Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 121743
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1242 PM CDT FRI SEP 12 2014

.UPDATE...
ISSUED AT 1242 PM CDT FRI SEP 12 2014

STILL LOOKING CLOSELY AT LOW TEMPERATURES TONIGHT BUT INITIAL PLANS
ARE TO ISSUE FROST ADVISORY GIVEN CLEARING SKIES AND LIGHT WINDS
TONIGHT FOR AREAS AWAY FROM MISSISSIPPI AND WISCONSIN RIVER VALLEYS.
COORDINATION TAKING PLACE WITH SURROUNDING NWS OFFICES.

ALSO CONCERNED WITH VALLEY FOG...ESPECIALLY SOUTH AND EAST OF LSE.
SOME WIND NOTED IN BUFKIT SOUNDINGS JUST OFF THE DECK SO NOT SURE OF
EXTENT OF IT. WILL KEEP PATCHY VALLEY FOG IN FORECAST.

NEED A COMBO WORD FOR FROST AND FOG.

&&

.SHORT TERM...(TODAY THROUGH THROUGH TONIGHT)
ISSUED AT 315 AM CDT FRI SEP 12 2014

MAIN CONCERNS INCLUDE RAIN CHANCES TODAY AND FROST POTENTIAL LATE
TONIGHT.

IR SATELLITE VERY EARLY THIS MORNING SHOWING INCREASING MID/HI-LEVEL
CLOUDINESS STREAMING IN FROM THE PLAINS. TEMPERATURES WERE IN THE
MIDDLE 30S ACROSS PORTIONS OF CENTRAL WI...AND IN THE LOWER/MIDDLE
40S ELSEWHERE ACROSS THE FORECAST AREA. WATER VAPOR IMAGERY/RAP
500MB ANALYSIS SHOWS THE MID/HIGH-LEVEL CLOUDINESS TIED TO A
DEEPENING TROUGH OF LOW PRESSURE DROPPING SOUTHEAST INTO THE
NORTHERN/CENTRAL PLAINS. RADAR MOSAIC SHOWING FAIRLY EXPANSIVE AREA
OF RAIN EXTENDING ACROSS NEBRASKA INTO NORTHWEST IA/FAR SOUTHERN MN.

WILL CONTINUE TO SEE THAT MID-LEVEL TROUGH DEEPEN AND ROTATE
SOUTHEASTWARD INTO/THROUGH THE UPPER MISSISSIPPI RIVER VALLEY
REGION TODAY INTO TONIGHT. MAIN DYNAMIC DRIVERS FOR RAINFALL WILL BE
STRONG 850-300MB PV-ADVECTION ALONG WITH DECENT 700-500MB
FRONTOGENESIS. MOST OF THIS FORCING APPEARS TO BE ACROSS NORTHEAST
IA INTO CENTRAL WI...SO PLACED HIGHEST/CATEGORICAL POPS THERE. WILL
LIKELY SEE AROUND 1/4 INCH OF RAINFALL ACROSS THIS AREA. ALSO...
FREEZING LEVEL WILL BE FAIRLY LOW FOR THIS TIME OF YEAR//AROUND
3KFT//...SO THIS WILL LIKELY HOLD TEMPERATURES DOWN QUITE A BIT. AS
A RESULT...HIGHS TODAY EXPECTED TO ONLY BE IN THE UPPER 40S TO THE
LOWER 50S AND THERE IS THE POTENTIAL FOR RECORD LOW HIGH READINGS.
PREVIOUS RECORD LOW HIGH FOR LA CROSSE FOR SEPTEMBER 12 WAS 51
DEGREES SET IN 1902 AND 53 DEGREES AT ROCHESTER SET IN 1989. WILL
HAVE TO WATCH THIS CLOSELY TODAY.

FOR TONIGHT...RAIN EXPECTED TO LINGER INTO THE EVENING HOURS...BUT
THEN STRONG SUBSIDENCE TAKES OVER AFTER MIDNIGHT WITH THE WAVE
PULLING OFF TO THE EAST AND SURFACE/MID-LEVEL RIDGE BUILDING IN.
THIS IS EXPECTED TO CLEAR SKIES FROM WEST TO EAST...BUT GFS AND
ESPECIALLY THE NAM HOLDING ONTO STRATUS THROUGH MOST OF THE NIGHT
EAST OF THE MISSISSIPPI. THINKING IF WE CLEAR OFF MORE
RAPIDLY...AND GIVEN LIGHT/CALM WINDS...WE COULD SEE SOME VERY CHILLY
TEMPERATURES AND SUBSTANTIAL FROST POTENTIAL. ON THE OTHER
HAND...WITH LINGERING LOWER LEVEL BOUNDARY MOISTURE AREAS OF FOG MAY
BE MORE LIKELY AND THUS HOLD DOWN FROST POTENTIAL. FOR THIS
REASON...KEPT FROST WORDING TO PATCHY/AREAS AND WILL LET UP TO THE
DAY SHIFT TO ASSESS FURTHER IF A HEADLINE WILL BE NEEDED.
OTHERWISE...THINKING THERE WILL BE QUITE A BIT OF FOG IN THE
MISSISSIPPI/WISCONSIN RIVER CHANNELS AND THEIR TRIBUTARIES.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 315 AM CDT FRI SEP 12 2014

HIGH PRESSURE WILL PROVIDE A SUNNY/COOL SATURDAY WITH HIGHS IN THE
MIDDLE 50S TO THE LOWER 60S.

ANOTHER CHANCE OF RAIN WILL COME ALONG SUNDAY AFTERNOON THROUGH
MONDAY AS A COLD FRONT SLIPS SOUTHEAST ACROSS THE REGION. PRE-COLD
FRONTAL WARMING ON SUNDAY SHOULD BOOST TEMPERATURES INTO THE 60S
WITH MONDAY ABOUT THE SAME OR A COUPLE DEGREES COOLER BEHIND THE
FRONT.

HIGH PRESSURE WILL BE THE DOMINANT WEATHER FEATURE FROM TUESDAY
THROUGH THURSDAY FOR DRY AND UNSEASONABLY COOL CONDITIONS. PLAN
ON HIGHS IN THE 60S AND LOWS IN THE 40S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1237 PM CDT FRI SEP 12 2014

MID LEVEL FRONTOGENETIC BAND PRODUCING RAIN MUCH OF TODAY CONTINUES
TO PRODUCE MVFR TO VFR CEILINGS. BULK OF LOWER CEILINGS ARE SOUTH
AND EAST OF TAF SITES...WITH CONDITIONS EXPECTED TO IMPROVE LATE IN
THE DAY AS THESE BANDS MOVE OFF WITH SHORT WAVE FORCING.

RAPID CLEARING EXPECTED GOING INTO THIS EVENING AS SURFACE RIDGE
BUILDS IN. WITH CLEARING SKIES...MOIST LOW LEVELS AND LIGHT WINDS...
SOME VALLEY FOG EXPECTED...ESPECIALLY SOUTH AND EAST OF KLSE. EXTENT
OF THIS UNCLEAR WITH 10-15 KTS ON HIGHER SIDE OF BOUNDARY LAYER.

VFR CONDITIONS WILL PREVAIL SATURDAY ONCE VALLEY FOG BURNS OFF AS
SURFACE RIDGE PASSES THROUGH.

&&

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

$$

UPDATE...SHEA
SHORT TERM...DAS
LONG TERM...DAS
AVIATION...SHEA


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