375
FXUS63 KARX 042019
AFDARX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
317 PM CDT SAT JUL 4 2009
SHORT TERM
TONIGHT THROUGH TUESDAY
MAIN FORECAST CONCERN WILL BE SHOWER/ISOLD THUNDERSTORM CHANCE GOING
INTO THIS EVENING...THEN AGAIN MONDAY INTO MONDAY NIGHT.
VERY INTERESTING WEATHER SCENARIO THIS AFTERNOON. WAVE OF LOW
PRESSURE NEAR KMCI MO. MAIN SHIELD OF RAIN/RAIN SHOWERS ASSOCIATED
WITH THE LOW NOW SLIPPING SOUTH/EAST OF THE WI/IA BORDERS
RESPECTIVELY. MEANWHILE...MID/HIGH CLOUD SHIELD WAS COVERING MOST OF
THE AREA ALONG AND SOUTH OF I-94. ON THE NORTHERN FRINGES OF THE
CLOUD SHIELD WHERE MORE HEATING WAS OCCURING HOWEVER...RAPID
DESTABILIZATION IS TAKING PLACE WITH LAPS INDICATING 0-2KM
MUCAPE IN THE 900-1500J/KG RANGE. DIFFERENTIAL HEATING/CONVERGENCE
ALONG THIS CLOUD EDGE PRODUCING IDEAL SETUP FOR NON-SUPERCELL
TORNADIC DEVELOPMENT. THERE HAVE BEEN A COUPLE OF REPORTS OF
ROTATION/FUNNELS IN ADAMS/WAUSHARA COUNTIES BETWEEN 1-2 PM. MODELS
SHOWING THIS WEAK CONVERGENT BOUNDARY CONVECTION SLIPPING EVER SO
SLOWLY SOUTHEAST ACROSS THE AREA THIS EVENING. HOWEVER...WITH LOSS
OF HEATING/CAPE BY SUNSET...CONVECTION WILL LIKELY DISSIPATE FAIRLY
RAPIDLY. HOPEFULLY ALL CONVECTION WILL BE DONE BY FIREWORKS DISPLAY
TIME. OTHERWISE...WITH HIGH PRESSURE BUILDING IN FROM THE
PLAINS...SKIES WILL BECOME MOSTLY CLEAR WITH LIGHT WINDS. THIS WILL
LIKELY SETUP A GOOD ENVIRONMENT FOR WI/MS RIVER VALLEY FOG. HAVE
ADDED THIS TO THE WX DATABASE LATE TONIGHT THROUGH EARLY SUNDAY
MORNING.
OTHERWISE...MODELS ARE IN FAIRLY GOOD AGREEMENT WITH OVERALL
SYNOPTIC PATTERN THROUGH THE PERIOD. SOME DIFFERENCES ARISE BETWEEN
GFS/NAM MONDAY NIGHT/TUE TIME FRAME WITH MCS PRODUCTION.
SUNDAY LOOKS DRY AS A WEAK RIDGE OF HIGH PRESSURE BUILDS INTO THE
AREA FROM THE PLAINS.
FOR MONDAY THROUGH MONDAY NIGHT...LOW PRESSURE WILL BE MOVING ACROSS
THE NORTHERN ROCKIES. THIS WILL SET UP DECENT AMOUNT OF MOISTURE
TRANSPORT/LIFT INTO THE NORTHERN PLAINS FOR POSSIBLE MCS
DEVELOPMENT. NORTHWEST FLOW ALOFT/CORFIDI VECTORS WILL PUT THE AREA
ON THE EASTERN FRINGES OF MCS PROPAGATION FROM THE NORTHERN PLAINS.
AS SUCH...HAVE ADDED A SMALL CHANCE OF SHRA/TS INTO THE MON/MON
NIGHT TIME FRAME.
AS STATED IN THE MODEL DISCUSSION...GFS AND NAM SHOW DIFFERENCES IN
HANDLING OF MCS ACTIVITY MONDAY NIGHT/TUESDAY. THE GFS WANTS TO
CONVECT ALONG/NORTH OF A WARM FRONT FROM ND INTO NORTHERN WI WHILE
THE NAM PUSHES THE MCS SOUTHEAST AND OUT OF THE AREA BY 12Z. WHILE
THE UNCERTAINTY EXISTS AND THE AREA REMAINING IN FAVORABLE MCS
GENERATION ZONE...WILL CARRY SMALL CHANCES OF SHRA/TS FOR NOW.
