FXUS63 KFSD 040335
AFDFSD
AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA
NATIONAL WEATHER SERVICE SIOUX FALLS SD
935 PM CST THU DEC 3 2009
.DISCUSSION...
THE DIFFERENCE IN CLOUD COVER IS VERY EVIDENT ACROSS THE FORECAST
AREA TONIGHT. CLOUDS CONTINUE TO HANG ON ACROSS THE JAMES RIVER
VALLEY KEEPING READINGS IN THE TEENS...WHILE AREAS FURTHER EAST HAVE
CLEARED OUT ACROSS SOUTHWEST MINNESOTA BLEEDING INTO NORTHWEST IOWA
ALLOWING TEMPERATURES TO FALL INTO THE SINGLE DIGITS. THE CLEARING
SKIES AND FRESH SNOW COVER HAVE ALLOWED THE ATMOSPHERE TO
DECOUPLE...CAUSING WINDS TO FALL OFF MORE THAN ANTICIPATED. STILL
EXPECTING PARTLY CLOUDY SKIES TONIGHT ALONG AND SOUTH OF A LINE FROM
BROOKINGS SD TO SPENCER IOWA...HOWEVER...SPENCER AND AREAS TO THE
SOUTH WILL HAVE A FEW HOURS OF CLEAR SKIES THIS EVENING ALLOWING
TEMPERATURES TO TANK THIS EVENING...THEN RISE AFTER MIDNIGHT AS
CLOUDS MOVE BACK IN. WILL STILL HAVE TO KEEP AN EYE ON TEMPS
THOUGH...AS WOULD NOT BE SURPRISED TO SEE SOMEONE FALL TO NEAR ZERO
TONIGHT WITH SUBZERO DEW POINTS CREEPING INTO THE FORECAST AREA.
UPDATED PRODUCTS OUT. /BT
&&
.AVIATION...
HIGHER END MVFR TO LOW END VFR CONDITIONS ARE EXPECTED THROUGH 00Z
SATURDAY. CLOUD LAYER COINCIDES WITH THE DENDRITIC LAYER...SO WOULD
NOT BE SURPRISED TO SEE A FEW FLURRIES OUT OF CLOUD DECK...BUT AM
NOT EXPECTED ANY REDUCTION IN VISIBILITY BELOW 6SM OR ANY
ACCUMULATION...SO HAVE LEFT MENTION OUT OF TAFS. CLOUDS WILL
GRADUALLY DECREASE DURING THE DAYTIME HOURS ON FRIDAY FROM WEST TO
EAST AS DRIER AIR WORKS IN FROM THE NORTH.
&&
.PREV DISCUSSION...
INTERESTING LITTLE SNOW. HAD A VERY NARROW BAND OF 4 TO 5 INCHES
OCCUR FROM CENTRAL AND EASTERN COTTONWOOD COUNTY IN SW MN...FALLING
OFF TO TWO INCHES TWO MILES SOUTH OF TRACY IN THE EXTREME SE
PORTIONS OF LYON COUNTY. SO SOMETHING VERY LOCAL HAPPENED IN THAT
AREA...LIKELY TERRAIN INDUCED. AT ANY RATE...THE UPPER QG FORCING IS
CONTINUING TO SLIDE SWD WHICH SHOULD HELP TO TAPER OFF THE SNOW IN
SW MN AND EXTREME NW IA THRU THE LATE AFTERNOON HRS. FOR THIS
EVENING...SHALLOW MOISTURE IS PRESENT WHICH SHOULD STRAIN OUT ONLY
SOME SCT INSTABILITY FLURRIES...WITH THE MOISTURE BECOMING EVEN MORE
SHALLOW AFTER MIDNIGHT. SO OPTED TO CHANGE THE OVERNIGHT FCST TO
DRY. INTERESTINGLY...SKY COVER IS A REAL CHALLENGE TONIGHT. A LOT OF
