Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 120411
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1110 PM CDT THU SEP 11 2014

.UPDATED...
ISSUED AT 1005 PM CDT THU SEP 11 2014

CLOUDS CLEARED OFF FAIRLY QUICKLY WITH SUNDOWN...WITH NEXT BATCH
ASSOCIATED WITH APPROACHING SHORTWAVE STILL ACROSS WESTERN MN/IA.
TEMPERATURES HAVE FALLEN OFF QUICKLY AS LIGHT SFC WINDS AIDED THE
DIURNAL COOLING. MID 30S LOOKING LIKELY ACROSS PARTS OF NORTH-
CENTRAL WI...AND PATCHY TO AREAS OF FROST COULD DEVELOP. GREATER
THREAT IN THE COLD DRAINAGE AREAS. HAVE ISSUED A FROST ADVISORY FOR
TAYLOR CO WI TO COVER THE POTENTIAL.

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 258 PM CDT THU SEP 11 2014

MAIN FORECAST CONCERNS TONIGHT INTO FRIDAY ARE PRECIPITATION CHANCES.

LATEST WATER VAPOR SATELLITE IMAGERY SHOWING VIGOROUS SHORTWAVE
TROUGH OVER MONTANA AND NORTHERN WYOMING AND WESTERLY FLOW OVER
UPPER MIDWEST AND GREAT LAKES REGION. LATEST VISIBLE SATELLITE
IMAGERY INDICATING CUMULUS CLOUDS DEVELOPING OVER MINNESOTA...AND
WESTERN WISCONSIN AND NORTHEAST IOWA. ALSO...VISIBLE SATELLITE
IMAGERY SHOWING MID LEVEL CLOUDS STREAMING EASTWARD IN ADVANCE OF
VIGOROUS SHORTWAVE TROUGH INTO NEBRASKA...SOUTH DAKOTA AND SOUTHWEST
MINNESOTA. NORTHERLY FLOW NEAR THE SURFACE...COOLER AIRMASS HAS
FILTER INTO THE FORECAST AREA...WITH TEMPERATURE READINGS IN
THE UPPER 40S TO UPPER 50S PER LATEST 20Z METARS.

THE LATEST 11.12Z GFS/NAM CONTINUE TO BE IN GOOD AGREEMENT IN MOVING
VIGOROUS SHORTWAVE TROUGH INTO THE UPPER GREAT LAKES REGION TONIGHT
INTO FRIDAY. THE 11.12Z GFS/NAM SHOW STRONG PV ADVECTION/ISENTROPIC
LIFT AND QG FORCING INTO THE FORECAST AREA AFTER 09Z FRIDAY IN
ASSOCIATION WITH SHORTWAVE TROUGH AND FOCUS THE STRONGEST
FORCING/LIFT TO BE OVER THE SOUTHERN FORECAST AREA DURING THE DAY
FRIDAY. WITH THE MODELS INDICATING GOOD RUN TO RUN CONSISTENCY WITH
THE SHORTWAVE TROUGH...CONFIDENCE IS INCREASING A FRONTOGENETICAL
BAND OF PRECIPITATION WILL DEVELOP AND MOVE OVER THE SOUTHERN
FORECAST AREA AFTER 09Z FRIDAY. HAVE INCREASED POPS AFTER 09Z
FRIDAY.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 258 PM CDT THU SEP 11 2014

NEXT CONCERN IS THE POTENTIAL FOR FROST AND FOG IN RIVER VALLEYS
FRIDAY NIGHT INTO SATURDAY MORNING. THE 11.12Z GFS/NAM CONTINUE TO
PROG COOLER AND DRIER AIR TO ADVECT INTO THE UPPER GREAT LAKES
REGION FRIDAY NIGHT BEHIND DEPARTING SHORTWAVE TROUGH. THE BIG
QUESTION WILL BE HOW FAST SKIES WILL CLEAR OUT FRIDAY EVENING/NIGHT
TO ALLOW FOR A RADIATIONAL COOLING NIGHT. THE LATEST 11.12Z NAM/GFS
BUFKIT SOUNDINGS ARE IN AGREEMENT CLOUDS WILL REMAIN OVER CENTRAL
WISCONSIN THROUGH 06Z SATURDAY...AND SKIES SHOULD BE CLEAR WEST OF
THE MISSISSIPPI RIVER BY 06Z SATURDAY...AS SURFACE RIDGE AXIS BUILDS
INTO WESTERN WISCONSIN. WITH THE COLDEST AIRMASS OVER THE FORECAST
AREA AND LIGHT WINDS...TEMPERATURES WILL FALL INTO THE 30S ACROSS
MUCH OF THE FORECAST AREA. AREAS TO PATCHY FROST CAN BE EXPECTED
WEST OF THE MISSISSIPPI RIVER AND EAST OF THE MISSISSIPPI RIVER. IN
ADDITION...THE 11.12Z GFS/NAM CONTINUE TO SHOW LIGHT WINDS BELOW
1000 FEET FRIDAY NIGHT/SATURDAY MORNING PER BUFKIT SOUNDINGS. WILL
CONTINUE MENTION OF PATCHY FOG AFTER 06Z SATURDAY.

