Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 290437
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1137 PM CDT TUE JUL 28 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 331 PM CDT TUE JUL 28 2015

LATEST WATER VAPOR SATELLITE IMAGERY SHOWS VIGOROUS SHORTWAVE TROUGH
OVER EASTERN IOWA AND SOUTHERN WISCONSIN. LATEST MOSAIC RADAR
INDICATING SHOWERS/THUNDERSTORMS HAVE WEAKENED WITH THE SHORTWAVE
TROUGH EARLY THIS AFTERNOON. LATEST 19Z SURFACE ANALYSIS SHOWING
COLD FRONT EXTENDING FROM WESTERN MINNESOTA INTO EASTERN NEBRASKA.

MAIN FORECAST CONCERNS TONIGHT ARE PRECIPITATION CHANCES AND
POTENTIAL FOR SEVERE THUNDERSTORMS THIS EVENING. WITH THE
SHORTWAVE TROUGH AND ASSOCIATED PRECIPITATION/CLOUDS OVER THE
FORECAST AREA MUCH OF TODAY...THIS HAS ALLOWED THE ATMOSPHERE TO
BE CAPPED OVER THE FORECAST AREA. THIS IS EVIDENT WITH THE LATEST
28.18Z RAP BUFKIT SOUNDINGS INDICATING A STRONG INVERSION OVER
MUCH OF THE FORECAST AREA. IN ADDITION...THE LATEST 28.17Z
HRRR/HOPWRF SHOW VERY LITTLE CONVECTION TO DEVELOP ALONG THE COLD
FRONT...DUE TO LACK OF CONVERGENCE ALONG FRONT...AND HINT AT
POSSIBLE DEVELOPMENT OF ISOLATED SHOWER/THUNDERSTORM MAINLY EAST
OF THE MISSISSIPPI RIVER AFTER 00Z WEDNESDAY. THE HRRR/HOPWRF
INDICATE SHOWER/THUNDERSTORM DEVELOPMENT SOUTH OF FORECAST AREA IN
CENTRAL IOWA...WHERE BETTER MOISTURE CONVERGENCE AND LIFT IS ALONG
OUTFLOW BOUNDARY FROM THIS MORNINGS MCS. DUE TO THE LOSS OF
INSTABILITY/FORECAST AREA CAPPED AND LACK OF MOISTURE CONVERGENCE
ALONG FRONT...HAVE REDUCED PRECIPITATION CHANCES ACROSS THE
FORECAST AREA THIS EVENING/TONIGHT. PLUS...WITH THE BETTER
LIFT/MOISTURE CONVERGENCE AND INSTABILITY SOUTH OF THE FORECAST
AREA. SEVERE WEATHER THREAT WILL BE CONFINED TO THE FAR SOUTHERN
PART OF THE FORECAST AREA OR SOUTH OF THE FORECAST AREA.

UPPER LEVEL TROUGH DIGS INTO THE GREAT LAKES REGION AND PRESSURE
GRADIENT TIGHTENS BEHIND COLD FRONT ACROSS THE FORECAST AREA
WEDNESDAY. THE 28.12Z GFS/NAM BUFKIT SOUNDINGS SUGGEST AREA WILL
MIX UP TO AROUND 800MB AND WINDS AT THIS LEVEL INCREASE TO AROUND
30 KNOTS. HAVE INCREASED WINDS/WIND GUSTS ACROSS THE FORECAST
AREA...ESPECIALLY IN THE HIGHER TERRAIN AND OPEN AREAS WEDNESDAY.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 331 PM CDT TUE JUL 28 2015

SURFACE RIDGE BUILDS INTO THE CENTRAL PLAINS THURSDAY INTO FRIDAY.
WITH SUBSIDENCE UNDERNEATH HIGH AND MAIN SHORTWAVE ENERGY OVER
LAKE SUPERIOR AND SOUTHERN CANADA...FORECAST AREA WILL REMAIN DRY
THROUGH THE END OF THE WEEK.

MAIN FORECAST CONCERNS FRIDAY NIGHT INTO TUESDAY ARE PRECIPITATION
CHANCES THROUGH THE PERIOD. THE 28.12Z GFS/ECMWF/GEM ARE IN
DECENT AGREEMENT IN DIGGING UPPER LEVEL TROUGH OVER THE GREAT
LAKES REGION THROUGH 00Z SUNDAY...THEN DIVERGE ON THE STRENGTH OF
THE UPPER LEVEL TROUGH. WHERE THE 28.12Z GFS/GEM ARE STRONGER
WITH THE UPPER LEVEL TROUGH OVER THE GREAT LAKES REGION THAN THE
ECMWF. THE 28.12Z GFS/GEM/ECMWF INDICATE DIFFERENCES IN TIMING OF
SHORTWAVE TROUGHS EMBEDDED IN THE NORTHWEST FLOW ALOFT OVER THE
GREAT LAKES REGION. THE 28.12Z GFS/GEM/ECMWF SUGGEST ENOUGH LIFT
AND MOISTURE CONVERGENCE IN ASSOCIATION WITH EACH SHORTWAVE TROUGH
TO WARRANT CHANCES OF SHOWERS/THUNDERSTORMS ACROSS MUCH OF THE
FORECAST AREA FROM SATURDAY NIGHT INTO TUESDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1137 PM CDT TUE JUL 28 2015

THE FRONT HAS ALREADY PASSED THROUGH KRST THIS EVENING AND WILL
HAVE GONE THROUGH KLSE BY 06Z. SHOWERS COMING NORTHEAST OUT OF
CENTRAL IOWA SHOULD CONTINUE TO MOVE NORTHEAST WITH THE 29.02Z
HRRR-CR SHOWING THESE MISSING KLSE WELL TO THE SOUTHEAST...SO DO
NOT PLAN TO INCLUDE ANY MENTION OF SHOWERS OR STORMS IN EITHER
TAF. STILL EXPECTING A BREEZY DAY WEDNESDAY ONCE THE INVERSION
MIXES OUT WITH WEST WINDS GUSTING INTO THE 25 TO 30 KNOT RANGE
FOR THE LATE MORNING THROUGH THE AFTERNOON. LOOKS LIKE THESE WINDS
SHOULD SETTLE DOWN EARLY WEDNESDAY EVENING.

&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...04



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