDDLE
AND UPPER 20S FOR SUNDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 533 AM CST MON FEB 23 2015

MAIN CONCERN THIS TAF PERIOD WILL BE SFC WINDS AND LLWS LATER THIS
AFTERNOON AND TONIGHT. ARCTIC HIGH WILL RETREAT TODAY WITH SFC WINDS
SWINGING SOUTH AND SOUTHWEST BY MID MORNING...THEN INCREASE THRU
THIS EVENING AS THE PRESSURE GRADIENT OVER THE AREA TIGHTENS. SOURCE
AIRMASS REGION FOR TODAY/MUCH OF TONIGHT IS THE CENTRAL/NORTHERN
PLAINS...WITH GOOD VFR CONDITIONS EXPECTED THRU THE PERIOD. EVEN
TIGHTER PRESSURE GRADIENT/STRONGER WINDS ALOFT...WITH WINDS AROUND
2KF FT AGL IN THE 50KT RANGE THIS EVENING...THEN 40KT RANGE LATE
TONIGHT. CONTINUED TO INCLUDE LLWS IN BOTH KRST/KLSE TAFS AFTER 02Z-
03Z WITH THE DIRECTIONAL CHANGE...AIDED BY A STRONG INVERSION
BETWEEN 950-925MB...200-220 SFC VS. 240 AT 2K FT THIS EVENING...THEN
MORE 220-240 SFC VS. 270-290 AT 2K FT LATER TONIGHT. STRONG
INVERSION WILL LIMIT THE 2K FT WINDS MIXING TO THE SFC...BUT WINDS
LATER THIS AFTERNOON/EVENING WILL STILL BE QUITE GUSTY.


&&

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

$$

UPDATE...WETENKAMP
SHORT TERM...04
LONG TERM....04
AVIATION.....RRS


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