Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 200451
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1151 PM CDT TUE AUG 19 2014

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 252 PM CDT TUE AUG 19 2014

WATER VAPOR IMAGERY COUPLED WITH RAP 500MB ANALYSIS SHOWING A MID-
LEVEL LOW OVER WESTERN UPPER MICHIGAN. COLD POOL ALOFT ASSOCIATED
WITH THE LOW PRODUCING WIDESPREAD CUMULUS/STRATOCUMULUS FIELD ACROSS
THE FORECAST AREA WITH RADAR EVEN SHOWING A FEW SHOWERS POPPING UP
ACROSS NORTHERN MN INTO NORTHERN WI. OTHERWISE...TEMPERATURE ACROSS
THE ARX FORECAST AREA WERE IN THE 70-80 DEGREE RANGE.

FOR TONIGHT...COULD SEE A FEW SHOWERS NORTHEAST OF I-94 THIS EVENING
BUT THEN EXPECTING CLOUDS TO DIMINISH LATE IN THE EVENING AND
THROUGH THE OVERNIGHT HOURS AS A RIDGE OF HIGH PRESSURE MOVES
OVERHEAD. THIS WILL SET UP FAVORABLE FOG POTENTIAL OVERNIGHT/EARLY
WEDNESDAY MORNING...ESPECIALLY FAVORED RIVER VALLEY LOCATIONS.
THINKING AREAS SOUTHWEST OF I-94 WILL BE MOST IMPACTED WHERE
CONFIDENCE IS HIGHER FOR CLEARING SKY CONDITIONS EXISTS. HELD OFF ON
DENSE FOG ADVISORY FOR NOW BASED ON INPUT FROM SURROUNDING
OFFICES...BUT EVENING FORECASTER WILL HAVE TO MONITOR CLOSELY FOR
POSSIBLE FOG HEADLINE. LOOK FOR LOWS TONIGHT IN THE MIDDLE 50S TO
THE LOWER 60S.

AFTER AREAS OF MORNING FOG...PLAN ON THE RIDGE OF HIGH PRESSURE TO
KEEP THE FORECAST AREA DRY THROUGH WEDNESDAY. AN APPROACHING WARM
FRONT FROM THE CENTRAL PLAINS/MID-MISSISSIPPI RIVER VALLEY WILL
LIKELY SPARK A FEW SHOWERS AND THUNDERSTORMS...BUT PRETTY CONFIDENT
THESE WILL REMAIN SOUTH OF THE AREA. OTHERWISE...EXPECTING HIGH
TEMPERATURES TO TOP OFF IN THE MID 70S TO THE LOWER 80S.

LOOK FOR SHOWERS AND THUNDERSTORMS TO BECOME LIKELY BY LATE
WEDNESDAY NIGHT AS THE WARM FRONT CONTINUES TO APPROACH THE REGION.
ALL MODELS SHOW 850MB MOISTURE TRANSPORT INCREASING INTO/OVER THE
FRONT...WITH BEST AXIS OF MOISTURE PLUME REMAINING JUST WEST OF THE
FORECAST AREA. IN FACT...THE GFS/NAM SHOWING PRECIPITABLE WATER
VALUES SURGING INTO THE 1.5-2 INCH RANGE. THIS COULD LEAD TO SOME
LOCALIZED HEAVIER RAINFALL AS WARM CLOUD LAYER DEPTH INCREASE TO
AROUND 4KM BY MORNING. MAY NEED TO MONITOR THE POTENTIAL FOR A FEW
SEVERE THUNDERSTORMS WITH LARGE HAIL INITIALLY WITH THE INCOMING
CONVECTION AS NAM INDICATING 1-6KM MUCAPE IN THE 2500-3500J/KG RANGE
COUPLED WITH 25-35KT BULK SHEAR.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 252 PM CDT TUE AUG 19 2014

