FXUS63 KUNR 290332
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
832 PM MST SAT NOV 28 2009

.DISCUSSION...03Z SURFACE ANALYSIS HAD HIGH OVER THE CWA. CLEARING
SKIES IN SUBSIDENCE REGION BEHIND UPPER TROUGH ALLOW TEMPERATURES
TO PLUMMET THIS EVENING. UPDATED FORECAST FOR LESS CLOUDS/LOWER
TEMPERATURES IN THE WEST.

&&

.PREV DISCUSSION... /ISSUED 235 PM MST SAT NOV 28 2009/ 

DISCUSSION...CURRENT SURFACE ANALYSIS HAS COLD FRONT SOUTH OF THE 
AREA...WITH FAIRLY TIGHT PRESSURE GRADIENT ACROSS SOUTHERN PORTIONS 
OF THE REGION. UPPER LEVEL ANALYSIS HAS LOW DIGGING SOUTHEASTWARD 
ACROSS THE SOUTHWEST CONUS...WITH WEAKER NORTHERN STREAM ENERGY 
CROSSING THE NORTHERN HIGH PLAINS. SKIES ARE MOSTLY CLOUDY ACROSS 
THE AREA WITH TEMPS IN THE 30S AND LOWER 40S...WARMEST ACROSS AREAS 
SOUTH AND EAST OF THE HILLS. REGIONAL RADARS SHOWING WIDELY 
SCATTERED LIGHT RAIN AND SNOW SHOWERS AS WAVE CROSSES.  

COOLER WX WILL PERSIST INTO NEXT WEEK...BUT WILL STILL REMAIN ABOVE 
AVERAGE THROUGH AT LEAST TUESDAY WITH DRY CONDITIONS. ANOTHER SYSTEM 
COULD DROP TEMPS TO BELOW AVERAGE LEVELS FOR THE SECOND HALF OF NEXT 
WEEK.  

FOR TONIGHT...CLOUDS WILL DECREASE AS WAVE SLIDES SOUTHEAST OF THE 
AREA. WINDS WILL ALSO DIMINISH THIS EVENING. TEMPS WILL DROP TO THE 
MID TEENS TO MID 20S BY MORNING. SUNDAY WILL BE A PLEASANT LATE 
NOVEMBER DAY WITH MOSTLY SUNNY SKIES AND HIGHS IN THE 40S. 

SOME MILDER AIR WILL BUILD INTO THE AREA LATER SUNDAY NIGHT AND 
MONDAY AS WEAK SHORTWAVE RIDGE SLIDES ACROSS. HIGHS ON MONDAY WILL 
REACH INTO THE 50S AT MOST LOCATIONS UNDER MOSTLY SUNNY SKIES.  

EXTENDED...COLD FRONT WILL SWEEP ACROSS THE CWA EARLY ON TUESDAY. 
STRONG COLD AIR ADVECTION BEHIND THE FRONT WILL BRING GUSTY 
NORTHWEST WINDS TO THE SOUTH DAKOTA PLAINS TUESDAY MORNING INTO 
TUESDAY AFTERNOON. TROUGH WILL SWING THROUGH THE CWA TUESDAY 
AFTERNOON INTO TUESDAY NIGHT...BRINGING A SLIGHT CHANCE OF SNOW 
SHOWERS TO NORTHEAST WYOMING AND FAR WESTERN SOUTH DAKOTA. 

EMBEDDED SHORTWAVES IN NORTHWEST FLOW ALOFT WILL MOVE ACROSS THE CWA 
ON WEDNESDAY BRINGING ADDITIONAL CHANCES FOR SNOW SHOWERS TO THE 
AREA. COLD SURFACE HIGH PRESSURE WILL BUILD INTO THE AREA WEDNESDAY 
NIGHT WITH LOWS EXPECTED TO DIP INTO THE TEENS TO NEAR SINGLE DIGITS 
ACROSS THE BLACK HILLS AND SOME LOCATIONS ON THE PLAINS. 

A WEAK RIDGE WILL APPROACH THE CWA ON THURSDAY WHILE A TROUGH DIVES 
INTO THE PACIFIC NORTHWEST. TROUGH WILL MOVE INTO THE CWA ON FRIDAY. 
AT THIS TIME GUIDANCE IS SUGGESTING A SIGNIFICANT COOL DOWN GOING 
INTO NEXT WEEKEND AND EARLY NEXT WEEK. RMOP SHOWING LOW 
PREDICTABILITY WITH THIS SCENARIO. HOWEVER...SEVERAL GFS ENSEMBLE 
MEMBERS SHOWING A COOL DOWN. THE ECMWF INDICATES RIDGING ACROSS THE 
WEST COAST WITH TEMPERATURES RECOVERING EARLY NEXT WEEK. GIVEN THE 
DEGREE OF UNCERTAINTY...WILL KEEP HIGH TEMPERATURES IN THE 30S FOR 
EARLY IN THE WEEKEND. 

AVIATION...VFR CONDITIONS ARE EXPECTED THROUGH THE FORECAST
PERIOD.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

HELGESON