FXUS63 KUNR 260235
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
735 PM MST FRI DEC 25 2009

.DISCUSSION...AT 02Z BLIZZARD CONDITIONS CONTINUE TO POUND WRN SD.
UPSLOPE MACHINE IS GOING STRONG WITH 15-25 INCHES IN NRN BLK HLS
ALREADY...WILL UP TOTALS TO 24-48 INCHES ACROSS THE AREA. DUAL
UPPER LOW CONTS TO SPIN WITH ONE CENTER IN NERN MISSOURI AND THE
OTHER IN FAR SERN SD...PLENTY OF MSTR CONDS TO WRAP AROUND SYSTEM
INTO WRN SD...AS SNOW WILL CONTINUE THRU NIGHT AND LIKELY INTO
SAT NIGHT. VERY DEEP SFC LOW IN JUST EAST OF OMAHA NEB. 

MOISTURE BEING DRAWN INTO STORM IS MOST IMPRESSIVE...ESP FOR LATE
DECEMBER...STORM IS SO BIG MOISTURE IS BEING DRAWN OF PACIFIC
OCEAN ACRS MEXICO/GULF OF MEXICO AND THEN UP EAST COAST BEFORE
WRAPPING BACK INTO NRN PLAINS. WILL LIKELY BE A LONG TIME BEFORE
WE SEE ANOTHER DECEMBER STORM LIKE THIS.

UPDATED PACKAGE TO INCREASE SNOW TOTALS IN NRN BLACK HILLS..REST
OF AREA...FCST SNOW TOTALS LOOK GOOD. WINDS AND TEMPS ALSO LOOK
GOOD FOR NOW AND WILL NOT ADJUST.

PREVIOUS FORECAST DISCUSSION:(300 PM MST)...
STORM SYSTEM WILL CONTINUE TO BRING BLIZZARD OR NEAR BLIZZARD 
CONDITIONS ACROSS MOST OF WESTERN SD THROUGH SATURDAY. FURTHER
SOUTH AND WEST INTO FAR SOUTHWESTERN SD AND NORTHEASTERN WY...SNOW 
AND WIND WILL BE LIGHTER FOR THE MOST PART...BUT TREACHEROUS 
CONDITIONS CAN BE EXPECTED AS WELL. AS WARMER AIR ALOFT ADVECTS INTO 
THE AREA TONIGHT... ATMOSPHERE WILL BECOME MORE FAVORABLE FOR 
SNOWFLAKE GROWTH AND THEREFORE HIGHER SNOWFALL RATES ACROSS THE SD 
PLAINS AND INTO THE NORTHERN HILLS AREA. WINDS WILL DECREASE A BIT 
OVERNIGHT AND SNOW MAY LIGHTEN UP IN INTENSITY AND COVERAGE AT TIMES 
LATER TONIGHT INTO SATURDAY...BUT THE BLIZZARD TO NEAR BLIZZARD 
CONDITIONS WILL CONTINUE ACROSS THE WARNED AREAS.    

SYSTEM WILL BE SLOW TO EXIT LATER SATURDAY AND SATURDAY NIGHT AS LOW 
STALLS OVER THE WESTERN GREAT LAKES AREA. UPSLOPE SNOWFALL OVER THE 
NORTHERN HILLS WILL PERSIST RIGHT INTO SATURDAY NIGHT. SOME LIGHT 
SNOW IS ALSO LIKELY TO LINGER ACROSS EASTERN PORTIONS OF THE CWA 
INTO SATURDAY NIGHT AND POSSIBLY SUNDAY AS WELL...BUT WINDS WILL 
GRADUALLY DECREASE AT MOST LOCATIONS SATURDAY NIGHT.

FOR SNOWFALL TOTALS...WILL GO WITH 3 TO 7 INCHES ACROSS FAR 
SOUTHWESTERN SD AND SOUTHERN AND WESTERN PARTS OF NORTHEASTERN WY. 
THE REST OF THE PLAINS...ESPECIALLY ACROSS WESTERN SD...WILL 
GENERALLY SEE 8 TO 15 INCHES OF SNOWFALL...HIGHEST AMOUNTS ACROSS 
RIDGES AND PARTS OF NORTHWESTERN SD...WITH SIGNIFICANT BLOWING AND 
DRIFTING. ACROSS THE NORTHERN HILLS AREA...1 TO 2 FEET OF SNOW IS A 
GIVEN...WITH SOME AREAS EASILY EXCEEDING 2 FEET.  

EXTENDED...UPPER RIDGE ACROSS THE AREA MONDAY. HOWEVER STRONG 
INVERSION WILL KEEP TEMPERATURES BELOW AVERAGE. SLIGHT WARMING ON 
TUESDAY/WEDNESDAY...WITH WARMEST TEMPERATURES NORTHEAST WYOMING AND 
BLACK HILLS. EXTENDED MODELS INDICATING UPPER TROF DROPPING OUT OF 
CANADA MID-WEEK...SOME LIGHT SNOW POSSIBLE WITH COLD FRONT WEDNESDAY 
NIGHT INTO THURSDAY. TEMPERATURES WELL BELOW AVERAGE FOR THE END OF 
THE WEEK AS ANOTHER 1040MB ARCTIC HIGH DROPS INTO THE NORTHERN 
PLAINS. 

&&

.AVIATION...WIDESPREAD IFR/LIFR VSBY EXPECTED THROUGH THE FORECAST
PERIOD AS SNOW AND BLOWING SNOW CONTINUES. 

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...BLIZZARD WARNING UNTIL 5 PM MST/6 PM CST SATURDAY FOR THE
     PLAINS OF WESTERN SOUTH DAKOTA AND NRN/ERN FOOTHILLS.
     WINTER STORM WARNING UNTIL 5 PM MST SATURDAY FOR THE NRN
     AND CNTRL BLKHLS.
     WINTER WEATHER ADVISORY UNTIL 5 PM MST SATURDAY FOR SRN
     BLKHLS AND EXTREME SWRN SD.
WY...BLIZZARD WARNING UNTIL 5 PM MST SATURDAY FOR NERN CROOK
     COUNTY.
     WINTER STORM WARNING UNTIL 5 PM MST SATURDAY FOR WYOMING
     BLKHLS AND CROOK COUNTY PLAINS.
     WINTER WEATHER ADVISORY UNTIL 5 PM MST SATURDAY FOR 
     CAMPBELL AND WESTON COUNTIES.

&&
$$