Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 252313
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
610 PM CDT TUE AUG 25 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 325 PM CDT TUE AUG 25 2015

CHALLENGES TONIGHT THROUGH WEDNESDAY INCLUDE CLOUD TRENDS...
TEMPERATURES AND FOG POTENTIAL. SOME DIFFERENCES BETWEEN MODELS
WITH REGARD TO HOW QUICKLY CLOUDS DISSIPATE AND MOVE OUT TONIGHT...
BUT OTHERWISE IN GOOD AGREEMENT AND WILL USE A BLENDED SOLUTION.

25.20Z SURFACE LOW ACROSS SOUTHERN HUDSON BAY WILL FINALLY BEGIN
TO LIFT NORTH AND EAST TONIGHT...ALLOWING EXPANSIVE STRATOCUMULUS
DECK ACROSS THE ENTIRE GREAT LAKES REGION TO SLOWLY MOVE OUT OF
THE FORECAST AREA. 25.18Z RAP 1 KM 90 PERCENT RELATIVE HUMIDITY
CONTOUR HAS BEEN A GOOD PROXY TO CURRENT CLOUD COVER AND SHOWS
MOST CLOUDS DISSIPATE AND/OR MOVE EAST OF THE FORECAST AREA BY
25.06Z. THIS IDEA IS ALSO SUPPORTED BY LATEST NSSL SYNTHETIC
IR...SO EXPECT CLEARING TO OVERSPREAD THE FORECAST AREA OVERNIGHT.
WITH LIGHT WINDS DEEPENING TO AROUND 2000 FT AGL BY 25.09Z...THINK
SOME VALLEY FOG IS POSSIBLE AND WILL CONTINUE TO MENTION IN LATEST
FORECAST. TEMPERATURES TONIGHT WILL BOTTOM OUT FROM THE MID 40S TO
LOWER 50S.

WEDNESDAY WILL BE MOSTLY SUNNY AND DRY AS SURFACE HIGH PRESSURE
SLIDES ACROSS THE UPPER MS RIVER VALLEY. WINDS WILL BE LIGHT FROM
THE NORTH-NORTHWEST WITH AFTERNOON HIGHS INTO THE UPPER 60S TO MID
70S.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 325 PM CDT TUE AUG 25 2015

SURFACE RIDGE AXIS MOVES OVER LAKE MICHIGAN BY 25.12Z...BUT LIGHT
WINDS WILL CONTINUE THROUGH THE MORNING...DEEPENING TO NEARLY 6000
FT AGL. FOG POTENTIAL WILL HINGE ON POSSIBLE HIGH CLOUDS...BUT
OTHERWISE A GOOD CHANCE AND WILL KEEP MENTION OF PATCHY VALLEY
FOG.

CLOUD COVER AND SOUTHERLY WINDS WILL INCREASE THROUGH THE DAY ON
THURSDAY AHEAD OF THE NEXT LOW PRESSURE SYSTEM. ANY PRECIPITATION
WILL REMAIN WEST OF THE FORECAST AREA...EXCEPT FOR A SMALL CHANCE
LATE IN THE EVENING MAINLY WEST OF THE HIGHWAY 52 CORRIDOR. RISING
925 TO 850 HPA TEMPERATURES WILL ALLOW AFTERNOON HIGHS TO REACH
THE MID TO UPPER 70S.

