Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 230109
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
809 PM CDT SUN MAR 22 2015

.UPDATE...
ISSUED AT 809 PM CDT SUN MAR 22 2015

CONFIDENCE CONTINUES TO GROW THAT A BAND OF HEAVY SNOW WILL
DEVELOP OVER THE NEXT FEW HOURS ACROSS SOUTHEAST
MINNESOTA...NORTHEAST IOWA AND SOUTHWEST WISCONSIN. STRONG
SURFACE TO 700MB UPRIGHT FRONTOGENESIS WILL LEAD TO AN EXTENDED
PERIOD OF HEAVY SNOW ALONG A LOW LEVEL DEFORMATION BAND ALONG THE
NORTHEAST PERIPHERY OF THE SURFACE LOW. SHORT TERM/MESO-MODELS
ARE ALL IN FAIRLY GOOD AGREEMENT IN THIS BAND DEVELOPING TO THE
SOUTHWEST OF THE INITIAL FGEN BAND THAT IS CURRENTLY ALONG THE
MN/WI BORDER ON DOWN INTO SOUTH CENTRAL WISCONSIN. SNOWFALL RATES
ARE EXPECTED TO BE IN THE 1 TO 2 INCH PER HOUR RANGE FOR A NUMBER
OF HOURS TONIGHT IN THIS REGION...SO FELT CONFIDENT ENOUGH TO
UPGRADE TO A WARNING IN THIS REGION. EXPECT THAT THE INITIAL BAND
WILL GRADUALLY WEAKEN OVER THE NEXT FEW HOURS AS THE BAND TO THE
SOUTHWEST TAKES OVER...SO IT WILL BE A QUICK DROP OFF FOR SNOW
AMOUNTS IN WESTERN WISCONSIN. NOT VERY CONCERNED WITH FREEZING
DRIZZLE AT THIS POINT AS THE LIFT LOOKS FAIRLY WEAK ONCE THE
SYSTEM DEPARTS AND ICE IS LOST IN THE COLUMN.

