Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 181944
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
244 PM CDT MON MAY 18 2015

.SHORT TERM...(THIS EVENING THROUGH TUESDAY)
ISSUED AT 243 PM CDT MON MAY 18 2015

MAIN CONCERN TONIGHT INTO TUESDAY ARE CLOUD TRENDS.

LATEST WATER VAPOR SATELLITE IMAGERY SHOWS UPPER LEVEL LOW/TROUGH
OVER SOUTHERN ONTARIO AND LAKE SUPERIOR. LATEST VISIBLE SATELLITE
IMAGERY INDICATING STRATUS DECK OF CLOUDS WRAPPING AROUND UPPER
LEVEL LOW/TROUGH INTO THE EASTERN DAKOTAS...MINNESOTA AND WESTERN
WISCONSIN.

THE FORECAST AREA WILL REMAIN UNDER THE INFLUENCE OF THE UPPER LEVEL
LOW/TROUGH TONIGHT INTO TUESDAY MORNING. THE 18.12Z GFS/NAM CONTINUE
TO SHOW STRATUS DECK CLOUDS TO WRAP AROUND THE UPPER LEVEL
LOW/TROUGH INTO THE FORECAST AREA TONIGHT...PER THE 18.12Z GFS/NAM
925 TO 850MB RELATIVE HUMIDITY FIELDS. AS THE UPPER LEVEL
LOW/TROUGH SLOWLY PULLS AWAY FROM THE FORECAST AREA...DRIER AIR
ADVECTS INTO THE AREA AND ERODES THE STRATUS DECK DURING THE DAY
TUESDAY...PER NAM/GFS BUFKIT SOUNDINGS.

.LONG TERM...(TUESDAY NIGHT THROUGH MONDAY)
ISSUED AT 243 PM CDT MON MAY 18 2015

SHORTWAVE/SURFACE RIDGE BUILDS INTO CENTRAL MINNESOTA AND INTO
CENTRAL WISCONSIN TUESDAY NIGHT. A WEAK SHORTWAVE TROUGH OVER
WESTERN IOWA AND NEBRASKA WILL SPREAD MID TO HIGH CLOUDS OVER MUCH
OF THE SOUTHERN HALF OF THE FORECAST AREA. THIS WILL INHIBIT ANY
RADIATIONAL COOLING AND POTENTIAL FROST ACROSS MUCH OF THE FORECAST
AREA. HOWEVER...AREAS TO PATCHY FROST IS POSSIBLE ACROSS PARTS OF
CENTRAL WISCONSIN...WHERE SKIES WILL REMAIN MOSTLY CLEAR MUCH OF
TUESDAY NIGHT.

THE 18.12Z GFS/NAM CONTINUE TO SHOW SHORTWAVE TROUGH TRACKING ACROSS
IOWA WEDNESDAY INTO THURSDAY EVENING. THE 18.12Z NAM INDICATE
SHORTWAVE TROUGH AND ASSOCIATED LIFT/PRECIPITATION...A SLIGHTLY
SLOWER PROGRESSION THAN PREVIOUS RUNS PER DPROG/DT. BOTH THE 18.12Z
GFS/NAM CONTINUE TO SHOW QG FORCING AND LIFT ABOVE 700MB ACROSS THE
SOUTHERN FORECAST AREA AFTER 18Z WEDNESDAY WITH THE DEEPER FORCING
AND VERTICAL MOTION SOUTH OF THE FORECAST AREA...WITH DRIER AIRMASS
OVER SOUTHEAST MINNESOTA AND WESTERN WISCONSIN...PRECIPITATION
CHANCES WILL BE CONFINED OVER THE SOUTHERN MOST FORECAST AREA. THE
18.12Z NAM/GFS BUFKIT SOUNDINGS/TIME HEIGHT CROSS SECTIONS SHOW THIS
AND WILL CONTINUE SMALL PRECIPITATION CHANCES OVER THE SOUTHERN MOST
FORECAST AREA AND INTRODUCE SMALL PRECIPITATION CHANCES DUE TO
SLOWER PROGRESSION OF SHORTWAVE...PER THE 18.12Z NAM/ECMWF.

MAIN FORECAST CONCERNS FROM THURSDAY NIGHT INTO MEMORIAL DAY WEEKEND
ARE PRECIPITATION CHANCES FOR MEMORIAL DAY WEEKEND. THE 18.12Z
GFS/ECMWF/GEM ARE IN GOOD AGREEMENT IN BUILDING SHORTWAVE RIDGE INTO
THE UPPER MIDWEST AND GREAT LAKES REGION FRIDAY AND SATURDAY...THEN
EJECT UPPER LEVEL TROUGH/LOW INTO THE GREAT LAKES REGION SATURDAY
NIGHT INTO MEMORIAL DAY. THE 18.12Z GFS/GEM/ECMWF CONTINUE TO SHOW
DECENT MOISTURE TRANSPORT/CONVERGENCE AND FORCING INTO THE FORECAST
AREA MEMORIAL DAY WEEKEND. THE BIGGEST DIFFERENCE IS TIMING OF THE
UPPER LEVEL TROUGH/LOW INTO THE CENTRAL UNITED STATES...AS THE GFS
IS SLIGHTLY FASTER THAN THE ECMWF. WILL CONTINUE TREND OF CHANCES OF
SHOWERS AND THUNDERSTORMS ACROSS THE FORECAST AREA FROM SATURDAY
INTO MEMORIAL DAY...WITH HIGHER CHANCES OCCURRING SUNDAY POSSIBLY
INTO MEMORIAL DAY. TEMPERATURES DURING THE MEMORIAL WEEKEND WILL BE
TRICKY...DUE TO PLACEMENT OF SURFACE WARM FRONT AND HOW FAR NORTH
WARMER AIR ADVECTS NORTHWARD INTO THE FORECAST AREA. FOR
NOW...TRENDS INDICATE TEMPERATURES WILL BE SLIGHTLY BELOW NORMAL
THROUGH THE WEEKEND...THIS IS EVIDENT WITH THE 18.12Z GEFS STANDARD
ANOMALIES SHOW AROUND MINUS 1 DEGREE CELSIUS BELOW NORMAL.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)
ISSUED AT 1232 PM CDT MON MAY 18 2015

MVFR STRATOCUMULUS WILL PERSIST AT THE TAF SITES THROUGH TONIGHT
WITH CLOUD BASES OF 2K-3KFT. ALSO...WINDY CONDITIONS WILL
CONTINUE WITH WEST WINDS OF 18 TO 22 KTS WITH GUSTS APPROACHING 30
KTS AT TIMES. THE WINDS WILL DIMINISH SLIGHTLY TONIGHT. CLOUDS
SHOULD START TO SCATTERED OUT BY MID MORNING ON TUESDAY WITH A
RETURN TO VFR CONDITIONS.


&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...WETENKAMP



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