Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 202002
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
302 PM CDT SAT SEP 20 2014

.SHORT TERM...(TONIGHT THROUGH SUNDAY NIGHT)
ISSUED AT 302 PM CDT SAT SEP 20 2014

MAIN CONCERN IS AREA OF CONVECTION MOVING THROUGH THIS EVENING WITH
SEVERE POTENTIAL.

WATER VAPOR THIS AFTERNOON SHOWING A VERY COMPACT/STRONG MID-LEVEL
CYCLONIC CIRCULATION MOVING THROUGH SOUTHERN MANITOBA INTO THE
DAKOTAS. IN RESPONSE TO THIS FEATURE...RADAR MOSAIC SHOWING A FAIRLY
INTENSE BAND OF SHOWERS AND THUNDERSTORMS WITH THIS WAVE EXTENDING N-
S ACROSS NORTHERN MN MOVING EAST-SOUTHEAST AT 40KT. WITH THIS
MOVEMENT...EXTRAPOLATION BRINGS THIS CONVECTION INTO NORTHWESTERN
PORTIONS OF OUR FORECAST AREA //SOUTHEAST MN INTO WEST CENTRAL WI//
BY 7 PM. MESOWRF MODELS IN GOOD AGREEMENT WITH THIS ASSESSMENT AS
WELL. THIS CONVECTION HAS A LOT OF DYNAMICS TO WORK WITH SUCH AS
STRONG 850-300MB PV-ADVECTION AND LIFT IN LEFT EXIT REGION OF 130KT
300MB JET. RAP/NAM NOT SHOWING A LOT OF MUCAPE...BUT SHEAR DYNAMICS
OF THE WAVE WILL PRODUCE PLENTY OF LIFT FOR STORMS. ALSO NOTED WAS 0-
3KM BULK SHEAR IN THE 30-35KT RANGE. SO...EXPECTING SOME FAIRLY
INTENSE/POSSIBLY SEVERE THUNDERSTORMS THROUGH THIS EVENING //MAINLY
IN THE 7-10 PM TIME FRAME// WITH A DAMAGING WIND THREAT ALONG WITH
SOME HAIL. IT APPEARS THE BEST DYNAMICS FOR HIGHEST SEVERE THREAT
WILL BE NORTH OF I-90. EXPECTING MOST OF THE ACTIVITY TO MOVE OUT OF
THE AREA BY MIDNIGHT.

AS THIS WAVE DIVES INTO THE GREAT LAKES REGION AFTER MIDNIGHT... A
TRAILING TROUGH ROTATES SOUTHWARD ACROSS THE AREA OVERNIGHT INTO
SUNDAY AND IS EXPECTED TO PRODUCE SCATTERED SHOWERS. BY LATER SUNDAY
AFTERNOON...MODELS INDICATING FAIRLY STRONG SUBSIDENCE AS HEIGHT
START TO BUILD IN FROM THE WEST. THIS SHOULD SHUT DOWN THE SHOWER
ACTIVITY. OTHERWISE...LOOK OR LOWS TONIGHT IN THE UPPER 40S ACROSS
NORTH CENTRAL WI TO THE LOWER 40S ACROSS THE REST OF THE FORECAST
AREA. HIGHS ON SUNDAY EXPECTED TO TOP OFF IN THE LOWER TO MIDDLE 60S.

HIGH PRESSURE BUILDS OVERHEAD SUNDAY NIGHT FOR CLEARING SKIES AND
LIGHT WINDS. THIS WILL LEAD TO GOOD RADIATIONAL COOLING CONDITIONS.
WITH A FAIRLY DAMP LOWER BOUNDARY LAYER FROM RECENT RAINS...
EXPECTING AREAS OF FOG TO FORM...SOME OF WHICH COULD BE LOCALLY
DENSE. THIS WILL ESPECIALLY TRUE IN THE RIVER VALLEYS AND THE
CRANBERRY BOG COUNTRY OF CENTRAL WI. PLAN ON LOW TEMPERATURES SUNDAY
NIGHT IN THE MIDDLE/UPPER 30S ACROSS CENTRAL WI...AND IN THE 40S
ELSEWHERE.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 302 PM CDT SAT SEP 20 2014

HIGH PRESSURE WILL BE THE DOMINANT WEATHER FEATURE FOR MONDAY
THROUGH TUESDAY FOR A QUIET/DRY PERIOD. PLAN ON MONDAY NIGHT LOWS IN
THE 40S WITH HIGHS MONDAY/TUESDAY IN THE UPPER 60S/LOWER 70S.