SLIGHTLY WARMER TEMPERATURES ARE EXPECTED SUNDAY...AS THE LATEST
11.12Z GFS/NAM/ECMWF INDICATE 850MB TEMPERATURES WARMING TO PLUS 6
TO PLUS 8 DEGREES CELSIUS...DUE TO SOUTHERLY FLOW ADVECTING WARMER
AIR INTO THE REGION.

MAIN FORECAST CONCERN ARE SMALL PRECIPITATION CHANCES SUNDAY NIGHT
INTO MONDAY...THEN TEMPERATURES TUESDAY INTO FRIDAY. THE 11.12Z
GFS/GEM/ECMWF ARE IN GOOD AGREEMENT IN DIGGING UPPER LEVEL TROUGH
OVER THE NORTHEAST UNITED STATES AND GREAT LAKES REGION THROUGH
THE PERIOD. ALL THE MODELS ARE ALSO IN DECENT AGREEMENT IN PUSHING
STRONG SHORTWAVE TROUGH INTO THE AREA SUNDAY NIGHT INTO
MONDAY...WITH MINOR DIFFERENCES IN PLACEMENT OF SURFACE FRONT. THE
11.12Z GFS SHOWS DECENT QG FORCING AND LIFT WITH SHORTWAVE
TROUGH...HOWEVER GFS BUFKIT SOUNDINGS CONTINUE TO INDICATE ZERO
INSTABILITY. WILL CONTINUE CHANCE OF SHOWERS ACROSS MUCH OF THE FORECAST
AREA. SURFACE RIDGE BUILDS INTO THE UPPER MIDWEST AND GREAT LAKES
REGION AND DOMINATES THE FORECAST AREA TUESDAY INTO THURSDAY.
A SLIGHT DIFFERENCE IS NOTED ON THE STRENGTH OF THE RIDGE BETWEEN
THE GFS AND ECMWF...AS GFS MORE AMPLIFIED THAN THE ECMWF BY 12Z
WEDNESDAY. THIS RIDGE SHOULD PROVIDE DRY WEATHER CONDITIONS AND
NEAR SEASONABLE TEMPERATURES WITH THE 11.12Z GEFS SHOWING ZERO TO
MINUS 0.5 DEGREE CELSIUS STANDARD ANOMALIES ACROSS THE GREAT LAKES
REGION TUESDAY INTO THURSDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY EVENING)
ISSUED AT 1110 PM CDT THU SEP 11 2014

MOST OF THE CLOUDS DISSIPATED WITH THE ADVENT OF SUNDOWN...BUT THE
NEXT BATCH IS APPROACHING FROM THE WEST...ASSOCIATED WITH A
SHORTWAVE TROUGH MOVING INTO THE NORTHERN PLAINS. THIS FEATURE WILL
MOVE ACROSS THE UPPER MISSISSIPPI RIVER VALLEY FRIDAY. QG
CONVERGENCE IS STRONGEST IN THE 500-300 MB LAYER...WITH THE BULK OF
THE FRONTOGENETIC FORCING HOLDING ACROSS IA. MOST MODEL SOLUTIONS
FAVOR KEEPING THE BULK OF THE PCPN CHANCES AND ACCUMULATIONS SOUTH
OF I-90. TIMING SUGGESTS MOVING IN AROUND 15Z...GIVE OR A TAKE A FEW
HOURS...AND EXITING BETWEEN 00-06Z SAT. WHAT KIND OF CIG/VSBY IMPACT
THE PCPN WOULD HAVE ON KRST/KLSE IS IN QUESTION...BEING ON THE
NORTHERN FRINGE OF THE ANTICIPATED PCPN SHIELD...AND HAVING SOME DRY
AIR ALREADY IN PLACE TO CONTEND WITH. NORTH-SOUTH RUNNING X-SECTION
SHOWS AN INCREASE IN MID LEVEL MOISTURE OVERNIGHT...SATURATING THE
LOW LAYERS BETWEEN 15-18Z FRI. BUFKIT SOUNDINGS FAVORING KEEPING VFR
CIGS THROUGH THE PERIOD OF THE PCPN-SHORTWAVE PASSAGE. GOING TO HOLD
THE FORECAST THIS WAY FOR NOW...BUT IF THE SYSTEM SHOULD SHIFT JUST
A BIT MORE NORTH...MVFR CIGS AND SOME LOWER VSBYS ARE LIKELY.

GOOD SUBSIDENCE POST THE SYSTEM SHOULD RESULT IN WEST-EAST CLEARING
OF THE CLOUDS LATER FRIDAY NIGHT. SFC WINDS STAY LIGHT...ALTHOUGH
THE DEPTH OF THE LIGHT WINDS IS IN QUESTION. COULD BE A FAVORABLE
NIGHT FOR VALLEY FOG AT KLSE IF CLOUDS CLEAR QUICKLY AND DEPTH OF
LIGHT WIND LAYER EXCEEDS 2 KFT. SOMETHING TO WATCH FOR.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...

WI...FROST ADVISORY FROM 1 AM TO 8 AM CDT FRIDAY FOR WIZ017.
MN...NONE.
IA...NONE.


&&

$$

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



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