Area Forecast Discussion
Issued by NWS La Crosse, WI

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000
FXUS63 KARX 311723
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
1223 PM 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 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1223 PM CDT THU JUL 31 2014

BULK OF THE AREA IS BETWEEN SHORTWAVES TODAY. DIURNAL WARMING/MIXING
LOOKING TO PRODUCE LITTLE MORE THAN A SCT TO LCL BKN VFR CUMULUS
DECK THIS AFTERNOON...WITH THREAT OF ANY SHRA/TSRA NORTH/EAST OF THE
TAF SITES. THESE CLOUDS TO DISSIPATE WITH SUNSET.

SFC WINDS REMAIN LIGHT TONIGHT WITH MODEL SOUNDINGS CONTINUING TO
SHOW WINDS OF LESS THAN 10KT THRU 700MB TONIGHT. THIS FAVORABLE FOR
LATE NIGHT/EARLY MORNING RADIATIONAL VALLEY FOG AT SITES LIKE KLSE.
HOWEVER LOWERING DEW POINTS AND MIXING THIS AFTERNOON THEN HOW MUCH
DEW POINTS RISE THIS EVENING REMAIN THE BIG QUESTIONS. 17Z DEW
POINTS REMAINED NEAR OR ABOVE TONIGHTS EXPECTED LOWS BUT THEY WERE
LOWERING AT MID DAY WITH THE DEEPER DIURNAL MIXING. INCLUDED A BCFG
SCT006 AT KLSE IN THE 09-13Z PERIOD FOR NOW. 00Z TAF CYCLE WILL HAVE
A BETTER FEEL FOR THE DEW POINT TRENDS TONIGHT AND IF BR/FG CHANCES
AT KLSE WOULD REQUIRE MORE OF A BR/FG MENTION AND SOME VSBY
RESTRICTION IN THE TAF. GOOD VFR EXPECTED FRI MORNING IN THE 13-18Z
PERIOD ONCE ANY BR/FG WOULD LIFT/BURN OFF.

JUST BEYOND THIS TAF PERIOD...THERE IS A STRONGER SIGNAL FOR SCT
SHRA/TSRA NEAR/AT THE TAF SITES...WITH SOME MVFR CONDITIONS FRI
AFTERNOON/EVENING. THIS AS A STRONGER SHORTWAVE...COOLER TEMPS ALOFT
AND A BIT MORE LOW LEVEL MOISTURE COMBINE TO PRODUCE MORE
INSTABILITY AND LIFT ACROSS THE AREA.

&&

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

$$

SHORT TERM...DTJ
LONG TERM....DTJ
AVIATION.....RRS



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