&&

.SHORT TERM...(THIS EVENING THROUGH TUESDAY NIGHT)
ISSUED AT 347 PM CDT SUN MAR 22 2015

BAND OF LIGHT SNOW HAS ALREADY DEVELOPED ACROSS THE REGION THIS
AFTERNOON IN THE ZONE OF MID LEVEL FRONTOGENESIS AND LEADING
ISENTROPIC UP GLIDE. THE MODELS HAVE CONTINUED THE TREND OF
SLOWING DOWN THE TIMING OF THE HEAVIEST SNOW AS THIS IS TIED MORE
TO THE ARRIVAL OF THE SHORT WAVE TROUGH OVER SOUTH DAKOTA. THE
22.12Z MODELS NOW ALL TAKE THIS SHORT WAVE TROUGH ACROSS THE AREA
PRODUCING A PERIOD OF WEAK TO MODERATE PV ADVECTION IN THE 500-300
MB LAYER. THE AREA WILL ALSO BE UNDER THE RIGHT ENTRANCE REGION OF
THE UPPER LEVEL JET FOR MUCH OF TONIGHT WITH ADDED OMEGA FROM
THIS. THE MODELS HAVE INCREASE THE FRONTOGENESIS AS THE WAVE COMES
IN NOW SHOWING A PERIOD OF MODERATE FRONTOGENESIS IN THE 750-700
MB LAYER WITH WEAK FRONTOGENESIS ABOVE THAT UP THROUGH AT LEAST
500 MB. THE LOW LEVEL WARM AIR ADVECTION ALSO LOOKS TO BE STRONGER
RESULTING IN SIGNIFICANTLY MORE ISENTROPIC UP GLIDE. THE 22.12Z
NAM HAS ABOUT 4 UBAR/S ON THE 285K SURFACE WHILE THE GFS CRANKS
THIS UP TO 6 UBAR/S OR HIGHER THIS EVENING. THIS INCREASE FORCING
IS EXPECTED TO CAUSE THE CURRENT BAND OF LIGHT SNOW TO INTENSIFY
THROUGH THE EVENING AS THE SHORT WAVE TROUGH APPROACHES. STILL
EXPECTING A PERIOD OF VERY STRONG OMEGA THROUGH THE DENDRITIC
GROWTH ZONE TO PRODUCE SOME HOURLY SNOWFALL RATES OF AT LEAST AN
INCH AN HOUR AND AT TIMES APPROACHING 2 INCHES AN HOUR. THE SNOW
FROM THIS MORNING AND EARLY AFTERNOON HAD SOME DECENT RATES AND
WAS ABLE TO ACCUMULATE QUICKLY ON GRASSY SURFACES. WITH EVEN
BETTER RATES EXPECTED OVERNIGHT...FEEL THERE WILL BE NO PROBLEMS
WITH ACCUMULATIONS AND THAT THE ROADS WILL ALSO BE IMPACTED AS THE
ROAD TEMPERATURES COME DOWN. WITH THE INCREASED FORCING AND HIGHER
RATES...THINK THE SNOWFALL ACCUMULATIONS WILL BE HIGHER THAN
PREVIOUSLY EXPECTED WITH A BAND OF 5 TO 8 INCHES POSSIBLE OVER
SOUTHEAST MINNESOTA AND POSSIBLY SMALL PORTIONS OF NORTHEAST IOWA
AND WESTERN WISCONSIN. FOR NOW...WILL UPGRADE THE ADVISORY TO A
WARNING FOR ALL OF SOUTHEAST MINNESOTA WITH AN EXPIRATION TIME OF
4 AM. WILL ALSO ADD A FEW MORE COUNTIES INTO THE ADVISORY AND FOR
SIMPLICITY...HAVE THE EXPIRATION OF THE ALL THESE COUNTIES BE 7
AM. STILL SOME POSSIBILITY OF A LOSS OF ICE IN THE CLOUDS AS THE
PRECIPITATION STARTS TO WIND DOWN AND HAVE CONTINUED THE MENTION
OF SOME FREEZING DRIZZLE...ALTHOUGH CONFIDENCE REMAINS LOW THAT
THIS WILL OCCUR AS THERE MAY NOT BE A LOT OF PRECIPITATION STILL
OCCURRING ONCE THE ICE IS LOST.

THIS SYSTEM SHOULD QUICKLY CLEAR OUT OF THE AREA MONDAY
MORNING...BUT THE BREAK IN PRECIPITATION WILL NOT LAST VERY LONG.
ENERGY OFF THE PACIFIC NORTHWEST COAST TODAY WILL MOVE INLAND AND
TRACK ALMOST STRAIGHT EAST TOWARD THE UPPER MIDWEST. THE MODELS
FOR NOW HAVE CONVERGED ON A SOLUTION OF KEEPING ALL THE SHORT WAVE
TROUGHS SEPARATE WITH NO PHASING OCCURRING AND STRENGTHENING THE
SOUTHERN MOST WAVE TO MAKE THIS THE DOMINANT WEATHER PRODUCER. THE
CURRENT TIMING WOULD SUGGEST THIS SOUTHERN WAVE WILL COME ACROSS
THE REGION TUESDAY NIGHT WITH MODERATE TO STRONG PV ADVECTION IN
THE 500-300 MB LAYER. THERE WILL ALSO BE THE POTENTIAL FOR THE
AREA TO GET UNDER THE LEFT EXIT REGION OF THE UPPER LEVEL JET
TUESDAY NIGHT. THE MAIN SURFACE LOW WILL FORM WITH THIS SOUTHERN
WAVE AND SHOULD TRACK FROM SOUTHERN IOWA/NORTHERN MISSOURI
NORTHEAST TOWARD LAKE MICHIGAN GOING SOUTH OF THE FORECAST AREA.
THIS WOULD PUT THE FORECAST AREA ON THE COLD SIDE OF THE
SYSTEM...BUT THIS SYSTEM STILL LOOKS TO BRING ENOUGH WARM AIR
NORTH WITH IT TO WRAP AROUND THE LOW TO POTENTIALLY KEEP THE BEST
SNOW TO THE NORTH OF THE REGION. THIS WILL ALSO RESULT IN STRONG
LOW LEVEL WARM AIR ADVECTION WITH THE GFS AGAIN SHOWING AROUND 6
UBAR/S OF UP GLIDE ON THE 290K SURFACE SPREADING ACROSS THE AREA
TUESDAY NIGHT. THERE ALSO LOOKS TO BE A PRETTY DECENT 850 MB
MOISTURE TRANSPORT SIGNAL INTO THE AREA. THE GFS DOES BRING IN
BETWEEN 100 AND 200 J/KG OF MUCAPE TUESDAY AFTERNOON ACROSS THE
VERY SOUTHERN SECTIONS. HAVE NOT ADDED ANY THUNDER TO THE FORECAST
AT THIS TIME...BUT WILL MONITOR MODEL TRENDS FOR POSSIBLE
INCLUSION LATER. WILL START TO BRING THE PRECIPITATION CHANCES IN
TUESDAY AFTERNOON AND SPREAD 80 TO 100 PERCENT CHANCES ACROSS THE
ENTIRE AREA TUESDAY NIGHT.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)
ISSUED AT 347 PM CDT SUN MAR 22 2015