LONG TERM
TUESDAY NIGHT THROUGH SATURDAY
MAIN CONCERN THROUGH THE PERIOD WILL BE SHOWER AND THUNDERSTORM
CHANCES.
LATEST GFS AND ECMWF IN GOOD AGREEMENT THROUGH FRIDAY THEN DIVERGE A
BIT BY SATURDAY. BOTH MODELS SHOWING LOW PRESSURE MOVING OUT OF THE
NORTHERN ROCKIES TUESDAY NIGHT...TO NEAR HUDSONS BAY BY THE END OF
THE PERIOD. THE AREA REMAIN UNDER BROAD SCALE ISENTROPIC
ASCENT/MOISTURE TRANSPORT SCHEME THROUGH WEDNESDAY AS THE WARM FRONT
FROM THE LOW SLOWLY LIFTS NORTHEASTWARD THROUGH THE UPPER MIDWEST.
THIS WILL CONTINUE TO GIVE THE AREA A DECENT SHOT AT SOME SHOWER AND
THUNDERSTORM ACTIVITY. THE COLD FRONT ASSOCIATED WITH THE LOW WILL
DROP SOUTHEAST ACROSS THE AREA THURSDAY NIGHT THROUGH FRIDAY AND
WILL CONTINUE TO PRODUCE A CHANCE OF SHOWERS AND THUNDERSTORMS. AS
STATED BEFORE...DIFFERENCES ARISE FRIDAY NIGHT THROUGH SATURDAY WITH
HOW FAR SOUTH THE COLD FRONT PROGRESSES. THE GFS SHOWS MORE HIGH
ZONAL MID-LEVEL FLOW ACROSS THE NORTHERN TIER CONUS AND THUS HANGS
THE FRONT ACROSS IA INTO NORTHERN IL. MEANWHILE...LOW PRESSURE
DEVELOPS OVER THE CENTRAL HIGH PLAINS...PROVIDING LIFT OVER THE
FRONTAL BOUNDARY FOR THE CHANCE OF SOME ELEVATED CONVECTION. THE
ECMWF ON THE OTHERHAND DEVELOPS A MORE NORTHWESTERLY FLOW ALOFT AND
DRIVES THE COLD FRONT FURTHER SOUTH INTO SOUTHERN IL/CENTRAL MO WITH
STRONGER HIGH PRESSURE BUILDING INTO THE AREA. THEREFORE...THE ECMWF
REMAINS DRY. WILL COMPROMISE FOR NOW AND CARRY A SMALLER CHANCE OF
SHOWERS/THUNDERSTORMS.
AVIATION
SHORT WAVE TROUGH MOVING EAST THROUGH THE CENTRAL PLAINS MAINTAINING
THE CLOUD SHIELD NORTHWARD INTO SOUTHERN MN/WI. SCATTERED LIGHT
SHOWERS HAVE BEEN OCCURRING ALL MORNING...AND THESE LOOK TO CONTINUE
THROUGH THE AFTERNOON. WHERE THERE WAS SOME CLEARING OVER CENTRAL MN
AND NORTHERN WI...DIFFERENTIAL HEATING ALLOWING FOR STEEP LAPSE
RATES AND SCATTERED CONVECTION. VERY SLOW-MOVING...SO IF ONE
DEVELOPS...EXPECT IT TO LINGER FOR A WHILE. MOST OF THIS HAS BEEN
ALONG AND NORTH OF A KEAU-KISW LINE SO FAR...BUT EXPECT THIS TO SAG
SOUTHWARD TOWARD THE TAF SITES LATE IN THE AFTERNOON OR EARLY THIS
EVENING. ACTIVITY SHOULD DIMINISH DIURNALLY. OUTSIDE OF THIS...
CEILINGS PRIMARILY VFR...BUT BRIEF MVFR CONDITIONS MAY BE SEEN NEAR
THE SHOWERS.
OVERNIGHT LOOKS VFR FOR THE MOST PART...BUT OPTED TO ADD SOME MIST
TO THE KRST TAF LATE TONIGHT...AND MAINTAINED THE POSSIBILITY FOR
VALLEY FOG AT KLSE WITH LIGHT FLOW AND MOIST BOUNDARY LAYER
REMAINING.
ARX WATCHES/WARNINGS/ADVISORIES
WI...NONE.
MN...NONE.
IA...NONE.
SHORT/LONG TERM...DAS
AVIATION..........MW
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