Issued by NWS Rapid City, SD
000 FXUS63 KUNR 210943 AFDUNR AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY NATIONAL WEATHER SERVICE RAPID CITY SD 243 AM MST SAT NOV 21 2009 .DISCUSSION...09Z SURFACE ANALYSIS HAD WEAK LOW OVER NORTHEASTERN WY. FAIRLY TIGHT GRADIENT NEAR LOW WITH GUSTY WINDS IN WY AND PORTIONS OF THE BLACK HILLS ABOVE THE INVERSION. WILL LEAVE ADVISORY IN PLACE UNTIL 600 AM. FOR TODAY...UPPER TROUGH OVER THE ROCKIES MOVES EAST DRAGGING COLD FRONT THROUGH THE CWA...WASHING OUT LATE. MOST HIGHS WILL OCCUR THIS MORNING WITH WEAK COLD AIR ADVECTION IN THE AFTERNOON. FOR TONIGHT...WEAK HIGH SLIPS THROUGH. HAVE DROPPED POPS GIVEN DRY NATURE OF LOWER TROPOSPHERE. SUNDAY...VERY TRANSIENT SHORTWAVE RIDGE OVER THE CWA WILL GIVE WAY TO FAST MOVING SHORTWAVE SUNDAY NIGHT. SURFACE HIGH QUICKLY SHIFTS SOUTH WITH RETURN FLOW OVER WESTERN PORTIONS OF THE CWA. DRY DURING THE DAY...BUT ENOUGH FORCING/MOISTURE PRESENT FOR LOW POPS SUNDAY NIGHT. TEMPERATURES NEAR GUIDANCE. MONDAY...SOME DIFFERENCES IN MODEL HANDLING OF SHORTWAVE TROUGH. 00Z NAM/ECMWF/GEM TRENDING SOUTH AND EAST. 00Z GFS MORE NORTHERLY TRACK. WILL GO WITH MODEL TRENDS AT THIS POINT...WHICH WILL KEEP BEST PRECIPITATION AWAY FROM THE CWA. EXTENDED...AFOREMENTIONED SYSTEM WILL CONTINUE ITS DEPARTURE ON TUESDAY...WITH SOME PRECIP POSSIBLY LINGERING OVER SOUTH CENTRAL SOUTH DAKOTA. GFS BRINGS NEXT WAVE THROUGH THE REGION TUESDAY NIGHT...THOUGH HAS HAD SOME TROUBLE WITH THE PLACEMENT OF THIS SYSTEM OVER THE PAST FEW RUNS. THEREFORE...HAVE LIMITED LOW POPS TO THE EASTERN/NRN CWFA. RIDGE STARTS BUILDING IN FOR MID-WEEK BRINGING A RETURN TO DRY CONDITIONS. && .AVIATION...GUSTY SOUTHWEST WINDS OVER THE NRN AND NERN FOOTHILLS OF THE BLKHLS AND OVER NERN WY WILL DIMINISH THIS MORNING. VFR CONDITIONS WILL PREVAIL THROUGH THE FORECAST PERIOD. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...WIND ADVISORY UNTIL 6 AM MST EARLY THIS MORNING FOR NORTHERN FOOT HILLS-STURGIS/PIEDMONT FOOT HILLS. WY...NONE. && $$ HELGESON/SCHILD
