174 
FXUS63 KUNR 171606
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1005 AM MDT SAT APR 17 2010

.DISCUSSION...CURRENT SURFACE ANALYSIS HAS HIGH PRESSURE CENTERED 
OVER THE EASTERN DAKOTAS...WITH LOW PRESSURE OVER SOUTH CENTRAL MT. 
FAIRLY TIGHT PRESSURE GRADIENT IS IN PLACE ACROSS FAR EASTERN WY AND 
WESTERN SD. UPPER LEVEL ANALYSIS SHOWS WEAK RIDGE OVER THE 
DAKOTAS...WITH SHORTWAVE IN SOUTHWEST FLOW OVER THE CENTRAL ROCKIES. 
SKIES RANGE FROM SUNNY ACROSS EASTERN AREAS TO PARTLY SUNNY/MOSTLY 
CLOUDY ACROSS MUCH OF NORTHEASTERN WY AND FAR SOUTHWESTERN SD. MID 
AND HIGH CLOUDS WILL CONTINUE TO INCREASE ACROSS THE AREA THROUGH 
THE AFTERNOON AND EVENING. TEMPS ARE CURRENTLY IN THE 40S AND LOWER 
50S. SOUTHEASTERLY WINDS ARE BREEZY TO WINDY ACROSS MOST OF 
NORTHEASTERN WY AND THE FAR WESTERN SD PLAINS.

ONLY MINOR ADJUSTMENTS MADE TO THE FORECAST FOR THIS AFTERNOON INTO 
TONIGHT. SHORTWAVE ENERGY WILL MOVE ACROSS WESTERN WY THIS AFTERNOON 
AND THEN ACROSS EASTERN WY AND WESTERN SD TONIGHT AND SUNDAY. LOOKS 
LIKE A FEW SHOWERS AND STORMS WILL DEVELOP ACROSS WY THIS 
AFTERNOON...ESPECIALLY THE HIGHER TERRAIN...AND COULD MAKE THEIR WAY 
INTO SOUTHERN PARTS OF NORTHEASTERN WY LATE IN THE DAY. OTHERWISE... 
MAIN CHANCES WILL HOLD OFF ACROSS WESTERN AND SOUTHERN PORTIONS OF 
THE CWA UNTIL THIS EVENING. HIGHS WILL BE IN THE UPPER 50S TO MID 
60S ACROSS THE PLAINS...50S IN THE BLACK HILLS. GUSTY 
SOUTH-SOUTHEAST WINDS WILL CONTINUE ACROSS THE PLAINS THROUGH THE 
AFTERNOON... STRONGEST FROM FAR NORTHEASTERN WY INTO NORTHWESTERN 
SD.    


PREVIOUS DISCUSSION...WATER VAPOR IMAGERY SHOWS UPPER RIDGING ACROSS 
THE REGION WITH AN ACTIVE SOUTHWESTERLY FLOW DEVELOPING ACROSS THE 
GREAT BASIN INTO THE WESTERN ROCKIES. SURFACE ANALYSIS SHOWS A BROAD 
AREA OF HIGH PRESSURE CENTERED OVER THE ND/MN BORDER WITH S/SERLY 
FLOW ACROSS THE AREA. TEMPERATURES WERE IN THE 30S TO LOWER 40S.

FOR TODAY...UPPER RIDGE ACROSS THE REGION WILL WEAKEN AS A SERIES OF 
SHORTWAVES APPROACH FROM THE WEST. WARM AIR ADVECTION NOT AS 
IMPRESSIVE AS MODELS WERE SHOWING YESTERDAY...SO HAVE DROPPED TEMPS 
A FEW DEGREES WITH EXPECTED HIGHS IN THE 50S TO LOWER 60S. VERY 
BREEZY SOUTHEASTERLY WINDS ARE ALSO EXPECTED TODAY ACROSS THE 
NORTHEAST WYOMING AND SOUTH DAKOTA PLAINS WITH WINDS AT 20 TO 30 MPH 
WITH HIGHER GUSTS. ISOLATED THUNDERSTORMS WILL BE POSSIBLE THIS 
AFTERNOON ACROSS PORTIONS OF NORTHEAST WYOMING AS THE SHORTWAVES 
CROSS INTO THE WESTERN CWA. MODELS CONTINUE TO SHOW VERY WEAK CAPE 
ACROSS THE AREA. HAVE REMOVED POPS FROM THE BLACK HILLS THIS 
AFTERNOON GIVEN THE DECENT CAP IN PLACE. TONIGHT...THE SHORTWAVE 
WILL CROSS THE CWA THROUGH THE NIGHT. THOUGH A FEW THUNDERSTORMS 
WILL BE POSSIBLE...BELIEVE THIS WAVE WILL MAINLY BRING PASSING 
CLOUDS TO THE AREA. THE LLJ WILL DEVELOP OVERNIGHT ALONG WITH THETA 
E ADVECTION ACROSS CENTRAL SOUTH DAKOTA WHICH COULD SUPPORT SOME 
SHOWERS OR STORMS...BUT WILL LEAVE 20 POPS SINCE COVERAGE SHOULD BE 
MINIMAL.

SEVERAL MORE WAVES WILL CROSS THE AREA SUNDAY BRINGING A CONTINUED 
CHANCE OF SHOWERS AND THUNDERSTORMS IN THE AFTERNOON AND EVENING. 
MODELS CONTINUE TO INDICATE WEAK INSTABILITY...HOWEVER IT DOES LOOK 
BETTER THAN TODAY. ALSO CIN VALUES APPEAR TO BE MUCH WEAKER. 
TEMPERATURES WILL BE SLIGHTLY WARMER AND WAA WILL CONTINUE WITH 
HIGHS IN THE LOWER 60S TO LOWER 70S. ON MONDAY...A WEAK UPPER LOW 
WILL SAG SOUTHEASTWARD ACROSS NORTH DAKOTA. BETTER INSTABILITY IS 
EXPECTED MONDAY WITH CAPE VALUES OF 400-800 J/KG ALONG WITH 
CONTINUED UPPER LEVEL FORCING ASSOCIATED WITH THE UPPER LOW...SO 
HAVE ADDED POPS MONDAY AFTERNOON AND EVENING.

EXTENDED...A WEAK UPPER LOW WILL DROP SOUTHWARD INTO THE EASTERN 
DAKOTAS ON TUESDAY. LEADING TO SLIGHTLY COOLER...THOUGH STILL WARMER 
THAN NORMAL...TEMPERATURES FOR BOTH TUESDAY AND WEDNESDAY. SHORTWAVE 
ENERGY ROTATING AROUND THE UPPER LOW WILL CREATE A SLIGHT CHANCE OF 
SHOWERS AND THUNDERSTORMS ON WEDNESDAY AND WEDNESDAY NIGHT. A MORE 
SIGNIFICANT UPPER SYSTEM WILL BE MOVING INTO GREAT BASIN ON THURSDAY 
AND WILL BRING AN INCREASED CHANCE OF PCPN TO OUR AREA FROM THURSDAY 
INTO NEXT WEEKEND. AT THIS TIME IT APPEARS IT SHOULD BE MAINLY A 
RAIN EVENT. TEMPS WILL COOL TO NEAR NORMAL THE LAST HALF OF THE WEEK.

&&

.AVIATION...VFR CONDS ARE EXPECTED THRU THE FCST PERIOD.

&&

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

$$