Issued by NWS Rapid City, SD
000 FXUS63 KUNR 162028 AFDUNR AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY NATIONAL WEATHER SERVICE RAPID CITY SD 228 PM MDT THU OCT 16 2008 .DISCUSSION...CURRENT WATER VAPOR IMAGERY SHOWS SHORTWAVE TROUGH OVER EASTERN MONTANA AND EASTERN WYOMING. LIGHT SHOWERS HAVE DEVELOPED ACROSS PORTIONS OF NORTHEAST WYOMING AND NORTHWEST SOUTH DAKOTA. EXPECT THESE SHOWERS TO INCREASE IN COVERAGE AND MOVE EASTWARD AS THE WAVE PROGRESSES EASTWARD LATE THIS AFTERNOON INTO THIS EVENING. DO NOT EXPECT MUCH PRECIPITATION OUT OF THIS SYSTEM THIS EVENING. TROUGH WILL PUSH OUT OF THE AREA OVERNIGHT WITH NORTHWEST FLOW ALOFT SETTING UP ACROSS THE AREA ON FRIDAY. SURFACE TROUGH WILL SET UP ACROSS WESTERN SOUTH DAKOTA ON FRIDAY AS A SURFACE HIGH BUILDS OVER THE CENTRAL ROCKIES. HIGH PRESSURE ALOFT WILL SLIDE OVER THE CWA ON SATURDAY AS THE SURFACE TROUGH REMAINS OVER WESTERN SOUTH DAKOTA. WEST TO SOUTHWEST FLOW NEAR THE SURFACE WILL PUMP WARM AND DRY AIR INTO SOUTHWEST SOUTH DAKOTA ON SATURDAY. HIGH TEMPERATURES ON SATURDAY WILL CLIMB INTO THE UPPER 70S TO AROUND 80 ACROSS SOUTHWEST SOUTH DAKOTA. WEAK DOWNSLOPE FLOW MAY ALLOW TEMPERATURES TO WARM INTO THE LOWER 80S ALONG THE EASTERN FOOTHILLS OF THE BLACK HILLS. UPPER RIDGE WILL TRANSITION TO ZONAL FLOW ON SATURDAY NIGHT AS THE NEXT SHORTWAVE APPROACHES FROM THE PACIFIC NORTHWEST. EXTENDED...A COLD FRONT WILL MOVE SOUTH THROUGH THE REGION ON SUNDAY AS A SHORT WAVE RACES EAST ALONG THE U.S./CNDN BORDER. THERE SHOULD BE ENOUGH LIFT DURING THE AFTN/EVE HOURS WITH JET ENERGY PASSING TO OUR NORTH AND WEAK FRONTOGENESIS TO PROVIDE SOME LIGHT PCPN. THUS...HAVE LOWERED TEMPS FOR BOTH SUNDAY AND SUNDAY NIGHT AS WELL AS INTRODUCE LOW POPS. MONDAY WILL LIKELY REMAIN ON THE COOL SIDE AS CANADIAN SFC HIGH TRACK FROM THE DAKOTAS INTO THE UPR MIDWEST AND COOL RETURN FLOW SETS UP ACROSS OUR CWFA. NEXT VIGOROUS TROF IS EXPECTED TO MOVE THROUGH THE NRN PLAINS ON TUESDAY/TUESDAY NIGHT PER THE GFS/ECMWF AND WILL PROVIDE ANOTHER CHANCE FOR PCPN AND A REINFORCING SHOT OF COOLER AIR. DRY WX AND SLIGHTLY WARMER TEMPS SHOULD ROUND OUT THE END OF THE WORK WEEK. && .AVIATION...VFR CIGS EXPECTED THROUGH TONIGHT WITH ANY LIGHT -SHRA COMING TO AN END FROM WEST TO EAST AFTER MIDNIGHT. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...NONE. WY...NONE. && $$ JW/JJ
