Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 110358
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1100 PM CDT WED SEP 10 2014

.SHORT TERM...(THIS EVENING THROUGH THURSDAY)
ISSUED AT 317 PM CDT WED SEP 10 2014

MAIN FORECAST CONCERNS TONIGHT INTO THURSDAY ARE CLOUD TRENDS.

LATEST 19Z SURFACE ANALYSIS SHOWS SURFACE LOW OVER EAST CENTRAL
WISCONSIN AND COLD FRONT EXTENDING SOUTHWEST INTO EASTERN IOWA.
LATEST KARX RADAR INDICATING RESIDUAL RAIN ASSOCIATED WITH THE
UPPER LEVEL TROUGH OVER NORTH CENTRAL WISCONSIN AND DRIZZLE ACROSS
SOUTHEAST MINNESOTA...NORTHEAST IOWA AND SOUTHWEST WISCONSIN IN
ASSOCIATION WITH THE PASSAGE OF THE SURFACE COLD FRONT. LATEST 19Z
METARS INDICATE TEMPERATURES HAVE FALLEN INTO THE UPPER 40S TO
MIDDLE 50S BEHIND COLD FRONT ACROSS MUCH OF THE FORECAST AREA.

TONIGHT AND THURSDAY...UPPER LEVEL TROUGH AND SURFACE LOW WILL
CONTINUE TO LIFT NORTHEAST OF THE FORECAST AREA. THE LATEST 10.12Z
GFS/NAM ARE SHOWING LOW LEVEL MOISTURE IN THE 925-850MB LAYER TO
REMAIN OVER THE FORECAST AREA THROUGH TONIGHT. THIS IS EVIDENT IN
BUFKIT SOUNDINGS WITH A WEAK INVERSION TRAPPING THE LOW LEVEL
MOISTURE. THE COMBINATION OF THE REGION UNDER THE INFLUENCE OF
CYCLONIC FLOW AND THE LOW LEVEL MOISTURE...THE LOW LEVEL STRATUS
WILL HAVE A HARD TIME TO ERODE ACROSS THE FORECAST AREA TONIGHT
AND HAVE ADJUSTED SKY GRIDS FOR THIS. WITH THE DAYTIME HEATING AND
DRIER AIR ADVECTING INTO THE AREA THURSDAY. THIS SHOULD ERODE THE
LOW STRATUS CLOUDS AND BECOME MORE OPEN CELLULAR...HENCE SOME
PARTIAL SUNSHINE CAN BE EXPECTED ACROSS FORECAST AREA THURSDAY.

.LONG TERM...(THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 317 PM CDT WED SEP 10 2014

NEXT CONCERN ARE PRECIPITATION CHANCES LATE THURSDAY NIGHT/FRIDAY...THE
POTENTIAL FOR FROST AND FOG IN VALLEYS FRIDAY NIGHT INTO SATURDAY
MORNING.

THE LATEST 10.12Z GFS/NAM ARE IN GOOD AGREEMENT IN DIGGING UPPER
LEVEL TROUGH OVER SOUTHERN ALBERTA AND NORTHERN ROCKIES AND MOVING
INTO THE GREAT LAKES REGION THURSDAY NIGHT INTO FRIDAY. BOTH THE
10.12Z GFS/NAM INDICATE STRONG PV ADVECTION AND DEEP QG FORCING IN
ASSOCIATION WITH THE UPPER LEVEL TROUGH. THIS COMBINED WITH STRONG
ISENTROPIC LIFT AT 305K SURFACE ACROSS THE SOUTHERN FORECAST AREA
WILL PRODUCE SHOWERS ACROSS THIS PART OF THE FORECAST
AREA...MAINLY AFTER 12Z FRIDAY. THE 10.12Z GFS/NAM BUFKIT
SOUNDINGS SHOW NONE TO LITTLE INSTABILITY ACROSS THE FORECAST
AREA. WILL CONTINUE NO MENTION OF THUNDER IN FORECAST.

