Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 212009
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
309 PM CDT MON APR 21 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 309 PM CDT MON APR 21 2014

MAIN FORECAST CONCERN IS WITH THE RAIN CHANCES WEDNESDAY AND
WEDNESDAY NIGHT.

SURFACE ANALYSIS EARLY THIS AFTERNOON INDICATES THE MAIN COLD
FRONT EXTENDED FROM NORTHERN WISCONSIN INTO SOUTHWEST IOWA CUTTING
ACROSS THE FORECAST AREA. LOCAL AND REGIONAL RADARS INDICATE WHAT
REMAINS OF THE SHOWERS WAS OUT AHEAD OF THE FRONT ACROSS EASTERN
WISCONSIN INTO EASTERN IOWA WITH SOME ACTIVITY STILL OVER
SOUTHWEST WISCONSIN. GIVEN THE MOVEMENT OF THIS ACTIVITY AND THE
FRONT...EXPECT THAT THIS WILL BE OUT OF THE FORECAST AREA BY 00Z
AND DO NOT PLAN TO HAVE ANY EVENING RAIN CHANCES IN THE FORECAST.
HIGH PRESSURE THEN BUILDS IN FROM THE NORTH TO DRY THINGS OUT
THROUGH TUESDAY NIGHT.

THE NEXT CHANCE FOR RAIN WILL MOVE BACK INTO THE AREA STARTING
WEDNESDAY. SHORT WAVE TROUGHS COMING ONTO THE PACIFIC COAST
TONIGHT WILL CROSS THE ROCKIES WEDNESDAY AND THEN MOVE OUT OVER
THE HIGH PLAINS AND UPPER MISSISSIPPI RIVER VALLEY WEDNESDAY
NIGHT. THE SHORT WAVE TROUGHS REMAINING NORTHWEST OF THE AREA
THROUGH WEDNESDAY...BOTH THE 21.12Z NAM AND GFS SHOW THE BEST PV
ADVECTION IN THE 500-300 MB LAYER ALSO STAYING TO THE NORTHWEST.
THAT WILL LEAVE THE LOW LEVEL THERMODYNAMIC FORCING AS THE PRIMARY
DRIVER FOR THE RAIN CHANCES. A SURFACE LOW WILL FORM WEDNESDAY IN
THE LEE OF THE SOUTHERN CANADIAN ROCKIES WITH A WARM FRONT
EXTENDING SOUTHEAST TO ANOTHER SURFACE LOW THAT SHOULD FORM OVER
EASTERN SOUTH DAKOTA OR NEBRASKA. THIS WHOLE COMPLEX WILL SHIFT
EAST WEDNESDAY NIGHT WITH THE WARM FRONT MAKING IT INTO WESTERN
MINNESOTA AND IOWA WITH THE SOUTHERN SURFACE LOW OVER IOWA OR
SOUTHERN MINNESOTA. INITIALLY THE FRONTOGENESIS DOES NOT LOOK TO
BE VERY WELL ORGANIZED AND JUST WEAK OVER THE AREA IN THE 850-500
MB LAYER AND THEN THE GFS SHOWS THIS DEEPENING INTO THE 1000-500
MB LAYER LATE WEDNESDAY NIGHT. THE ISENTROPIC UP GLIDE BEGINS TO
MOVE IN WEDNESDAY AFTERNOON ON THE 300K SURFACE AND INCREASES TO
AROUND 5 UBAR/S WEDNESDAY NIGHT. ALSO LATE WEDNESDAY NIGHT...THE
FIRST OF THE SHORT WAVE TROUGHS SHOULD START TO WORK ACROSS THE
AREA WITH THE GFS SHOWING THE PV ADVECTION IN THE 500-300 MB LAYER
BECOMING MODERATE IN STRENGTH.

WILL SHOW THE RAIN CHANCES MOVING INTO THE WESTERN SECTIONS
WEDNESDAY MORNING AND THEN OVERSPREADING THE ENTIRE AREA WEDNESDAY
AFTERNOON. WITH THE INCREASE IN THE ISENTROPIC UP GLIDE WEDNESDAY
AFTERNOON...MAINTAINED 60 TO 70 PERCENT RAIN CHANCES FOR A GOOD
SHARE OF THE AREA. LITTLE OVERALL CHANGE IN THE RAIN CHANCES
WEDNESDAY EVENING...OTHER THAN EXPANDING THE 60 TO 70 PERCENT TO
COVER ALMOST THE ENTIRE AREA. THEN AS THE PV ADVECTION INCREASES
ALONG WITH THE LOW LEVEL JET INTO THE AREA...UPPED THE RAIN
CHANCES TO 80 TO 90 PERCENT OVERNIGHT WEDNESDAY FOR ALMOST THE
ENTIRE AREA. NEITHER THE NAM OR GFS SHOWS HARDLY ANY CAPE COMING
INTO THE REGION DURING THIS PERIOD...SO LIMITED THE THUNDER
CHANCES TO WEDNESDAY NIGHT WHEN THE FORCING LOOKS TO BE THE BEST
AND JUST WENT WITH AN ISOLATED MENTION.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 309 PM CDT MON APR 21 2014

