Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 241505
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1000 AM CDT FRI OCT 24 2014

.UPDATED...
ISSUED AT 1000 AM CDT FRI OCT 24 2014

DENSE FOG IS LINGERING ACROSS THE AREA LATE THIS MORNING...AND HAVE
EXTENDED MOST OF THE ADVISORY THROUGH NOON. HOWEVER...HAVE CONCERNS
THAT THIS WILL NOT BE LONG ENOUGH.

LOW LEVEL MOISTURE TRANSPORT AHEAD OF AN APPROACHING
TROUGH/SHORTWAVE IS RESULTING IN DROPPING VSBYS ACROSS NORTH-CENTRAL
IA - SOME LOCATIONS DROPPING FROM 10 TO 1/4 MILE IN 2 HOURS. THIS
PLUME OF MOISTURE TRANSITIONS ACROSS WESTERN WI LATER THIS
AFTERNOON...FUNNELING MORE MOISTURE UNDER THE INVERSION. DENSE FOG
COULD LINGER INTO THE MID AFTERNOON HOURS. THE FOG IS TRANSITIONING
FROM RADIATIONAL TO MORE ADVECTIVE TYPE FOG. LOTS OF WIND TO THE
WEST...10 TO 20 MPH...PUSHING THE FOG NORTHWARD. NOT SURE THAT
MIXING WILL HAVE ANY IMPACT ON THE VSBYS UNTIL MID/LATE AFTERNOON.

.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 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 635 AM CDT FRI OCT 24 2014

IFR/LIFR CONDITIONS THIS MORNING RESULTING FROM A WEAK PRESSURE
GRADIENT AND VERY MOISTURE LOWER BOUNDARY LAYER. LOOKING FOR A
GRADUAL IMPROVEMENT INTO MVFR CATEGORY IN THE 19-20Z TIME FRAME. A
WEAK WEATHER SYSTEM MOVING INTO THE REGION WILL ALSO PRODUCE A FEW
SHRA DURING THE AFTERNOON HOURS...BUT THINKING THE SHRA WILL BE
ISOLATED IN NATURE ENOUGH TO EXCLUDE FROM THE TAFS FOR NOW. MAY
HAVE TO RE- EVALUATE THIS THOUGH AS THE MORNING WEARS ON. PLAN ON
KRST/KLSE SLIPPING BACK INTO IFR CONDITIONS THIS EVENING AS THE
BOUNDARY LAYER COOLS WITH STILL VERY MOIST CONDITIONS. APPEARS
WINDS WILL THEN SHIFT AND PICK UP OUT OF THE WEST AFTER
MIDNIGHT...SCOURING OUT THE STRATUS AND FOG.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...DENSE FOG ADVISORY UNTIL NOON CDT TODAY FOR WIZ017-029-034-
     041>044-053>055-061.

MN...DENSE FOG ADVISORY UNTIL NOON CDT TODAY FOR MNZ095-096.

IA...DENSE FOG ADVISORY UNTIL NOON CDT TODAY FOR IAZ008>011-018-019-
    029-030.

&&

$$

UPDATE....RIECK
SHORT TERM...MW
LONG TERM...MW
AVIATION...DAS



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