FXUS63 KFSD 041653
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1055 AM CST FRI DEC 4 2009
.DISCUSSION...
FRESHENED UP THE GRIDS SOME FOR THE MID MORNING HOURS...TWEAKING
MAINLY ONLY SKY COVER THE MOST. THE HOURLY TEMPS CONT TO BE IN GREAT
SHAPE. THEREFORE IT LOOKS LIKE OUR MAX TEMPS TODAY WL BE VERY CLOSE
TO OUR GOING FCST. BACK TO THE CLOUDS...PERUSED OVER THE 12Z UTC
NAM40 SNDGS...AND THEY STRONGLY HINT AT A THIN LAYER OF INSTABILITY
CUMULUS DEVELOPING FOR THE REST OF THE DAY...GENERALLY ALONG AND
EAST OF A YANKTON TO DE SMET SD LINE. THEREFORE THE CLEAR AREA IN SW
MN SHOULD BEGIN TO FILL IN RATHER RAPIDLY DURING MIDDAY. SO OUR ERN
TWO THIRDS WL LIKELY SEE A MOSTLY CLOUDY TO PARTIAL FILTERED
SUNSHINE FOR THE REMAINDER OF THE DAY. NOW OUR WRN THIRD MAY REMAIN
FAIRLY CLEAR...AS THE SDNGS ARE QUITE A BIT DRIER IN THAT AREA.
THINKING THAT HURON TO MITCHELL WILL BE PARTLY CLOUDY...WITH SUNNY
OR MOSTLY SUNNY AROUND CHAMBERLAIN. WL PROBABLY FRESHEN UP THE ZFP
AFTER 11 AM...MAINLY TO FINE TUNE SKY COVER. WL KEEP THE MENTION OF
A CHC OF FLURRIES THIS AFTERNOON WHERE WE HAVE THEM NOW...WHICH IS
WHERE THE LOW LEVEL MOISTURE IS THE DEEPEST. /MJF
&&
.PREV DISCUSSION...
WNWLY FLOW OF COLD AND FAIRLY MOIST LOW LVL AIR OVER CWA WITH
PATCHWORK OF SC CLOUDS AND SCT FLUR THIS MRNG. THIS SHOULD GET
SCOURED OUT FM W TO E OVER THE CWA THIS AFTN WITH DRYING AND
WARMING FM ALOFT. HOWEVER...NOT CONDUCIVE TO MUCH MIXING AND
WITH LIGHT SNOW COVER...CUT BACK HIGHS A LIT FOR TDA. TEMPS SHOULD
DROP PRETTY FAST THIS EVE WITH CLRG AND BEFORE SSWLY FLOW KICKS IN.
SATURDAY BEST DAY OF FCST WITH SOME MIXING DOWN OF WARMER AIR FROM
ALOFT...MAINLY IN SRN CWA...WITH SNOW COVER RESTRICING WARMING UP
NORTH ESP FM BKX TO SWRN MN. THEN THE USUAL ADVENTURE WITH FLIP/
FLOPPING MODELS. GFS DID A SWAP WITH THE NAM FM YESTERDAY FOR THE
LATE SUN SYSTEM...WITH NOW THE GFS MUCH WEAKER AND FURTHER SOUTH.
HOWEVER...CANADIAN AND ECMWF STILL SUPPORT CHCS -SN DVLPG NEWD INTO
THE CWA MAINLY SOUTH OF I90 BY SUN NGT WITH SHORT WAVE AND LOBE OF
ISENTROPIC LIFT...WITH STILL AN INCH OR TWO PSBL MAINLY NWRN IA...
SO WILL NOT DROP THE BALL BASED ON THE GFS. THIS MODEL ALSO ALL OVER
THE PLACE WITH PSBLY MAJOR WAVE CRASHING NEWD INTO THE CNTRL PLAINS
TUES...AND THE NOTORIOUS 06Z GFS RUN HAS REALLY BACKED OFF. BUT A
COMPOSITE OF THE ECMWF...CANADIAN...AND GFS WOULD STILL IMPLY A
PRETTY GOOD CHC OF AT LEAST LIGHT SNOW MOVING NEWD OVER THE SERN HLF
OF THE CWA LATER MON NGT INTO TUES NGT...SO UPPD THE POPS SOME FM
PREV FCST. OTRW CUT BACK THE TEMPS SOME ACROSS THE BOARD FM SUN THRU
TUES WITH NRN STREAM DOMINATION OF CANADIAN AIR AND POTENTIALLY NEW
SNOW. HOPEFULLY LATER RUNS OF THE GFS WILL SETTLE DOWN TO SOME KIND
OF SOLUTION FOR LATER FCSTS./ RYRHOLM
&&
.AVIATION...
LATEST NAM40 SNDGS SUGGEST MVFR CIGS PREVAILING E OF THE JAMES RIVER
VALLEY THIS AFTERNOON...AS INSTABILITY CU FORMS DUE TO VERY COLD AIR
ALOFT. THERE MAY BE A FEW FLURRIES UNDER THESE CLOUDS HERE AND
THERE...BUT OVERALL THE VIS WL LIKELY BE VFR MOST OF THE TIME. ALONG
AND EAST OF THE JAMES RIVER VALLEY...WE SHOULD BE PRIMARILY VFR THIS
AFTERNOON. TONIGHT AFTER THE SUN SETS...LOOKS LIKE THE FSD FORECAST
AREA WL HAVE VFR CONDS. /MJF
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
$$