COLD AIR INSTABILITY CU DEVELOPED THIS AFTN AS EXPECTED. ONCE THE
SUN SETS...A LOT OF THIS COULD DRY UP LEAVING A VARIABLY CLOUDY OR
EVEN PARTLY CLOUDY SKY. RIGHT NOW...I HAVE MOSTLY CLOUDY WHICH MAY
BE TOO PESSISMISTIC. SO THE EVENING SHIFT WL HAVE TO WATCH THE SKY
COVER REAL CLOSE. CONCERNING TEMPS...SEEING WHAT HAPPENED TO THIS
MORNING LOWS...AT ABOUT 15 TO 20...DECIDED TO LOWER TONIGHTS LOWS TO
VERY CLOSE TO COLD MET READINGS. ESPECIALLY NOTING THAT THERE MAY BE
AT LEAST SOME PARTIAL CLEARING GOING ON AND LESS WIND. /MJF
MOST OF FRI...AT LEAST THE MRNG AND ERY AFTN...SHUD LIKEWISE SEE A
LOT OF LINGERIN CLOUDS BUT ALSO WITH SIGNIFICANT BREAKS. ELECTED TO
BRING A FEW FLRYS BACK INTO FCST FOR LATE MRNG AND ERY AFTN IN PART
OF SWRN MN DOWN TO SPW. BY THE END OF THE DAY THO TREND SHUD BE FOR
DECENT CLEARING FROM THE W/SW. THIS TREND SHUD CONT FRI NGT WITH SAT
BEING A LONG ADVERTISED BENIGN WX DAY. COLD DAYTIME TEMPS SHUD
MODERATE A LTL BY THEN WITH MET GUIDNCE HIGHS LOOKING REASNBL.
MIXED SIGNALS ON SUN/SUN NGT SNOW THREAT. MODELS HAVE IMPROVED ON
TIMING AGREEMENT WITH CANADIAN AND ECMWF NOT SLOWING THINGS DOWN A
LOT LIKE THEY DID YSTDY. ON THE OTHER HAND MODELS ALSO KEEP WAVE
PRETTY WEAK COMING ACRS...AND ECMWF KEEPS LGT SNOW MOSTLY S OF FCST
AREA. WILL GO WITH GFS FOR NOW AND KEEP TOP 50 PCT POPS FOR SERN CWA
FOR SUN AFTN AND EVE. AMOUNTS NOT LIKELY TO BE EXCITING BUT AS
HAPPENED TODAY SOMEONE CUD GET A CPL OR 3 INCHES OF FLUFF. TEMPS
SHUD COOL BACK DOWN A LTL AS THIS SYS MOVES OFF WITH A CONTD DRY
FCST FOR MON.
MIXED SIGNALS ALSO ON TUE/TUE NGT SYS...BUT IT IS BEGINNING TO LOOK
LIKE THE GFS IS DAMPENING OUT SYS TOO MUCH AS IT COMES ACRS.
NOGAPS...CANADIAN...AND ECMWF HAVE MUCH BETTER SYSTEMS COMING ACRS
THO THE CANADIAN IS ON OUR SRN END. THAT FAR AHEAD WILL GO 30 POPS
TOPS WITH SO MANY QUESTIONS ON THE SYSTEM PLUS TIMING THAT FAR AHD.
WE SHUD BE ABLE TO GET MORE SPECIFIC WITH HIER POPS AS WELL AS WE
GET CLOSER...IF SYS DOES INDEED TURN OUT TO BE SGINIFICANT. BHND
SYS...WILL GO DRY FOR WED AND THU AND KEEP ANY WARMING TO MODEST
LEVELS. ECMWF HAD FOR SVRL RUNS BEEN WARMING TEMPS STGLY LATE NEXT
WEEK BUT LATEST RUN BACKS DOWN QUITE A BIT. OF COURSE THERE MAY BE A
POTENTIAL FOR SNOW COVER TO AFFECT TEMPS AS WELL.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
$$
WILLIAMS
