Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 211738
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1238 PM CDT TUE OCT 21 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 319 AM CDT TUE OCT 21 2014

THE FORECAST AREA REMAINS UNDER WEAK CYCLONIC FLOW ALOFT PER LATEST
WATER VAPOR SATELLITE AND VAD WIND PROFILES ACROSS THE GREAT
LAKES REGION. THE CYCLONIC FLOW ALOFT CONTINUES TO WRAP STRATUS
DECK OF CLOUDS INTO NORTHERN AND CENTRAL WISCONSIN PER LATEST FOG
PRODUCT SATELLITE. LATEST 08Z SURFACE ANALYSIS SHOWS SURFACE RIDGE
OVER SOUTHERN ONTARIO AND NORTHERN MINNESOTA. TEMPERATURES ACROSS
THE FORECAST HAVE DROPPED INTO THE UPPER 20S TO LOWER 40S...PER
LATEST METARS.

MAIN FORECAST CONCERNS TONIGHT IS FOG POTENTIAL IN RIVER VALLEYS.

SURFACE RIDGE BUILDS INTO THE EASTERN HALF OF WISCONSIN AND
REMAINS IN CONTROL OF THE GREAT LAKES REGION TODAY INTO TONIGHT.
SUBSIDENCE UNDERNEATH THE SURFACE RIDGE WILL ALLOW SKIES TO BECOME
MOSTLY SUNNY ACROSS THE ENTIRE FORECAST AREA TODAY.

TONIGHT...WITH LIGHT SOUTHERLY WINDS AT THE SURFACE AND CLEAR
SKIES...AN INVERSION DEVELOPS ACROSS THE FORECAST AREA AND ALLOWS
THE POTENTIAL OF FOG TO FORM IN RIVER VALLEYS AFTER 06Z
WEDNESDAY. HOWEVER...THE 21.00Z GFS/NAM BUFKIT SOUNDINGS CONTINUE
TO SHOW OVER 10 KNOTS OF WIND JUST ABOVE THE SURFACE...AT AND ABOVE
200 FEET. THIS STRONG OF WIND WILL INHIBIT WIDESPREAD FOG
FORMATION IN THE RIVER VALLEYS. AT THIS TIME...HAVE LEFT MENTION
OF PATCHY FOG IN THE MISSISSIPPI RIVER AND TRIBUTARIES.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 319 AM CDT TUE OCT 21 2014

NEXT CONCERN ARE PRECIPITATION CHANCES WEDNESDAY NIGHT INTO
THURSDAY. UPPER LEVEL TROUGH/LOW OVER SOUTHERN ARIZONA AND NEW
MEXICO IS EXPECTED TO LIFT NORTHWARD INTO THE UPPER GREAT LAKES
REGION WEDNESDAY NIGHT INTO THURSDAY. CONFIDENCE IS INCREASING THE
FORECAST AREA WILL RECEIVE PRECIPITATION...AS THE 21.00Z
GFS/NAM/ECMWF INDICATE ENOUGH QG FORCING AND ISENTROPIC LIFT IN
ASSOCIATION WITH THE UPPER LEVEL TROUGH/LOW TO PRODUCE SHOWERS
ACROSS THE FORECAST AREA AFTER 06Z THURSDAY. THE 21.00Z GFS/NAM
ARE IN GOOD AGREEMENT IN DEVELOPING A FRONTOGENETICAL BAND OF
PRECIPITATION OVER SOUTHEAST MINNESOTA AND WESTERN WISCONSIN AND A
COMPLEX OF SHOWERS...POSSIBLY ISOLATED THUNDERSTORMS TO FORM OVER
EASTERN IOWA SOUTH OF THE FORECAST AREA ON NOSE OF WEAK 925-850MB
MOISTURE TRANSPORT BY 18Z THURSDAY. THE 21.00Z NAM SHOWS 0-6KM
MOST UNSTABLE CAPE OF 200 J/KG ACROSS THE WESTERN FORECAST AREA
WITH THE UPPER LEVEL TROUGH/LOW. AN ISOLATED THUNDERSTORM IS
POSSIBLE ACROSS THE SOUTHERN AND WESTERN FORECAST AREA. WITH THE
INSTABILITY VERY WEAK...WILL LEAVE MENTION OF THUNDER OUT OF THE
FORECAST.

