858 FXUS63 KUNR 311524 AFDUNR AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY NATIONAL WEATHER SERVICE RAPID CITY SD 924 AM MDT SUN MAR 31 2013 .UPDATE... ISSUED AT 925 AM MDT SUN MAR 31 2013 15Z SURFACE MAP SHOWS COLD FRONT BACKING INTO WESTERN SOUTH DAKOTA...JUST WEST OF A BUFFALO-UNION CENTER-PHILIP-WINNER LINE. BAND OF SNOW LOCATED ACROSS NORTHEAST MONTANA INTO SOUTHWEST NORTH DAKOTA. COLD FRONT WILL CONTINUE SLOW WESTWARD MOVEMENT THROUGH THE DAY AS BEST PRESSURE FALLS SLIDE SOUTH OF THE BLACK HILLS. 12Z NAM/RAP CONTINUE TO SHOW DEEPER MIXING ACROSS NORTHEAST WYOMING INTO SOUTHWEST SOUTH DAKOTA OFFSETTING LOW LEVEL CAA ON NORTHEASTERLY WINDS. HAVE LOWERED HIGHS ACROSS NORTHWEST SOUTH DAKOTA AS CLOUDS/PRECIPITATION WILL LIMIT WARMING. MINOR ADJUSTMENTS MADE TO POPS...BEST CHANCE OF ACCUMULATING SNOW WILL REMAIN JUST NORTH AND EAST OF THE FORECAST AREA. && .SHORT TERM...TODAY THROUGH MONDAY NIGHT ISSUED AT 302 AM MDT SUN MAR 31 2013 NORTHERN STREAM IMPULSE CONTINUES TO DIVE SE ON THE BACKSIDE OF THE PERSISTENT HUDSON BAY VORTEX. THIS SYSTEM WILL SUPPORT INCREASING LARGE SCALE ASCENT/LL CONVERGENCE PER A FGEN RESPONSE/AND A LL COLD FRONT INTO THE REGION TODAY. FORECAST MODELS CONTINUE TO ADJUST EAST PER THE BULK OF HEIGHT FALLS/CAA...WITH RESULTANT/ASSOCIATED FORCING FIELDS SHIFTING EAST AS WELL. THE SHIFT WILL ALSO SUPPORT WARMER TEMPS THAN PREVIOUS INDICATIONS SUGGESTED...ESP ACROSS THE SW THIRD OF THE FA TODAY...WITH WARMER CONDITIONS EXPECTED MONDAY AS WELL. CLOUDS WILL GRADUALLY INCREASE ACROSS THE FA NORTH TO SOUTH TODAY. INCREASING LL FORCING WITH A WEAK FGEN RESPONSE...WILL SUPPORT A BAND OF RAIN OR SNOW ACROSS THE FAR NE THROUGH SE PORTIONS OF THE FA TODAY...WITH THE BEST COLLOCATION OF FORCING BEING ACROSS THE FAR NE LATE THIS MORNING INTO THE AFTERNOON. OTHERWISE...VERY DRY LL/S WITH LACK OF SIG FORCING WILL SUPPORT DRY CONDITIONS ACROSS THE REMAINDER OF THE FA. HENCE...ADJUSTED POPS TO REMOVE WX MENTION ACROSS THE WESTERN 2/3 OF THE FA...RETAINING CHANCE TO LIKELY POPS ACROSS THE EAST. LL THERMAL FIELDS AND TIMING SUGGESTS THE MAJORITY OF PRECIP WILL FALL AS RAIN OR A MELTING SNOW...WHICH LIMITS ANY ACCUMS TO AT MOST A DUSTING. FORCING WILL QUICKLY SHIFT SE OUT OF THE FA THIS AFTERNOON...WITH POSSIBLE LINGERING RAIN/SNOW SHOWERS ACROSS FAR EASTERN SOUTH CENTRAL SD THIS EVENING. ALSO ADJUSTED TEMPS TODAY TO RAISE THE SW THIRD OF THE FA 1-4 DEGREES...WITH WARM THERMAL FIELDS/DEEP MIXING EXPECTED...COUPLED WITH A PERIOD OF MODERATE INSOLATION. ONLY OTHER WX CONCERN TODAY WILL BE A PERIOD OF STRONG GUSTY WINDS OVER THE NORTHERN AND EASTERN BLACK HILLS FOOTHILLS AND ADJACENT SD PLAINS. CURRENT DATA SUGGEST WINDS COULD TOUCH WIND ADV CRITERIA THIS AFTERNOON THERE...INCLUDING RAPID CITY. DEEP MIXING THIS AFTERNOON WITH FLOW ENHANCEMENT AROUND THE HILLS COUPLED WITH A STRENGTHENING PRESSURE GRADIENT PER THE ADVANCING IMPULSE WOULD SUPPORT A DECENT ENVIRONMENT FOR STRONG WINDS. HOWEVER...MARGINAL NUMBERS WITH CONCERNS ON CLOUD COVER AND AREAL CONVERGE OF STRONG WINDS PRECLUDES A WIND ADV ISSUANCE ATTM. WILL LET THE DAY SHIFT REASSESS. MONDAY...A SFC RIDGE WILL RESIDE OVER THE FAR EASTERN DAKOTAS AND WILL SLIDE EAST WITH WAA ENSUING QUICKLY ACROSS THE FA. LL EASTERLY WINDS ACROSS THE SD PLAINS MAY HAMPER T RISES. HOWEVER...CLEAR SKIES SHOULD SUPPORT DEEP MIXING MOST PLACES. EASTWARD BIAS OF THE EASTERN CONUS UPPER TROUGH WILL SUPPORT WARMER THERMALS FIELDS THAN PREVIOUS INDICATIONS. HENCE...WARMED TEMPS MOST PLACES. OTHERWISE...QUIET WEATHER EXPECTED WITH MOSTLY CLEAR SKIES. .LONG TERM...TUESDAY THROUGH SATURDAY ISSUED AT 302 AM MDT SUN MAR 31 2013 THE NORTHERN PLAINS WILL BE UNDER THE INFLUENCE OF AN UPPER RIDGE FOR TUESDAY AND WEDNESDAY...BRINGING DRY CONDITIONS AND ABOVE AVERAGE TEMPERATURES. UPPER RIDGE FLATTENS WEDNESDAY NIGHT AS A COLD FRONT CROSSES THE AREA...BRINGING SMALL CHANCES FOR PRECIPITATION. COULD SEE OCCASIONAL SHOWERS LATE IN THE WEEK AS WEAK ENERGY CROSSES THE REGION. && .AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING ISSUED AT 302 AM MDT SUN MAR 31 2013 A COLD FRONT WILL CROSS THE AREA TODAY BRINGING VERY GUSTY NORTH TO NORTHWEST WINDS DURING THE AFTERNOON AND EARLY EVENING. THERE WILL BE A CHANCE OF RAIN AND SNOW LATE THIS AFTERNOON AND OVERNIGHT...PRODUCING MVFR/IFR CONDITIONS...MAINLY ACROSS NORTHWEST SOUTH DAKOTA. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...NONE. WY...NONE. && $$ UPDATE...7 SHORT TERM...JC LONG TERM...15 AVIATION...15