Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 211902
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
200 PM CDT SUN SEP 21 2014

.SHORT TERM...(TONIGHT)
ISSUED AT 200 PM CDT SUN SEP 21 2014

THE VIGOROUS UPPER LEVEL SHORTWAVE TROUGH THAT BROUGHT THE
SHOWERS/STORMS TO THE REGION LAST NIGHT WAS TRACKING ACROSS THE
EASTERN GREAT LAKES EARLY THIS AFTERNOON. SFC FRONT EXTENDED
WESTWARD FROM SYSTEMS/S LOW...BACK ACROSS WI. ADD IN FAVORABLE LOW
LEVEL LAPSE RATES AND SPOTTY/SCATTERED SHOWERS CONTINUED ACROSS
CENTRAL-EASTERN WI.

THE BOUNDARY WILL SLIP SOUTH BY THE EVENING WITH HIGH PRESSURE
BUILDING INTO IA/MO OVERNIGHT. A LOT OF DIURNAL ELEMENTS TO THE
CURRENT CLOUD MASS ACROSS THE REGION...AND WITH THE LOSS OF DAYTIME
HEATING AND SINKING AIR ASSOCIATED WITH THE HIGH...EXPECT THESE
CLOUDS TO CLEAR QUICKLY THIS EVENING. COULD SEE SOME FOG IN THE
RIVER VALLEYS FOR MONDAY MORNING.

.LONG TERM...(MONDAY THROUGH SUNDAY)
ISSUED AT 200 PM CDT SUN SEP 21 2014

GFS/ECMWF/GEM ALL IN GOOD AGREEMENT WITH BUILDING A STRONG UPPER
LEVEL RIDGE ACROSS THE CENTRAL U.S. FOR MUCH OF THIS WEEK. ALL WANT
TO SLIP A SHORTWAVE TROUGH FROM THE WEST COAST INTO THE
CENTRAL/NORTHERN PLAINS TUE...THEN TRIES TO LIFT IT EAST/NORTHEAST
ACROSS THE UPPER MISSISSIPPI RIVER VALLEY. GEM/GFS SPLIT THE UPPER
LEVEL ENERGY...TAKING A PIECE NORTH OF THE AREA...AND HANGING A
SOUTHERN PIECE OVER THE PLAINS. ASSOCIATED SFC FRONT ISN/T OVERLY
CONVERGENT IN THE LATEST SOLUTIONS. SOME LOW LEVEL MOISTURE
TRANSPORT COULD HELP FUEL SOME SHOWERS. THE GFS/GEM AND EVEN THE NAM
WOULD HOLD ANY PCPN ACROSS MN...PUSHING INTO SOUTHERN CANADA. SOME
SHOWER CHANCES OVER IA AND WEST INTO THE PLAINS. PREVIOUS EC RUN
FAVORED KEEPING THE SHORTWAVE TOGETHER...THUS STRONGER AND MORE
CONVERGENT TOWARD THE SFC WITH THE FRONT. HOWEVER...THE 12Z RUN IS
NOW MORE INLINE WITH THE SPLITTING SOLUTION. WILL LEAN THIS WAY.

THE BIT OF SOUTHERN ENERGY COULD RETROGRADE TO THE WEST WHILE THE
UPPER RIDGE CONTINUES TO ASSERT ITSELF. A SFC HIGH SETS UP SHOP OVER
THE EASTERN GREAT LAKES...PUTTING THIS REGION UNDER SOUTHERLY FLOW.
TEMPS WILL WARM...WITH 850 MB TEMPS CLIMBING FROM AROUND 8 C ON
MONDAY TO 16 C FRI. NAEFS 850 MB TEMP ANOMALIES POINTING TO +2
ACROSS SOUTHERN CANADA FOR THU-SAT...BUT 0-1 LOCALLY. STILL...LOOKS
LIKE ABOVE NORMAL TEMPERATURES TOWARD THE END OF THE WEEK...AND
COULD BE A VERY MILD OKTOBERFEST FOR THOSE IN THE LA CROSSE AREA.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1225 PM CDT SUN SEP 21 2014

HIGH PRESSURE WILL BUILD INTO THE REGION TONIGHT. MODELS INDICATING
THE N-S RIDGE AXIS WILL HANG UP JUST WEST OF THE MISSISSIPPI RIVER.
BUKIT MODEL SOUNDING SHOWING THE LOWER BOUNDARY LAYER IN THE
MISSISSIPPI RIVER CHANNEL DECOUPLING WITH SURFACE WINDS BECOMING
LIGHT AND VARIABLE AFTER MIDNIGHT. THE COMBINATION OF LINGERING
CLOUD COVER TODAY WITH CLEARING THIS EVENING...AND GIVEN RELATIVELY
MOIST LOWER BOUNDARY LAYER FROM RECENT RAINFALL...ALONG WITH LACK OF
GOOD MIXING WITH DECOUPLING WINDS...IS PRODUCING INCREASING
CONFIDENCE FOR SOME FOG FORMATION IN THE MISSISSIPPI RIVER CHANNEL
LATE TONIGHT/EARLY MONDAY MORNING. THINKING NORTHWEST WINDS AT 5-
10KT AT BLUFFTOP MAY HELP TO STIR FOG MORE INTO A STRATUS LAYER.
HOWEVER...NOT CONFIDENT THAT THIS FOG/STRATUS WILL SET UP DIRECTLY
OVER THE KLSE AIRPORT. PREVIOUS FORECAST HAD P6SM BCFG/SCT002
MENTION FROM 09-12Z...AND THIS SEEMS REASONABLE GIVEN AFOREMENTIONED
SIGNALS. PLAN ON STAYING WITH THIS WITH 18Z ISSUANCE AND HAVE THE
EVENING SHIFT FORECASTER MONITOR CLOSELY FOR POSSIBLE DETERIORATING
CONDITIONS. THINKING KRST WILL STAY VFR GIVEN MORE STIRRING/DRYING
WITH WEAK WEST-NORTHWEST WINDS.

&&

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

$$

SHORT TERM...RIECK
LONG TERM....RIECK
AVIATION.....DAS


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