FOCUS THEN TURNS TO HOW FAST SKIES CLEAR AND DRIER AIR ADVECTS INTO
THE REGION FRIDAY NIGHT. THE 10.12Z GFS IS SLIGHTLY FASTER IN
BUILDING RIDGE INTO THE FORECAST AREA THAN THE 10.12Z NAM/ECMWF.
THIS WILL HAVE IMPACTS ON HOW QUICKLY THE ASSOCIATED MOISTURE/CLOUDS
AND PRECIPITATION PUSHES EAST OF FORECAST AREA TO ALLOW FOR A GOOD
RADIATIONAL COOLING NIGHT. THE 10.12Z ECMWF/GFS/NAM SHOW 850MB
TEMPERATURES FALLING TO AROUND ZERO DEGREES CELSIUS TO PLUS 1 DEGREE
CELSIUS BY 12Z SATURDAY. LOW TEMPERATURES ARE EXPECTED TO FALL INTO
THE 30S ACROSS THE FORECAST AREA...IF SKIES CLEAR AND WINDS BECOME
LIGHT. SOME AREAS COULD SEE SOME FROST SATURDAY MORNING...AT THIS
TIME...WILL LEAVE MENTION OUT OF THE FORECAST. IN ADDITION...THE
10.12Z GFS/NAM BUFKIT SOUNDINGS AT LSE INDICATE WINDS LESS THAN 10
KNOTS BELOW 1000 FEET FRIDAY NIGHT. COMBINED WITH SOME
PRECIPITATION AROUND THE FORECAST AREA ON FRIDAY...HAVE INTRODUCED
PATCHY FOG IN RIVER VALLEYS EARLY SATURDAY MORNING.

MAIN FORECAST CONCERN ARE SMALL PRECIPITATION CHANCES SUNDAY INTO
MONDAY...THEN TEMPERATURES THE TUESDAY INTO WEDNESDAY. THE 10.12Z
GFS/GEM/ECMWF ARE IN GOOD AGREEMENT IN DIGGING UPPER LEVEL TROUGH
INTO THE NORTHEAST UNITED STATES AND GREAT LAKES REGION BY 12Z
MONDAY. THE ONE DIFFERENCE BETWEEN THE 10.00Z GFS/GEM/ECMWF IS
TIMING OF THE EMBEDDED SHORTWAVE TROUGH PUSHING INTO THE GREAT
LAKES REGION SUNDAY INTO MONDAY. THE MODELS ARE INDICATING DECENT
PV ADVECTION AND DEEP QG FORCING IN ASSOCIATION WITH SHORTWAVE
TROUGH. THE 10.12Z GFS BUFKIT SHOWS LITTLE IF ANY INSTABILITY
ACROSS FORECAST AREA. WILL CONTINUE WITH CHANCE OF SHOWERS ACROSS
MUCH OF THE FORECAST AREA SUNDAY INTO MONDAY. WITH THE REGION
UNDER NORTHWEST FLOW ALOFT AND COOLER AIR ADVECTING INTO THE GREAT
LAKES REGION BEHIND SHORTWAVE TROUGH/SURFACE FRONT...TEMPERATURES
WILL REMAIN SLIGHTLY BELOW NORMAL SUNDAY THROUGH WEDNESDAY. AS
THE 10.12Z GEFS SHOW 850MB STANDARD ANOMALIES OF MINUS 0.5 TO
MINUS 1 DEGREE CELSIUS OVER THE FORECAST AREA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1100 PM CDT WED SEP 10 2014

CLOUD SHIELD OF MOSTLY MVFR CIGS CONTINUES TO EXTEND WESTWARD INTO
THE NORTHERN PLAINS...PER LATEST FOG/STRATUS SATELLITE IMAGERY AND
SFC OBS. BUFKIT AND RH TRENDS ARE TO KEEP THESE LOW CLOUDS ACROSS
THE TAF SITES THROUGH WED MORNING. AFTER THAT...MODELS START TO
DISAGREE WITH HOW QUICKLY THE CIGS WILL LIFT...WITH THE GFS BEING
THE QUICKER. VFR CIGS ARE EVIDENT OVER CENTRAL MN...AND 850 MB WINDS
ARE NEARLY DUE SOUTH OVERNIGHT THROUGH WED MORNING...BUT 700 MB
WINDS WESTERLY. THE BUMP IN CIGS COULD COME EARLIER THAN PREVIOUSLY
THOUGHT...AND HAVE SKETCHED THIS INTO THE FORECAST - ALTHOUGH STILL
PESSIMISTIC WITH A LATE AFTERNOON IMPROVEMENT. THIS WILL BE THE MAIN
STICKING POINT FOR THE FORECAST.

&&

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

$$

SHORT TERM...DTJ
LONG TERM....DTJ
AVIATION.....RIECK



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