LATEST GFS/ECMWF STILL SHOWING A TROUGH OF LOW PRESSURE EJECTING OUT
OF THE INTERMOUNTAIN WEST...REACHING THE UPPER MISSISSIPPI RIVER
VALLEY REGION BY LATE TUESDAY NIGHT THEN LINGERING THROUGH WEDNESDAY
NIGHT. THIS IS EXPECTED TO FUEL A FEW SHOWERS/POSSIBLY A
THUNDERSTORM OR TWO. OTHERWISE...PLAN ON TEMPERATURES IN THE
LOWER/MIDDLE 70S FOR HIGHS WEDNESDAY.

FOR THE PERIOD FRIDAY THROUGH SATURDAY...THE GFS AND EC SHOW THE
TROUGH EITHER RETROGRADING BACK INTO THE SOUTHWEST CONUS OR
WEAKENING...LEAVING OUR AREA UNDER A RIDGE. THIS LOOKS TO GIVE THE
AREA AN EXTENDED PERIOD OF PLEASANT/DRY EARLY FALL CONDITIONS. LOOKS
LIKE HIGHS WILL BE IN THE 70S WITH LOWS IN THE 50S. IF THE ECMWF
PANS OUT WITH ITS STRONGER RIDGE SOLUTION...HIGHS COULD REACH THE
LOWER 80S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1145 AM CDT SAT SEP 20 2014

SFC FRONT SLIDING ACROSS THE REGION...WITH SATELLITE IMAGERY
POINTING TO SKC SKIES POST FRONT. EXPECTING VFR CONDITIONS THROUGH
THE AFTERNOON INTO THE EARLY EVENING.

AN UPPER LEVEL SHORTWAVE TROUGH WILL DRIVE SOUTHEAST ACROSS THE
NORTHERN PLAINS AND THEN THROUGH THE UPPER MISSISSIPPI RIVER VALLEY
TONIGHT. A COLD FRONT AT THE SFC WILL ACCOMPANY THE SHORTWAVE...AND
HELP FIRE A LINE OF SHOWERS/ISOLATED THUNDERSTORMS AS IT MOVES
THROUGH. COULD SEE SOME HIGHER GUSTS AROUND THE STRONGER STORMS -
WITH AN ISOLATED SEVERE THREAT EARLY IN THE EVENING.

UPSTREAM OBS WITH THE SHORTWAVE POINT TO AN AREA OF MVFR CIGS IN THE
2-2.5 KFT RANGE. MODEL RH FIELDS AND BUFKIT SOUNDINGS FAVOR THIS
TOO...ESPECIALLY ALONG AND EAST OF THE MISSISSIPPI RIVER. MOST OF
THIS APPEARS POST THE APPROX 3 HOUR WINDOW WHEN A -SHRA/TS THREAT IS
HIGHLIGHTED. SPEAKING OF WHICH...WITH INSTABILITY MINIMAL AT
BEST...WILL KEEP MENTION TO -SHRA RATHER THAN -TSRA. DYNAMICS DO
APPEAR STRONG ENOUGH FOR SOME ISOLD THUNDER...BUT NOT CONFIDENT
ENOUGH TO INCLUDE IN TAFS AT THIS TIME.

FRONT LIKELY LINGERS ACROSS THE REGION FOR THE BETTER PART OF
SUNDAY...BEFORE HIGH PRESSURE AND SUBSIDENCE WORKS IN BY THE
EVENING. KLSE COULD BE UNDER MVFR CLOUDS FOR THE BETTER PART OF THE
MORNING...POTENTIALLY LINGERING THROUGH THE AFTERNOON.

&&

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

$$

SHORT TERM...DAS
LONG TERM...DAS
AVIATION...RIECK


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