653 FXUS63 KUNR 131027 AFDUNR AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY NATIONAL WEATHER SERVICE RAPID CITY SD 327 AM MST SUN DEC 13 2015 .SHORT TERM...TODAY THROUGH MONDAY NIGHT ISSUED AT 259 AM MST SUN DEC 13 2015 UPPER LOW SPINS OVER NEW MEXICO...AS A WEAK UPPER WAVE PUSHES THROUGH THE NORTHERN PLAINS WITH DRIER AIR BEHIND IT. NEXT SYSTEM IS BEGINNING TO FORM AS A WAVE OFF THE PAC NW COAST. MID CLOUDS ARE CLEARING ACROSS THE CWA FROM THE WEST...AND FOG IS DEVELOPING ACROSS THE SD PLAINS AND WRAPPING AROUND THE SOUTHERN HILLS INTO NORTHEASTERN WY. WEAK BAND OF SNOW LINGERS ACROSS SOUTH CENTRAL SD. WITH WEAK HIGH PRESSURE OVER THE DAKOTAS...WINDS ARE LIGHT AND EASTERLY. TEMPS ARE IN THE 20S. EXPECT FOG TO LINGER ACROSS THE SD PLAINS AT LEAST THROUGH THIS MORNING... WHILE LOW CLOUDS MAY PERSIST ACROSS CENTRAL SD THROUGH THE AFTERNOON. HIGH PRESSURE WILL KEEP WINDS LIGHT. HIGH TEMPS WILL RANGE FROM THE MID 30S ACROSS THE CLOUDIER CENTRAL SD TO THE LOWER 40S ACROSS NORTHEASTERN WY. LIGHT EASTERLY WINDS TONIGHT...ALONG WITH PLENTY OF LOW-LEVEL MOISTURE...IS EXPECTED TO RESULT IN FOG REDEVELOPMENT THIS EVENING INTO MONDAY MORNING. FORECAST SOUNDINGS SUGGEST THE POSSIBILITY OF FREEZING DRIZZLE WITHIN THE FOG. HOWEVER...WINDS FROM SURFACE INTO THE DRY LAYER ARE VERY LIGHT AND THEREFORE NOT MUCH SHEAR TO WORK WITH FOR FORMING FREEZING PRECIPITATION. ADDED PATCHY FREEZING FOG ACROSS THE WESTERN SD PLAINS TO GRIDS FOR NOW. LOWS WILL BE IN THE MID TEENS TO MID 20S. WEST COAST TROUGH WILL STRENGTHEN AS IT MOVES EASTWARD...FORMING A CLOSED UPPER LOW OVER NV/UT BY 18Z MONDAY. MODELS ARE IN PRETTY GOOD AGREEMENT ON TRACK/TIMING OF THE LOW...AND ARE CONTINUING THE TREND OF SLOWING THE SYSTEM DOWN. HAVE REDUCED POPS MONDAY/MON NIGHT ACROSS WESTERN SD. STILL EXPECTING PRECIP TO BEGIN MOVING INTO NORTHEASTERN WY LATE MONDAY...WITH GOOD FRONTOGENESIS/Q-VECTOR CONVERGENCE DEVELOPING THERE MON EVENING...ALONG WITH VERY DEEP MOISTURE PROFILES AS 700MB LOW MOVES OVER NORTHERN CO. BY TUES MORNING...EXPECT LESS THAN AN INCH OF SNOWFALL OVER WESTERN SD...WITH A FEW INCHES OF SNOW IN NORTHEASTERN WY. .LONG TERM...TUESDAY THROUGH SATURDAY ISSUED AT 259 AM MST SUN DEC 13 2015 MODELS IN DECENT AGREEMENT THROUGH MID WEEK. UPPER LOW MOVES INTO CENTRAL NEBRASKA TUESDAY...AND THROUGH SOUTHEAST SOUTH DAKOTA/NORTHWEST IOWA TUESDAY NIGHT. BY WEDNESDAY MORNING...GFS ACCELERATES UPPER LOW NORTHEAST FASTER THEN ECMWF. ECMWF KEEPS SOME SNOW ACROSS THE FORECAST AREA INTO WEDNESDAY. SNOW WILL BE ONGOING TUESDAY MORNING ACROSS NORTHEAST WYOMING/FAR WESTERN SOUTH DAKOTA...AND WILL SPREAD EASTWARD THROUGH THE DAY. A SLOWER START TO SNOW ANTICIPATED ACROSS EASTERN PORTIONS OF FORECAST AREA WITH DRIER NORTHEAST LOW LEVEL FLOW. DEEP LIFT ACROSS NORTHEAST WYOMING/FAR WESTERN SOUTH DAKOTA THROUGH TUESDAY WILL BE AIDED BY NORTH-NORTHEAST UPSLOPE FLOW. SNOW CONTINUES INTO TUESDAY NIGHT...WITH BEST LIFT SHIFTING INTO WESTERN/CENTRAL SOUTH DAKOTA. STILL SOME UNCERTAINTY WITH AVAILABLE MOISTURE AND SNOW RATIOS WITH THIS EVENT. BEST CHANCE OF 6+ INCHES OF SNOW APPEAR TO BE OVER PORTIONS OF NORTHEAST WYOMING INTO THE BLACK HILLS AND PLAINS EAST OF THE BLACK HILLS. WILL ISSUE WINTER STORM WATCH FOR THOSE AREAS ...THOUGH FURTHER ADJUSTMENTS WILL LIKELY BE NEEDED AS WE GET CLOSER TO THE EVENT. WILL BE WINDY ON THE PLAINS TUESDAY AFTERNOON/TUESDAY NIGHT AS PRESSURE GRADIENT INCREASES. WILL INCLUDE AREAS OF BLOWING SNOW. DRY WEATHER AND A SLOW WARMING TREND FOR THE END OF THE WEEK INTO THE WEEKEND. && .AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING ISSUED AT 259 AM MST SUN DEC 13 2015 AREAS OF IFR/LIFR FOG WILL CONTINUE THROUGH THIS MORNING ACROSS MUCH OF NORTHWEST/WEST CENTRAL SOUTH DAKOTA...WITH SOME PATCHY FOG IN NORTHEAST WYOMING. THE FOG WILL DISSIPATE THIS MORNING...WITH SOME LINGERING IFR CIGS ACROSS SOUTH CENTRAL SOUTH DAKOTA INTO EARLY AFTERNOON. FOG SHOULD REFORM ACROSS THE AREA LATE THIS EVENING AND CONTINUE INTO MONDAY MORNING. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...WINTER STORM WATCH FROM LATE MONDAY NIGHT THROUGH LATE TUESDAY NIGHT FOR SDZ012-013-024>026-028-030>032-042>044-072>074. WY...WINTER STORM WATCH FROM LATE MONDAY NIGHT THROUGH LATE TUESDAY NIGHT FOR WYZ057-071. WINTER STORM WATCH FROM MONDAY AFTERNOON THROUGH TUESDAY EVENING FOR WYZ054>056. && $$ SHORT TERM...POJORLIE LONG TERM...7 AVIATION...7