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.
$$
