Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 251954
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
254 PM CDT MON AUG 25 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 254 PM CDT MON AUG 25 2014

MAIN FORECAST CONCERN IS WITH THE RAIN CHANCES THROUGH THE PERIOD.

SURFACE ANALYSIS THIS AFTERNOON SUGGESTS THE COLD FRONT IS MAKING
SLOW EASTWARD PROGRESS THROUGH THE WESTERN SECTIONS OF THE
FORECAST AREA. DEW POINTS REMAIN IN THE 70S AHEAD OF THE FRONT BUT
THEN DROP OFF INTO THE 50S ACROSS CENTRAL MINNESOTA. LOCAL AND
REGIONAL RADARS SHOW THE LINE OF STORMS THAT MOVED THROUGH
OVERNIGHT EXTEND FROM SOUTHEAST WISCONSIN INTO EASTERN IOWA AND
ARE STARTING TO INTENSIFY AGAIN.

THE EXPECTATION THROUGH THE REST OF THE AFTERNOON INTO THE EVENING
IS THAT THE ONGOING ACTIVITY WILL CONTINUE TO MOVE AWAY FROM THE
AREA AS THE FRONT PROGRESSES THROUGH THE FORECAST AREA. SOME
ADDITIONAL ACTIVITY FORMING ON THE WESTERN PART OF THE FRONT OVER
THE MISSOURI RIVER VALLEY. THE 25.17Z HRRR SUGGESTS THIS WILL
TRACK INTO CENTRAL IOWA BEFORE DIMINISHING. HOWEVER...CONFIDENCE
IN THIS MODEL OUTPUT IS NOT THAT HIGH. OUTPUT FROM THE 25.15Z
HOP-WRF DOES SUGGEST THIS MAY SURVIVE AND COME ACROSS NORTHEAST
IOWA THIS EVENING AND WILL SHOW SOME SMALL RAIN CHANCES FOR THIS.
ADDITIONAL CONVECTION SHOULD FORM OVERNIGHT ALONG THE COLD FRONT
AS A SHORT WAVE TROUGH COMES OUT OF THE CENTRAL ROCKIES. THE
MOISTURE TRANSPORT INTO THE FRONT DOES NOT LOOK TO BE ALL THAT
STRONG TONIGHT AND AS CANADIAN HIGH PRESSURE BUILDS IN FROM THE
NORTH...THE BULK OF THE RAIN TONIGHT SHOULD REMAIN OVER CENTRAL
AND SOUTHERN IOWA.

THE HIGH WILL GRADUALLY MOVE EAST-SOUTHEAST ACROSS THE UPPER
MIDWEST AND BE OVER THE U.P. OF MICHIGAN BY WEDNESDAY NIGHT. THIS
IS EXPECTED TO KEEP THE FRONT FAR ENOUGH SOUTH THAT MOST OF THE
CONVECTION ALONG IT FROM TUESDAY THROUGH WEDNESDAY SHOULD STAY TO
THE SOUTH. CANNOT RULE OUT THE SOUTHERN PARTS OF THE FORECAST AREA
GETTING CAUGHT ON THE NORTH EDGE OF THE COMPLEXES THAT FORM ALONG
THE FRONT AND WILL SHOW SOME 20 TO 40 PERCENT RAIN CHANCES FOR
THIS SCENARIO.

BY WEDNESDAY NIGHT THE HIGH WILL START TO MOVE FARTHER OFF TO THE
EAST ALLOWING DEEPER MOISTURE TO START RETURNING TO THE AREA. THIS
MOISTURE RETURN SHOULD OCCUR AHEAD OF STRONGER SHORT WAVE TROUGH
EJECTING NORTHEAST OUT OF THE CENTRAL ROCKIES. THIS WAVE SHOULD
BRING AT LEAST SOME WEAK PV ADVECTION IN THE 500-300 MB LAYER INTO
THE AREA ALONG WITH 1 TO 3 UBAR/S OF UP GLIDE ON THE 310K
ISENTROPIC SURFACE. SHOULD SEE ACTIVITY DEVELOP TO THE
WEST/SOUTHWEST OF THE AREA WEDNESDAY EVENING AND THEN MOVE IN
DURING THE OVERNIGHT HOURS.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 254 PM CDT MON AUG 25 2014

THE SHORT WAVE TROUGH THAT COMES OUT WEDNESDAY NIGHT WILL TRACK
ACROSS THE UPPER MIDWEST THURSDAY AND SHOULD BE THE FIRST OF
SEVERAL WAVES AS THE MEAN LONG WAVE TROUGH SLOWLY MOVES EAST AS IT
BUMPS INTO THE RIDGING OVER THE EASTERN CONUS. DIFFERENCES BETWEEN
THE 25.12Z ECMWF AND GFS ON HOW FAST THE LONG WAVE TROUGH WILL
MOVE EAST WITH THE ECMWF BEING SLOWER THAN THE GFS. ALSO
DIFFERENCES ON HOW MUCH RIDGING WILL OCCUR BEHIND THIS LONG WAVE
TROUGH AHEAD OF THE NEXT SYSTEM MOVING ONTO THE PACIFIC NORTHWEST
COAST. WITH SUCH DIFFERENCES BETWEEN THE MODELS PLAN TO STAY WITH
THE MODEL CONSENSUS GRIDS AND SHOW RAIN CHANCES THROUGH MUCH OF
THE PERIOD WITH THE HIGHEST CHANCES THURSDAY AND THURSDAY NIGHT AS
THE FIRST SHORT WAVE TROUGH COMES ACROSS THE REGION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1258 PM CDT MON AUG 25 2014

VFR CONDITIONS ARE EXPECTED THROUGH THE FORECAST PERIOD. A COLD
FRONT WILL PUSH SOUTH AND EAST OF THE TAF SITES LATE THIS
AFTERNOON INTO THIS EVENING. THE FRONT LOOKS TO STALL OVER
PORTIONS OF CENTRAL OR NORTHERN IOWA INTO CENTRAL ILLINOIS AND
WILL BE THE FOCUS FOR SHOWERS AND STORMS. THIS ACTIVITY  WILL
REMAIN SOUTH OF THE TAF SITES THE NEXT FEW DAYS AS HIGH PRESSURE
BUILDS IN. PLAN ON MID TO HIGH CLOUDS PUSHING NORTH OF THE SHOWER
AND STORM ACTIVITY THIS EVENING INTO THE OVERNIGHT HOURS.


&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION...WETENKAMP


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