Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 210819
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
319 AM 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 06Z TAFS THROUGH 06Z TUESDAY NIGHT)
ISSUED AT 1100 PM CDT MON OCT 20 2014

THE MOSTLY VFR BLANKET OF CLOUDS HAS PERSISTED THROUGH THE EVENING
HOURS ACROSS WI...ALTHOUGH RECENT SATELLITE IMAGERY SUGGESTING SOME
ERODING STARTING ON THE WESTERN EDGES. AT THE MOMENT...THE BACKEDGE
REMAINS JUST EAST/NORTH OF KLSE. 850-700 MB WINDS VEER TO THE
NORTHEAST OVERNIGHT THOUGH...AND THIS COULD BRING DOWN THE CLOUDS
FROM NORTHERN WI. RAP/NAM 850 MB RH FIELDS ERODE/MOVE EAST
OVERNIGHT...ALTHOUGH LINGER SOME 925 MB RH. GOING TO HOLD THE COURSE
WITH SKC/SCT CONDITIONS FOR KLSE RIGHT NOW...KEEPING THE CLOUD
SHIELD JUST ON THE DOORSTEP. IF IT WOULD MOVE IN...CIGS LOOK VFR
NEAR 4KFT AT THIS TIME.

LIGHT WINDS WILL BECOME EASTERLY OVERNIGHT...AND GRADUALLY MORE
SOUTHEAST THROUGH THE DAY TUE. SOME INCREASE TOWARD 10 KTS AT KRST
BY AFTERNOON.

HIGH PRESSURE AND LIGHT WINDS THE NEXT COUPLE OVERNIGHTS-MORNINGS
BRINGS TO QUESTION IF FOG COULD DEVELOP IN THE RIVER VALLEYS. AT
THIS TIME...CHANCES LOOK SMALL. RAP SOUNDINGS KEEP WINDS STIRRING
JUST ABOVE THE LOW LEVEL INVERSION OVERNIGHT...12+ KTS AT 200 FT.
NOT CONDUCIVE FOR DENSE FOG FORMATION AT KLSE. GFS/NAM SOUNDINGS
SIMILAR FOR TUE NIGHT...KEEPING 10+ KTS OF WINDS JUST OFF THE SFC.
IF A DEEPER LIGHT WIND FIELD WOULD BE REALIZED...THE FG THREAT
INCREASES.


&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION.....RIECK



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