FXUS63 KFSD 280308
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
908 PM CST FRI NOV 27 2009

.DISCUSSION...
WITH CI/CS PATCHY AT BEST ACRS CWA THIS EVNG...AND LIGHT GRADIENT
SURROUNDING THE WK TROUGH/FRONTAL ZONE THRU FAR WRN CWA...RAPID 
TEMPERATURE FALL THIS EVENING HAS FAR OUTDONE THAT PICTURED IN 
EARLIER GRIDS. UPDATED RIGHT AROUND SUNSET...BUT EVEN THE DROP AT 
THAT TIME WAS INSUFFICIENT BY MID EVENING FOR SOME OF THE TYPICAL
RADIATIVE COOLING SUSPECTS. HOWEVER...WHEN LOOKING AT THE OVERALL 
NIGHT...ONLY FOUND IT NECESSARY TO NUDGE SOME LOWER ELEVATION SPOTS 
DOWN A DEGREE OR TWO...AS EXPECT THAT MOST AREAS ARE PROBABLY 
CLOSING IN ON FIRST APPROACH TO LOWS WITHIN THE NEXT COUPLE OF HOURS 
BEFORE WARMER TMPS ALFT AND AT LEAST SOME S/E GRADIENT AHEAD AND 
INCREASING NLY GRADIENT BEHIND WK WIND SHIFT WORKS INTO THE 
EQUATION...ALONG WITH THE PATCHY HIGH CLDS. DID INSERT SOME PATCHY
FOG INTO FAR ERN AREAS AHEAD OF THE WIND SHIFT...WITH T/TD SPREAD
SUGGESTED IN RUC TO BE SMALL ENOUGH FOR DEEP ENOUGH TO WARRANT A 
LITTLE FOG MENTION. NO CHANGES TO ZFP EXPECTED...UPDATED THE PFM
RECENTLY.  /CHAPMAN
&&

.AVIATION...
VFR ACRS THE CWA THRU 21Z SATURDAY. SC WL DEVELOP IN THE HON VCNTY 
AFTER 21Z WITH CIGS BKN040.

&&

.PREV DISCUSSION...
CI/CS HAS THINNED...MORE SHUD BE SPREADING ACRS THE AREA JUST N OF 
FCST AREA TNGT BUT SKIES OVER OUR AREA SHUD BE CLR TO PTCLDY. WEAK 
AND DIFFUSE CDFNT WILL BE DVLPG NEAR WRN END OF FCST AREA AND DRIFTG 
EWD OVER AREA TNGT INTO ERY SAT MRNG. NAM/NAM12 SEEM TO HANDLE WEAK 
AND BROAD WSHFT REASNBLY WITH GNLY LGT NRLY/NNWRLY SFC WNDS DVLPG 
OVER MOST OF AREA BY DAYBREAK. REASNBL COOLING CONDS SHUD ALLOW 
TEMPS TO DROP TO NEAR GUIDNCE LOWS...A COMPROMISE BTWN WARMER MET 
AND COOLER MAV TEMPS LOOKS GOOD. FOR NOW EXPECT THAT THOSE WNDS WILL 
BE LGT ENUF AND FNT DIFFUSE ENUF TO NEGATE ANY MIXING STG ENUF TO 
PRODUCE A LATE NGT TEMP RISE.  /WILLIAMS

NOT A LOT GOING ON IN THE INTERMEDIATE TERM. MAIN FEATURE IS A WEAK 
MID AND UPPER S/W MOVG ACROSS THIS AREA SAT NIGHT. MOISTURE IS 
RATHER SHALLOW...THEREFORE ONLY KEPT THE MENTION OF FLURRIES GOING 
SAT NIGHT. OTHERWISE WE ARE LOOKING AT DRY CONDS THRU MONDAY AS THE 
NRN STREAM TAKES OVER WITH INCREASING UPPER RIDGING AS TIME 
PROGRESSES. CONCERNING TEMPS...MOST LOCATIONS MIX TO AROUND 900MB ON 
SATURDAY WITH THE STOUT NW FLOW OFF THE SFC. THEREFORE WARMED UP MAX 
TEMPS ON SATURDAY ABOUT A CATEGORY. THE ONE EXCEPTION IS AROUND 
HURON WHERE INCREASING CLOUDS IN THE AFTERNOON MAY SHUT OFF THEIR 
WARMING SOME. OTHERWISE IT WL BE COOLER ON SUNDAY...THEN SEVERAL 
DEGS WARMER ON MONDAY.    /MJF

IN THE EXTENDED MON NIGHT THRU FRIDAY...IN GENERAL A LARGE AND COLD 
UPPER TROF GETS CARVED OUT THRU THE EXTENDED PERIOD ACROSS THE ERN 
HALF OF THE CONUS. THE DEVIL IS IN THE DETAILS AT THE INITIAL PHASE 
OF THE UPPER TROF...IN HOW QUICKLY THE COLD AIR RUSHES INTO THIS 
AREA. THE GFS WAS BY FAR THE QUICKEST SOLUTION WITH THE INITIAL 
CDFNT ON TUE. IT WAS QUICKER THEN THE ENS MEAN...MOST ENS MEMBERS...
AND FASTER THAN THE 00Z GLOBAL GEM AND ECMWF. THE LATEST 12Z ECMWF 
THREW A CURVE BALL AT ALL OF THIS...AND ALSO GREATLY SPED UP ITS 
CDFNT PASSAGE ON TUE TO NEARLY MATCH THE LATEST GFS RUNS. IF THIS 
HAPPENS...WE MAY BE TOO WARM ON TUE AND WL HAVE TO ADJUST TONIGHT OR 
ON SATURDAYS FCST. WILL SEE. BUT OTHERWISE WE ARE LOOKING AT A 
SEASONABLY CHILLY FCST WED THRU FRI. SOME MODIFICATION IN TEMPS ARE 
IN ORDER ON FRIDAY AS THE UPPER LOW BEGINS MOVG EWD...AND WE MAY 
HAVE TO WARM THAT REGION MORE WITH SATURDAYS FCST. SO FAR LEFT THE 
EXTENDED DRY...BUT WOULD NOT RULE OUT SOME FLURRIES AT LEAST ON 
THURSDAY.   /MJF

&&

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

$$