FXUS63 KARX 192015
AFDLSE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
315 PM CDT THU JUN 19 2003

FORECAST CONCERNS THIS PACKAGE...TEMPERATURES THROUGH SATURDAY...THEN
SHRA/TSRA CHANCES FOR SAT NIGHT THRU EXTENDED PERIOD.

18Z DATA ANALYSIS SHOWS CANADIAN HIGH PRESSURE CENTERED OVER THE WEST
END OF LAKE SUPERIOR. WV IMAGERY AND SFC OBS SHOW A DEEP DRY AIRMASS
HAS SETTLED OVER THE REGION. DEWPOINTS ACROSS THE AREA HAVE FALLEN
INTO THE UPPER 30S AND 40S. EARLY AFTERNOON TEMPERATURES ABOUT 10F
COOLER THAN WED...EVEN WITH THE DRY AIRMASS AND ABUNDANT SUNSHINE.
FEW CUMULUS DEVELOPED OVER WESTERN WI AND EASTERN MN...BEING DEPICTED
QUITE WELL BY 12Z ETA CUMULUS RULE.

12Z MODELS SHOW NO MAJOR INITIALIZATION ERRORS...AND OFFER QUITE
SIMILAR SOLUTIONS TO EACH OTHER AND THEIR PREVIOUS RUNS THRU 84 HRS.
12Z GFS MAINTAINS GOOD CONTINUITY WITH ITS 00Z RUN TO 120 HRS. BOTH
ETA/GFS REFLECT REALITY OF SFC AND UPPER LEVEL FEATURES QUITE WELL
AT 18Z...THOUGH BOTH WERE TOO HIGH WITH THE DEWPOINTS ACROSS THE
REGION. FAVORED A BLEND OF ETA/GFS THIS CYCLE...THOUGH WHAT MINOR
MODEL DIFFERENCES THERE ARE LOOK TO HAVE LITTLE IMPACT ON THE
SENSIBLE WEATHER THRU SUNDAY.

FOR THE SHORT TERM...QUIET WEATHER TONIGHT THRU FRI NIGHT AS HIGH
PRESSURE RIDGE AT THE SFC AND ALOFT...WITH THE DEEP DRY AIRMASS...
REMAINS OVER THE REGION. PREVIOUS GRID FORECAST QUITE WELL TRENDED
FOR TONIGHT THRU SAT. CU RULE ON BOTH ETA/GFS INDICATING NO CUMULUS
DEVELOPMENT UNDER THE DRY HIGH ON FRI. COOLEST CORE OF THE HIGH
PASSES OVER THE AREA TONIGHT...WITH THE LIGHTEST WINDS OF THE NEXT
FEW NIGHTS. WITH THE LOW DEWPOINTS/DRY AIRMASS IN PLACE...COOL
LOOKING GUIDANCE LOWS FOR TONIGHT LOOK TO BE IN THE BALLPARK. UNDER
SUNNY SKIES AND 850MB TEMPS ABOUT 3C WARMER THAN TODAY...FAVORED
BLEND OF GUIDANCE HIGHS FOR FRI. WITH CENTER OF THE HIGH DRIFTING OFF
AND SOUTH/SOUTHEAST WINDS INCREASING...GUIDANCE LOWS FOR FRI NIGHT
LOOK REASONABLE. MID LEVEL RIDGE AXIS SHIFTS EAST OF THE AREA EARLY
SAT...WITH THE AREA COMING UNDER DEEPER SOUTH/SOUTHWEST FLOW AS THE
FIRST SHORTWAVE EJECTS OUT OF THE WESTERN TROUGH. MOISTURE INCREASES
THRU THE DAY SAT AS THE HIGH CONTINUES TO MOVE EAST AND THE LEE
TROUGH ADVANCES ACROSS THE PLAINS. MODEL SOUNDINGS AND CAPE/LIFTED
INDEX PROGS INDICATING LITTLE IN THE WAY OF INSTABILITY INTO THE
FORECAST AREA UNTIL SAT NIGHT. CLOUDS TO INCREASE ACROSS THE AREA
SAT...BUT MAINTAINED A DRY FORECAST. MOISTURE/INSTABILITY CONTINUE TO
INCREASE SAT NIGHT WITH APPROACH OF THE SFC-MID LEVEL TROUGH.
PREVIOUS GRID FORECAST OF SHRA/TSRA CHANCE SAT NIGHT LOOKS GOOD. WITH
INCREASING CLOUDS...SOUTH WINDS AND MOISTURE...RAISED SAT NIGHT LOWS
ABOVE GUIDANCE. DECENT 850MB MOISTURE TRANSPORT/WARM ADVECTION...
CAPES OF 1500-2500 J/KG...ALONG WITH 850-7H Q-G CONVERGENCE AHEAD OF
THE APPROACHING TROUGH INDICATED ACROSS THE AREA ON SUN.

MEDIUM RANGE MODELS CONTINUE TO SHOW DECENT CONTINUITY WITH EACH
OTHER AND THEIR PREVIOUS RUNS IN THE MON TO WED TIME FRAME. PER
MEDIUM RANGE MODELS AND ENSEMBLES...CONFIDENCE REMAINS GOOD WITH
TROUGHING REMAINING OVER THE NORTHWEST U.S./NORTHERN PLAINS THRU THE
PERIOD. MON THRU THU LOOKS TO BE AN UNSETTLED PERIOD ACROSS THE UPPER
MIDWEST WITH SEVERAL CHANCES OF TSRA. CONFIDENCE RATHER LOW WITH
TIMING OF INDIVIDUAL EPISODES OF TSRA. OPERATIONAL MODELS AND
ENSEMBLES SHOWING TIMING OF SHORTWAVE TRIGGERS OUT OF THE WESTERN
TROUGH FOR NEXT WEEK IS DIFFICULT AT BEST AT THIS TIME. POSITION OF
SFC TROUGH/OUTFLOW BOUNDARIES FROM SUN/SUN NIGHT CONVECTION WILL HAVE
AN IMPACT ON SHRA/TSRA CHANCES INTO EARLY NEXT WEEK AS WELL. WITH THE
UPPER TROUGH AND BOUNDARIES IN THE AREA...CONTINUED THE BROAD CHANCE
SHRA/TSRA ACROSS THE FORECAST AREA MON THRU THU...THOUGH ENTIRE
PERIOD WILL NOT BE WET.

.LSE...WATCHES/WARNINGS/ADVISORIES...NONE.

$$
RRS