Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 291953
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
253 PM CDT MON SEP 29 2014

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY NIGHT)
ISSUED AT 253 PM CDT MON SEP 29 2014

MAIN FOCUS OF THE FORECAST IS ON THE RAIN CHANCES TUESDAY NIGHT
THROUGH WEDNESDAY NIGHT.

THE COLD FRONT HAD JUST ABOUT MADE IT THROUGH THE FORECAST AREA AS
OF 29.18Z AND IS EXPECTED TO BE SOUTH OF THE AREA BY 30.00Z. LOCAL
AND REGIONAL RADARS SHOWING A WEAK BAND OF SHOWERS BEHIND THE
FRONT WORKING SOUTHEAST ACROSS WISCONSIN. SOME OF THESE COULD
STILL BE OVER SOUTHWEST WISCONSIN AT 00Z AND PLAN TO CARRY A SMALL
RAIN CHANCE ACROSS THE SOUTH VERY EARLY IN THE EVENING TO COVER
THIS.

AFTER TONIGHT...THE ATTENTION TURNS TO THE UPPER LEVEL LOW LIFTING
OUT OF THE ROCKIES. IN THE LARGE SCALE...THIS SYSTEM IS HANDLE
SIMILARLY BY THE 29.12Z MODELS BUT SOME OF THE DETAILS ON THE
TIMING AND STRENGTH OF THE EMBEDDED SHORT WAVE TROUGHS STILL HAVE
DIFFERENCES AMONG THE MODELS. THE GENERAL CONSENSUS IS THAT THE
UPPER LEVEL LOW WILL LIFT NORTH INTO MONTANA/SOUTHERN CANADA
TONIGHT AND WEAKEN AS A SHORT WAVE TROUGH COMING ACROSS THE
SOUTHERN ROCKIES STRENGTHENS AND HELPS FORM A NEW UPPER LEVEL LOW
OVER THE DAKOTAS BY LATE TONIGHT OR EARLY TUESDAY. THIS UPPER
LEVEL LOW IS THEN ALSO EXPECTED TO LIFT NORTH INTO CANADA TUESDAY
NIGHT WHILE THE MEAN LONG WAVE TROUGH REMAINS OVER THE WESTERN
UNITED STATES. THIS WILL ALLOW SEVERAL WEAKER SHORT WAVE TROUGHS
EMBEDDED IN THIS SOUTHWEST FLOW TO COME ACROSS THE UPPER MIDWEST.
WHERE THE DIFFERENCES IN THE MODELS ARISE IS WITH THE HANDLING OF
THESE SECONDARY WEAKER WAVES THAT WILL COME ACROSS THE REGION FROM
TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. AS EACH OF THESE WAVES
COMES ACROSS THEY ARE EXPECTED TO PRODUCE A PERIOD OF WEAK TO
OCCASIONALLY MODERATE PV ADVECTION IN THE 500-300 MB LAYER. THEY
ARE ALSO EXPECTED TO PRODUCE WEAK TO MODERATE QG CONVERGENCE IN
THE 1000-500 MB LAYER. THE BEST LOW LEVEL WARM AIR ADVECTION
SHOULD STAY SOUTH OF THE REGION...WHICH WILL ALSO KEEP THE BEST
ISENTROPIC UP GLIDE TO THE SOUTH...BUT STILL ENOUGH WARM AIR
ADVECTION TO PRODUCE BETWEEN 1 AND 2 UBAR/S OF UP GLIDE ON THE
305K ISENTROPIC SURFACE FROM TUESDAY NIGHT THROUGH WEDNESDAY
NIGHT. THE MOISTURE TRANSPORT WILL INITIALLY START OUT WEST OF THE
AREA TUESDAY NIGHT WITH THE EASTERN CONVERGENT SIDE OF THIS
WORKING INTO THE WESTERN SECTIONS OF THE AREA LATE TUESDAY NIGHT.
THIS MOISTURE TRANSPORT SHOULD SEE A DIURNAL WEAKENING WEDNESDAY
WITH THE MAIN AXIS THROUGH THE AREA AND BY WEDNESDAY NIGHT WHEN IT
STARTS TO STRENGTHEN AGAIN...IT SHOULD START VEERING OFF TO THE
EAST OF THE AREA. FOR NOW...PLAN TO CARRY A 60 TO 70 PERCENT
CHANCE OF RAIN IN A NORTH/SOUTH CORRIDOR STARTING TUESDAY NIGHT IN
THE WEST AND WORKING THIS EAST ACROSS THE FORECAST AREA THROUGH
WEDNESDAY NIGHT. IT WOULD APPEAR THAT ONCE THE MODELS COME INTO
BETTER CONSENSUS...THAT THESE RAIN CHANCES WILL NEED TO BE RAISED
TO 80 OR HIGHER. THE CHANCES FOR THUNDER WITH THIS EVENT DO NOT
APPEAR TO BE TOO HIGH. IT LOOKS LIKE THERE WILL BE SOME MINIMAL MU
CAPE AVAILABLE THE WHOLE TIME...BUT THIS SHOULD BE ON THE ORDER OF
500 J/KG OR LESS AND ENOUGH TO KEEP SOME ISOLATED THUNDER IN THE
FORECAST.

