FXUS63 KFSD 221624
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1025 AM CST TUE DEC 22 2009

.DISCUSSION...
FOG HAS BECOME DENSE IN A SMALL PART OF NWRN IA FROM IDA GROVE TO 
STORM LAKE/SLB. HAVE NOT GONE WITH ADVY AS IT SHUD NOT BCM MORE 
WDSPRD...AND EXPECT VSBYS TO SLWLY INCRS TO NEAR A MILE ERY THIS 
AFTN. HAVE HANDLD IT IN SHORT TERM FCSTS/NOWCASTS. OTRW NOT TOO MUCH 
CHANGE...MAY EXTEND AREAS OF FOG MENTN THRU THIS AFTN THO FOG SHUD 
NOT BE DNS. ASIDE FROM SOME MOISTURE DEPOSITS IN THE FOG...REAL 
FREEZING DRZL DOES NOT SEEM TO BE GOING BUT WILL KEEP THAT AND A FEW 
ST TYPE FLRYS WITH THE COPIOUS LO LVL MOISTURE ARND. TEMPS OF 
COURSE PRETTY STATIC WITH MAYBE A RISE OF A CPL DEGS THIS AFTN. 
ERLY/NERLY BREEZE ALSO UNLIKELY TO CHANGE MORE THAN A SMIDGEON. NO 
REASON TO CHANGE WINTER STORM FCST AT THIS POINT...MODELS IN GNRL 
COMIGN IN ARE IN SYNCH WITH FCST...AND ANY DETAILS WILL BE WORKED ON 
FOR AFTN PACKAGE.

&&

AVIATION...
IFR CIGS AND AREAS OF IFR VSBYS IN STRATUS...BR...PATCHY FZDZ AND 
FLURRIES WILL CONT THRU WED MRNG. PATCHY LIFR IN FOG THIS MRNG NWRN 
IA SHUD GIVE WAY TO JUST IFR BY 18Z-19Z. OTRW IFR TO MVFR VSBYS MAY 
TEND TO GO MORE IFR AGAIN AFT 00Z. CIGS SHUD STAY SOLIDLY BLO 1K FT 
THRU 23/18Z.

&&

.PREV DISCUSSION...
EVERYTHING ON TRACK FOR A MAJOR WINTER STORM IN OUR CWA...BUT STILL 
A QUESTION ON HOW FAR WEST THE BEST...OR WORST...FOCUS WILL BE AS 
MODELS STILL SHIFTING NWWD FM PREV RUNS. U.S. MODELS RATHER 
INCONSISTENT AND GOOFY LOOKING WITH VARIOUS PINWHEELING WAVES ARND 
DIGGING UPR TROF EVOLVING TO MAJOR WRAPAROUND UPR LOW BY THU NGT. 
COMPOSITE OF ALL MODELS...INCLUDING MORE CONSISTENT ECMWF AND 
CANADIAN SHOW BEST FOCUS ALG AND WEST OF DVLPG INVERTED TROF RIGHT 
ALONG INTERSTATE 29 FROM WED NGT THRU THU EVE. SO SHIFTED HEAVIEST 
SNOWFALL WNW FM PREV FCST OVER SD PTN OF CWA...AND ADDED A MIX OF 
SNOW...SLEET...AND FRZG RAIN IN THE SERN CWA...MAINLY NWRN IA...
FROM WED THRU THU. MIXED PRECIP WILL CHANGE TO ALL SNOW BY THU NGT 
AS UPR LOW COLLAPSES EWD AND AIR MASS COOLS FROM ALOFT. THIS SYSTEM 
WILL PULL IN LOTS OF GULF MOISTURE AND QPF WILL BE HEAVY. HPC AND 
GFS SNOW AMOUNTS EXTREMELY HEAVY...BUT SHADED BACK UNTIL THERE IS 
MORE CONFIDENCE FOR AREA OF BEST SNOWFALL FOR LATE WED THRU THU NGT.
APPEARS FIRST BIG SHOT OF LIFT AND PRECIP WILL MOVE NWWD OVER CWA
FM WED AFTN THRU THU MRNG...WITH A PSBL BREAK SERN CWA THU MRNG...
BEFORE IT ALL FILLS IN AGAIN THU AFTN AND EVE. WENT WITH WARNING
IN SD PART OF CWA WHERE BEST SNOWFALL SHOULD OCCUR WITH THIS 
SYSTEM...AND LEFT WATCH TO THE EAST WHERE THERE IS LESS CONFIDENCE 
ON HOW SYSTEM PANS OUT. MASSAGED TEMPS UP A LIT BIT FM PREV FCST AS 
SYSTEM PULLS IN SOME MILDER MOIST AIR FM THE SE WED THRU THU. STG 
NLY WINDS WILL KICK IN BACKSIDE OF DVLPG LOW PRES AND GIVE WDSPRD 
BLWG SNOW SPRDG FM W TO E IN CWA THU AFTN AND EVE... AND SYSTEM
MAY EVOLVE TO A BLIZZARD AT SOME POINT.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
IA...WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY 
     AFTERNOON FOR IAZ001>003-012>014-020>022-031-032.

MN...WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY 
     AFTERNOON FOR MNZ089-090-098.

     WINTER STORM WATCH FROM WEDNESDAY EVENING THROUGH FRIDAY 
     AFTERNOON FOR MNZ071-072-080-081-097.

NE...WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY 
     AFTERNOON FOR NEZ013-014.

SD...WINTER STORM WARNING FROM NOON WEDNESDAY TO 6 PM CST FRIDAY FOR 
     SDZ050-057>070.

     WINTER STORM WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY 
     AFTERNOON FOR SDZ071.

     WINTER STORM WARNING FROM 6 PM WEDNESDAY TO 6 PM CST FRIDAY FOR 
     SDZ038>040-052>056.

&&

$$
WILLIAMS