FXUS63 KARX 060804
AFDARX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
304 AM CDT SAT SEP 6 2008

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

MAIN FORECAST CONCERNS ARE ON PRECIPITATION CHANCES LATE TONIGHT AND
SUNDAY AND THEN AGAIN MONDAY AND MONDAY NIGHT.

AT 08Z WATER VAPOR IMAGERY SHOWS SHORTWAVE ROTATING THROUGH
SOUTHERN WISCONSIN. LIGHT PRECIPITATION ASSOCIATED WITH IT HAD MOVED
INTO EASTERN WISCONSIN. INFRARED SATELLITE IMAGERY STILL SHOWING
SOME LINGERING STRATUS ACROSS THE FORECAST AREA...BUT AREAS THAT
HAVE CLEARED FOG WAS BEGINNING TO FORM.

06.00Z NAM/GFS CONTINUE TO SHOW LONGWAVE TROUGH TO RESIDE ACROSS THE
UPPER MISSISSIPPI RIVER VALLEY REGION THROUGH THE PERIOD.
DIFFERENCES DO OCCUR WITH TIMING AND STRENGTH OF SHORTWAVES
AFFECTING THE AREA. THE FIRST WILL BE LATE TONIGHT AND SUNDAY WITH
ANOTHER ONE MONDAY AND MONDAY NIGHT. HAVE USED A BLEND APPROACH IN
HANDLING BOTH OF THESE WAVES.

IN THE NEAR TERM...SHORTWAVE TO CONTINUE TO MOVE AWAY FROM THE AREA
THIS MORNING. LINGERING STRATUS AND FOG WILL DISSIPATE THIS
MORNING...BUT RUC AND NAM MODEL SOUNDINGS SHOW CUMULUS TO
REDEVELOP BY MIDDAY. WEAK HIGH PRESSURE AT THE SURFACE WILL KEEP
THINGS DRY TODAY WITH TEMPERATURES SIMILAR TO YESTERDAY.

FIRST SHORTWAVE MOVES THROUGH THE LONGWAVE TROUGH AND APPROACHES THE
AREA LATE TONIGHT AND SUNDAY. POTENTIAL VORTICITY ADVECTION ALONG
WITH UPPER LEVEL DIVERGENCE DUE TO COUPLED JET WILL ENHANCE LIFT
ACROSS THE AREA. ISENTROPIC UPGLIDE ON THE 300K SURFACE REACHES THE
WESTERN AREAS LATE TONIGHT AND ACROSS THE REMAINDER OF THE FORECAST
AREA ON SUNDAY. WITH CONSISTENT SIGNAL...HAVE RAISED POPS INTO THE
LIKELY CATEGORY FOR MOST LOCATIONS...ESPECIALLY ACROSS THE CENTRAL
AND NORTHERN SECTIONS.

AS WAVE PUSHES EAST SUNDAY NIGHT WILL HOLD ON TO EVENING POPS WITH
DRY CONDITIONS AFTER MIDNIGHT. THIS BREAK WILL BE SHORT LIVED AS
YET ANOTHER SHORTWAVE HEADS TOWARD THE AREA. GFS FASTER IN TAKING
THIS WAVE ACROSS IOWA ON MONDAY...WHILE NAM KEEPS BULK OF
LIFT/PRECIPITATION MONDAY NIGHT. WITH WARM FRONT RESIDING WELL TO OUR
SOUTH BOTH THE GFS AND NAM SHOWING BAND OF FN CONVERGENCE TO THE
NORTH OF THE SURFACE BOUNDARY. THIS FORCING/LIFT WILL HAVE TO BATTLE
A SOMEWHAT DRY SURFACE TO 700MB LAYER OVER THE FORECAST AREA THAT MAY
INHIBIT THE NORTHERN EXTENT OF THE SATURATION. HAVE CONTINUED POPS IN
THE CHANCE CATEGORY BOTH MONDAY AND MONDAY NIGHT WITH THE HIGHER ONES
ACROSS THE SOUTHERN ZONES CLOSER TO THE STRONGER FORCING.

TEMPERATURES RATHER TRICKY WITH CLOUDS AND PRECIPITATION AROUND THE
AREA. WENT NEAR GUIDANCE FOR AFTERNOON HIGHS TODAY THEN BELOW
GUIDANCE WITH CLOUDS AND RAIN EXPECTED SUNDAY. SIMILAR TO PREVIOUS
GRIDDED FORECAST.

.LONG TERM...TUESDAY THROUGH FRIDAY

NO CHANGES MADE TO THIS TIME FRAME. BOTH 06.00Z GFS AND ECMWF SHOW
GOOD CONSISTENCY THROUGH THE PERIOD. SURFACE HIGH PRESSURE SETTLES
OVER THE AREA TUESDAY AND PUSHES EASTWARD BY WEDNESDAY AS RETURN
FLOW AHEAD OF THE NEXT SHORTWAVE OVERSPREADS THE AREA. WARM
ADVECTION SHOWERS AHEAD OF APPROACHING WAVE ON WEDNESDAY WITH BETTER
CHANCES FOR RAIN WEDNESDAY NIGHT AS COLD FRONT MOVES ACROSS THE
AREA. SYSTEM LOOKS TO EXIT BY THURSDAY NIGHT WITH DRY WEATHER FOR
THE END OF THE WORK WEEK. TEMPERATURES LOOK TO REMAIN BELOW NORMAL
THROUGH THE PERIOD...ESPECIALLY WITH AFTERNOON HIGHS. CURRENT
GRIDDED DATABASE HAS ALL THIS WELL IN HAND.

&&

.AVIATION...TODAY AND TONIGHT

CONCERN THIS MORNING WILL BE FOG POTENTIAL IN WAKE OF DEPARTING
SHORTWAVE TROUGH. IFR FOG/STRATUS DEVELOPED AT KRST TAF SITE WITH
CLEARING SKIES. EXPECT FOG ALSO TO DEVELOP AT KLSE ONCE MID CLOUD
COVER DEPARTS EAST WITHIN THE NEXT HOUR OR SO. FOG/STRATUS WILL LIFT
AROUND 15Z ONCE GOOD MIXING OCCURS WITH WESTERLY AIRFLOW. WEAK AREA
OF HIGH PRESSURE WILL KEEP THE AREA DRY TODAY. OTHERWISE...COLD AIR
ALOFT WILL PRODUCE ENOUGH INSTABILITY FOR SCT-BKN CUMULUS FIELD WITH
BASES IN THE 3-4KFT RANGE AFTER 17Z. ANOTHER MID-LEVEL SHORTWAVE
TROUGH WILL ROTATE EAST INTO THE UPPER MIDWEST THIS EVENING AND
OVERNIGHT FOR A CHANCE OF -SHRA AT THE KRST/KLSE TAF SITES AFTER
MIDNIGHT. WILL LIKELY INTRODUCE A VCSH MENTION AT THE KRST/KLSE TAF
SITES AFTER 06Z WITH THE 12Z TAF ISSUANCE. OTHERWISE...EXPECTING VFR
CONDITIONS OVERNIGHT.

&&

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

$$

SHORT/LONG TERM...RABERDING
AVIATION..........DAS

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