Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 011748
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1248 PM CDT TUE SEP 1 2015

.SHORT TERM...(TODAY THROUGH TONIGHT)
ISSUED AT 316 AM CDT TUE SEP 1 2015

WATER VAPOR SATELLITE IMAGERY AND RAP ANALYSIS EARLY THIS MORNING
SHOWING A LARGE/DEEP CLOSED LOW ALONG THE COAST OF BRITISH COLUMBIA
WITH DOWNSTREAM RIDGE IN PLACE ACROSS THE EASTERN CONUS/UPPER
MISSISSIPPI RIVER VALLEY REGION.  FAIRLY MUGGY AIRMASS IN PLACE
ACROSS THE AREA WITH TEMPERATURES AS OF 3 AM IN THE MIDDLE 60S TO
LOWER 70S WITH DEW POINTS IN THE MIDDLE/UPPER 60S. ALSO SOME AREAS
OF FOG IN HUMID SOUTHERLY FLOW ACROSS PORTIONS OF NORTHEAST
IA/SOUTHEAST MN.

FOR TODAY...LOOK FOR ANY FOG/STRATUS TO BURN OFF BY MID-MORNING.
MEANWHILE...EMBEDDED WEAK MID-LEVEL TROUGH IN GENERAL SOUTHWEST FLOW
ALOFT HEADING NORTHEAST ACROSS NORTHERN WI INTO CANADA EARLY THIS
MORNING AND SHOULD KEEP ANY SHOWER CHANCES NORTH OF OUR FORECAST
AREA. INTERIM RIDGE BUILDS IN THE REST OF TODAY WITH FAIRLY STRONG
800-750MB SUBSIDENCE INVERSION/CAP IN PLACE. WILL SEE SOME CUMULUS
DEVELOPMENT BELOW THE INVERSION...BUT SHOULD REMAIN DRY.
OTHERWISE...MAIN STORY WILL BE HEAT AS HIGHS TOP OFF WELL INTO THE
80S WITH A FEW SPOTS NEARING 90 ACROSS FAR SOUTHWEST WI. COMBINE
THESE TEMPERATURES WITH DEW POINTS IN THE UPPER 60S/LOWER 70S AND
HEAT INDICES IN THE 90S ALONG AND SOUTH OF I-94 WILL BE SEEN.

FOR TONIGHT...MODELS DEPICTING A MID-LEVEL TROUGH EJECTING OUT OF
THE CENTRAL PLAINS TOWARD THE UPPER MISSISSIPPI RIVER REGION. NAM
SHOWING A DECENT SURGE OF 950-700MB MOISTURE TRANSPORT AHEAD OF THE
WAVE. AS A RESULT...WILL BRING A SLIGHT CHANCE OF
SHOWERS/THUNDERSTORMS INTO THE AREA AFTER MIDNIGHT. OTHERWISE...
ANOTHER MUGGY NIGHT IN STORE WITH LOWS ONLY DROPPING INTO THE MIDDLE
60S TO THE LOWER 70S.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 316 AM CDT TUE SEP 1 2015

MODELS SHOW THAT MID-LEVEL TROUGH MENTIONED ABOVE MOVING ACROSS THE
AREA WEDNESDAY/WEDNESDAY NIGHT. COOLER AIR ALOFT/STEEPER MID-LEVEL
LAPSE RATES WILL SERVE AS TRIGGER FOR SCATTERED
SHOWERS/THUNDERSTORMS. NAM DEPICTING 0-3KM MUCAPE IN THE 4-5KJ/KG BY
AFTERNOON BUT MAY BE A BIT OVERDONE GIVEN ITS HIGHER DEWPOINT BIAS.
BULK SHEAR ONLY 15-20KT. SO...LOOKING FOR MAINLY PULSE TYPE
THUNDERSTORMS. CANNOT RULE OUT SOME SUB-SEVERE HAIL AND WIND WITH
THE STRONGER STORMS DURING THE LATE AFTERNOON. MEANWHILE...VERY
WARM/MUGGY CONDITIONS CONTINUE WITH HIGHS WELL INTO THE 80S/FEW
LOWER 90S WITH HEAT INDICES IN THE UPPER 80S TO MIDDLE 90S.

STILL A CHANCE OF A FEW LINGERING SHOWER/STORMS THURSDAY MAINLY EAST
OF THE MISSISSIPPI RIVER AS THE WAVE DEPARTS OFF TO THE EAST. LOOK
FOR HIGHS WELL INTO THE 80S AGAIN WITH HEAT INDICES AGAIN IN THE
UPPER 80S TO THE MIDDLE 90S.

THURSDAY NIGHT THROUGH SATURDAY NIGHT LOOKS LIKE A DRY PERIOD AS
LATEST GFS/NAM SHOWING MID/UPPER RIDGE AMPLIFICATION ACROSS THE
REGION. IT WILL REMAIN VERY WARM AND MUGGY THROUGH THIS PERIOD WITH
HIGHS FRIDAY AND SATURDAY STAYING WELL INTO THE 80S/NEAR 90.
OVERNIGHT LOWS LOOK TO REMAIN IN THE MIDDLE 60/NEAR 70 RANGE.

SHOWER/THUNDERSTORM CHANCES INCREASE SUNDAY AFTERNOON INTO LABOR DAY
AS BOTH THE ECMWF/GFS BREAK DOWN THE RIDGE WITH APPROACHING NORTHERN
PLAINS TROUGH/COLD FRONT. CONFIDENCE INCREASING ENOUGH TO GO WITH
LIKELY POPS SUNDAY NIGHT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1248 PM CDT TUE SEP 1 2015

A SHORTWAVE TROUGH WILL APPROACH THE REGION FROM NEBRASKA/SOUTH
DAKOTA TONIGHT BRINGING INCREASING HIGH AND MID LEVEL CLOUDS TO
THE TAF SITES ALONG WITH THE POSSIBILITY OF SOME SHOWERS AND
THUNDERSTORMS LATE TONIGHT INTO WEDNESDAY MORNING. AHEAD OF THE
TROUGH WINDS WILL INCREASE INTO THE 25 TO 30 KT RANGE FROM 500
THROUGH AROUND 2 FT. THINKING SURFACE WINDS WILL STAY UP JUST
ENOUGH TO PREVENT LLWS BUT WILL HAVE TO KEEP A CLOSE EYE ON
SURFACE WINDS TONIGHT. WITH THESE WINDS INCREASING WE SHOULD SEE
ENOUGH MIXING TO PREVENT FOG BUT CANNOT RULE OUT SOME MVFR
VISIBILITIES IN HAZE WITH SOME SMOKE ACROSS THE REGION COMBINED
WITH A MOIST AIRMASS. HAVE KEPT THUNDERSTORMS OUT OF THE TAFS AT
THIS TIME WITH LOW CONFIDENCE THAT THEY WILL IMPACT THE TAF SITES.
MAY HAVE TO INCLUDE THEM IN THE KRST TAF IF MESOSCALE MODEL TRENDS
CONTINUE THIS AFTERNOON.

&&

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

$$

SHORT TERM...DAS
LONG TERM...DAS
AVIATION...WETENKAMP


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