Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 250434
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1133 PM CDT MON AUG 24 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 306 PM CDT MON AUG 24 2015

MAIN CONCERNS TONIGHT THROUGH TUESDAY INCLUDE CLOUD COVER...WIND
AND TEMPERATURES. 24.12Z GLOBAL MODEL SUITE IN GOOD AGREEMENT AND
WILL USE A BLENDED APPROACH FOR FORECAST.

24.20Z SURFACE ANALYSIS SHOWS A STRONG LOW PRESSURE SYSTEM ACROSS
EASTERN ONTARIO WITH AN ELONGATED HIGH PRESSURE AXIS ACROSS THE
CENTRAL DAKOTAS INTO EASTERN NE/KS. EXPANSIVE STRATOCUMULUS DECK
ACROSS MUCH OF EASTERN MN/WI WILL SHRINK IN COVERAGE AFTER SUNSET
WITH CLEARING OCCURRING ACROSS MOST OF THE FORECAST AREA. THE
EXCEPTION BEING ACROSS NORTHERN WI CLOSER TO THE SURFACE LOW. ALSO
EXPECT BREEZY NORTHWEST WINDS TO DIMINISH OVERNIGHT WITH NOCTURNAL
INVERSION. IMMEDIATELY ABOVE THE INVERSION...NORTHWEST WINDS FROM
15 TO 25 KTS WILL PREVENT ANY VALLEY FOG FORMATION.

STUBBORN SURFACE LOW ACROSS EASTERN ONTARIO WILL MAKE VERY LITTLE
EASTWARD PROGRESS ON TUESDAY...BUT LOW PRESSURE CENTER WILL BEGIN
TO FILL...INCREASING 5-6 HPA OVER 24 HOURS. THIS WILL ALLOW
SURFACE PRESSURE GRADIENT TO WEAKEN THROUGH THE DAY. ONLY AROUND
20 KTS WITHIN THE MIXED BOUNDARY LAYER TUESDAY AFTERNOON...SO
NORTHWEST BREEZES FROM 10 TO 15 MPH SEEM REASONABLE. WILL STILL
SEE AFTERNOON CUMULUS DEVELOP AS CONVECTIVE TEMPERATURES ARE
REACHED...BUT SHOULD BE CONFINED MAINLY TO AREAS NORTH AND EAST OF
THE I-94 CORRIDOR. MOST OTHER AREAS LIKELY TO REMAIN MOSTLY TO
PARTLY SUNNY. TEMPERATURES WILL BE SIMILAR TO TODAY...POSSIBLY A
DEGREE OR TWO WARMER IN PLACES THAT SEE A BIT MORE SUNSHINE.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 306 PM CDT MON AUG 24 2015

SURFACE HIGH PRESSURE WILL BE FIRMLY IN CONTROL TUESDAY NIGHT
THROUGH THURSDAY. ALTHOUGH THIS PERIOD WILL BE PRECIPITATION
FREE...DID ADD PATCHY VALLEY FOG BOTH WEDNESDAY AND THURSDAY
MORNINGS FROM 09-15Z GIVEN CLEAR SKIES AND RELATIVELY DEEP LIGHT
WINDS AS SURFACE RIDGE AXIS SLIDES ACROSS THE UPPER MS RIVER
VALLEY. TEMPERATURES WILL MODERATE WEDNESDAY/THURSDAY AS LOW-MID
LEVEL THERMAL RIDGE PUSHES EAST. MOST AREAS SHOULD CLIMB BACK INTO
THE 70S BY THURSDAY.

THE NEXT BEST CHANCE FOR SHOWERS AND THUNDERSTORMS WILL BE
THURSDAY NIGHT THROUGH FRIDAY AS A BROAD EASTERN PACIFIC TROUGH
UNDERCUTS THE 500 HPA ROCKIES RIDGE AND MOVES INTO THE CENTRAL
PLAINS. COMPARED TO YESTERDAY/S 12Z MODEL RUNS...THE GFS/ECMWF
HAVE FLIP-FLOPPED WITH THE GFS NOW MUCH WETTER COMPARED TO THE
DRIER ECMWF. THIS APPEARS DUE TO THE FACT THAT THE ECMWF DROPS
THE TROUGH FARTHER SOUTH...PLACING MOST OF ITS PRECIPITATION
ACROSS IA/MO. IN BOTH MODELS...INSTABILITY IS RATHER WEAK...SO NOT
EXPECTING ANY SEVERE CONVECTION. WILL MAINTAIN CHANCE POPS FOR
THIS PERIOD UNTIL BETTER MODEL CONSENSUS IS REACHED. WITH CLOUD
COVER AND POSSIBLE RAIN...FRIDAY/S TEMPERATURES WILL TAKE A BIT OF
A HIT...BUT STILL TOP OUT IN THE LOWER TO MID 70S.

LINGERING RAIN CHANCES SATURDAY MAINLY EAST OF THE MS RIVER BEFORE
A RETURN TO DRY CONDITIONS SUNDAY/MONDAY. 500 HPA RIDGE FINALLY
MOVES EAST AS A LARGE PACIFIC TROUGH CRASHES ONTO THE PACIFIC
NORTHWEST COAST LATE IN THE PERIOD. MAIN IMPACT WILL BE WARMING
TEMPERATURES WITH AFTERNOON HIGHS LIKELY TO CRACK THE 80 DEGREE
MARK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1133 PM CDT MON AUG 24 2015

WILL BE DEALING WITH CONTINUED HIGHER BASED AND THIN STRATUS DECK AS
IT ROTATES AROUND LARGE UPPER LOW OVER SOUTHERN ONTARIO. ALTHOUGH
VFR THROUGHOUT...TYPICAL CHALLENGE IS TRYING TO TIME EVENTUAL
CLEARING. BACK EDGE IS VERY PERSISTENT AND CONSISTENT THIS
EVENING... AND WITH SHORT TERM GUIDANCE SUGGESTING ANOTHER MINOR
WAVE AROUND BACKSIDE OF LOW BRINGING REINFORCEMENT OF CLOUDS...
HAVE SLOWED DOWN CLEARING TREND EVEN MORE.

AFTER 25.18Z THOUGH...PRETTY GOOD SIGNAL FOR MOISTURE TO RETREAT
EAST SO EXPECT CLEARING TO WORK IN BY TUESDAY EVENING AS WINDS
CONTINUE TO DIMINISH AS WELL.

GRADIENT WILL HAVE TO BE WATCHED LOOKING AHEAD TO WEDNESDAY MORNING
FOR VALLEY FOG GIVEN LIGHTER WINDS.

&&

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

$$

SHORT TERM...ROGERS
LONG TERM...ROGERS
AVIATION...SHEA


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