Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 231205
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
505 AM MST TUE DEC 23 2014

.UPDATE...
ISSUED AT 502 AM MST TUE DEC 23 2014

SNOWFALL IS GRADUALLY WEAKENING ACROSS THE PLAINS OF CROOK COUNTY
AND OVER THE NW SD PLAINS. WILL ALLOW THE ADVISORY TO EXPIRE
ACROSS THESE LOCATIONS. KUDX RADAR IS SHOWING UPSLOPE ENHANCEMENT
AFFECTING SNOWFALL RATES OVER THE SRN THIRD OF BUTTE COUNTY...SO
HAVE EXTENDED THE ADVISORY UNTIL 19Z. NO OTHER CHANGES NEEDED AT
THIS TIME.

&&

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
ISSUED AT 315 AM MST TUE DEC 23 2014

DEEP UPPER TROUGH CONTINUES TO AFFECT THE CNTRL THIRD OF THE CONUS
THIS MORNING WITH UPPER LOW CENTERED OVER IA. SURFACE LOW PRESSURE
IS STACKED BELOW UPPER LOW...AND WITH SURFACE HIGH BUILDING ACROSS
ID...RESULTING TIGHT PRESSURE GRADIENT KEEPING STRONG NW WINDS
ACROSS THE WRN SD PLAINS AND NE WY PLAINS. KUDX RADAR SHOWS
WRAPAROUND PRECIP CONTINUING TO AFFECT ALL OF SD WITH THE HEAVIEST
AND MOST PERSISTENT SNOW FALLING ACROSS THE NRN BLKHLS AND TWO
SEPARATE BANDS EAST AND SOUTHEAST OF THE BLACK HILLS. PRECIP WILL
GRADUALLY END TODAY FROM NW TO SE AS THE STORM SYSTEM SLIDES EAST.
MOST AREAS WILL SEE ACCUMULATING SNOW END BY 19Z...EXCEPT ACROSS
SCNTRL SD WHERE SNOW WILL END THROUGH THE AFTERNOON. ALL HEADLINES
CURRENTLY IN EFFECT STILL LOOK APPROPRIATE. FIRST HEADLINE
EXPIRATION IS COMING SOON AT 12Z...SO WILL LET IT END WITH THE
FORECAST PACKAGE ISSUANCE.

UPPER RIDGING AND SURFACE HIGH PRESSURE WILL SLIDE IN TONIGHT
BRINGING BACK MUCH QUIETER WEATHER. WINDS WILL DECREASE THROUGH THE
AFTERNOON...AND BECOME RELATIVELY LIGHT TONIGHT ALONG WITH
DECREASING CLOUDS. LOW LEVEL RETURN FLOW SETS UP ACROSS THE AREA
CHRISTMAS EVE. SW WINDS WILL DEVELOP WEDNESDAY MORNING BRINGING
WARMER TEMPERATURES TO THE AREA. HIGHS WILL REACH THE MID 30S TO
MID 40S. MID/HIGH CLOUDS WILL INCREASE FROM THE WEST THROUGH THE
DAY AS THE NEXT SYSTEM APPROACHES THE REGION. CHANCES FOR SNOW
RETURNING INCREASE LATE WED NIGHT INTO CHRISTMAS MORNING.

.LONG TERM...THURSDAY THROUGH MONDAY
ISSUED AT 315 AM MST TUE DEC 23 2014

ACTIVE NW FLOW WILL SUPPORT ANOTHER STORM SYSTEM INTO THE REGION
THE MIDDLE OF THIS WEEK. DEVELOPING BLOCKING PATTERN PER
APPRECIABLE HEIGHT RISES OVER GREENLAND...COUPLED WITH MASSIVE
WESTERN NOAM RIDGING WILL THEN EVENTUALLY SUPPORT ARCTIC AIR SOUTH
INTO THE CONUS TOWARD THE END OF THE PERIOD. THE ECMWF IS
CURRENTLY THE MOST AGGRESSIVE MODEL PER WESTERN NOAM
RIDGING...SUPPORTING HEIGHT RISES TO NEAR THE NORTH POLE BY MONDAY
OF NEXT WEEK...SUPPORTING THE STRONGEST PUSH OF ARCTIC AIR SOUTH.
HOWEVER...FORECAST MODELS ONLY OFFER SHORT STAY OF ARCTIC AIR
GIVEN AN EASTWARD SHIFT OF THE GOA UPPER LOW...WHICH HAS BEEN THE
PERSISTENT PATTERN LATE THIS FALL/EARLY WINTER.