FRIDAY NOW LIKELY TO BE CLOUDY AND WET AS AN EASTERN PACIFIC
TROUGH UNDERCUTS THE WESTERN CONUS 500 HPA RIDGE AND MOVES INTO
THE UPPER MIDWEST. 25.12Z MODEL SUITE PRODUCES A WELL DEFINED
DEFORMATION PRECIPITATION AXIS ALONG ENHANCED 850 TO 700 HPA
FRONTOGENESIS NORTH OF THE SURFACE LOW. ALTHOUGH THE GFS/ECMWF
SURFACE LOW TRACKS ARE SIMILAR...MOVING FROM EAST-CENTRAL NE
ACROSS SOUTHERN IA THROUGH THE DAY...THE ECMWF PAINTS THE HIGHEST
RAINFALL A BIT FARTHER SOUTH COMPARED TO THE GFS/NAM WHICH ARE
HIGHEST ACROSS THE FORECAST AREA. THE PAST THREE RUNS OF THE GFS
HAVE BEEN SIMILAR...LENDING HIGHER CONFIDENCE TO ITS NORTHERN
SOLUTION. WILL INCREASE POPS INTO THE LIKELY CATEGORY ON FRIDAY.
HOWEVER...INSTABILITY STILL LOOKS VERY WEAK AND WILL CAP
THUNDERSTORM CHANCES TO 20 PERCENT WITH LIGHT TO MODERATE SHOWERS
BEING THE DOMINATE MODE. STILL A BIT EARLY TO GET TOO SPECIFIC
WITH RAINFALL AMOUNTS...BUT SOME AREAS COULD SEE AMOUNTS IN
EXCESS OF AN INCH THROUGH FRIDAY NIGHT. WITH CLOUDS AND RAIN...
FRIDAY WILL BE COOL WITH HIGHS IN THE UPPER 60S TO NEAR 70
DEGREES.

SOME LINGERING SHOWERS POSSIBLE SATURDAY...ESPECIALLY EAST OF THE
MS RIVER...BUT OTHERWISE SHOULD SEE IMPROVING CONDITIONS WITH
DECREASING CLOUD COVER AND RAIN CHANCES FROM WEST TO EAST. HIGHS
WILL REBOUND BACK INTO THE MID 70S. SUNDAY THROUGH TUESDAY LOOK
DRY WITH NO MAJOR SYSTEMS ON THE HORIZON. BIGGER CONCERN WILL BE
RISING TEMPERATURES AS 500 HPA RIDGE AXIS FOLDS OVER ACROSS THE
UPPER MIDWEST...RESULTING IN TEMPERATURES RISING INTO THE LOWER TO
MID 80S BY THE EARLY PART OF NEXT WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 610 PM CDT TUE AUG 25 2015

CLOUDS FINALLY SHOWING SIGNS OF GIVING WAY AND EASING EAST OF KLSE
EARLY THIS EVENING...PER SATELLITE TRENDS AND MESO MODELED RH
FIELDS. HIGH PRESSURE WORKS IN TONIGHT...AND WILL BE THE MAIN WEATHER
FEATURE THROUGH THU. WINDS WILL GENERALLY BE LIGHT AND NORTHERLY
THROUGH WED.

WITH THE HIGH OVERHEAD...AND LIGHT SFC WINDS...VALLEY FOG BECOMES A
CONCERN. KLSE T/TD DIFF AT 23Z WAS 17 F...GENERALLY GOOD FOR
OVERNIGHT FOG FORMATION. HOWEVER...A NORTH SFC WIND...EVEN
LIGHT...IS USUALLY A DETERRENT FOR DENSE FOG AT THE AIRPORT.
ALSO....RAP/NAM/HRRR BUFKIT SOUNDINGS KEEP WINDS STIRRED NEAR THE
SFC THROUGH 06Z. MIGHT BE TOO SHORT OF A TIME TO ALLOW FOR EXTENSIVE
FOG IN THE VALLEY. SO A FEW THINGS GOING FOR IT...AND A FEW NOT.
BCFG BKN003 LOOKS A BIT MORE LIKELY THAN SUB 1/2SM FG AT THIS TIME.
WILL LEAVE CURRENT FORECAST AS IT...AND FOLLOW EVENING TRENDS TO SEE
WHAT ADJUSTMENTS MAY BE NEEDED.

THU MORNING SHOWS MORE PROMISE FOR FG AT KLSE.

&&

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

$$

SHORT TERM...ROGERS
LONG TERM...ROGERS
AVIATION...RIECK



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