Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 301727
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1227 PM CDT SUN AUG 30 2015

...UPDATE...
ISSUED AT 905 AM CDT SUN AUG 30 2015

VISIBILITIES IN THE FOG ACROSS PORTION OF SOUTHEAST MN/NORTHEAST IA
AND NORTH-CENTRAL WI WERE STEADILY IMPROVING AS OF 14Z...WITH ANY
DENSE FOG IN THESE AREAS BECOMING QUITE PATCHY. THUS THE DENSE FOG
ADVISORY WAS ALLOWED TO EXPIRE AT 9 AM. SOME PATCHY DENSE FOG
REMAINED IN THE MS/WI RIVER VALLEYS. WILL CONTINUE TO HANDLE THIS
WITH AN SPS STATEMENT. THIS FOG IS EXPECTED TO THIN/DISSIPATE
THROUGH 1030 AM.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 341 AM CDT SUN AUG 30 2015

MOST IMMEDIATE CONCERN IS PATCHY DENSE FOG EARLY THIS MORNING.
BECAUSE NOT ALL LOW CLOUD FROM YESTERDAY DISSIPATED AND THE FACT
THAT 0.5 KM SOUTHWEST WINDS ARE INCREASING FROM NOW UNTIL
SUNRISE...WIDESPREAD DENSE FOG IS IN QUESTION. THERE HAVE BEEN
SOME SITES ACROSS THE REGION THAT HAVE REPORTED ONE-HALF MILE OR
LESS IN FOG...BUT NOT CONSISTENTLY AS VISIBILITY GOES UP AND DOWN
OVER RELATIVELY SHORT PERIODS. FOR NOW...WILL COVER FOG THREAT
WITH A SPS...BUT MONITOR CAREFULLY FOR MORE WIDESPREAD PERSISTENT
LOW VISIBILITY THAT COULD NECESSITATE AN ADVISORY.

WHETHER STRATUS OF FOG...MOST AREAS SHOULD WAKE UP TO GRAY/FOGGY
SKIES. HOWEVER...LOW-LEVEL MOISTURE SHOULD BEGIN TO MIX OUT AFTER
SUNRISE AS BOUNDARY LAYER DEEPENS TO BETWEEN 1500 AND 2000 FT BY
MIDDAY. SHOULD FINALLY BEGIN TO SEE A FAIR AMOUNT OF SUN BY EARLY
TO MID AFTERNOON. WITH A SLOW START TO WARMING FOR THE DAY...
DROPPED TEMPERATURES A FEW DEGREES WITH HIGHS NOW EXPECTED IN THE
MID TO UPPER 70S. FOR AREAS THAT SEE A BIT MORE SUN...HIGHS MAY
WARM INTO THE LOWER 80S.

EXPECT MOSTLY CLEAR SKIES TONIGHT WITH LIGHT SOUTHERLY WINDS. WILL
KEEP PATCHY VALLEY/BOG FOG MENTION...BUT ITS OCCURRENCE IS A BIT
LESS CERTAIN. MODEL SOUNDINGS SHOWING NEAR SURFACE SATURATION...
BUT ALSO 15 TO 20 KTS IMMEDIATELY ABOVE THE NOCTURNAL INVERSION.
THIS SET-UP MAY BE MORE FAVORABLE FOR LOW STRATUS THAN FOG...BUT
SOMETHING TO WATCH. LOWS TONIGHT WILL DROP INTO THE 60S.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 341 AM CDT SUN AUG 30 2015

MONDAY THROUGH WEDNESDAY...500 HPA RIDGE MOVES INTO THE EASTERN
CONUS...ALTHOUGH PERHAPS A BIT FLATTER THAN PREVIOUSLY FORECAST
GIVEN WEAK SHORT-WAVES MOVING THROUGH SOUTHWEST FLOW ALOFT. MAIN
IMPACT WILL BE WARMING TEMPERATURES WITH DAILY HIGHS IN THE 80S...
ALTHOUGH SOME VALLEY LOCATIONS COULD APPROACH 90 DEGREES GIVEN
FAVORABLE SOUTH-SOUTHWEST SURFACE WIND. RIDGE AXIS RETROGRADES
BACK ACROSS THE SOUTHERN PLAINS FOR LATE IN THE WEEK...RESULTING
IN THUR/FRI/SAT POSSIBLY BEING THE WARMEST DAYS OF THE WEEK WITH
MANY LOCATIONS INTO THE UPPER 80S...PERHAPS 90 DEGREES.

WILL KEEP PERIODIC 20-30 POPS THROUGH THE WEEK...ALTHOUGH THINK
DRY CONDITIONS WILL BE THE RULE SINCE AXIS OF MAXIMUM MID-LEVEL
MOISTURE TRANSPORT REMAINS MAINLY WEST OF THE FORECAST AREA AND
DEEP LAYER SHEAR IS WEAK. BEST CHANCE FOR MORE WIDESPREAD SHOWERS
AND THUNDERSTORMS HOLDS OFF UNTIL LATE SATURDAY INTO SUNDAY AS
EASTERN PACIFIC TROUGH/COLD FRONT FINALLY PUSH FAR ENOUGH EAST TO
IMPACT THE UPPER MS RIVER VALLEY. WILL INTRODUCE HIGH END CHANCE
POPS FOR THIS PERIOD. WITH CLOUDS/POSSIBLE RAIN AND APPROACHING
COLD FRONT...COULD SEE TEMPERATURES BEGIN TO RETREAT AS EARLY AS
NEXT SUNDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1227 PM CDT SUN AUG 30 2015

MVFR STRATO-CU REMAIN PROBLEMATIC EARLY THIS AFTERNOON. HOWEVER...
VIS IMAGERY SHOWED THE LOWER CLOUD DECK WAS ERODING WITH DIURNAL
WARMING/MIXING AND INCREASING SOUTHWEST FLOW IN THE SFC-900MB LAYER.
APPEARS DECK WILL BREAK UP AT KRST AROUND 19Z AND AROUND 20Z AT
KLSE. GOOD VFR EXPECTED FOR THE LATE AFTERNOON AND EVENING
HOURS...BEING AIDED BY MORE SOUTHWEST WIND IN THE SFC-900MB LAYER
FOR STIRRING/MIXING. STILL A SIGNAL FOR SOME INCREASE OF 925MB
MOISTURE TO SPREAD NORTHEAST ACROSS IA TONIGHT...WITH LOWER CLOUDS
RETURNING FOR LATER TONIGHT. THE MOISTURE APPEARS QUITE SHALLOW AND
WITH AROUND 25KTS OF WIND JUST ABOVE THE NOCTURNAL INVERSION THERE
MAY BE TOO MUCH FLOW FOR A SOLID CLOUD DECK WITH THE SHALLOW/THIN
MOISTURE LAYER. LEFT CLOUDS LATE TONIGHT AS A SCT005 LAYER. WILL
HAVE TO WATCH TO OUR SOUTH ACROSS IA LATER TONIGHT IF THERE MAY BE A
MORE SOLID LOW CLOUD DECK ADVECTING NORTHEAST. THE WINDS JUST ABOVE
THE INVERSION LAYER TO HELP KEEP LATE NIGHT/EARLY MORNING BR/FG TO A
MINIMUM AS WELL. DIURNAL WARMING/MIXING EXPECTED TO RESULT IN SCT
CUMULUS ON MONDAY.

&&

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

&&

$$

UPDATE.......RRS
SHORT TERM...ROGERS
LONG TERM....ROGERS
AVIATION.....RRS


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