FXUS63 KFSD 270151
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
750 PM CST THU NOV 26 2009

.DISCUSSION...
TEMPERATURES FALLING OFF QUITE QUICKLY THIS EVENING WITH JUST A FEW 
CIRRUS CLOUDS AND LIGHT WINDS PREVAILING.  HAVE LOWERED FORECAST 
LOWS AT KSPW AS TEMPERATURES THERE ARE ALREADY APPROACHING THE 
FORECAST LOW.  WHILE TEMPERATURE SHOULD LEVEL OUT OVER THE NEXT FEW 
HOURS...REDUCED LOW TEMPERATURE TO JUST BELOW GUIDANCE VALUES WHICH 
IS JUST SLIGHTLY BELOW CURRENT DEW POINT VALUES.  

WITH VERY LITTLE PRESSURE GRADIENT AND VERY STOUT INVERSION ACROSS 
THE AREA...EXPECT TO MIXING REALLY STRUGGLE THROUGH THE MORNING 
HOURS. AS A RESULT...HAVE SLOWED WARMING...BUT NOT ALTERED FORECAST 
HIGHS. OTHERWISE...FORECAST IN GREAT SHAPE. /BT

&&
.AVIATION...
VFR CONDITIONS ARE EXPECTED THROUGH 00Z SAT.

&&
.PREV DISCUSSION...
AFTER SFC RDG CONTS TO MOVE EWD OVER AREA THIS AFTN AND ERY EVE...WE 
WILL TRANSITION TO A WARMING LO LVL FLOW WITH OF COURSE SFC WNDS AND 
WARMNG LAGGING BHND LVLS JUST ABV. STILL EXPECT A DECENT EVE TEMP 
DROP OVR ERN ESPLY SERN FCST AREA BUT THEN TEMPS SHUD LVL OFF AND 
PRBLY RISE A DEG OR TWO IN SOME AREAS. WHILE MET GUIDNCE OFTEN FAILS 
TO ACCOUNT FOR ENUF EVE TEMP FALL IN THESE WARM ADVECTION 
PATTERNS...IN THIS CASE THINK IT IS BETTER THAN THE COOLER MAV WITH 
THE WARMING BEING SO STG. DECOUPLING WILL KEEP SFC WNDS FROM PICKING 
UP MUCH BUT A LGT BREEZE ARND 5 KTS WITH THE WARMING WILL STILL HAVE 
SOME EFFECT. CLDS SHUD REMAIN ONLY AREAS OF CI/CS PASSING OVER 
AREA...NEVER REALLY GETTING TOO GREAT IN CVRG OR THICKNS AND DECRG 
FROM THE W LATER TNGT. CUD BE PTCLDY OR MOCLR WITH THE CI SHOWING UP 
UNDER THE WAXING MOON IN THE EVE. /WILLIAMS

FRIDAY STILL LOOKING LIKE A VERY MILD DAY WITH TEMPERATURES RUNNING 
ABOUT 15 TO 20 DEGREES ABOVE NORMAL. A FAIRLY STRONG INVERSION TO 
START THE MORNING NEEDS TO BE OVERCOME...BUT WITH PLENTY OF SUNSHINE 
AND A LIGHT SOUTHERLY WIND...SHOULD NOT BE ANY PROBLEMS. STILL 
AIMING FOR HIGHS FROM AROUND 50 IN SW MN TO NEAR 60 ALONG THE MO 
RIVER VALLEY.

FRIDAY NIGHT QUIET WITH WINDS GOING FROM LIGHT SOUTHERLY TO 
NORTHWEST ABOUT 10 MPH AS A WEAK WAVE MOVES ACROSS NEBRASKA INTO 
IOWA. SKIES SHOULD REMAIN MOSTLY CLEAR HOWEVER WITH LOWS GENERALLY 
IN THE MID 20S TO AROUND 30.

SATURDAY ANOTHER MILD DAY AHEAD OF THE NEXT LARGER SCALE WAVE...SO 
MOSTLY SUNNY MUCH OF THE DAY WITH INCREASING MID AND HIGH CLOUDS BY 
AFTERNOON. HIGHS FROM THE MID 40S TO LOWER 50S. DO EXPECT SLIGHTLY 
FASTER FALLING TEMPERATURES LATE AFTERNOON AND EARLY EVENING AS 
COOLER AIR LEAKS SOUTHWARD.

SATURDAY NIGHT INTO SUNDAY WILL SEE THE APPROACH OF THIS SHEARING 
OUT WAVE...SO MORE CLOUD COVER AND COOLER. WILL CONTINUE DRY BUT A 
FEW FLURRIES WOULD NOT BE OUT OF THE QUESTION. HIGHS COOLER BUT 
STILL ABOVE NORMAL...RANGING FROM THE MID 30S IN SW MN TO THE LOWER 
40S ALONG THE MO RIVER VALLEY.

IN THE LATTER PERIODS(MON/THU)...LOOKS LIKE SOME POTENTIALLY BIG 
CHANGES THROUGH THE PERIOD AS A LARGE SCALE TROF DEVELOPS OVER THE 
CENTRAL UNITED STATES. MONDAY AND TUESDAY LOOK FAIRLY MILD AS A 
NORTHERN STREAM WAVE PASSES WITH RIDGING DEVELOPING AHEAD OF THE 
NEXT WAVE PROGGED FOR TUESDAY NIGHT. THE SOUTHERN UNITED STATES WILL 
SEE A FAIRLY POTENT JET STREAK PASS...WHICH THEN LOOKS TO PHASE WITH 
THE NORTHERN STREAM LATE WEDNESDAY INTO THURSDAY WHICH SETS UP THE 
STRONG CENTRAL U.S. TROF. THE MAIN EFFECTS FROM THIS TROF LIKELY NOT 
TO BE PRECIPITATION BUT REALLY JUST WINDIER AND COLDER CONDITIONS. 
WHILE SOME LIGHT SNOWFALL A POSSIBILITY...NOTHING TO REALLY GRAB ON 
TO AT THIS TIME...SO WILL JUST GO WITH THE COLDER TEMPERATURES. 
MONDAY SHOULD BE THE EARLY BEGINNINGS OF A BRIEF WARM UP...WITH 
TEMPERATURES CLIMBING INTO THE MID 40S IN SC SD. BY TUESDAY...MOST 
OF THIS WARMING WILL SPREAD ACROSS THE ENTIRE CWA AND HAVE BUMPED 
HIGHS UP INTO THE MID 40S TO LOWER 50S. WOULD NOT BE OUT OF THE 
QUESTION TO END UP GETTING EVEN WARMER. BUT...THE NEXT NORTHERN 
STREAM WAVE WILL SWING COLDER AIR SOUTHWARD ON WEDNESDAY AND LIKELY 
BECOME REINFORCED AS THE TWO STREAM PHASE AND DEEPEN THE TROF BY 
THURSDAY. SO...HAVE BACKED OFF HIGHS INTO THE 30S BOTH WEDNESDAY AND 
THURSDAY WITH A FEW 20S ON THURSDAY. /08

&&

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

$$