Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 310840
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
340 AM CDT MON AUG 31 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 340 AM CDT MON AUG 31 2015

EARLY THIS MORNING...LOW STRATUS HAS QUICKLY DEVELOPED ACROSS
NORTH-CENTRAL IA AND ALONG THE MN/IA BORDER AS WELL AS ACROSS
NORTHERN WI. 31.07Z RAP SHOWS THIS STRATUS FILLING-IN ACROSS MUCH
OF THE FORECAST AREA BY SUNRISE. THESE CLOUDS...COMBINED WITH
BRISK WEST-SOUTHWEST WIND JUST OFF THE SURFACE SHOULD PRECLUDE
WIDESPREAD DENSE FOG...BUT CAN STILL EXPECT SOME AREAS OF REDUCED
VISIBILITY...ESPECIALLY FOR THOSE AREAS THAT REMAIN MOSTLY CLEAR
FOR A LONGER PERIOD.

AS QUICKLY AS THE STRATUS DEVELOPS...MOST HIGH RESOLUTION MODELS
DISSIPATE IT JUST AS QUICKLY BY LATE MORNING AS 15 TO 20 KTS MIX
WITHIN DEEPENING BOUNDARY LAYER. EXPECT A RETURN TO AT LEAST
PARTLY SUNNY SKIES BY EARLY AFTERNOON. PRIMARY IMPACT OF CLOUDS
WILL BE TO SLOW TEMPERATURE RISE THROUGH THE DAY...SO DROPPED
AFTERNOON HIGHS A FEW DEGREES INTO THE LOWER TO MID 80S.

TONIGHT NOT LIKELY TO BE COMPLETELY CLOUD FREE AND WITH 10 TO 20
KTS ATOP NOCTURNAL INVERSION...FOG THREAT SHOULD BE LOWER THAN THE
PAST COUPLE NIGHTS. TEMPERATURES WILL DROP INTO THE MID TO UPPER
60S.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 340 AM CDT MON AUG 31 2015

MAIN STORY FOR THE WEEK CONTINUES TO BE WELL ABOVE NORMAL
TEMPERATURES WITH A BROAD 500 HPA RIDGE PARKED ACROSS THE EASTERN
CONUS. WITH 925 HPA TEMPERATURES GENERALLY WOBBLING BETWEEN 24 AND
26 CELSIUS...DAILY HIGHS HIGHS WILL TOP OUT IN THE MID TO UPPER
80S WITH SOME 90 PLUS DEGREE READINGS ALONG AND EAST OF THE MS
RIVER.

WILL KEEP 20-30 PERCENT MODEL CONSENSUS POPS WEDNESDAY NIGHT
THROUGH FRIDAY...BUT THINK MAJORITY OF THE WEEK WILL REMAIN DRY.
MULTIPLE WEAK/ILL-RESOLVED SHORT-WAVES MOVE ACROSS THE REGION IN
SOUTHWEST FLOW ALOFT THAT COULD PROVIDE A FOCUSING MECHANISM FOR
CONVECTION. HOWEVER...AXIS OF MAXIMUM MID-LEVEL MOISTURE TRANSPORT
REMAINS WEST OF THE FORECAST AREA...CLOSER TO THE WESTERN CONUS
TROUGH. DAILY INSTABILITY IS PRESENT WITH ABOVE NORMAL TEMPERATURES/
SURFACE DEWPOINTS IN THE 60S...BUT LARGE SCALE RIDGE SQUASHES ANY
DEEP LAYER SHEAR OF SIGNIFICANCE. FOR NOW...DIFFICULT TO PROVIDE
DETAILS ON TIMING OR COVERAGE IF ANYTHING DOES DEVELOP SO BROAD-
BRUSHED POPS SEEM REASONABLE.

BETTER CHANCES FOR SHOWERS AND THUNDERSTORMS RETURN SATURDAY NIGHT
INTO SUNDAY AS 31.00Z GFS/ECMWF ATTEMPT TO BREAK DOWN EASTERN
CONUS RIDGE BY MOVING A BROAD PACIFIC TROUGH INTO THE ROCKIES/
NORTHERN PLAINS. GFS IS MUCH QUICKER IN DOING SO COMPARED TO THE
SLOWER ECMWF...SO DEFINITE TIMING ISSUES EMERGE. FOR NOW...A
BLENDED APPROACH IS PRUDENT RESULTING IN CHANCE POPS SATURDAY
NIGHT THROUGH THE DAY ON SUNDAY. SHOULD SEE TEMPERATURES FALL BACK
TO MORE SEASONABLE LEVELS ONCE TROUGH PASSES...BUT WHETHER THIS
OCCURS BY SUNDAY OR EARLY NEXT WEEK IS YET TO BE SEEN.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1125 PM CDT SUN AUG 30 2015

LIGHT SFC WINDS...HIGH PRESSURE IN THE VICINITY...AND T/TD SPREAD
AROUND 2 F AT LATE EVENING ALL SUPPORT DENSE FOG IN THE RIVER VALLEY
AT KLSE. HOWEVER...THE DEPTH OF THE LIGHT WIND LAYER DOES NOT.
BUFKIT HRRR/RAP/NAM SOUNDINGS ALL POINT TO 10+ KTS OF WIND WITHIN A
COUPLE HUNDRED FEET OF THE SURFACE. THIS STIRRING GENERALLY
PRECLUDES DENSE FOG FORMATION IN THE VALLEY - OR AT LEAST ITS
ABILITY TO SPREAD. IN ADDITION...IT CAN WORK AGAINST A LOW STRATUS
LAYER DEVELOPING. HOWEVER...WITH WIDESPREAD LOW LEVEL SATURATION
ACROSS THE REGION...MVFR BR IS CERTAINLY POSSIBLE...AT KLSE AND
KRST.

AS FOR CIGS...HRRR/RAP INCREASE THE LOW SATURATION ACROSS THE
SOUTH...WHICH COULD MANIFEST AS LOW STRATUS AND/OR THICK FOG. LATEST
RUNS KEEP THIS STRATUS/FOG THREAT SOUTH OF THE TAF SITES...AND WILL
HAVE THE FORECAST FOLLOW SUIT.

IT WILL BE ANOTHER EARLY MORNING OF CLOSELY FOLLOWING
OBS/TRENDS...WITH UPDATES MADE IF NEEDED.

&&

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

$$

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


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