Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 231902
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1202 PM MST TUE DEC 23 2014

.UPDATE...
ISSUED AT 1201 PM MST TUE DEC 23 2014

SNOW CONTINUES TO DIMINISH ACROSS THE AREA...INCLUDING THE UPSLOPE
SNOW OVER THE NORTHERN HILLS. A COUPLE BANDS OF SNOW PERSIST ACROSS
THE PLAINS...BUT EXPECT THOSE TO DECREASE SOON. NORTHWEST WINDS
REMAIN BREEZY AND WILL CONTINUE TO CREATE SOME BLOWING SNOW AND
REDUCED VISIBILITIES THIS AFTERNOON...ESPECIALLY ACROSS SOUTH
CENTRAL SD...ALTHOUGH VISIBILITIES HAVE BEEN GRADUALLY IMPROVING.
WILL LET THE WINTER WEATHER ADVISORIES EXPIRE AS PLANNED...AS WELL
AS THE WESTERNMOST WINTER STORM WARNINGS...LEAVING SOUTH CENTRAL SD
WINTER STORM WARNINGS GOING THROUGH THE AFTERNOON.

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 18Z TAFS THROUGH 18Z WEDNESDAY)
ISSUED AT 1022 AM MST TUE DEC 23 2014

SNOW SHOWERS AND MVFR/IFR CIGS AND VIS PRESENT ACROSS MUCH OF
WESTERN SD AT THIS TIME... WITH LOCAL IFR/LIFR CONDITIONS IN THE
NRN BLACK HILLS... WHILE NERN WYOMING IS SEEING SOME CLEARING AND
VFR/MVFR CONDITIONS. EXPECT SNOW SHOWERS TO TAPER OFF FROM WEST TO
EAST THIS AFTERNOON... WITH CIGS/VIS GRADUALLY IMPROVING. BY
SUNSET... MOST AREAS IN WESTERN SD AND NERN WYOMING SHOULD HAVE
VFR CONDITIONS... THE EXCEPTION BEING THE SOUTH CENTRAL PLAINS OF
SOUTH DAKOTA WHERE SOME SNOW SHOWERS AND LOW CLOUDS MAY STILL
LINGER FOR SEVERAL HOURS AFTER SUNSET.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER STORM WARNING UNTIL 6 PM CST THIS EVENING FOR SDZ046-047-
     049.

WY...NONE.
&&

$$

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






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