Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 301725
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1225 PM CDT WED JUL 30 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 308 AM CDT WED JUL 30 2014

MAIN FORECAST CONCERNS ARE PRECIPITATION CHANCES TODAY.

LATEST WATER VAPOR SATELLITE SHOWS SEVERAL SHORTWAVE TROUGHS
ROTATING AROUND THE CLOSED UPPER LEVEL LOW OVER SOUTHERN HUDSON
BAY. LATEST MOSAIC RADAR INDICATES SHOWER/THUNDERSTORM ACTIVITY
FROM LATE EVENING HAVE DISSIPATED OVER THE AREA EARLY THIS
MORNING. THIS IS DUE TO LOSS OF HEATING AND LIFT ASSOCIATED WITH
IMPULSE MOVING SOUTHEAST OF FORECAST AREA.

THE FORECAST AREA WILL REMAIN UNDER THE INFLUENCE OF THE CLOSED
UPPER LEVEL LOW OVER SOUTHERN HUDSON BAY TODAY INTO TONIGHT.
CONFIDENCE IS NOT AS HIGH AS YESTERDAY WITH DEVELOPMENT OF SHOWERS
AND ISOLATED THUNDERSTORMS...AS THE LATEST 30.00Z GFS/NAM AND RAP
SHOW WEAKER INSTABILITY AND A SLIGHTLY STRONGER CAP ATMOSPHERE
OVER THE FORECAST AREA PER BUFKIT SOUNDINGS. HOWEVER...THE
GFS/NAM/RAP CONTINUE TO SHOW WEAK SHORTWAVE ENERGY TO MOVE ACROSS
THE EASTERN PARTS OF THE FORECAST AREA. THIS WILL PROVIDE ENOUGH
LIFT DURING THE PEAK HEATING OF THE DAY TO WARRANT A SMALL CHANCE
OF PRECIPITATION...ALBEIT 20 TO 30 PERCENT...OVER THE FORECAST
AREA MAINLY THIS AFTERNOON INTO EARLY THIS EVENING.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 308 AM CDT WED JUL 30 2014

WITH SEVERAL SHORTWAVE TROUGHS WRAPPING AROUND THE UPPER LEVEL
CLOSED LOW INTO THE GREAT LAKES REGION. DIURNAL CONVECTION LOOKS
POSSIBLE AGAIN THURSDAY AND WILL CARRY SMALL CHANCES OF
PRECIPITATION OVER THE FORECAST AREA.

STRONGER SHORTWAVE ENERGY MOVES OVER THE AREA FRIDAY...WITH THE
30.00Z GFS/NAM SHOWING STEEPENING LAPSE RATES AND CAPE RANGING FROM
A FEW HUNDRED TO AROUND 1000 J/KG ACROSS FORECAST AREA PER BUFKIT
SOUNDINGS. PLUS...THE 30.00Z GFS/NAM INDICATE PV ADVECTION TO ADD IN
VERTICAL MOTION IN ASSOCIATION WITH SHORTWAVE ENERGY. CONFIDENCE IS
INCREASING THAT SCATTERED SHOWERS AND THUNDERSTORMS WILL DEVELOP
OVER THE FORECAST AREA DURING THE AFTERNOON HOURS AND CONTINUE INTO
THE EARLY EVENING HOURS. HAVE INCREASE PRECIPITATION CHANCES
ACROSS THE FORECAST AREA.

MAIN FORECAST CONCERNS SATURDAY INTO TUESDAY ARE PRECIPITATION
CHANCES SUNDAY INTO TUESDAY. THE LATEST 30.00Z GFS/ECMWF/GEM ARE
INDICATING SHORTWAVE RIDGING BUILDING INTO THE NORTHERN PLAINS AND
GREAT LAKES REGION SATURDAY. THEN...A SHORTWAVE TROUGH/SURFACE
FRONT BREAKS DOWN RIDGE AND PUSHES INTO THE UPPER MIDWEST AND
GREAT LAKES REGION SUNDAY THROUGH EARLY NEXT WEEK. THE 30.00Z
GFS/ECMWF/GEM DIFFER SIGNIFICANTLY ON PLACEMENT AND TIMING OF THE
SURFACE FRONT/SHORTWAVE TROUGH...AS MODELS SHOW SURFACE FRONT
REMAINING NEARLY STATIONARY OVER THE UPPER MIDWEST AND GREAT LAKES
REGION. THIS WILL HAVE IMPACTS ON WHERE PRECIPITATION SETS UP OVER
FORECAST AREA THROUGH THIS PERIOD. THE 30.00Z GFS/GEM/ECMWF
INDICATE DECENT MOISTURE TRANSPORT/CONVERGENCE IN ASSOCIATION WITH
SHORTWAVE TROUGH/SURFACE FRONT. WITH SIGNIFICANT DIFFERENCES
BETWEEN THE MODELS ON PLACEMENT AND TIMING...CONFIDENCE IS LOW ON
WHERE PRECIPITATION WILL OCCUR OVER FORECAST AREA.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1225 PM CDT WED JUL 30 2014

SIMILAR SET-UP TO TUESDAY...WITH DIURNAL WARMING BUILDING SOME
MODEST INSTABILITY ACROSS THE AREA THIS AFTERNOON...AND ANOTHER
SHORTWAVE ROTATING AROUND THE JAMES BAY MID LEVEL AND SOUTHEAST
ACROSS THE UPPER MIDWEST THIS AFTERNOON/EVENING. SCT TO LOCALLY BKN
VFR CUMULUS EXPECTED THIS AFTERNOON...WITH ISOLATED TO WDLY SCT
SHRA/-TSRA ACROSS THE FCST AREA IN ROUGHLY THE 20Z-03Z TIME-FRAME.
GIVEN THE TYPICAL UNCERTAINTIES WITH COVERAGE AND TIMING OF SCT
DIURNAL CONVECTION...ONLY INCLUDED VCSH FOR THE LATE AFTERNOON/EARLY
EVENING HOURS AT BOTH KRST/KLSE FOR NOW. ONCE CONVECTION DEVELOPS
AND SOME TIMING CAN BE DETAILED...TAFS WOULD BE UPDATED FOR A SHORT
PERIOD OF MVFR VSBYS AND POTENTIAL TSRA/CB.

LIGHT WINDS AGAIN TONIGHT WITH LITTLE CHANGE OF THE OVERALL AIRMASS
ACROSS THE UPPER MIDWEST. IT IS NOW THE END OF JULY AND GETTING INTO
THE MORE FREQUENT RADIATIONAL VALLEY FOG TIME OF THE YEAR. PATCHY TO
AREAS OF VALLEY FOG EXPECTED AGAIN TONIGHT IN THE 09-13Z PERIOD.
ADDED BCFG TO KLSE FROM 09-13Z TO ACCOUNT FOR SOME FG/BR IN THE
VALLEYS NEAR KLSE BUT NOT NECESSARILY OVER THE AIRFIELD. IF IT RAINS
AT KLSE IN THAT 20-02Z PERIOD...LIKELY WILL BE A PERIOD OF AT LEAST
MVFR VSBYS AT KLSE IN THE 10-13Z PERIOD THU MORNING.

&&

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

$$

SHORT TERM...DTJ
LONG TERM....DTJ
AVIATION.....RRS



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