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864
FXUS63 KARX 010841
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
341 AM CDT FRI AUG 1 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 341 AM CDT FRI AUG 1 2014

MAIN FORECAST CONCERNS FOR TODAY ARE ON THE POTENTIAL FOR ISOLATED
STRONG TO POSSIBLY SEVERE THUNDERSTORMS THIS AFTERNOON.

A BROAD LOW PRESSURE SYSTEM CENTERED NEAR JAMES BAY WILL START TO
LIFT NORTHEAST TODAY. MEANWHILE A SHORTWAVE TROUGH WILL DROP SOUTH
OUT OF SOUTHERN ONTARIO/NORTHERN MINNESOTA TODAY BRINGING SHOWERS
AND THUNDERSTORMS TO THE REGION. 0-1 KM MLCAPE VALUES CLIMB INTO
THE 1500 TO 2000 J/KG RANGE AHEAD OF THE TROUGH. AMPLE CAPE NOTED
IN THE HAIL GROWTH ZONE TO SUPPORT MARGINALLY SEVERE HAIL. 0-6 KM
BULK SHEAR VALUES ARE RATHER WEAK IN THE 15 TO 20 KT RANGE.
CONSIDERING THE CAPE AND SHEAR VALUES...THE MOST LIKELY STORM MODE
WOULD BE MULTICELL STORMS WITH THE STRONGEST CELLS POSSIBLY
PRODUCING SOME LARGE HAIL. CANNOT RULE OUT SOME GUSTY WINDS AS THE
STORMS COLLAPSE WITH FORECAST SOUNDINGS SHOWING A DRY SUB CLOUD
LAYER...RESEMBLING A SMALL INVERTED V TYPE SOUNDING. FORECAST
MODELS ARE GOOD AGREEMENT DEVELOPING AN AREA OF SHOWERS AND
THUNDERSTORMS OVER PORTIONS OF WEST CENTRAL INTO NORTH CENTRAL
WISCONSIN THIS AFTERNOON WITH THIS ACTIVITY GRADUALLY PUSHING
SOUTH THROUGH THE LATE AFTERNOON INTO THE EARLY EVENING HOURS.
WOULD EXPECT TO SEE BRIEF HEAVY DOWNPOURS WITH THE STORMS AND
POSSIBLY SOME HAIL RANGING IN SIZE FROM PEA TO POSSIBLY QUARTER
SIZE OR A LITTLE LARGER IF MORE CAPE BUILDS THIS AFTERNOON. THIS
ACTIVITY WILL GRADUALLY WANE DURING THE EVENING HOURS AS IT SLIDES
SOUTH. AREAS OF FOG WILL BE A CONCERN TONIGHT OVER VALLEY
LOCATIONS AND CENTRAL WISCONSIN AS WINDS DIMINISH IN THE EVENING.
WINDS WILL BE NEARLY CALM AT THE SURFACE TONIGHT AND LIGHT THROUGH
10 KFT. THESE LIGHT WINDS COMBINED WITH ANY RAIN THAT FALLS THIS
AFTERNOON AND EVENING WILL CREATE FAVORABLE CONDITIONS FOR FOG
DEVELOPMENT.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 341 AM CDT FRI AUG 1 2014