FOCUS THEN TURNS TO TEMPERATURES FRIDAY INTO SUNDAY...AND PRECIPITATION
CHANCES SUNDAY NIGHT INTO MONDAY. THE 21.00Z GFS/ECMWF ARE IN GOOD
AGREEMENT IN BUILDING UPPER LEVEL RIDGE INTO THE CENTRAL UNITED
STATES FRIDAY INTO THE WEEKEND. MINOR DIFFERENCES ARE INDICATED ON
AMPLIFICATION AND PROGRESSION OF THE UPPER LEVEL RIDGE BETWEEN THE
ECMWF AND GFS. THIS WILL HAVE MINOR IMPACTS ON HOW FAR NORTH
WARMER AIRMASS PUSHES NORTHWARD ACROSS FORECAST AREA.
HOWEVER...BOTH THE MODELS SHOW STRONG WARMER AIR ADVECTING INTO
THE FORECAST AREA THIS WEEKEND AND 850MB TEMPERATURES WARMING UP
TO PLUS 18 DEGREES CELSIUS BY 00Z MONDAY. TEMPERATURES FRIDAY INTO
THE WEEKEND ACROSS THE FORECAST AREA WILL BE ABOVE NORMAL...WITH
HIGH TEMPERATURES RANGING FROM THE 60S INTO THE LOWER 70S.

UPPER LEVEL RIDGE BUILDS INTO EASTERN UNITED STATES SUNDAY NIGHT
INTO MONDAY AND SOUTHWESTERLY FLOW DEVELOPS OVER THE CENTRAL UNITED
STATES. THE 21.00Z GFS/ECMWF EJECT A SHORTWAVE TROUGH INTO THE UPPER
MIDWEST AND GREAT LAKES REGION SUNDAY NIGHT INTO MONDAY...WITH THE
MODELS SHOWING DIFFERENCES ON PLACEMENT AND TIMING OF THE SHORTWAVE
TROUGH. BOTH THE MODELS INDICATE DECENT LIFT AND MOISTURE
CONVERGENCE TO WARRANT CHANCES OF PRECIPITATION ACROSS MUCH OF THE
FORECAST AREA SUNDAY NIGHT INTO MONDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1238 PM CDT TUE OCT 21 2014

VFR CONDITIONS ARE EXPECTED THROUGH THE FORECAST PERIOD. HIGH
PRESSURE WILL BUILD INTO EASTERN WISCONSIN TONIGHT AS A TROUGH OF
LOW PRESSURE DEEPENS OVER THE PLAINS. THE LOCAL AREA WILL BE
POSITIONED BETWEEN THESE TWO FEATURES PRODUCING AN INCREASING
PRESSURE GRADIENT. THIS WILL IMPACT THE POTENTIAL FOR VALLEY FOG
FORMATION  TONIGHT AT KLSE...WITH WINDS JUST ABOVE THE VALLEY
STAYING IN THE 13 TO 20 KT RANGE. THIS WILL PROMOTE MIXING AND
SHOULD INHIBIT VALLEY FOG FORMATION. CANNOT RULE OUT SOME SCT
VALLEY STRATUS OR PATCHY FOG BUT CONDITIONS SHOULD REMAIN VFR
THROUGH THE NIGH INTO WEDNESDAY MORNING. WINDS WILL INCREASE LATE
TONIGHT AT KRST INTO THE 8 TO 12 KT RANGE OUT OF THE SOUTHEAST AS
THE GRADIENT TIGHTENS.

&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...WETENKAMP



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