Hail in Iowa, August 11, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LA CROSSE WI
300 PM CDT SUN AUG 11 2002

MAIN FORECAST CONCERNS CONTINUE TO CENTER ON RAIN CHANCES...FROM
TONIGHT THROUGH MONDAY...AND INTO EARLY TUESDAY.  TEMPERATURE TRENDS
ALSO REMAIN ON THE FOREFRONT.

19Z SURFACE ANALYSIS SHOWS LOW PRESSURE EXTENDING FROM THE DAKOTAS UP
INTO MANITOBA.  WEAK HIGH PRESSURE RUNS FROM THE GREAT LAKES REGION
SOUTH INTO THE LOWER OHIO RIVER VALLEY.  SOUTHERLY FLOW ACROSS THE
UPPER MIDWEST IN THIS REGIME HAS RESULTED IN AN INCREASE IN
TEMPERATURES AND HUMIDITY IN THE BOUNDARY LAYER.  CONVECTION WAS
GOING MOST OF THE DAY FROM NORTHEAST NEBRASKA INTO NORTHERN IA WHERE
THE WARM ADVECTION AND MOISTURE CONVERGENCE WAS FOCUSED.  THIS
ACTIVITY WANED THROUGH THE DAY...BUT THE UNSTABLE AIRMASS HAS ALLOWED
CONVECTION TO FIRE IN HIT-AND-MISS FASHION OVER EASTERN IA AND DOWN
ACROSS MO/KS.  A WARM FRONT REACHED EAST FROM THE DAKOTA LOW ALONG A
LINE FROM NEAR FARGO OVER TO NEAR SIREN WI. CONVECTION HAS ALSO FIRED
ALONG THIS BOUNDARY IN THE LAST 90 MINUTES.

MODELS AGAIN IN REASONABLE AGREEMENT...AND SOLUTIONS CLOSE TO GOING
FORECAST.  NOT MUCH ADJUSTMENT NEEDED EXCEPT AS NOTED BELOW.

WARM FRONT TO CONTINUE MOVING NORTHWARD THIS EVENING WITH THAT
CONVECTION TRACKING NORTH OF THE FORECAST AREA.  SOME SCATTERED
THUNDERSTORMS WILL BE POSSIBLE ABOUT ANYWHERE OVER THE FORECAST
AREA...MAINLY THIS EVENING...WITH THE INSTABILITY PRESENT AND THE
PEAK TEMPERATURE TIME OF DAY. LATER THIS EVENING...LOW LEVEL MOISTURE
TRANSPORT AGAIN INCREASES...AND THIS SHOULD ASSIST MORE DEVELOPMENT
OVER IA/MN.  THE LOW AND COLD FRONT OVER THE DAKOTAS WILL CONTINUE TO
MOVE EASTWARD.  AS THESE FEATURES COME TOGETHER...EXPECT A PRETTY
WIDESPREAD AREA OF PRECIPITATION TO APPROACH THE WESTERN PART OF THE
FORECAST AREA LATE TONIGHT...AND MOVE THROUGH ON MONDAY/MONDAY NIGHT.
 TREND OF THE MODELS THE LAST 3 RUNS HAS BEEN FOR A SLIGHTLY SLOWER
PROGRESSION OF THE FRONTAL PASSAGE WITH EACH SUCCESSIVE RUN.  WITH
THIS IN MIND...HAD TO INCREASE RAIN CHANCES INTO THE LIKELY CATEGORY
MONDAY NIGHT. ALSO RAISED LOW TEMPERATURES BOTH TONIGHT AND MONDAY
NIGHT AS WE WONT SEE THE CLEARING OR INVASION OF COLDEST AIR AS
QUICKLY.  SOME LINGERING RAIN POSSIBLE IN THE FAR SOUTHEAST COUNTIES
EARLY TUESDAY...BUT THEN THE RAIN THREAT SHOULD PUSH EAST OF THE
AREA. FOCUS THEN SHIFTS TO THE TEMPERATURES FOR TUESDAY AND
WEDNESDAY.  850 MB TEMPERATURES NOT FORECAST TO BE QUITE AS COLD AS
PREVIOUS RUNS SUGGESTED /6 DEG C AS OPPOSED TO 2 DEG C/.  HOWEVER...
THESE COOL TEMPERATURES SHOULD STILL RESULT IN BELOW NORMAL READINGS
TUESDAY AND TUESDAY NIGHT.  THIS ALREADY ACCOUNTED FOR IN THE
FORECAST.

LOOKING OUT FROM MID-WEEK INTO THE WEEKEND...PARADE OF RATHER
SIGNIFICANT WAVES IN THE WEST TO NORTHWEST FLOW WILL RESULT IN A
ROLLER COASTER RIDE FOR TEMPERATURES AND RAIN CHANCES.  NEXT WAVE
WITH ATTENDANT COLD FRONT DUE IN WEDNESDAY NIGHT OR THURSDAY...WITH
ANOTHER ONE ON ITS HEELS FOR FRIDAY AND SATURDAY.  AHEAD OF EACH
DISTURBANCE TEMPERATURES SHOULD WARM TO NEAR NORMAL...BUT THEN A
COOL DOWN FOLLOWS EACH.

.LSE...NONE.

MW