MODELS SHOWING THE WARM FRONT PUSHING NORTHEAST THROUGH THE AREA ON
THURSDAY FOR THE CONTINUED LIKELIHOOD OF SHOWERS AND THUNDERSTORMS.
MODELS ALSO SHOWING 850MB MOISTURE TRANSPORT WANING THROUGH THE
MORNING HOURS AND EVENTUAL CAPPING ALONG AND WEST OF THE MISSISSIPPI
DURING THE AFTERNOON HOURS. AS SUCH...DIVIDED POPS INTO
MORNING/AFTERNOON TIME PERIODS. STILL LOOKING AT THE POTENTIAL FOR
SOME LOCALIZED HEAVY RAINFALL THROUGH THE MORNING HOURS WITH
PRECIPITABLE WATER VALUES LINGERING IN THE 1.5 TO 2 INCH RANGE.
OTHERWISE...LOOK FOR SUBSTANTIALLY MORE HUMID CONDITIONS AS DEW
POINTS CREEP UP INTO THE LOWER 70S. THESE DEW POINTS COMBINED WITH
DAYTIME HIGHS WELL INTO THE 80S FOR MOST OF THE AREA ARE EXPECTED
TO PRODUCE HEAT INDICES IN THE 90 TO 100 DEGREE...HIGHEST ALONG AND
WEST/SOUTH OF THE MISSISSIPPI/WISCONSIN RIVERS.

FOR THURSDAY NIGHT THROUGH THE REST OF THE PERIOD...FORECAST
CONFIDENCE WANES FAIRLY RAPIDLY. MODEL CONSENSUS SHOWS A MID-LEVEL
RIDGE TRYING TO ESTABLISH ITSELF OVER THE CENTRAL CONUS.
HOWEVER...MESSY FLOW WITH MONSOONAL TAP WILL BE IN PLACE ACROSS THE
INTERMOUNTAIN/PLAINS REGION. TIMING OF THESE WAVES PRETTY UNCERTAIN
AT THIS TIME. AS SUCH...WILL KEEP LOW-MEDIUM RANGE
SHOWER/THUNDERSTORM CHANCES IN THROUGH THE PERIOD. TEMPERATURES
THROUGH THE PERIOD LOOK TO STAY AT OR A FEW DEGREES ABOVE NORMAL
THROUGH THE WEEKEND...WITH PERHAPS SOME COOLING EARLY NEXT WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1151 PM CDT TUE AUG 19 2014

CONFIDENCE REMAINS FAIRLY HIGH THAT VALLEY FOG WILL DEVELOP
OVERNIGHT WITH THE MAIN CONCERN JUST BEING WITH SOME SCATTERED MID
LEVEL CLOUDS THAT HAVE BEEN DROPPING SOUTHEAST FROM
MINNESOTA/NORTHWEST WISCONSIN. OTHERWISE...DEW POINT SPREADS ARE
LOW...WINDS ARE CALM AT THE SURFACE AND LIGHT ON UP THROUGH THE
LOWEST 3KFT. THE MAIN QUESTION IS JUST WITH HOW FAST THE FOG WILL
FORM AND THEN DISSIPATE OVERNIGHT. ONSET STILL APPEARS TO BE
AROUND 9Z WITH DISSIPATION COMING AROUND 14-15Z BASED ON
CLIMATOLOGY. WITH THE RIDGE OVERHEAD...WINDS WILL REMAIN CALM WITH
SKIES CLEAR FOR MUCH OF THE DAY BEFORE SHOWERS AND THUNDERSTORMS
DEVELOP WEDNESDAY EVENING. THIS CONVECTION LOOKS LIKE IT WILL
DEVELOP ALONG A NORTHWEST TO SOUTHEAST BAND AND COULD BE HEAVY AT
TIMES...BRINGING VISIBILITY CONDITIONS TO IFR/MVFR.

&&

.HYDROLOGY...WEDNESDAY NIGHT INTO THURSDAY
ISSUED AT 252 PM CDT TUE AUG 19 2014

THERE IS THE LIKELIHOOD FOR SHOWERS AND THUNDERSTORMS WITH THE
POTENTIAL FOR HEAVY RAINFALL WEDNESDAY NIGHT INTO THURSDAY MORNING.
EXPECTING FAIRLY WIDESPREAD 1/4 TO 3/4 INCH RAINFALL WITH LOCALIZED
GREATER THAN 1 INCH AMOUNTS. THIS RAINFALL COMBINED WITH RECENT
POCKETS OF HEAVY RAINS ACROSS PORTIONS OF THE FORECAST AREA COULD
LEAD TO SOME LOCALIZED FLOODING CONCERNS. WILL KEEP A CLOSE EYE ON
LOCALIZED FLOODING CONCERN AND THE POTENTIAL FOR A FLASH FLOOD WATCH
HEADLINE 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.
&&

$$

SHORT TERM...DAS
LONG TERM....DAS
AVIATION...HALBACH
HYDROLOGY...DAS



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