457 
FXUS63 KARX 190135
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
835 PM CDT MON MAR 18 2013

.SHORT TERM...TONIGHT INTO TOMORROW
835 PM CDT MON MAR 18 2013

WITH WINDS NOT LOOKING TO SUBSIDE OVERNIGHT AND A FRESH SNOW PACK
OF 2 TO 5 INCHES RESTING ON TOP OF A CRUSTED OVER SNOW BASE...HAVE
DECIDED TO EXTEND THE WINTER WEATHER ADVISORY FOR THE ENTIRE
FORECAST AREA THROUGH 10 AM DUE TO BLOWING SNOW.
CLIMATOLOGICALLY...BLOWING SNOW TENDS TO SUBSIDE WITHIN A FEW
HOURS AFTER THE SNOW ENDS...BUT VISIBILITY REMAINS LOW AND LOCAL
SHERIFF DEPARTMENTS ARE REPORTING TERRIBLE ROAD CONDITIONS. DUE TO
THIS...DECIDED TO ERR ON THE SIDE OF CAUTION AND EXTEND THE
ADVISORY FOR THE OVERNIGHT HOURS INTO TOMORROW MORNING. UPDATE
WILL BE OUT SHORTLY.

.LONG TERM...THURSDAY THROUGH MONDAY 
227 PM CDT MON MAR 18 2013

THIS SYSTEM WILL FINALLY MOVE FAR ENOUGH TO THE EAST TO ALLOW HIGH
PRESSURE TO BUILD OVER THE UPPER MIDWEST EARLY IN THE PERIOD. THE
HIGH IS EXPECTED TO REMAIN CENTERED OVER MANITOBA WITH THE RIDGE
AXIS EXTENDING DOWN INTO THE REGION. THIS SETS UP THE PROBLEM OF
WHEN WILL THE RIDGE WILL GIVE WAY. AS THE 18.12Z MODELS SHOW A
SYSTEM COMING OFF THE CANADIAN ROCKIES AND UNDERCUTTING THE
WEAKENING UPPER LEVEL RIDGE AS WE HEAD INTO THE WEEKEND. THE
GENERAL CONSENSUS IS THAT THIS WILL BE A TWO PART SYSTEM WITH THE
SOUTHERN PART OF THE SYSTEM COMING OUT OF THE CENTRAL
ROCKIES...MOVING ACROSS THE LOWER MISSISSIPPI RIVER VALLEY TOWARD
THE OHIO RIVER VALLEY. MODEL DIFFERENCES ON HOW MUCH ENERGY WILL
BE TRAILING BEHIND WITH THE NORTHERN PART OF THE SYSTEM OVER THE
HIGH PLAINS. THE GFS SHOWS MORE ENERGY HERE THAN EITHER THE 18.12Z
ECMWF OR GEM WHICH RESULTS IN IT PULLING THE SURFACE LOW FARTHER
NORTH AND HAVING A TROUGH OF LOW PRESSURE EXTENDING NORTH FROM IT
BACK TOWARD THE TRAILING NORTHERN ENERGY. WITH THIS SCENARIO THE
GFS SHOWS PRECIPITATION OVER THE AREA WHILE THE ECMWF AND GEM ARE
DRY FOR SATURDAY AND SATURDAY NIGHT. THE ECMWF DOES SHOW A LITTLE
BIT OF PRECIPITATION OVER THE AREA SUNDAY THROUGH MONDAY AS THE
NORTHERN ENERGY SLIDES ACROSS THE UPPER MIDWEST. WILL HONOR THE
GFS SOLUTION AND SHOW SOME VERY LOW END PRECIPITATION CHANCES
SATURDAY AND SATURDAY NIGHT. WILL DO THE SAME WITH THE ECMWF WITH
SMALL CHANCES SUNDAY AND MONDAY.

&&

.AVIATION...TONIGHT AND TUESDAY
624 PM CDT MON MAR 18 2013

STRONG WINDS AND BLOWING SNOW TO CONTINUE THROUGH THE EVENING AND
OVERNIGHT HOURS AS A LOW PRESSURE SYSTEM MOVES INTO THE GREAT
LAKES REGION. THIS BLOWING SNOW HAS DROPPED VISIBILITY DOWN TO
AROUND 1 1/2SM AT RST AND...COMBINED WITH SOME SNOW SHOWERS...HAS
BROUGHT LSE DOWN TO 2SM AT TIMES THIS AFTERNOON. AS THE FRESH SNOW
BECOMES MORE COMPACTED THIS EVENING...EXPECT THAT THE BLOWING SNOW
WILL BECOME LESS OF A CONCERN WITH VISIBILITY GRADUALLY IMPROVING.
CONFIDENCE IN WHEN THAT WILL OCCUR AT RST IS NOT VERY HIGH...BUT
BROUGHT THE VISIBILITY UP TO MVFR AROUND 5Z AS A STARTING POINT.
THE NEXT QUESTION IS WITH WHEN/IF THE CEILINGS CLEAR OUT.
CURRENTLY...THE CLEARING IS ALONG AND EAST OF THE SURFACE RIDGE IN
THE EASTERN DAKOTAS. SHORT TERM MODEL GUIDANCE SUGGESTS THAT THIS
CLEARING WILL BE INTO THE REGION AROUND DAY BREAK TOMORROW
MORNING...BUT THE SYSTEM APPEARS TO STALL A BIT WHICH COULD MEAN
THAT THE CLOUDS HOLD ON FOR A BIT LONGER. EVEN IF SKIES CLEAR FOR
A BIT IN THE MORNING...IT APPEARS THAT A 2KFT DECK WILL
REDEVELOP IN THE AFTERNOON DUE TO THE STEEP LOW LEVEL LAPSE RATES
AND LEFTOVER LOW LEVEL MOISTURE. WINDS WILL STAY STRONG THROUGH
THE PERIOD THOUGH VERY GRADUALLY DIMINISHING INTO TOMORROW AFTERNOON.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
835 PM CDT MON MAR 18 2013

WI...WINTER WEATHER ADVISORY UNTIL 10 AM CDT TUESDAY FOR WIZ017-029-
     032>034-041>044-053>055-061.

MN...WINTER WEATHER ADVISORY UNTIL 10 AM CDT TUESDAY FOR MNZ079-
     086>088-094>096.

IA...WINTER WEATHER ADVISORY UNTIL 10 AM CDT TUESDAY FOR IAZ008>011-
     018-019-029-030.


&&

$$

SHORT TERM...HALBACH
LONG TERM...04
AVIATION...HALBACH