Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 191232
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
732 AM CDT TUE AUG 19 2014

.UPDATE...
ISSUED AT 730 AM CDT TUE AUG 19 2014

A WEST WIND OF 5 MPH HAS DEVELOPED ACROSS CENTRAL WISCONSIN...
DUE TO THE SURFACE LOW THAT WAS SITTING THERE SHIFTING OFF TO THE
EAST. THIS BREEZE WAS ENOUGH TO QUICKLY IMPROVE VISIBILITIES IN
THE DENSE FOG ADVISORY AREA...THUS THE DENSE FOG ADVISORY HAS BEEN
CANCELLED A LITTLE EARLY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 411 AM CDT TUE AUG 19 2014

AREAS OF DENSE FOG HAVE DEVELOPED OVER PORTIONS OF CENTRAL WISCONSIN
EARLY THIS MORNING. A DENSE FOG ADVISORY HAS BEEN ISSUED FOR
JACKSON...CLARK...AND TAYLOR COUNTIES WHERE THE VISIBILITY HAS
FALLEN TO 1/4 MILE OR LESS. LOOK FOR THIS FOG TO DISSIPATE BETWEEN 8
AND 9 AM THIS MORNING.

LATEST WATER VAPOR IMAGERY SHOWED A VIGOROUS UPPER LEVEL TROUGH OVER
THE UPPER MISSISSIPPI  RIVER VALLEY...PUSHING SOUTHEAST. SHOWERS
AND THUNDERSTORMS HAVE MOVED EAST OF THE FORECAST AREA EARLY THIS
MORNING. THE TROUGH WILL CONTINUE TO SWING ACROSS THE AREA TODAY
AND IS EXPECTED TO GENERATE SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS. NAM FORECAST SOUNDINGS SHOW TALL SKINNY CAPE
PROFILES TODAY WITH ONLY 400-500 J/KG OF SBCAPE NOTED. MESOSCALE
MODELS ARE REALLY NOT GENERATING MUCH CONVECTION THIS
AFTERNOON...MAINLY SHOWING SCATTERED SHOWERS FOR LOCATIONS NORTH
OF INTERSTATE 90. AFTER WE DESTABILIZE LATE THIS MORNING INTO THIS
AFTERNOON WE SHOULD SEE THE SCATTERED SHOWERS AND ISOLATED STORMS
DEVELOP. THIS ACTIVITY WILL THEN TAPER OFF LATE THIS AFTERNOON
INTO THIS EVENING WITH THE LOSS OF DAYTIME HEATING. PLAN ON HIGHS
TODAY RANGING FROM THE LOWER 70S OVER NORTH CENTRAL WISCONSIN TO
THE UPPER 70S ACROSS NORTHEAST IOWA. FOCUS TURNS TO DENSE FOG
POTENTIAL LATE TONIGHT INTO WEDNESDAY MORNING...ESPECIALLY ALONG
VALLEY LOCATIONS. SURFACE HIGH PRESSURE SETTLES OVER THE FORECAST
AREA LATE TONIGHT SETTING THE STAGE FOR LIGHT WINDS FROM THE
SURFACE THROUGH 4 KFT. WITH SKIES BECOMING MOSTLY CLEAR AND DEW
POINTS IN THE UPPER 50S TO LOWER 60S WE SHOULD SEE AREAS OF DENSE
FOG DEVELOP. ALSO...THE NAM FORECAST SOUNDING AT KLSE LOOKS VERY
FAVORABLE FOR A VALLEY FOG EVENT.

.LONG TERM...(WEDNESDAY THROUGH MONDAY)
ISSUED AT 411 AM CDT TUE AUG 19 2014

AFTER SOME MORNING FOG...PARTLY TO MOSTLY SUNNY SKIES WILL BE THE
RULE ACROSS THE AREA ON WEDNESDAY AS LOW PRESSURE LIFTS NORTH OUT
OF THE CENTRAL PLAINS. THE LOW WILL PUSH A WARM FRONT INTO THE
FORECAST AREA WEDNESDAY NIGHT INTO THURSDAY MORNING...BRINGING A
VERY JUICY AIRMASS INTO THE REGION. PRECIPITABLE WATER VALUES
INCREASE TO 1.8 TO 2.1 INCHES AND WARM CLOUD DEPTH TO 4.4 KM. THE
STORMS DURING THIS TIMEFRAME. A BAND OF SHOWERS AND THUNDERSTORMS
LOOKS TO LIFT NORTHEAST ACROSS THE FORECAST AREA FROM LATE
WEDNESDAY NIGHT INTO THURSDAY MORNING. THE THUNDERSTORMS WILL BE
VERY EFFICIENT RAIN PRODUCERS AND COULD DROP 1 TO 2 INCHES OF
RAINFALL IN A SHORT AMOUNT OF TIME. THE WHOLE SYSTEM IS
PROGRESSIVE SO THIS SHOULD LIMIT FLOODING CONCERNS BUT GIVEN THE
AIRMASS CANNOT RULE OUT NEEDING SOME HYDROLOGY HEADLINES WEDNESDAY
NIGHT INTO TUESDAY MORNING. THE SHOWERS AND STORMS SHOULD LIFT
NORTHEAST THROUGH THE DAY ON THURSDAY LEAVING A VERY HUMID AIRMASS
ACROSS THE FORECAST AREA IN THE WAKE OF THIS ACTIVITY.

