Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 260820
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
320 AM CDT SAT JUL 26 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 320 AM CDT SAT JUL 26 2014

LATEST WATER VAPOR SATELLITE IMAGERY INDICATING UPPER LEVEL CLOSED
LOW OVER SOUTHERN SASKATCHEWAN AND WEST TO EAST ZONAL FLOW OVER
THE NORTHERN PLAINS. WEAK SHORTWAVE TROUGH OVER CENTRAL AND
EASTERN SOUTH DAKOTA EMBEDDED IN WEST TO EAST ZONAL FLOW IS
PRODUCING SHOWERS AND ISOLATED THUNDERSTORMS OVER CENTRAL SOUTH
DAKOTA PER MOSAIC RADAR.

MAIN FORECAST CONCERNS ARE PRECIPITATION CHANCES TODAY INTO TONIGHT.

THE 26.00Z GFS/NAM ARE IN GOOD AGREEMENT IN MOVING WEAK IMPULSE OVER
CENTRAL SOUTH DAKOTA INTO THE SOUTHERN PART OF THE FORECAST AREA.
THE 26.00Z GFS/NAM ARE INDICATING ISENTROPIC LIFT AT 315K SURFACE
AND PRODUCE LIGHT QPF ACROSS PARTS OF NORTHEAST IOWA AND SOUTHWEST
WISCONSIN. THE LATEST 26.05Z HRRR IS INDICATING THE SHRA/TSRA OVER
CENTRAL SOUTH DAKOTA TO WEAKEN AND POSSIBLY PRODUCE LIGHT SHOWERS OR
SPRINKLES OVER THE SOUTHERN PART OF THE FORECAST AREA. BUFKIT
SOUNDINGS SHOW QUITE A BIT OF DRY AIRMASS BELOW 700MB OVER THE
SOUTHERN FORECAST AREA. HOWEVER...WITH THE LIFT ASSOCIATED WITH THE
WEAK IMPULSE...THIS MAY PRODUCE AN ISOLATE SHRA/TSRA ACROSS SOUTHERN
FORECAST AREA THIS MORNING INTO THE EARLY AFTERNOON HOURS. HAVE
INTRODUCE A SMALL CHANCE OF PRECIPITATION OVER NORTHEAST IOWA AND
PARTS OF SOUTHWEST WISCONSIN.

UPPER LEVEL CLOSED LOW OVER SOUTHERN SASKATCHEWAN MOVES SOUTH
INTO THE GREAT LAKES REGION TONIGHT. THE 26.00Z GFS/NAM SUGGEST
INCREASING FORCING/LIFT AFTER 06Z OVER NORTHERN PARTS OF THE
FORECAST AREA AND INDICATE ELEVATED CAPE ASSOCIATED WITH UPPER
LEVEL CLOSED LOW. WILL CONTINUE TREND OF PRECIPITATION CHANCES
ACROSS THE NORTHERN PARTS OF THE FORECAST AREA.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 320 AM CDT SAT JUL 26 2014

SUNDAY...THE 26.00Z GFS/NAM CONTINUE TO SHOW DECENT 500-300MB PV
ADVECTION AND DEEP QG FORCING ASSOCIATED WITH THE CLOSED UPPER LEVEL
LOW OVER MUCH OF THE NORTHERN AND EASTERN PART OF THE FORECAST
AREA. CONFIDENCE IS INCREASING THIS AREA WILL SEE SHOWERS AND
POSSIBLY AN ISOLATED THUNDERSTORM.

THE 26.00Z GFS/GEM/ECMWF ARE IN GOOD AGREEMENT DIGGING UPPER LEVEL
TROUGH OVER THE EASTERN UNITED STATES SUNDAY NIGHT INTO FRIDAY. THE
MAIN DIFFERENCE BETWEEN THE MODELS IS TIMING THE VERY WEAK IMPULSES
EMBEDDED IN THE NORTHERLY FLOW ALOFT INTO THE GREAT LAKES REGION.
THE MODELS CONTINUE TO PRODUCE LIGHT QPF OVER PARTS OF THE
FORECAST AREA MAINLY FROM WEDNESDAY INTO FRIDAY. HOWEVER...WITH
VERY WEAK MOISTURE CONVERGENCE AND VERY WEAK IMPULSES EMBEDDED IN
NORTHERLY FLOW. CONFIDENCE IN PRECIPITATION CHANCES IS LOW THROUGH
THIS PERIOD.

TEMPERATURES SUNDAY NIGHT INTO FRIDAY WILL BE UNSEASONABLY COOL
THROUGH MIDDLE OF THE WEEK AND MODERATE TO NEAR NORMAL BY END OF THE
WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1154 PM CDT FRI JUL 25 2014

THE FIRST 6 HOURS OR SO OF THE AVIATION FORECAST IS VERY
PROBLEMATIC. CEILINGS HAVE BEEN GRADUALLY LOWERING THROUGH THE
EVENING DUE TO A COMBINATION OF NOCTURNAL COOLING AND A LITTLE
MORE MOISTURE BEING SENT NORTHWARD INTO THE TAF SITES. EVEN SOME
DRIZZLE HAS FORMED...REDUCING VISIBILITIES TO MVFR AT RST.
MEANWHILE...DRIER AIR AS EXPECTED IS BEGINNING TO MOVE INTO
SOUTHEAST MN WITH TOB NOW VFR. AS WE HEAD THROUGH THE EARLY
MORNING HOURS...ANTICIPATING THAT DRIER AIR TO MOVE INTO RST...
CAUSING THE CLOUDS TO SCATTER OUT AND THUS GO VFR. HOWEVER...THIS
SAME CLEARING MAY ALLOW IFR OR LOWER VISIBILITY BR TO DEVELOP...
WHICH IS NOTED IN A TEMPO GROUP. ANY FOG SHOULD DISSIPATE QUICKLY
AFTER SUNRISE. AT LSE...IT APPEARS THE CLEARING MAY TAKE LONGER TO
GET THERE...THUS HAVE LEFT THE PREVIOUS PLAN OF CONDITIONS
CLIMBING TO VFR AFTER 13Z. ITS POSSIBLE LSE DROPS TO IFR EARLY
THIS MORNING. AFTER 13Z...PLENTIFUL DRY AIR LOOKS TO BE PRESENT
ABOVE THE SURFACE TO NEARLY 10000 FT TO ALLOW FOR VFR CONDITIONS.

&&

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

$$

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



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