Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 282031
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
331 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 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)
ISSUED AT 1218 PM CDT TUE JUL 28 2015

VSBYS IMPROVING/GOOD AT BOTH TAF SITES FOR THE AFTERNOON AS THE
FIRST BAND OF SHRA/TSRA WEAKENS/EXITS. LOW LEVEL MOISTURE AND
OUTFLOW BEHIND THE DISSIPATING BAND OF SHRA/TSRA PRODUCING SOME MVFR
STRATO-CU ACROSS THE AREA THRU THE EARLY AFTERNOON HOURS. WITH
DIURNAL WARMING/MIXING THIS SHOULD MIX/LIFT TO A SCT VFR DECK BY MID
AFTERNOON...WITH SOME BRISK SOUTHEAST TO SOUTH WINDS. CONSIDERABLE
UNCERTAINTY REMAINS WITH THE CHANCES OF MORE SHRA/TSRA AT THE TAF
SITES THIS EVENING. TIMING OF 01-04Z AT KRST AND 03-06Z AT KLSE
APPEARS REASONABLE. HOWEVER...LOOKING LIKE THIS MAY COME ACROSS THE
AREA AS MORE OF A LINE OF SCT SHRA/TSRA AND LEFT MENTION OF IT AS
VCTS/CB IN BOTH TAFS. DRIER PUSHES IN BEHIND THE COLD FRONT LATER
THIS EVENING/OVERNIGHT...WITH GENERALLY GOOD VFR EXPECTED ONCE ANY
SHRA/TSRA IN THE LINE/NEAR THE FRONT WOULD EXIT THE AREA.

TIGHTER PRESSURE GRADIENT OVER THE AREA WED. WITH MODEL SOUNDINGS
SHOWING MIXING TO 800MB WED AFTERNOON...BRISK/GUSTY WEST TO
NORTHWEST WINDS 15-20KT G25-30KTS EXPECTED BY LATE WED MORNING AND
FOR WED AFTERNOON.


&&

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

$$

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



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