UPPER RIDGING BUILDS INTO THE FORECAST AREA ON SATURDAY.
HOWEVER...FORECAST  SOUNDINGS  SHOW SURFACE BASED CAPE VALUES
CLIMBING TO AROUND 800 J/KG. NOT SEEING A LOT OF SUPPORT FOR
SHOWERS AND STORMS SATURDAY AFTERNOON WITH WEAK SUBSIDENCE OVER
THE REGION BUT CANNOT RULE OUT AN ISOLATED SHOWER OR THUNDERSTORM
OVER PORTIONS OF SOUTHWEST WISCONSIN INTO EXTREME NORTHEAST IOWA
WITH WEAK SURFACE CONVERGENCE OVER THESE AREAS. NORTHWEST FLOW
THEN RETURNS TO THE REGION ON SUNDAY AS A WEAK COLD FRONT SLIDES
INTO THE AREA FROM THE NORTHERN PLAINS. FORECAST MODELS ARE
SHOWING SOME DIFFERENCES IN TIMING THIS FRONT INTO THE FORECAST
AREA. THE NAM IS THE QUICKEST BRINGING THE FRONT THROUGH DURING
THE DAY ON SUNDAY PRODUCING SHOWERS ANDS STORMS ACROSS MUCH OF THE
FORECAST AREA. THE ECMWF IS A LITTLE SLOWER BRINGING THE BOUNDARY
IN SUNDAY EVENING INTO MONDAY MORNING. THE BOUNDARY STARTS TO
SLOW AS IT APPROACHES THE INTERSTATE 90 CORRIDOR AND COULD
POSSIBLY STALL OVER THE AREA. SEVERAL WEAK SHORTWAVES THEN MOVE
OVER THE REGION SUNDAY NIGHT THROUGH TUESDAY AND INTERACT WITH THE
BOUNDARY BRINGING CHANCES FOR SHOWERS AND STORMS TO THE AREA.

LOW PRESSURE LOOKS TO DEVELOP OVER THE CENTRAL PLAINS TUESDAY NIGHT
INTO WEDNESDAY. THE BIG QUESTION IS WHERE WILL A WARM FRONT SET
UP ACROSS THE UPPER MIDWEST. THE ECMWF SHOWS THE FRONT STRETCHING
FROM SOUTHERN SOUTH DAKOTA...SOUTHEAST THROUGH CENTRAL IOWA INTO
CENTRAL ILLINOIS. THIS SOLUTION IS THE OUTLIER AT THIS POINT WITH
THE GFS/GEM SHOWING THE FRONT MUCH FURTHER TO THE NORTH...NEAR OR
JUST NORTH OF THE INTERSTATE 90 CORRIDOR. WILL HAVE TO KEEP A VERY
CLOSE EYE ON THIS FRONT AS IT WILL HAVE A HUGE IMPACT ON WHERE THE
SHOWER AND THUNDERSTORM ACTIVITY OCCURS. HAVE LEANED MORE TOWARD
THE GFS/GEM SOLUTION FOR THE TUESDAY INTO WEDNESDAY TIMEFRAME.
SHOWERS AND THUNDERSTORMS CHANCES LINGER THROUGH THE END OF NEXT
WEEK AS SEVERAL DISTURBANCES CONTINUE TO IMPACT THE REGION IN
NORTHWEST FLOW ALOFT. TEMPERATURES LOOK TO REMAIN BELOW NORMAL
THROUGH THE END OF NEXT WEEK.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1149 PM CDT THU JUL 31 2014

LIGHT WINDS AND CLEAR SKIES EARLY THIS MORNING BRINGS UP CONCERN
FOR VALLEY FOG AT LSE. TEMPERATURE/DEWPOINT SPREADS HAVE REALLY
LOWERED TO A POINT WHERE THEY ARE FAVORABLE FOR VALLEY FOG. THE
ONLY ISSUE IS IT HAS BEEN A FEW DAYS SINCE THE LAST MEASURABLE
RAIN. WITH THE FAVORABLE TEMPERATURE/DEWPOINT SPREAD...HAVE
LOWERED THE CEILING AND VISIBILITY IN THE 10-12Z TEMPO GROUP TO
LIFR. ANY FOG AND STRATUS SHOULD QUICKLY DISSIPATE AFTER 13Z.

VFR CONDITIONS ARE GENERALLY EXPECTED OTHERWISE THROUGH THE
EVENING. HOWEVER...THERE IS POTENTIAL FOR SOME SHOWERS AND STORMS
TO PASS THROUGH THE TAF SITES LATE IN THE AFTERNOON / EARLY
EVENING. CONTINUED TO MENTION A VCTS FOR THIS POTENTIAL.

LOOKING AHEAD...ANOTHER VALLEY FOG NIGHT IS POSSIBLE FOR LSE FOR
LATE FRIDAY NIGHT.

&&

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

$$

SHORT TERM...WETENKAMP
LONG TERM...WETENKAMP
AVIATION...AJ




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