Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 300808
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
308 AM 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 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1153 PM CDT TUE JUL 29 2014

SHOWERS ARE FINALLY DISSIPATING WITH LOSS OF DAYTIME HEATING...
DESPITE TRACKING FARTHER WEST THAN PREVIOUSLY EXPECTED. BOTH TAF
SITES SHOULD BE PRECIP FREE THROUGH THE MORNING HOURS. POTENTIAL
EXISTS AGAIN DURING THE AFTERNOON FOR SHOWERS TO DEVELOP...THOUGH
COVERAGE SHOULD BE LESS THAN WHAT OCCURRED ON TUESDAY.
NEVERTHELESS...FEEL CONFIDENT ENOUGH TO INCLUDE A VCSH AT BOTH
TAF SITES. THESE SHOWERS WILL THEN DISSIPATE DURING THE EVENING
HOURS...PERHAPS QUICKER THAN TODAY GIVEN LESS COVERAGE.

OVERALL VFR CONDITIONS WILL CONTINUE. THE BIG THING TO WATCH FOR
IS POTENTIAL FOR FOG FORMATION THIS MORNING. CLOUDS ARE SCATTERING
OUT AROUND THE REGION. GIVEN RECENT RAIN AND LIGHT WINDS...AT A
MINIMUM EXPECTING SOME BR TO FORM PRIOR TO SUNRISE. ITS POSSIBLE
VISIBILITIES GO EVEN LOWER.


&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...AJ



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