Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 240825
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
325 AM CDT FRI OCT 24 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 244 AM CDT FRI OCT 24 2014

FOG AND CLOUDS THE INITIAL CONCERN TODAY...THEN SMALL RAIN
CHANCES THIS AFTERNOON AND EVENING. 07Z NEPHANALYSIS AND
SATELLITE FOG ENHANCEMENT IMAGERY SHOWING EXTENSIVE LOW CLOUD
AND DENSE FOG SHROUDING THE FORECAST AREA. THIS THANKS TO THE
RAIN AND CLOUD COVER YESTERDAY. MEANWHILE A WEAK SHORT WAVE TROUGH
WAS APPROACHING FROM THE EASTERN DAKOTAS WHICH WILL PASS THIS
AFTERNOON. WARM ADVECTION AND MOISTURE TRANSPORT SUGGESTED BY
MODELS FOR THE AFTERNOON HOURS...WITH SEVERAL OF THE SHORT TERM
MESOSCALE MODEL SOLUTIONS PAINTING SOME VERY LIGHT QPF ACROSS THE
LOCAL AREA. PLENTY OF CHALLENGES TO CONTEND WITH.

FIRST...LOCAL STUDIES AND USE OF GOES-R CLOUD THICKNESS PRODUCT
SUGGEST THAT THE LOW CLOUD WILL BE VERY DIFFICULT TO MIX OUT.
COMBINE THAT WITH THE ADDED WARM ADVECTION AND MOISTURE
TRANSPORT...AS WELL AS MORE CLOUD COVER ALOFT TO LIMIT THE INFLUX
OF SUNSHINE TO HELP MIX AND ERODE THE BOUNDARY LAYER INVERSION...
OUR FEELING IS THAT THE AREA WILL STAY CLOUDY THROUGH THE DAY. DO
ANTICIPATE THAT THE DENSE FOG WILL LIFT...BUT WE MAY NEED TO
EXTEND THE ADVISORY BEYOND THE 10 AM EXPIRATION TIME IN SOME
AREAS.

WITH SHORT WAVE APPROACHING...WEAK Q-G SIGNAL SEEN IN THE LOWER
LAYERS. WHILE THE FORCING IS SOMEWHAT LIMITED...THERE IS ENOUGH
THAT WARRANTS INCLUSION OF LOW CHANCES FOR LIGHT RAIN SHOWERS
THIS AFTERNOON AND EARLY EVENING...MAINLY SOUTH OF I-90. THANKS
FOR THE COORDINATION MKX/DVN/DMX.

FOR TONIGHT...DO ANTICIPATE SOME CLEARING...BUT FORECAST SOUNDINGS
SHOW THE LOW LEVEL INVERSION REMAINS IN PLACE. FEEL THERE IS
POTENTIAL FOR SOME AREAS OF FOG AGAIN. COULD BE SOME PATCHY AREAS
OF DENSE FOG...BUT DIFFICULT TO PIN DOWN AT THIS TIME. WILL ALLOW
DAY SHIFT TO GET A BETTER GRASP ON POTENTIAL BASED ON WHAT
TRANSPIRES WITH RESPECT TO CLOUD/FOG/RAIN TODAY.

TEMPERATURES LIKELY TO BE SURPRESSED TODAY THANKS TO ALL OF THE
ABOVE...SO HAVE UNDERCUT PREVIOUS FORECAST AND EVEN GUIDANCE.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 244 AM CDT FRI OCT 24 2014

