Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 011916
AFDARX

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

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY)
ISSUED AT 216 PM CDT TUE SEP 1 2015

SULTRY START TO SEPTEMBER WITH BROAD UPPER RIDGE ACROSS MUCH OF
CENTRAL AND EASTERN U.S.  FOCUS IN SHORT TERM WILL BE WEAK SHORT
WAVE TROUGH MOVING OUT OF THE CENTRAL PLAINS TONIGHT. DETERMINISTIC
MODELS ARE A BIT SLOWER WITH THIS FEATURE BUT MESO-SCALE MODELING
PUSHES RAIN THREAT IN A BIT EARLIER.

NAM CONTINUES TO BE MOST BULLISH WITH SHORT WAVE BUT HINTS OF IT IN
01.12Z GFS/ECMWF AS WELL LEADS TO A BIT MORE CONFIDENCE TONIGHT AND
WEDNESDAY. SUBTLE MOISTURE TRANSPORT AND FORCING WITH THIS WAVE
COULD GENERATE MORE SHOWERS AND THUNDERSTORMS TO THE WEST TONIGHT...
WHICH COULD DRIFT INTO THE AREA DURING THE OVERNIGHT. SEEMS LIKE
NORTHWEST FORECAST AREA MOST LIKELY TO GET RAIN...AND WITH HIGH
PRECIPITABLE WATER VALUES AND SLOWER MOVEMENT OF WAVE...BUMPED UP
OVERALL RAIN THREAT INTO WEDNESDAY. COVERAGE STILL A BIT
QUESTIONABLE GIVEN FORCING NOT OVERLY IMPRESSIVE. SHEAR IS MARGINAL
SO OUTSIDE OF A STORM PRODUCING HEAVY RAIN AND PERHAPS A LITTLE
HAIL...NOT EXPECTING SEVERE WEATHER.

SHORT WAVE WILL GRADUALLY DRIFT INTO THE GREAT LAKES WEDNESDAY SO
WISCONSIN SIDE MORE LIKELY TO SEE SOME SHOWERS AND THUNDERSTORMS
DURING DAY WITH LOWERING RAIN THREATS TO THE WEST. AGAIN...HAVE
INCREASED OVERALL RAIN THREAT.

GIVEN MORE CLOUD COVER AND RAIN THREAT...HAVE LOWER HIGHS A LITTLE
NORTH OF INTERSTATE 90 BUT IT WILL REMAIN QUITE WARM TO THE SOUTH
WHERE NEAR HEAT ADVISORY CONDITIONS WILL DEVELOP FOR 3RD DAY IN A
ROW.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 216 PM CDT TUE SEP 1 2015

GIVEN RELATIVELY WEAK FLOW ACROSS CENTRAL CONUS...PREVIOUSLY
MENTIONED WAVE COULD HAVE SOME LINGERING IMPACTS INTO WEDNESDAY
NIGHT...BUT BULK OF THURSDAY SHOULD BE DRY AS FEATURE EXITS.

UPPER FLOW AMPLIFIES FOR REST OF WEEK INTO HOLIDAY WEEKEND.

AS RIDGE BUILDS INTO AREA...OVERALL RAIN THREAT APPEARS TO BE
LOWERING. HARD TO DETAIL IF ANY WEAK SHORT WAVE COULD EJECT OUT OF
SOUTHWEST FLOW TO THE WEST BUT MEDIUM RANGE GUIDANCE IS TRENDING ON
KEEPING THESE FEATURES MAINLY WEST WITH AREAS OF RAIN OR STORM
COMPLEXES GOING BY TO THE NORTHWEST. ENSEMBLE MODEL BLENDS HAVE BEEN
TRENDING DRIER GIVEN THESE SHIFTS AND WOULD AGREE THE OVERALL RAIN
THREAT IS JUST TOO LOW TO KEEP INCLUDING AT THIS POINT.

IT WILL REMAIN VERY WARM AND MUGGY AS WELL WITH HEAT INDEX VALUES
LIKELY IN THE 90 TO 100 DEGREE RANGE.

BY SUNDAY THOUGH...UPPER TROUGH BEGINS TO SWEEP INTO NORTHERN PLAINS
AND SOUTHERN CANADIAN PRAIRIES. THIS FASTER FLOW AND LIKELY
INCREASING FORCING COULD LEAD TO A MORE ORGANIZED STORM COMPLEX AND
SOME POSSIBLE SEVERE WEATHER...ESPECIALLY TO THE WEST/NORTHWEST.
FOLLOWING THIS IDEA...RAIN CHANCES RE-ENTER FORECAST LATE SUNDAY
INTO MONDAY AND WILL HAVE TO SEE HOW THIS EVOLVES IN TIME.

&&

.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...SHEA
LONG TERM...SHEA
AVIATION...WETENKAMP



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