ANOTHER ROUND OF MODERATE TO STRONG PV ADVECTION WILL COME ACROSS
THE AREA THURSDAY AS THE MAIN SHORT WAVE TROUGH ROTATES ACROSS
THE AREA AHEAD OF THE UPPER LEVEL LOW TRACKING ACROSS THE UPPER
MIDWEST TOWARD THE GREAT LAKES. THE GFS SUGGESTS THE FRONTOGENESIS
WILL STILL NOT BE WELL ORGANIZED AND WILL CONTINUE TO BE WEAK IN
THE 1000-500 MB LAYER. THE ISENTROPIC UP GLIDE WILL STILL BE OVER
THE EASTERN SECTIONS OF THE AREA THURSDAY MORNING BUT THEN MOVE
OUT WITH THE PASSAGE OF THE SHORT WAVE TROUGH. WITH THE GOOD
FORCING...MAINTAINED A 70 TO 80 PERCENT RAIN CHANCE ACROSS THE
ENTIRE AREA THURSDAY MORNING FOR THE ENTIRE AREA AND THEN ACROSS
THE NORTHEAST SECTIONS THURSDAY AFTERNOON WITH A LOWERING BACK TO
ABOUT 50 PERCENT ACROSS THE WEST. IF THE MODELS ARE CORRECT...THE
CAPE REALLY DOES NOT ARRIVE UNTIL THURSDAY AFTERNOON WHEN THE
FRONT MOVES THROUGH ALLOWING THE WARMER AIR TO START SPREADING IN.
IF THIS IS CORRECT...THERE MAY NOT BE A WHOLE LOT OF STORMS WITH
THIS ENTIRE SYSTEM AND CUT BUT ON THE THUNDER CHANCES THURSDAY
MORNING...BUT MAINTAINED THE WIDESRPEAD CHANCES THURSDAY
AFTERNOON. AS FOR SEVERE CHANCES THROUGH THIS ENTIRE PERIOD...IT
LOOKS LIKE AMPLE 0-6KM SHEAR SHOULD BE IN PLACE...SO CAPE LOOKS
TO BE THE LIMITING FACTOR. CAN NOT TOTALLY RULE OUT SOME SEVERE
THREAT...BUT UNLESS MORE WIDESPREAD CAPE ARRIVES THAN WHAT THE
MODELS CURRENTLY INDICATE...WOULD NOT EXPECT ANYTHING MORE THAN
SOME ISOLATED SEVERE STORMS AT BEST.

ONCE THIS SYSTEM MOVES OUT...THE 21.12Z ECMWF HAS TRENDED TOWARD
THE GFS SOLUTIONS OF SHOWING STRONGER RIDGING BOTH ALOFT AND AT
THE SURFACE OVER THE UPPER MIDWEST FOR THE REMAINDER OF THE
PERIOD. HOWEVER...THE ECMWF STILL IS NOT AS STRONG AS THE GFS WITH
THE UPPER LEVEL RIDGING AND ALLOWS A COUPLE OF WEAK SHORT WAVE
TROUGHS TO COME ACROSS OVER THE WEEKEND. WITH THE STRONGER SURFACE
HIGH THOUGH...IT LIMITS THE RAIN CHANCES TO MAINLY SOUTHERN
MINNESOTA AND WISCONSIN AND SOUTHWARD. MADE SOME COLLABORATED
ADJUSTMENTS TO THE PRECIPITATION CHANCES SUNDAY THROUGH MONDAY TO
REFLECT THE MORE SOUTHWARD TREND OF THE PRECIPITATION.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1255 PM CDT MON APR 21 2014

A COLD FRONT WILL PUSH EAST OF THE TAF SITES THIS AFTERNOON AS
HIGH PRESSURE STARTS TO BUILD IN FROM THE NORTHERN PLAINS. A BKN
MVFR STRATUS DECK WILL SCATTER OUT AND EVENTUALLY CLEAR THIS
AFTERNOON AS DRIER AIR PUSHES IN FROM THE NORTHWEST. PLAN ON GUSTY
NORTHWEST WINDS OF 17 TO 20 KTS THIS AFTERNOON WITH GUSTS IN THE
25 TO 30 KT RANGE. THE WINDS WILL SUBSIDE INTO THE 7 TO 10 KT
RANGE LATE THIS EVENING. VFR CONDITIONS ARE EXPECTED FROM LATE
THIS AFTERNOON THROUGH THE OVERNIGHT HOURS INTO TUESDAY MORNING.


&&

.HYDROLOGY...
ISSUED AT 1255 PM CDT MON APR 21 2014

MINOR FLOODING CONTINUES ON THE MISSISSIPPI RIVER AT MCGREGOR.
ALONG THE MISSISSIPPI RIVER...RIVER LEVELS ARE EXPECTED TO
GRADUALLY FALL THROUGH MID WEEK BUT THEN WILL LEVEL OFF OR RISE
SLIGHTLY AS RUNNOFF FROM SNOWMELT OVER NORTHWEST WISCONSIN AND
CENTRAL INTO PORTIONS OF NORTHERN MINNESOTA MAKES ITS WAY INTO THE
LOCAL AREA. RIVER LEVELS ARE EXPECTED TO REMAIN ELEVATED INTO NEXT
WEEK.

&&

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

$$

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



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