Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 290809
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
309 AM CDT FRI AUG 29 2014

.SHORT TERM...(TODAY THROUGH SUNDAY)
ISSUED AT 309 AM CDT FRI AUG 29 2014

THE MAIN FORECAST CONCERN IS WITH THE RAIN CHANCES THROUGH THE
PERIOD.

LOCAL AND REGIONAL RADARS SHOWING AN AREA OF SHOWERS AND STORMS
ACROSS SOUTHERN MINNESOTA INTO CENTRAL IOWA. THIS ACTIVITY HAS
BEEN MOVING NORTHEAST AND THE 29.00Z HRRR SEEMED TO HAVE A DECENT
HANDLE ON THIS. IT SUGGESTS THAT IT WILL CONTINUE TO MOVE
NORTHEAST INTO THE AREA AND MAY SHOW A DIMINISHING TREND AS IT
OUTRUNS THE AVAILABLE CAPE. THE 29.06Z RAP ANALYSIS SUGGESTED
THERE WAS AROUND 250 J/KG OF MU CAPE OVER THE WESTERN SECTIONS
WITH THIS DROPPING TO NEAR ZERO OVER WESTERN AND CENTRAL
WISCONSIN. WHILE THE THUNDER MAY DIMINISH AS THE SYSTEM CONTINUES
TO WORK NORTHEAST...THE AREAL COVERAGE MAY NOT CHANGE MUCH AS THE
29.05Z RAP INDICATES THE ACTIVITY IS ON THE NOSE OF THE 850 MB LOW
LEVEL JET AND THIS MAINTAINS ITS INTENSITY AS IT LIFTS NORTHEAST
THROUGH THE AREA FOR THE REMAINDER OF THE NIGHT. PLAN TO START THE
DAY WITH AT LEAST A 70 PERCENT CHANCE OF RAIN OVER MUCH OF CENTRAL
INTO PARTS OF WESTERN WISCONSIN AND THEN DIMINISH THESE DOWN TO 30
TO 50 PERCENT BY LATE MORNING AS THE AREA GETS IN BETWEEN
SYSTEMS. BOTH THE HRRR AND 29.00Z HI-RES ARW SUGGEST MOST IF NOT
ALL OF THE AREA COULD BE RAIN FREE FOR A SHORT WHILE LATE THIS
MORNING.

THIS DRY PERIOD WILL NOT LAST VERY LONG AS THE MEAN LONG WAVE
TROUGH WILL START TO APPROACH FROM THE WEST IN THE AFTERNOON WITH
A STRONG SHORT WAVE TROUGH EMBEDDED IN THE FLOW. THIS IS EXPECTED
TO PRODUCE WEAK TO MODERATE PV ADVECTION IN THE 500-300 MB LAYER
DURING THE AFTERNOON AND EVENING. THE 29.00Z NAM SUGGEST THERE
COULD ALSO BE SOME COUPLED JET DYNAMICS FROM THE RIGHT ENTRANCE
REGION OF THE MAIN JET CORE ACROSS THE NORTHERN GREAT LAKES INTO
SOUTHEAST CANADA AND FROM THE LEFT EXIT REGION OF A SECONDARY JET
ROUNDING THE BASE OF THE LONG WAVE TROUGH. THE CAPE WILL INCREASE
IN THE AFTERNOON...ESPECIALLY ACROSS THE SOUTHEAST TWO-THIRDS OF
THE FORECAST AREA...WHERE THE NAM INDICATES THE POTENTIAL OF
1500-2500 J/KG OF ML CAPE. THIS MAY BE A LITTLE ON THE HIGH SIDE
AS IT IS SHOWING WIDESPREAD LOWER 70S DEW POINTS WHEN THESE MAY
ONLY BE IN THE UPPER 60S TO AROUND 70. NONE THE LESS...EXPECT TO
SEE AN INCREASE IN THE ACTIVITY DURING THE AFTERNOON INTO THE
EVENING AND WILL PUSH THE RAIN CHANCES BACK UP INTO THE 70 TO 80
PERCENT RANGE BY EVENING WHEN THE FORCING IS THE BEST. THE
ACTIVITY SHOULD START TO MOVE OUT OF THE AREA LATE TONIGHT INTO
SATURDAY MORNING AND THEN END DURING THE AFTERNOON AS THE LONG
WAVE TROUGH MOVES PAST THE AREA. IF THE CAPE ADVERTISED BY THE
MODELS CAN BE REALIZED...THEN THERE COULD SOME POTENTIAL FOR
SEVERE STORMS. THE 0-3KM BULK SHEAR SHOULD BE IN THE 30 TO 40 KNOT
RANGE WHICH WOULD BE ENOUGH TO SUPPORT SOME STRONG WINDS.

