FXUS63 KFSD 281040
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD
440 AM CST SAT NOV 28 2009

.DISCUSSION...
RELATIVELY QUIET FORECAST THROUGH THE PERIOD...WITH CONCENTRATION ON 
MILD ROLLER COASTER TEMPERATURES THROUGH THE EARLY PART OF THE WEEK 
AND TIMING OF MUCH STRONGER COLD FRONT TUESDAY/TUESDAY NIGHT.

FOR TODAY...LOOKING AT MAINLY HIGH LEVEL MOISTURE STREAMING ACROSS 
THE NORTHERN PORTIONS OF THE CWA UNTIL LATE AFTERNOON...WHEN DEEPER 
MID LEVEL MOISTURE WORKS INTO FAR NORTHWEST CWA AHEAD OF APPROACHING 
UPPER WAVE. NORTHWEST LOW LEVEL FLOW SHOULD ALLOW FOR MODEST MIXING 
TO AROUND 900MB...YIELDING HIGHS IN THE MID 40S TO LOWER 50S TODAY.

MAIN QUESTION WITH THE UPPER WAVE FOR TONIGHT IS WHETHER WE WILL SEE 
ANY PRECIP REACHING THE GROUND. BEST DYNAMIC SUPPORT WITH NORTHERN 
STREAM WAVE REMAINS NORTH OF OUR AREA...GIVING LOCATIONS TO OUR 
NORTH THE BEST CHANCE OF SEEING FULL LAYER SATURATION. FORECAST 
SOUNDINGS FROM BOTH 00Z NAM AND 00Z GFS MAINTAIN SOMEWHAT DRIER AIR 
IN 800-700MB LAYER...ESPECIALLY ALONG/SOUTH OF THE I-90 CORRIDOR. 
THUS HAVE TRIMMED BACK FLURRY MENTION TO NORTHERN TWO TIERS OF 
COUNTIES IN OUR CWA. MUCH DRIER AIR WORKING IN BEHIND THE WAVE TO 
PROVIDE CLEARING SKIES ACROSS THE NORTHWEST LATE TONIGHT...WITH 
PARTLY SUNNY SKIES EXPECTED ACROSS THE NORTH AGAIN ON SUNDAY WITH 
COOLER MID LEVEL AIR ALLOWING FOR CU DEVELOPMENT BY LATE MORNING. 
WESTERLY WIND SHOULD AGAIN PROVIDE MODEST MIXING...THOUGH COOLER 
THAN TODAY WITH HIGHS IN THE UPPER 30S TO MID 40S.

UPPER RIDGING WILL PROVIDE MORE SUNSHINE ON MONDAY...AND THAT ALONG 
WITH STRONGER WESTERLY LOW LEVEL FLOW SHOULD LEAD TO WARMER DAY WITH 
HIGHS IN THE MID 40S TO LOWER 50S. SOUTHWEST FLOW AHEAD OF THE NEXT 
FRONTAL SYSTEM SHOULD KEEP TEMPS MILD MONDAY NIGHT...ESPECIALLY IN 
HIGHER ELEVATIONS AND DOWNSLOPE AREAS EAST OF THE BUFFALO RIDGE. 

MODELS STILL HAVING DIFFICULTY SETTLING ON TIMING OF FRONTAL PASSAGE 
TUESDAY...WITH OPERATIONAL GFS REMAINING THE FASTEST SOLUTION WHILE 
THE 00Z ECMWF BACKED OFF FROM ITS PREVIOUS TREND TOWARD THE GFS AND 
NOW FAVORING THE SLOWER END OF THE SPECTRUM...CLOSER TO THE 00Z 
OPERATIONAL GEM AND GFS ENSEMBLE MEAN. 00Z NAM WAS OUTLIER TO THE 
SLOW SIDE...AND OPTED TO FAVOR ECMWF/GEM BLEND FOR TIMING THE 
BOUNDARY FOR NOW. THIS PLACES THE FRONT IN OUR SOUTHEAST CWA BY 00Z 
WEDNESDAY...AND WOULD EXPECT NORTHWEST AREAS OF THE CWA TO REMAIN 
COOLER...POSSIBLY EVEN SEEING FALLING TEMPS IN THE AFTERNOON...WHILE 
SOUTHEAST AREAS ENJOY ONE MORE MILD DAY BEFORE PROVERBIAL BOTTOM 
DROPS OUT. THOUGH THE BOTTOM IN THIS CASE REALLY JUST MEANS GETTING 
TEMPERATURES CLOSER TO OR JUST A LITTLE BELOW SEASONAL NORMALS...IN 
CONTRAST TO THE WELL ABOVE NORMAL TEMPERATURES WHICH HAVE BEEN SEEN 
THROUGH THE MONTH OF NOVEMBER.

&&

.AVIATION...
LIGHT FOG IN RIVER VALLEYS ALONG AND EAST OF INTERSTATE 29 MAY 
REDUCE VSBYS BELOW 6SM INTERMITTENTLY THROUGH 14Z. VFR CONDITIONS 
EXPECTED FROM 14Z-06Z. WINDS WILL GRADUALLY TURN TO THE NORTHWEST 
AND SLOWLY INCREASE TO 10 TO 15 KTS BY MID TO LATE AFTERNOON. WINDS 
SHOULD SLOWLY DIMINISH AFTER 06Z TONIGHT...ESPECIALLY IN THE JAMES 
VALLEY. CIGS MAY FALL BELOW MVFR NORTH OF I90 AFTER MIDNIGHT...BUT 
EXPECTED TO STAY ABOVE MVFR IN THE MISSOURI VALLEY INTO SUX AND SLB.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.

$$
 JH/SCHUMACHER