FXUS63 KFSD 080808 CCA
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA  
NATIONAL WEATHER SERVICE SIOUX FALLS SD
310 AM CDT THU MAY 8 2003

COMPLEX FORECAST OVER THE NEXT 24 HOURS AS UPPER LOW MOVES ACROSS 
THE CWA.  REALLY TWO DIFFERENT MECHANISMS FOR PRECIPITATION ACROSS 
THE CWA TODAY.  IN THE WESTERN CWA...PRIMARILY WILL SEE STRATIFORM 
RAIN DUE TO ISENTROPIC LIFT OVER COLDER AIR PRODUCED BY EVAPORATIVE 
COOLLING.  EXPECT RAIN TO BEGIN AS SHOWERS EARLY IN THE SOUTH 
CENTRAL AND THEN BY MID MORNING BECOME GENERAL STRATIFORM RAIN.  
WHILE HOURLY AMOUNTS WILL BE LIGHT...TOTAL RAINFALL THROUGH THE 
EVENT WILL LIKELY BE A WIDESPREAD HALF INCH.  IN THE EASTERN 
CWA...PRECIPITATION WILL BE MORE CONVECTIVELY DRIVEN.  FIRST WAVE OF 
PRECIPITATION EXPECTED TO MOVE INTO THE SUX CITY AREA BY MID MORNING 
AND THEN PROGRESS NORTHEAST THROUGH THE DAY.  THEN EXPECT A 
BREAK...ESPECIALLY ACROSS NORTHWEST IOWA LATER THIS AFTERNOON.  THIS 
WILL ALLOW THE 850 MB FRONT TO APPROACH AND AS THE UPPER WAVE 
REACHES THE AREA THIS EVENING...EXPECT ANOTHER AREA OF THUNDERSTORMS 
TO DEVELOP IN EASTERN NEBRASKA AND MOVE ACROSS NORTHWEST IOWA.  THIS 
WILL BRING ANOTHER BATCH OF RAIN FROM SUX TO SPW AREA. THERE IS THE 
POTENTIAL FOR AN INCH OR MORE OF RAIN OVER A LARGE AREA BETWEEN THE 
TWO AREAS OF CONVECTION ACROSS NORTHWEST IOWA.  EXPECT THIS 
CONVECTION TO END AFTER MIDNIGHT.  IN THE WEST...AN INVERTED TROUGH 
FORMS ACRS NEBRASKA THIS AFTERNOON AND MOVES INTO SRN SD BY 06Z.  
PCPN WILL BE ALL AHEAD OF THE TROUGH AGAIN AND ANY CHANCE OF RAIN 
WILL END WITH ITS PASSAGE.  BY 12Z...THE TROUGH EXTENDS FROM NEAR 
WINDOM MN TO HURON SD.

ON FRIDAY...LOW CLOUDS WILL LINGER ALONG AND NORTH OF THE INVERTED 
TROUGH.  THIS TROUGH WILL HANG OUT AROUND THE NRN EDGE OF THE CWA 
MUCH OF THE MORNING.  THIS WILL MEAN A CONTINUED CHANCE OF RAIN 
THROUGH THE MORNING.  IT WILL ALSO MEAN HIGH TEMPERATURES STRUGGLING 
TO GET ABOVE 60 DEGREES.  IN THE SRN CWA...SKIES ARE EXPECTED TO 
CLEAR.  WITH WESTERLY FLOW AND 850 MB TEMPS AROUND 10C...TEMPS WILL 
RISE WELL INTO THE 60S WITH THE MISSOURI VALLEY SEEING 70 DEGREES.  
ON FRIDAY NIGHT...CLOUDS WILL COME BACK INTO THE CWA AHEAD OF THE 
NEXT SYSTEM.  HOWEVER...WITH THE UPPER ENERGY STILL BACK IN THE 
ROCKIES AND THE 850 MB TEMP GRADIENT OVER SRN NEBRASKA...DO NOT 
EXPECT PRECIPITAITON TO REACH THE CWA.

LARGE MODEL DIFFERENCES ON SATURADAY.  THE CANADIAN HAS AN OPEN WAVE 
AND LITTLE PRECIPITATION WHILE THE ETA AND GFS SHOW PRECIPITATION 
DEVELOPING ALONG THE 700 MB FRONTOGENESIS AXIS ON SATURDAY AND 
CONTINUING INTO SATURDAY NIGHT.  WITH THE PRECIPITATION COMES 
EVAPORATIVE COOLING WILL KEEP 850 MB AOB 5C.  THIS WILL MEAN TEMPS 
IN THE 50S ACROSS THE CWA WITH THE COOLEST TEMPS WHERE RAIN IS MOST 
LIKELY IN THE EASTERN CWA.  RAIN WILL END FROM WEST TO EAST SATURDAY 
NIGHT.  WITH COLD AIR ALOFT TEMPS WL FALL INTO THE 30S IN THE WEST 
WITH 40S IN THE EAST.

.FSD...NONE

$$

SCHUMACHER