HIGH PRESSURE BUILDS IN ON SATURDAY...AND WILL BE CENTERED
DIRECTLY OVERHEAD SUNDAY MORNING. THUS A DRY AND MAINLY CLEAR
PERIOD IS ANTICIPATED. SOUTHERLY WINDS CRANK UP ON SUNDAY AHEAD
OF THE NEXT LONG WAVE TROUGH APPROACHING FROM SASK/MT REGION.
WARM ADVECTION AND ISENTROPIC UPGLIDE AHEAD OF THIS TROUGH WILL
LEAD TO THE DEVELOPMENT OF CLOUD AND SOME SHOWERS. SOME QUESTION
ON HOW QUICKLY THE DEEPER SATURATION WILL TAKE PLACE FOR SHOWER
DEVELOPMENT SUNDAY NIGHT. BEST CHANCES DO APPEAR TO LIE ALONG AND
NORTH OF THE I-94 CORRIDOR...BUT SPREAD OUT THE RAIN CHANCES TO
ACCOUNT FOR POSSIBLE EARLIER SATURATION. BRIEF DRY PERIOD AS
THE MAIN WARM ADVECTION WING MOVES NORTH. BUT THE COLD FRONT WILL
FOLLOW MONDAY/MONDAY NIGHT. BEST CHANCE FOR RAIN LIKELY TO BE
MONDAY NIGHT...AND EVEN SOME SUPPORT FOR THUNDER. TEMPERATURES
LOOK TO BE QUITE MILD...ESPECIALLY ON MONDAY.

MAIN TROUGH PASSES ON TUESDAY...WITH WRAP AROUND MOISTURE AND COLD
ADVECTION LEADING TO POTENTIAL FOR MORE LIGHT SHOWERS. HIGH
PRESSURE SHOULD PROVIDE FOR MAINLY DRY AND TRANQUIL WEATHER FOR
WEDNESDAY AND THURSDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1139 PM CDT THU OCT 23 2014

THE FOG HAS SETTLED IN AT BOTH TAF SITES WITH IFR CONDITIONS. THE
VISIBILITY HAS YET TO COME DOWN TO IFR AT KLSE AS THE VALLEY SEEMS
TO BE PROTECTING IT SOME...AS IT IS AT OTHER MISSISSIPPI RIVER
VALLEY AIRPORTS. HOWEVER...BELIEVE THIS IS ONLY TEMPORARY AND WILL
CONTINUE THE TREND OF BRINGING THE VISIBILITY DOWN TO 1/4SM FOR
THE OVERNIGHT INTO FRIDAY MORNING. THE TREND IN THE RAP THIS
EVENING HAS NOT BEEN AS QUICK TO DISSIPATE THE FOG AS THE
AFTERNOON RUNS SO HAVE HELD ON TO THE LOW VISIBILITIES THROUGH THE
MIDDLE OF THE MORNING WITH THE LOW CEILINGS DISSIPATING DURING THE
LAST HALF OF THE MORNING. THE MODELS CONTINUE TO SHOW A MID LEVEL
SHORT WAVE TROUGH COMING ACROSS THE AREA FRIDAY AFTERNOON WITH
MIXED SIGNALS WHETHER THIS WILL PRODUCE A MVFR CEILING OR NOT. THE
24.00Z NAM CONTINUES TO BE THE MOST AGGRESSIVE AND HAS MVFR
CEILINGS DEVELOPING EARLY IN THE AFTERNOON. THE 24.02Z RAP AND
24.00Z GFS HAVE ALSO TRENDED THIS WAY WHILE THE 23.21Z SREF MEAN
REMAINS DRIER. MIXED SIGNALS IN THE NUMERICAL GUIDANCE AS WELL
WITH THE GFS BASED MOS AND LAMP GUIDANCE NOT SHOWING ANYTHING FOR
THE AFTERNOON WHILE THE NAM BASED MOS HAS THE MVFR CEILINGS. FOR
NOW...WILL CONTINUE WITH JUST SHOWING SOME SCATTERED CLOUDS AS
CONFIDENCE IN THE AMOUNT OF MOISTURE WITH THIS SYSTEM REMAINS LOW.


&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL 10 AM CDT THIS MORNING FOR WIZ017-029-
     032>034-041>044-053>055-061.

MN...DENSE FOG ADVISORY UNTIL 10 AM CDT THIS MORNING FOR MNZ079-
     086>088-094>096.

IA...DENSE FOG ADVISORY UNTIL 10 AM CDT THIS MORNING FOR IAZ008>011-
     018-019-029-030.

&&

$$

SHORT TERM...MW
LONG TERM...MW
AVIATION...04



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