FXUS63 KFSD 250058
AFDFSD

AREA FORECAST DISCUSSION FOR SOUTHEAST SD/SOUTHWEST MN/NORTHWEST IA 
NATIONAL WEATHER SERVICE SIOUX FALLS SD
657 PM CST THU DEC 24 2009

.DISCUSSION...
BAND OF MODERATE TO HEAVY SNOW STRETCHING FROM AROUND FALLS CITY 
NEBRASKA TO BROOKINGS SD STALLING NEAR THE I29 CORRIDOR. THIS LIKELY 
DUE TO THE WESTWARD EXPANSION OF UPPER LEVEL SUPPORT FROM IOWA AND 
THE SLOW SOUTHEASTWARD DRIFTING WAVE IN WESTERN SD. MOISTURE NOT 
BEING ALLOWED TO EXPAND WEST VERY MUCH AND IS GETTING SQUEEZED OUT 
RIGHT OVER AND JUST EAST OF I29. SO...MAY NEED TO BUMP UP SNOW 
AMOUNTS A LITTLE FROM SIOUX CITY TO BROOKINGS...ESPECIALLY WITH THE 
RAPID EXPANSION OF THE NEXT AREA OF PRECIPITATION MOVING NORTHWEST 
FROM CENTRAL IA...WHICH SHOULD ALSO RUN MERGE WITH THIS BOUNDARY. 
CONDITIONS IN NW IA VERY CLOSE TO BLIZZARD...BUT WITH WINDS GUSTING 
TO AROUND 30 MPH AND THE LOW PRESSURE EXPECTED TO WOBBLE BACK TO THE 
WEST A LITTLE MORE...FEEL THAT SUSTAINED WINDS GREATER THAN 40 MPH 
EAST OF I29 WILL BE MORE DIFFICULT TO COME BY. SO WILL LEAVE 
HEADLINES AS IS FOR NOW. /08 

&&

.PREV DISCUSSION...
STORM WELL ON TRACK TO PRODUCE WIDESPREAD SNOW TONIGHT. CURRENT 
RADAR AND WATER VAPOR SHOWING AN ABUNDANCE OF MOISTURE STREAMING N 
AHEAD OF AN UPPER LEVEL LOW. DEEP STRONG THETAE ADVECTION...COUPLED 
WITH NEG DIVQ ALOFT SETS THE STAGE FOR SNOW TO SPREAD WEST ACROSS 
THE CWA THE REMAINDER OF THIS AFTERNOON AND THIS EVENING. THIS ALSO 
SETS THE STAGE FOR SNOW TO BE HEAVY AT TIMES...WITH RATES AS HIGH AS 
1 INCH PER HR. GRADIENT WINDS WILL SLOWLY INCREASE ACROSS THE 
AREA...AS SFC LOW DEVELOPS OVER MO AND LIFTS N INTO IA. WINDS WILL 
INCREASE OUT OF THE NW TO 25 TO 35 MPH...WITH GUST OVER 40 MPH 
ACROSS MUCH OF SE SD TONIGHT AND THROUGH TOMORROW. A BLIZZARD 
WARNING HAS BEEN ISSUE...BEGINNING AT MIDNIGHT TONIGHT FOR SE SD. A 
WINTER STORM WARNING REMAINS IN EFFECT FOR SW MN AND NW IA TONIGHT. 
CONDITIONS WILL MAKE TRAVEL EXTREMELY DIFFICULT TONIGHT ACROSS THE 
AREA... REGARDLESS OF THE TYPE OF WARNING. THE COMBINATION OF STRONG 
WINDS AND FALLING SNOW WILL BE SIGNIFICANTLY REDUCE VISIBILITIES... 
PRODUCING WHITEOUT CONDITIONS OVER MUCH OF THE AREA TONIGHT.       

UPPER LOW WILL CONT TO MEANDER AND LIFT NWD THRU IA FRI INTO FRI 
NIGHT WITH SFC LOW RETROGRADING NWWD INTO NW IA BY 18Z FRI. THIS 
WRAP PLENTY ON MOIST AIR ALOFT WWD ACRS CWA THRU FRI NIGHT AND WITH 
SOUNDINGS INDICATING PRECIP WL BE ALL SNOW...SHUD ACCUM QUITE HEAVY 
ACRS THE CWA WITH THE HEAVIEST AMOUNTS ALONG AND E IF I29. STRONG NW 
WINDS WL ALSO PERSIST ACRS AREAS W OF I29 THRU FRI NITE...AND WL 
ACTUALLY DECREASE DURING THE DAY E OF I29 AS SFC LOW RETROGRADES AND 
TIGHTEST SFC GRAD SHIFTS TO AREAS W OF I29. SO THEREFORE WL CONT WS 
WARN E OF I29 WITH BLIZZARD WARNING TO THE WEST. BY THE TIME THE 
SNOW TAPERS OFF LATER FRI NIGHT...12+ INCHES OF SNOW WL OCCUR ACRS A 
LARGE PART OF THE CWA WITH PSBLY FAR WRN CWA REMAINING BLO 12 
INCHES. WITH RETROGRADING SFC LOW AND WARMER AIR ALOFT WRAPPING 
WWD...TEMPS WILL ACTUALLY BE WARMER ACRS THE W ON FRI WITH HIGHS 
NEAR 30 ACRS THE FAR E. THIS WL BE A VERY WET SNOW WITH RATIOS 
CLOSER TO 10:1. 

WL NEED TO LINGER LIGHT SNOW ACRS THE CWA ON SAT AS UPPER LOW 
MEANDERS ACRS THE WRN GREAT LAKES REGION. THIS WL KEEP WNDS UP ACRS 
THE CWA THRU SAT NIGHT. ANY SNOW ACCUM ON SAT SHUD GENLY BE AN INCH 
OR LESS. 

WL ADD MENTION OF FLURRIES FOR SUN AS WRAP AROUND CONTS. DID NOT 
CHANGE EXTENDED FCST MUCH WITH TEMPS BLO NORM WITH ALL THE FRESH 
SNOW COVER. CUD SEE A LTL LIGHT SNOW WED OR THU WITH WEAK S/W BUT 
MODELS DIFFER ON TIMING AND FOR NOW WL LEAVE DRY UNTIL MODELS GET A 
BETTER HANDLE.    

&&

.AVIATION...
SNOW WILL SPREAD FROM SW MN AND NW IA THIS AFTERNOON...ACROSS SD 
THIS EVENING. FALLING SNOW COMBINED WITH STRONG NW WINDS OF 25 TO 
40 MPH WILL PRODUCE IFR CIGS AND VISBYS TONIGHT AND TOMORROW. VISBYS 
WILL BE NEAR ZERO AT TIMES. 

&&

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

MN...WINTER STORM WARNING UNTIL NOON CST SATURDAY FOR MNZ071-072-080-
     081-089-090-097-098.

NE...WINTER STORM WARNING UNTIL MIDNIGHT CST TONIGHT FOR NEZ013-014.

     BLIZZARD WARNING FROM MIDNIGHT TONIGHT TO NOON CST SATURDAY FOR 
     NEZ013-014.

SD...WINTER STORM WARNING UNTIL MIDNIGHT CST TONIGHT FOR SDZ038>040-
     050-052>071.

     BLIZZARD WARNING FROM MIDNIGHT TONIGHT TO NOON CST SATURDAY FOR 
     SDZ038>040-050-052>071.

&&

$$