FXUS63 KFSD 232046
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD
245 PM CST WED DEC 23 2009

.DISCUSSION...
INIT SHOT OF PCPN MOVG INTO SRN FCST AREA AND BACKING NWWD PRETTY 
MUCH AS EXPECETD. PCPN BEGAN AS ZR/IP FROM SUX E AND QUICKLY WENT 
TO SNOW AT SUX AS EXPECTED. SOME ZR/IP WILL LINGER LONGER E OF SUX 
BUT XCP FOR SLB AREA...PCPN SHUD GO MOSTLY TO SNOW THIS EVE. 
MEANWHILE...SNOW SHUD BACK UP INTO THE FAR WRN FCST AREA THO WITH 
SOMEWHAT LESS INTENSITY TO THE W. SNOW ACCUM FOR TNGT SHUD BE MOSTLY 
2-4 INCHES AS SUPPORT FOR ANY REALLY DECENT SNOWBURSTS WANES WITH 
TIME. CONTINUED INDICATIONS OF SOME WARMING ALF SHUD BRNG A MINOR 
RESURGENCE OF ZR/IP E OF SUX AND UP N TO ABOUT SPW LATE TNGT... 
OUSIDE OF THIS AREA PCPN WILL BE SNOW. MEANWHILE...WITH MOISTURE BUT 
ONLY WEAK SUPPORT BEHIND THIS BAND AS IT MOVES ON N/NW...PCPN 
INTENSITY SHUD DROP OFF FROM THE S OVER ERN FCST AREA DURG THE 
NIGHT...THO WILL KEEP HI 80 TYPE POPS FOR LATE TNGT AS LIGHT LOW 
BASED PCPN LIKELY TO CONT.

COLDER AIR FLOWING INTO WRN FCST AREA AS SYS CONTS TO DVLP SHUD DROP 
TEMPS INTO THE TEENS FAR W LATE TNGT...OR ABOUT 10 DEGS COLDER THAN 
CURRENT VALUES. FRTHR E...LOWS SHUD TEND TO BE 5 DEGS OR LESS COLDER 
THAN CURRENT READINGS. THE COLD AIR SURGE IN THE FAR W WILL BE AIDED 
BY INCREASING NNWRLY WINDS. WINDS SHUD BE STG ENUF TO CAUSE AREAS OF 
BLOWING SNOW FAR W LATE TNGT. THO THERE MAY NOT BE A LOT OF BLOWABLE 
SNOW YET...FALLING SNOW WILL BE ONGOING OUT W SO THE BLOWING SNOW 
SEEMS APPROPRIATE. /WILLIAMS

FIRST SHOT OF SNOW WL BE EXITING CWA IN THE EARLY MORN...AND MOST OF 
DAY MAY ONLY SEE LIGHT SNOW AHEAD OF MAIN UPPER LOW THAT WL LIFT NWD 
THU NITE INTO FRI. SO WL KEEP WDSPRD SNOW ON THU BUT GENLY ON THE  
LIGHT SIDE DURING THE DAY WITH MAYBE AND INCH OR TWO AT BEST. WINDS 
SHUD GRADUALLY PICK UP DURING THE DAY ESPEC WRN CWA AND EXPECT TO 
SEE BLOWING SNOW DEVELOP ALONG AND W OF I29 BY AFTERNOON.

NRN STREAM UPPER LOW DIGGING SEWD ACRS ERN MT WL BEGIN TO PHASE IN 
WITH SRN WAVE COMING OUT TX ON THU AND THIS SHUD REALLY HELP TO 
INTENSIFY SFC LOW ACRS NRN ARK THU AFTN AND THEN MOVE NWD INTO IA BY 
FRI MORN. VERY MOIST ELY FLOW ALOFT WILL CONT TO THEN ADVECT WWD 
OVER COLDER AIR IN THE LOW LEVELS TO CREATE A WDSPRD OVER RUNNING 
SNOW ACRS THE CWA THU NIGHT ALL THE WAY INTO SAT MORN. THIS SHUD 
EASILY ALLOW SNOWFALL AMOUNTS TO BE IN THE 12 TO 20 INCH RANGE ACRS 
THE CWA WITH THE LOWER AMOUNTS ACRS FAR WRN CWA. THE OTHER FACTOR WL 
BE THE WINDS THAT WL INCREASE ACRS THE REGION THU NITE INTO SAT AS 
NRN UPPER LOW PHASES WITH SRN STREAM. EVEN THO NOT EXPECTED TO SEE 
STG CAA WITH THE PHASING...STILL ENOUGH TIGHTENING OF SFC GRAD TO 
PRODUCE GUSTS TO 35 TO 40 MPH THU NITE INTO FRI NITE. AT LEAST TEMPS 
WL NOT BE BITTERLY COLD WITH THIS SYS AS ISOTHERMAL SOUNDING UP TO 
AROUND H7 SO NOT EXPECTING SUB ZERO TEMPS WITH THIS STORM. IN 
FACT...TEMPS MAY HOLD STEADY THRU FRI NIGHT BEFORE FINALLY STARTING 
TO COOL AS UPPER LOW BEGINS TO PULL AWAY. WL NEED TO KEEP CHC OF S- 
AND BS ACRS CWA THRU SAT EVE...ALTHO BULK OF ACCUM SNOW SHUD BE OVER 
BY FRI EVE. 

SUN WL REMAIN CLOD AND WITH UPPER LOW OVR GREAT LAKES REGION...PBLY 
WL NOT SEE MUCH SUN. WL KEEP TEMPS BLO NORM MON THRU WED. MAY SEE A 
CHC OF S- ON WED WITH WEAK S/W. FOR NOW WL LEAVE SUN THRU WED DRY 
WITH MAIN FOCUS OF THIS FCST ON THIS BIG STORM.  

&&

.AVIATION...
CONDS SHUD BE GNLY IFR IN PCPN AND FOG THRU FCST 25/00Z. A FEW AREAS 
OF 3-5SM THRU 03Z...MAINLY AHEAD OF PCPN. ON THE OTHER 
HAND...POCKETS OF LIFR LIKELY IN PCPN THRU FCST PD. EVEN WHEN PCPN 
SHOWS SOME LETUP IN INTENSITY DURG THE NGT...IFR SHUD CONT IN LGT 
PCPN AND FOG. 

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
IA...WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR IAZ001>003-
     012>014-020>022-031-032.

MN...WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR MNZ089-090-098.

     WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR MNZ071-
     072-080-081-097.

     WINTER STORM WARNING FROM 6 PM THIS EVENING TO 6 AM CST         
     SATURDAY FOR MNZ071-072-080-081-097.

NE...WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR NEZ013-014.

SD...WINTER STORM WARNING UNTIL 6 AM CST SATURDAY FOR SDZ050-057>071.

     WINTER WEATHER ADVISORY UNTIL 6 PM CST THIS EVENING FOR 
     SDZ038>040-052>056.

     WINTER STORM WARNING FROM 6 PM THIS EVENING TO 6 AM CST         
     SATURDAY FOR SDZ038>040-052>056.

&&

$$