ONCE THE RAIN ENDS SATURDAY...IT APPEARS THAT SOME WEAK RIDGING
WILL BUILD OVER THE AREA FOR A DRY SATURDAY NIGHT. THIS RIDGING
WILL THEN QUICKLY BE PUSHED OUT OF THE AREA SUNDAY AS YET ANOTHER
LONG WAVE TROUGH STARTS TO COME IN FROM THE NORTHERN ROCKIES.
HOWEVER...IT APPEARS THE TIMING OF THIS SYSTEM WOULD BE SUCH THAT
THERE WILL ONLY BE A SMALL CHANCE FOR SOME ADDITIONAL RAINS ACROSS
THE FAR WESTERN SECTIONS SUNDAY AFTERNOON.

.LONG TERM...(SUNDAY NIGHT THROUGH THURSDAY)
ISSUED AT 309 AM CDT FRI AUG 29 2014

PRETTY DECENT AGREEMENT BETWEEN THE MEDIUM RANGE MODELS THAT THIS
NEXT SYSTEM WILL MOVE ACROSS THE UPPER MIDWEST SUNDAY NIGHT AND
MONDAY. THE 29.00Z ECMWF AND GFS BOTH INDICATE THE EMBEDDED SHORT
WAVE TROUGH COULD PRODUCE MODERATE TO STRONG PV ADVECTION IN THE
500-300 MB LAYER WHILE THE 29.00Z GEM SHOWS WEAK TO MODERATE PV
ADVECTION. ALL THREE MODELS DO SHOW THE COLD FRONT WITH THIS
SYSTEM PASSING THROUGH LATE SUNDAY NIGHT INTO MONDAY MORNING WITH
A SOLID SHIELD OF RAIN ALONG AND AHEAD OF IT. WILL SHOW 60 TO 80
PERCENT RAIN CHANCES SUNDAY NIGHT FROM EAST TO WEST AND 30 TO 60
PERCENT CHANCES MONDAY. HOWEVER...IF THE TIMING OF THE SYSTEM
REMAINS THE SAME...THE MONDAY RAIN CHANCES MAY HAVE TO BE
INCREASED...ESPECIALLY IN THE MORNING. THE TIMING OF THE FRONT IS
NOT IDEAL FOR SEVERE CHANCES...BUT THE GFS DOES SHOW 500-1000 J/KG
OF ML CAPE PERSISTING SUNDAY NIGHT AHEAD OF THE FRONT WITH AROUND
40 KNOTS OF 0-6KM SHEAR. THIS WOULD BE SUFFICIENT TO SUPPORT SOME
STRONGER STORMS THAT COULD PRODUCE SOME STRONG WINDS. ANOTHER COLD
FRONT LOOKS TO MOVE THROUGH LATE IN THE PERIOD FOR ADDITIONAL RAIN
CHANCES WEDNESDAY NIGHT INTO THURSDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1140 PM CDT THU AUG 28 2014

ALTHOUGH RAIN SHOWERS FROM EARLIER THIS EVENING HAVE MOVED
NORTHEAST OF TAF AIRFIELDS...A SECONDARY AREA OF CONVECTION HAS
DEVELOPED ACROSS CENTRAL IA. THESE STORMS ARE EXPECTED TO WEAKEN
AS THEY MOVE NORTHEASTWARD...BUT SHOULD IMPACT KRST AND KLSE
BETWEEN 29.08 AND 29.14Z. PERIODS OF HEAVY RAIN AND VISIBILITY
RESTRICTIONS TO ONE MILE WILL BE THE PRIMARY IMPACTS. EXPECT
MVFR/IFR CEILINGS TO PERSIST THROUGH THE NIGHT ONLY TO SLOWLY LIFT
FRIDAY MORNING. ADDITIONAL SHOWERS AND THUNDERSTORMS ARE EXPECTED
FRIDAY AFTERNOON/EVENING WITH AN APPROACHING COLD FRONT. WILL
CONTINUE TO HIGHLIGHT THIS THREAT USING TEMPO GROUPS UNTIL BETTER
TIMING/COVERAGE CERTAINTY IS ACHIEVED. LIGHT SOUTHEAST WIND WILL
GRADUALLY BECOME MORE SOUTHERLY THROUGH THE PERIOD.


&&

.HYDROLOGY...
ISSUED AT 309 AM CDT FRI AUG 29 2014

PLAN TO CONTINUE WITH THE HYDROLOGIC OUTLOOK THIS MORNING. NOT
OVERLY CONCERNED ABOUT ANY FLOODING THREATS AS THE RAIN THURSDAY
DID NOT TURN OUT TO BE AS HEAVY AS EXPECTED AND THE CURRENT
FORECAST IS FOR ANOTHER 1 TO 1.5 INCHES THROUGH SATURDAY. WILL
LIKELY BE SOME LOCALLY HIGHER AMOUNTS THOUGH AS THE CONDITIONS ARE
STILL IN PLACE FOR SOME HEAVY RAIN TO OCCUR. PRECIPITABLE WATERS
WILL REMAIN IN THE 1.5 TO 2 INCH RANGE WITH WARM CLOUD DEPTHS OF
3.5 TO 4 KM WHICH WILL HELP TO MAKE THE CONVECTION EFFICIENT RAIN
PRODUCERS.

&&

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

$$

SHORT TERM...04
LONG TERM...04
AVIATION...ROGERS
HYDROLOGY...04



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