Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 182324
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
624 PM CDT THU SEP 18 2014

.SHORT TERM...(TONIGHT THROUGH FRIDAY NIGHT)
ISSUED AT 232 PM CDT THU SEP 18 2014

SURFACE MAP THIS AFTERNOON HAS HIGH PRESSURE CENTERED OVER THE GREAT
LAKES REGION. STRATUS THAT FORMED UNDER THE HIGH OVERNIGHT HOLDING
TOUGH EAST OF THE MISSISSIPPI RIVER BUT ERODING SLOWLY BUT SURELY ON
THE WESTERN FRINGES TOWARD THE NORTHEAST. THIS IS DUE TO DAYTIME
HEATING AND INCREASING SOUTH WINDS ON THE BACK SIDE OF THE HIGH FOR
SOME MIXING. TEMPERATURES THIS AFTERNOON VERY REFLECTIVE OF THE
AMOUNT OF STRATUS WITH NORTH CENTRAL WI IN THE MIDDLE 40S YET UNDER
THE CLOUD...AND IN THE UPPER 60S/AROUND 70 WEST OF THE RIVER IN
SUNSHINE.

FOR TONIGHT...THE HIGH WILL CONTINUE ITS EASTWARD DRIFT INTO THE
NORTHEAST CONUS WHILE LOW PRESSURE APPROACHES FROM THE NORTHERN
PLAINS. MODELS SHOWING INCREASING LOW-LEVEL MOISTURE TRANSPORT AND
WARM AIR ADVECTION ACROSS THE PLAINS INTO NORTHERN MN...KEEPING
SHOWER/THUNDERSTORM CHANCES ACROSS THAT AREA. MEANWHILE...INCREASING
SOUTH WINDS ACROSS THE AREA SHOULD CONTINUE TO MIX STRATUS OUT
THROUGH THE NIGHT. OTHERWISE...PLAN ON LOWS TONIGHT IN THE UPPER
40S THE MIDDLE 40S.

AS THE LOW CONTINUES TO PULL EAST ALONG JUST NORTH OF THE BOUNDARY
WATERS OF NORTHERN MN ON FRIDAY...A WARM FRONT WILL WORK ACROSS THE
UPPER MISSISSIPPI RIVER REGION WITH 850MB TEMPERATURES INCREASING
INTO THE 13-21C RANGE. ALSO OF NOTE WILL BE EASTERN PERIPHERY OF
STRONG 850MB MOISTURE TRANSPORT EDGING INTO WESTERN WI. KEPT 20-50
SHOWER/THUNDERSTORM CHANCE CONFINED ALONG/NORTH OF I-94 WHERE BETTER
CHANCE OF MORE ELEVATED NATURE SHOWER/THUNDERSTORMS WILL EXIST IN
CLOSER PROXIMITY TO STRONGER MOISTURE TRANSPORT. FRIDAY WILL ALSO
SEE A PRETTY TIGHT PRESSURE GRADIENT ACROSS THE AREA FOR BREEZY
SOUTH WINDS IN THE 15 TO 30 MPH RANGE. PLAN ON HIGHS IN THE UPPER
60S ACROSS NORTHERN WISCONSIN TO THE MIDDLE 70S ACROSS THE REST OF
THE ARX FORECAST AREA.

A COLD FRONT WILL THEN PUSH SOUTHEASTWARD INTO THE AREA FRIDAY NIGHT
FOR INCREASING SHOWER/THUNDER CHANCES. NAM CAPE SEEMS A BIT HIGH DUE
TO OVER-FORECASTED DEW POINTS AROUND 70. GFS SEEMS REASONABLE WITH 0-
3KM MUCAPE OF 1000-2000J/KG. QUESTIONS REMAIN ON HOW THE CAP HOLDS
OVERNIGHT...BUT BUFKIT DOES SHOW THE CAP WEAKENING THROUGH THE
OVERNIGHT HOURS WITH STEEPENING MID-LEVEL/700-500MB LAPSE RATES.
NAM/GFS 0-3KM BULK SHEAR STILL PRETTY IMPRESSIVE IN THE  35-45KT
RANGE...SO THE POTENTIAL IS THERE FOR SOME ROTATING UPDRAFTS CAPABLE
OF LARGE HAIL PRODUCTION ALONG WITH A DAMAGING WIND THREAT. WILL
CONTINUE TO KEEP A CLOSE EYE ON THIS.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 232 PM CDT THU SEP 18 2014