THUR...STRONG UPPER REVEL WAVE WILL SUPPORT A DECENT FGEN RESPONSE
OVER THE FA...WITH LIFT CENTERED AROUND THE DGZ. SNOW EXPECTED WITH
ACCUMS LIKELY ACROSS THE SOUTHERN 2/3 AS THE UPPER TROUGH PIVOTS
OVER THE REGION. GIVEN MOISTURE PROFILES AND LIFT PERIOD...CURRENT
SNOW ACCUMS OF 1-4 INCHES ARE ANTICIPATED ACROSS MUCH OF THE
AREA...WITH THE HIGHEST ACCUMS ACROSS THE SOUTHERN THIRD. FORECAST
MODELS ARE SUGGESTING A SECONDARY DEFORMATION ZONE OVER SCENTRAL SD
THUR NIGHT AS THE SFC LOW DEEPENS AND GOMEX MOISTURE LINKS WITH THIS
SYSTEM. SNOW TOTALS COULD BE HIGHER THERE IF THIS PROCESS OCCURS AND
WORKS EFFICIENTLY. RAISED POPS ALL PLACES IN THE THUR/THUR NIGHT
PERIOD...ESP THE SOUTHERN 2/3. GUSTY NW WINDS MAY ALSO BE OF
CONCERN...SUPPORTING BLOWING SNOW.

FRI-MON...DRY WEATHER EXPECTED THROUGH SAT...BEFORE THE NEXT SYSTEM
DIVES SE ACROSS THE ROCKIES SUNDAY. ANOTHER FGEN RESPONSE LOOKS
LIKELY WHICH WILL SUPPORT SNOW CHANCES ACROSS THE AREA ONCE AGAIN.
KEPT CLOSE TO PREVIOUS POP NUMBERS. LONG MERIDIONAL FLOW TRAJECTORIES
WITH THIS SYSTEM CONTINUE TO SUPPORT AN ARCTIC FRONT INTO THE
REGION SUNDAY NIGHT INTO MONDAY. MODELS HAVE BEEN CONSISTENTLY
PROGGING THIS FEATURE...WHICH MAKES SENSE GIVEN WEAK BLOCKING
PATTERN...RAISING CONFIDENCE OF OCCURRENCE. HENCE...SIDED WITH THE
COOL SIDE OF GUIDANCE GIVEN GREENLAND BLOCKING AND EXPECTED WESTERN
NOAM RIDGING. IF THIS ARCTIC OUTBREAK DOES MATERIALIZE TO THE DEGREE
OF THE 00Z ECMWF...TEMPS WOULD NEED TO BE CUT EVEN MORE EARLY NEXT
WEEK...ESP WITH EXPECTED SNOW COVER.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)
ISSUED AT 425 AM MST TUE DEC 23 2014

SNOW/BLOWING SNOW WILL CONTINUE OVER WESTERN SD THROUGH
MORNING...AND ACROSS SCENTRAL SD INTO THE AFTERNOON. WIDESPREAD
MVFR/IFR CIGS AND IFR VSBYS EXPECTED...WITH LIFR CONDITIONS IN
THE HEAVIEST SNOW AND WIND. GUSTY NORTHWEST WINDS WILL CONTINUE
WITH THE STRONGEST WINDS JUST EAST OF THE BLACK HILLS. THIS WILL
SUPPORT AREAS OF BLOWING SNOW WELL AFTER SNOWFALL STOPS...WITH VIS
RESTRICTIONS OF MVFR TO IFR ON THE SD PLAINS IN BLOWING SNOW.
CONDITIONS WILL GRADUALLY IMPROVE WEST TO EAST...BUT MVFR CIGS
WILL LIKELY LINGER MUCH OF THE DAY. VFR CONDITIONS EXPECTED
TONIGHT MOST PLACES...WITH MVFR CIGS LINGERING OVER SCENTRAL SD
THROUGH EVENING.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL NOON MST TODAY FOR SDZ024-025-031-032-
     042>044.

     WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR SDZ046-047-
     049.

     WINTER WEATHER ADVISORY UNTIL NOON MST TODAY FOR SDZ012>014-026-
     028-030-041-072-073.

WY...WINTER STORM WARNING UNTIL NOON MST TODAY FOR WYZ057.

&&

$$

UPDATE...13
SHORT TERM...13
LONG TERM...JC
AVIATION...JC






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