Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 310807
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
307 AM CDT THU JUL 31 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 307 AM CDT THU JUL 31 2014

MAIN FORECAST CONCERNS ARE SMALL PRECIPITATION CHANCES TODAY INTO
THIS EVENING.

LATEST MOSAIC RADAR SHOWS SHOWERS HAVE WEAKENED AND MOVE SOUTHEAST
OF FORECAST AREA. THIS IS IN RESPONSE TO LOSS OF INSTABILITY AND
LIFT IN ASSOCIATION WITH WEAK IMPULSE MOVING INTO SOUTHEAST
WISCONSIN. LATEST METARS INDICATE PATCHY TO AREAS OF FOG HAVE FORM
ACROSS CENTRAL WISCONSIN AND WILL CONTINUE TO LINGER INTO THE
MORNING HOURS BEFORE ERODING WITH DAYTIME HEATING.

BLOCKING PATTERN ALOFT WILL CONTINUE ACROSS MUCH OF THE NORTH
AMERICA CONTINENT THROUGH FRIDAY. SHORTWAVE ENERGY WRAPPING AROUND
CLOSED LOW OVER SOUTHERN HUDSON BAY WILL PRODUCE ANOTHER POSSIBILITY
OF ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS MAINLY EAST OF
THE MISSISSIPPI RIVER THIS AFTERNOON INTO THE EVENING HOURS...AS THE
31.00Z GFS/NAM 31.03Z AND RAP CONTINUE TO SHOW UP TO 1000 J/KG CAPE
PER BUFKIT SOUNDINGS. WILL CONTINUE WITH SMALL CHANCES OF
PRECIPITATION EAST OF THE MISSISSIPPI RIVER.

TONIGHT...THE 31.00Z GFS/NAM BUFKIT SOUNDINGS ACROSS MUCH OF THE
FORECAST AREA ARE INDICATING LESS THAN 10 KNOTS OF WIND AND DEVELOP
AN INVERSION AFTER 06Z FRIDAY. HAVE INTRODUCED AREAS OF FOG IN THE
FAVORABLE RIVER VALLEYS AND CENTRAL WISCONSIN...PATCHY FOG
ELSEWHERE.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 307 AM CDT THU JUL 31 2014

FRIDAY...THE 31.00Z GFS/NAM/ECMWF SHOW A STRONGER SHORTWAVE TROUGH
ROTATING AROUND CLOSED UPPER LEVEL LOW TO TRACK ACROSS THE AREA. NAM
AND GFS INDICATE STEEPENING LAPSE RATES AND INCREASE INSTABILITY OF
500 TO AROUND 1400 J/KG ACROSS THE FORECAST AREA. THE MODELS SHOW
WINDS ALOFT WEAKENING OVER THE AREA AND PRODUCE 0-3KM SHEAR OF LESS
THAN 15 KNOTS. THE THUNDERSTORMS WILL BE CAPABLE OF PRODUCING SMALL
HAIL...POSSIBLY AN ISOLATED LARGE SEVERE HAIL...DUE TO COOLER AIR
ALOFT...STEEP LAPSE RATES AND INSTABILITY.

HEIGHTS RISE AND SHORTWAVE RIDGE BUILDS INTO THE UPPER MIDWEST AND
GREAT LAKES REGION SATURDAY. SUBSIDENCE UNDERNEATH RIDGE WILL ALLOW
FOR A BREAK IN PRECIPITATION CHANCES AND DRY WEATHER CONDITIONS
ACROSS THE FORECAST AREA.

MAIN FORECAST CONCERNS SUNDAY INTO WEDNESDAY ARE PRECIPITATION
CHANCES THROUGH THE PERIOD. THE 31.00Z GFS/ECMWF/GEM CONTINUE TO
INDICATE SHORTWAVE RIDGE BREAKING DOWN OVER THE NORTHERN PLAINS AND
GREAT LAKES REGION SUNDAY INTO EARLY NEXT WEEK. HOWEVER...THE MODELS
DIFFER ON TIMING AND PLACEMENT OF SHORTWAVE TROUGHS/SURFACE FRONT
THROUGH THE PERIOD. THIS WILL HAVE IMPACTS ON THE FOCUS OF SHOWERS
AND THUNDERSTORM DEVELOPMENT ACROSS THE UPPER GREAT LAKES REGION
DURING THE PERIOD. THE 31.0ZZ GFS/ECMWF/GEM SHOW DECENT MOISTURE
TRANSPORT AND CONVERGENCE IN ASSOCIATION WITH THE SHORTWAVE
TROUGHS/SURFACE FRONT THROUGH THE PERIOD. CONFIDENCE IN TIMING AND
PLACEMENT OF SHORTWAVE TROUGHS/SURFACE FRONT IS LOW THROUGH THE
PERIOD. GIVEN THE LIFT AND MOISTURE CONVERGENCE ACROSS THE FORECAST
AREA...CHANCE OF PRECIPITATION ARE WARRANTED THROUGH MUCH OF THE
PERIOD.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z THURSDAY NIGHT)
ISSUED AT 1148 PM CDT WED JUL 30 2014

MAIN AVIATION CONCERN IS VALLEY FOG POTENTIAL AT LSE. SKIES HAVE
CLEARED OUT AND WINDS ARE LIGHT. THESE CONDITIONS SHOULD MAINTAIN
THEMSELVES THROUGH THE REST OF THE NIGHT. WORRIED THAT PREVIOUS
MODEL FORECASTS OF A 10-20 KT WIND AT 1000 FT ABOVE LSE OVERNIGHT
ARE A BIT TOO HIGH GIVEN CALM WINDS CURRENTLY AT THE OFFICE WHICH
IS ABOUT 600 FT ABOVE LSE. THEREFORE...HAVE INTRODUCED AN IFR
VISIBILITY TEMPO GROUP BETWEEN 10-12Z AT LSE. CONDITIONS WILL HAVE
TO BE MONITORED OVERNIGHT. ANY VALLEY FOG OR STRATUS PRODUCED FROM
IT SHOULD MIX OUT QUICKLY...LIKELY BY 1315Z.

OTHERWISE...VFR CONDITIONS ARE ANTICIPATED THROUGH THURSDAY
EVENING. A FEW SHOWERS COULD DEVELOP BUT CHANCES ARE TOO LOW TO
EVEN MENTION A VCSH. LOOKING AHEAD...MORE VALLEY FOG POTENTIAL
EXISTS AT LSE FOR FRIDAY MORNING.


&&

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

$$

SHORT TERM...DTJ
LONG TERM...DTJ
AVIATION...AJ


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