SHOWERS AND THUNDERSTORMS WILL STILL BE POSSIBLE ON SATURDAY MAINLY
SOUTH OF I-90 AS THE FRONT PUSHES OUT OF THE AREA. WILL ALSO STILL
HAVE TO KEEP A CLOSE ON EYE ON A SLIGHT SEVERE CHANCE AS CAPE
REMAINS ELEVATED IN THE 1500-2500J/KG RANGE BY 18Z ALONG WITH 0-3KM
BULK SHEAR OF 25-35KT. SO...STILL A LARGE HAIL/DAMAGING WIND THREAT
GIVEN THESE PARAMETERS. WITH A RELATIVELY WARM START SATURDAY
MORNING IN THE 60S...LOOK FOR HIGHS SATURDAY TO TOP OFF IN THE
70S...AND POSSIBLY A FEW LOWER 80 READINGS ACROSS FAR NORTHEAST
IA/SOUTHWEST WI.

CYCLONIC FLOW ALOFT BRINGS ANOTHER WEAK MID-LEVEL TROUGH INTO THE
REGION SATURDAY NIGHT...MAINLY NORTH OF I-94 FOR A CHANCE OF
SHOWERS.

CONTINUED SHOWER CHANCES INTO SUNDAY MAINLY NORTH OF I-94 AS MODELS
SHOW A WEAK BACKDOOR COLD FRONT SWING INTO THE AREA.
OTHERWISE...LOOK FOR HIGHS SUNDAY IN THE MIDDLE 60S ACROSS NORTH
CENTRAL WI...AND IN THE UPPER 60S/NEAR 70 ACROSS THE REST OF THE ARX
FORECAST AREA.

STRONG HIGH PRESSURE BUILDS INTO THE UPPER MISSISSIPPI RIVER VALLEY
REGION MONDAY...HOLDING THROUGH WEDNESDAY FOR A STRETCH OF PLEASANT
EARLY AUTUMN WEATHER. PLAN ON HIGHS IN THE 60S ON MONDAY...WARMING
INTO THE MIDDLE 60S/LOWER 70S TUESDAY AND WEDNESDAY.

MODELS SHOWING A TROUGH MOVING OUT OF THE INTERMOUNTAIN WEST INTO
THE PLAINS AND EVENTUALLY WASHING OUT IN THE RIDGE BY THE TIME IT
REACHES THE UPPER MISSISSIPPI VALLEY REGION. A FEW SHOWERS WILL BE
POSSIBLE WITH THIS FEATURE ALONG AND WEST OF THE MISSISSIPPI.
OTHERWISE...PLEASANT EARLY AUTUMN TEMPERATURES CONTINUE WITH HIGHS
IN THE UPPER 60S/LOWER 70S.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 624 PM CDT THU SEP 18 2014

VFR CONDITIONS EXPECTED THROUGH THE PERIOD. HIGH PRESSURE CENTERED
JUST EAST OF LAKE SUPERIOR WILL CONTINUE TO MOVE EAST AWAY FROM
THE REGION. A DEVELOPING STORM SYSTEM OVER SOUTH CENTRAL CANADA
WILL MOVE EAST THROUGH THE PERIOD WITH THE AREA OF LOW PRESSURE
REACHING ONTARIO BY LATE FRIDAY AFTERNOON. A COLD FRONT WILL TRAIL
SOUTHWEST FROM THE LOW ACROSS NORTHWEST MINNESOTA INTO SOUTH
DAKOTA. THE GRADIENT WILL TIGHTEN BETWEEN THESE TWO FEATURES AND
WILL KEEP THE WINDS SUSTAINED BETWEEN 5 AND 10 KNOTS OVERNIGHT.
THIS IS EXPECTED TO BE ENOUGH TO KEEP ANY FOG FROM FORMING DESPITE
THE 18.18Z NAM SHOWING SATURATION OCCURRING AT THE SURFACE FOR
KLSE. THE WINDS ALOFT WILL INCREASE DRAMATICALLY WHICH WILL AID IN
THE MIXING TO KEEP THE FOG FROM FORMING AND WILL ALSO BE CLOSE TO
CREATING LOW LEVEL WIND SHEAR CONDITIONS. ONCE THE INVERSION
BREAKS FRIDAY MORNING...GOOD MIXING INTO THESE STRONGER WINDS WILL
OCCUR WITH SUSTAINED SOUTH WINDS AROUND 20 KNOTS EXPECTED FRIDAY
AFTERNOON WITH GUSTS AROUND 30 KNOTS. NOT EXPECTING MUCH IN THE
WAY OF CLOUD COVER AS MID LEVEL TEMPERATURES WARM AHEAD OF THE
COLD FRONT CAPPING OFF THE ATMOSPHERE.

&&

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

$$

SHORT TERM...DAS
LONG TERM...DAS
AVIATION...04



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