.LONG TERM...(THURSDAY THROUGH MONDAY)
ISSUED AT 253 PM CDT MON SEP 29 2014

THIS SYSTEM SHOULD FINALLY GET PUSHED PAST THE AREA BY THE END
OF THE WORK WEEK WITH SOME LINGERING RAIN CHANCES THURSDAY NIGHT
ACROSS THE ENTIRE AREA AND OVER THE NORTHEAST HALF FRIDAY. WITH
THE NORTHWEST FLOW THAT SETS UP BEHIND THIS SYSTEM...THE MODELS
SUGGEST A FAST MOVING SHORT WAVE TROUGH WILL DROP ACROSS THE GREAT
LAKES REGION OVER THE WEEKEND AND COULD BRING SOME SHOWERS TO THE
AREA SUNDAY INTO SUNDAY NIGHT. OTHERWISE...TEMPERATURES WILL BE
TURNING MUCH COOLER WITH BELOW NORMAL READINGS. HIGHS BOTH FRIDAY
AND SATURDAY SHOULD BE IN THE 50S AND THEN SLIGHTLY WARMER FOR
SUNDAY AND MONDAY...RETURNING BACK TO THE 60S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1232 PM CDT MON SEP 29 2014

A COLD FRONT CONTINUED TO PUSH SOUTH ACROSS THE AREA EARLY THIS
AFTERNOON. A BROAD AREA OF MVFR CLOUDS COVERED MUCH OF MN/WI
BEHIND THE FRONT...WITH SOME LCL IFR CIGS/VSBYS IN BR RIGHT BEHIND
THE FRONT. THE IFR CIGS/VSBYS ABOUT TO CLEAR THE KRST AREA AS SOME
DRIER SFC-925MB AIR AND STRONGER SUBSIDENCE BEHIND THE FRONT
ARRIVES. BAND OF POST-FRONTAL -SHRA WAS SPREADING SOUTHEAST ACROSS
MAINLY WI...AND MAY CLIP THE KLSE AREA. INCLUDED A 19-22Z VCSH
MENTION AT KLSE FOR NOW.

THE LOWER CLOUDS/MOISTURE STUCK IN/UNDER A STRONG AND STRENGTHENING
INVERSION NEAR 900MB TONIGHT INTO TUE. ONCE THE MID LEVEL SHORTWAVE
AND STRONGEST LOW LEVEL COLD ADVECTION PASS...SUBSIDENCE WEAKENS.
APPEAR THE MOISTURE/MVFR CLOUDS WILL PERSIST THRU THE NIGHT INTO TUE
MORNING. THESE CLOUDS AND NORTHEAST GRADIENT WINDS OF 5-7KTS WILL
LIMIT THE RADIATIONAL VALLEY FOG POTENTIAL TONIGHT AND LEFT ANY LATE
NIGHT/EARLY MORNING BR OUT OF BOTH THE TAFS. WILL REMAIN OPTIMISTIC
THAT SOME DIURNAL WARMING/MIXING TUE MORNING AND ANTI-CYCLONIC FLOW
WITH THE SFC-925MB RIDGE AXIS WILL HELP BREAK UP THE LOWER CLOUD
DECK.


&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION...RRS



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