WITH THE SYSTEM THAT COMES IN TUESDAY...ONCE THE SOUTHERN SHORT
WAVE TROUGH MOVES PAST...THE UPPER MIDWEST WILL COME UNDER THE
INFLUENCE OF THE NORTHERN SHORT WAVE TROUGH. THIS WAVE IS EXPECTED
TO GO ACROSS THE UPPER MIDWEST AND GREAT LAKES AND EVENTUALLY
MERGE WITH THE OTHER SHORT WAVE TROUGH OVER SOUTHEAST CANADA. MOST
OF THE FORCING FROM THIS NORTHERN SHORT WAVE TROUGH SHOULD PASS BY
TO THE NORTH OF THE AREA...BUT ENOUGH TO KEEP SOME 20 TO 40
PERCENT CHANCE ACROSS THE NORTHERN SECTIONS OF THE FORECAST AREA
FOR WEDNESDAY NIGHT AND THURSDAY. THE PASSAGE OF THIS SYSTEM WILL
ALLOW FOR A RETURN TO NORTHWEST FLOW ALOFT AND ANOTHER SYSTEM TO
DROP ACROSS THE REGION THIS UPCOMING WEEKEND. THE MAIN PART OF
THIS SHORT WAVE SHOULD STAY ACROSS SOUTHERN CANADA ALONG WITH THE
SURFACE LOW...BUT A COLD FRONT SHOULD COME THROUGH TO PRODUCE
ANOTHER CHANCE OF A RAIN/SNOW MIX SATURDAY NIGHT INTO SUNDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 646 PM CDT SUN MAR 22 2015

A BAND OF HEAVY SNOW HAS MOVED INTO THE REGION AND WILL BECOME
MORE WIDESPREAD THIS EVENING AS A SYSTEM APPROACHES FROM THE WEST.
VISIBILITIES MAY DROP DOWN TO A QUARTER OF A MILE AT TIMES THIS
EVENING BEFORE THE SYSTEM DROPS DOWN TO THE SOUTHEAST OVERNIGHT.
CONDITIONS SHOULD IMPROVE BY DAYBREAK TOMORROW MORNING AS DRIER
AIR MOVES BACK INTO THE REGION. UNTIL THEN...CONDITIONS WILL
LIKELY STAY IFR/LIFR THROUGH MUCH OF THE NIGHT.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...WINTER STORM WARNING UNTIL 7 AM CDT MONDAY FOR WIZ053>055-061.

     WINTER WEATHER ADVISORY UNTIL 4 AM CDT MONDAY FOR WIZ032>034-
     041>043.

MN...WINTER STORM WARNING UNTIL 4 AM CDT MONDAY FOR MNZ079-086>088-
     094>096.

IA...WINTER WEATHER ADVISORY UNTIL 7 AM CDT MONDAY FOR IAZ008-019-029.

     WINTER STORM WARNING UNTIL 7 AM CDT MONDAY FOR IAZ009>011-030.

&&

$$

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



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