BEYOND THURSDAY THE FORECAST BECOMES CHALLENGING WITH MODELS IN
DISAGREEMENT ON HOW MUCH RIDGING BUILDS INTO THE FORECAST AREA.
THE ECMWF IS THE MOST AGGRESSIVE AND BUILDS HEAT ACROSS THE AREA
GOING INTO THIS WEEKEND. THE GFS KEEPS THE WARM FRONT LINGERING
OVER THE FORECAST AREA ON FRIDAY WITH CONTINUE CHANCES FOR HEAVY
RAINFALL. A HOT AIRMASS IS FOCUSED JUST SOUTH OF THE AREA GOING
INTO THIS WEEKEND AND IT WOULD TAKE MUCH TO GET THE STEAMY AIR
INTO NORTHEAST IOWA AND FAR SOUTHWEST WISCONSIN SO WILL HAVE TO
KEEP A VERY CLOSE EYE ON HOW MUCH RIDGING CAN BUILD OVER THE
AREA...AND WHERE THE FRONT SETS UP. CONVECTION WILL HAVE A HUGE
IMPACT ON TEMPERATURES AND THE LOCATION OF THE BOUNDARY. COOLER
AIR THEN LOOKS RETURN EARLY  NEXT WEEK AS THE BOUNDARY IS PUSHED
TO THE SOUTH OF THE UPPER MISSISSIPPI RIVER VALLEY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 635 AM CDT TUE AUG 19 2014

COOLER AIR FLOWING INTO THE REGION COMBINED WITH RECENT RAINS HAS
LED TO STRATUS DEVELOPMENT OVER RST...AND IS GRADUALLY APPROACHING
LSE. CEILINGS HAVE FALLEN TO LIFR AT RST WITH EVEN SOME IFR/MVFR
BR THERE TOO. ANTICIPATING AN IFR OR MVFR DECK TO FORM SHORTLY AT
LSE. DAYTIME HEATING AND INCREASING NORTHWEST WINDS WILL WORK
TOGETHER ON THE STRATUS AT BOTH TAF SITES...CAUSING CEILINGS TO
RISE THROUGH THE MORNING. BY 19Z...BOTH SITES SHOULD BE VFR. HIGH
PRESSURE BUILDS INTO THE REGION THIS EVENING...CAUSING SKIES TO
CLEAR AND WINDS TO BECOME LIGHT. WITH PLENTIFUL LINGERING MOISTURE
AT THE GROUND...THE SETUP IS VERY FAVORABLE FOR FOG...ESPECIALLY
IN RIVER VALLEYS. VISIBILITIES AND CEILINGS ARE LIKELY TO PLUMMET
TO VLIFR AT LSE BY 10Z...WITH IFR BR OR EVEN LOWER LIKELY AT RST.


&&

.HYDROLOGY...WEDNESDAY NIGHT INTO THURSDAY
ISSUED AT 411 AM CDT TUE AUG 19 2014

THERE IS THE POTENTIAL FOR THUNDERSTORMS  WITH HEAVY RAINFALL
WEDNESDAY NIGHT INTO THURSDAY MORNING. THESE STORMS COULD PRODUCE 1
TO 2 INCHES OF RAINFALL WITH LOCALLY HIGHER AMOUNTS POSSIBLE. THIS
RAINFALL COMBINED WITH RECENT HEAVY RAINS ACROSS PORTIONS OF THE
FORECAST AREA COULD LEAD TO FLOODING CONCERNS. A FLASH FLOOD WATCH
MAY BE NEEDED WEDNESDAY NIGHT INTO THURSDAY MORNING ONCE CONFIDENCE
INCREASES ON EXACTLY WHERE THE HEAVIER RAINFALL WILL OCCUR.

&&

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

$$

UPDATE...AJ
SHORT TERM...WETENKAMP
LONG TERM...WETENKAMP
AVIATION...AJ
HYDROLOGY...WETENKAMP


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