Area Forecast Discussion
Issued by NWS La Crosse, WI

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FXUS63 KARX 050447
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1147 PM CDT TUE AUG 4 2015

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 308 PM CDT TUE AUG 4 2015

LATEST WATER VAPOR SATELLITE IMAGERY INDICATING UPPER LEVEL TROUGH
OVER THE HUDSON BAY/GREAT LAKES REGION AND UPPER LEVEL RIDGE OVER
THE NORTHERN PLAINS. LATEST 20Z SURFACE ANALYSIS SHOWING HIGH
PRESSURE OVER EASTERN IOWA AND SOUTHERN MINNESOTA PROVIDING
MOSTLY/PARTLY SUNNY SKIES ACROSS THE FORECAST AREA.

MAIN FORECAST CONCERN TONIGHT IS THE POSSIBILITY OF FOG
DEVELOPMENT IN RIVER VALLEYS AND PARTS OF CENTRAL WISCONSIN
TONIGHT. SURFACE RIDGE BUILDS INTO EASTERN WISCONSIN AND WILL
PROVIDE LIGHT WINDS ACROSS THE FORECAST AREA. INVERSION DEVELOPS
OVER THE FORECAST AREA...WITH DRY AIRMASS ENTRENCHED OVER THE
REGION. AT THIS TIME...PATCHY FOG WILL BE POSSIBLE IN RIVER
VALLEYS AND AREAS OF FOG POSSIBLE OVER PARTS OF CENTRAL WISCONSIN.

HIGH PRESSURE REMAINS IN CONTROL OF THE FORECAST AREA WEDNESDAY AND
PROVIDE DRY WEATHER AND SEASONAL TEMPERATURES.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 308 PM CDT TUE AUG 4 2015

FOCUS THEN TURNS TO THURSDAY INTO FRIDAY...THE NAM/GFS DPROG/DT
INDICATING SLIGHT AMPLIFICATION OF UPPER LEVEL RIDGE AND SURFACE
WARM FRONT PLACEMENT FURTHER NORTH THAN PREVIOUS RUNS. THIS WOULD
IMPACT TIMING OF LIFT/MOISTURE CONVERGENCE IN ASSOCIATION WITH
SHORTWAVE TROUGH PUSHING INTO NORTHERN MINNESOTA THURSDAY. HAVE
REDUCED PRECIPITATION CHANCES AND CONFINED SMALL PRECIPITATION
CHANCES OVER THE NORTHWEST AND NORTHERN PARTS OF THE FORECAST
AREA THURSDAY.

THE 04.12Z GFS/NAM/ECMWF ARE IN GOOD AGREEMENT IN INCREASING
LIFT/925-850MB MOISTURE TRANSPORT/CONVERGENCE INTO THE FORECAST AREA
WITH SHORTWAVE TROUGH/SURFACE LOW/FRONT THURSDAY NIGHT INTO FRIDAY.
SHOWERS/THUNDERSTORMS ARE LIKELY THURSDAY NIGHT INTO FRIDAY ACROSS
MUCH OF THE FORECAST AREA.

TEMPERATURES THURSDAY INTO FRIDAY WILL BE NEAR NORMAL WITH HIGHS
CLIMBING INTO THE MIDDLE 70S TO LOWER/MIDDLE 80S.

MAIN FORECAST CONCERNS ARE PRECIPITATION CHANCES FRIDAY NIGHT
THROUGH MONDAY. THE 04.12Z GFS/ECMWF/GEM ARE IN GOOD AGREEMENT IN
BUILDING UPPER LEVEL RIDGE OVER THE CENTRAL AND SOUTHERN PLAINS
STATES THROUGH MONDAY...THEN AMPLIFY RIDGE OVER THE ROCKY MOUNTAINS
AND NORTHERN PLAINS TUESDAY. MAIN DIFFERENCES BETWEEN THE MODELS
ARE PLACEMENT AND TIMING OF SHORTWAVE TROUGHS OVER-TOPPING THE
UPPER LEVEL RIDGE INTO THE UPPER MIDWEST/GREAT LAKES REGION.
BASED ON THIS...CONFIDENCE IS LOW ON PRECIPITATION CHANCES THROUGH
MONDAY. THE 04.12Z GFS/ECMWF ARE IN AGREEMENT IN AMPLIFYING UPPER
LEVEL RIDGE OVER THE NORTHERN PLAINS AND ROCKY MOUNTAINS MONDAY
NIGHT AND TUESDAY. THIS SHOULD ALLOW FOR DRY CONDITIONS ACROSS THE
FORECAST AREA.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)
ISSUED AT 1147 PM CDT TUE AUG 4 2015

WHILE LIGHT WINDS EXTEND UP TO 7K FEET...THE TEMPERATURE/DEW POINT
DEPRESSION STILL REMAIN IN THE 7 TO 10 DEGREE RANGE. DUE TO
THIS...JUST EXPECT SOME AREAS OF VALLEY FOG WHICH COULD
POTENTIALLY IMPACT KLSE BETWEEN 05.10Z AND 05.13Z. OTHER THAN THIS
POTENTIAL ISSUE...NO OTHER IMPACTS ARE ANTICIPATED.

&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...BOYNE


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