273 
FXUS63 KUNR 100923
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
323 AM MDT FRI AUG 10 2012

.DISCUSSION...CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER
WESTERN MT...WITH FRONTAL BOUNDARY STRETCHING SOUTHEASTWARD INTO
THE CENTRAL HIGH PLAINS. CANADIAN HIGH PRESSURE IS LOCATED OVER
EASTERN ND AND MN...WITH COOLER TEMPERATURES IN THAT DIRECTION.
UPPER LEVEL ANALYSIS SHOWS HIGH PRESSURE CENTERED OVER THE FOUR
CORNERS REGION...WITH RIDGING OVER THE ROCKIES. WEAK DISTURBANCES
ARE NOTED ON WATER VAPOR IMAGERY ROTATING AROUND THE RIDGE.
IMAGERY IS ALSO SHOWING MONSOONAL MOISTURE OVER MUCH OF THE
WESTERN CONUS. REGIONAL RADARS ARE SHOWING MOST OF THE SHOWER AND
THUNDERSTORM ACTIVITY HAS ENDED ACROSS THE REGION...BUT ISOLATED 
SHOWERS AND A FEW LIGHTNING STRIKES ARE NOTED FROM WESTERN ND INTO
NORTHWESTERN AND CENTRAL SD WITH LOW LEVEL JET IN THE VICINITY.
THIS ACTIVITY SHOULD DISSIPATE AROUND OR SHORTLY AFTER SUNRISE. SKIES
ARE GENERALLY PARTLY CLOUDY WITH TEMPERATURES IN THE 60S AND LOWER
70S. WINDS ARE FROM THE EAST TO SOUTHEAST AT 5 TO 15 MPH AT MOST
LOCATIONS.

UNSETTLED WEATHER CAN BE EXPECTED THROUGH SATURDAY AS LOW PRESSURE
OVER MT AND ASSOCIATED COLD FRONT SLOWLY CROSS THE AREA. THERE
WILL BE A GOOD CHANCE FOR SHOWERS AND THUNDERSTORMS AS DEVELOPING
SHORTWAVE MOVES ACROSS THE NORTHERN PLAINS. SHORT RANGE MODELS ARE
IN DECENT AGREEMENT ON TRACK OF LOW AND SHORTWAVE...BUT SHOW SOME
DIFFERENCES ON TIMING AND WHERE THE BETTER CHANCES FOR PCPN WILL
OCCUR. HAVE MADE SOME ADJUSTMENTS TO FORECAST...MAINLY TO LOWER
POPS A BIT ACROSS SOUTHERN AREAS. THE BETTER CHANCES FOR SHOWERS
AND THUNDERSTORMS RIGHT NOW LOOK TO BE ACROSS EASTERN
MT...NORTHEASTERN WY...ND...AND NORTHERN SD WITH THIS SYSTEM. AFTER A
VERY WARM DAY ACROSS THE AREA TODAY...SOME COOLER TEMPS CAN BE
EXPECTED OVER THE WEEKEND...ESPECIALLY ACROSS NORTHWESTERN SD.

FOR TODAY...SKIES WILL BE PARTLY CLOUDY IN GENERAL...WITH MAIN
INCREASE IN CLOUDS FROM THE WEST LATER IN THE AFTERNOON. THE MOST
SUNSHINE WILL LIKELY BE ACROSS AREAS SOUTH AND EAST OF THE BLACK
HILLS. HIGHS WILL BE IN THE MID 80S TO MID 90S...WARMEST ACROSS
THE SOUTHWESTERN SD PLAINS. BREEZY SOUTHEASTERLY WINDS WILL
DEVELOP ACROSS MUCH OF THE AREA LATE THIS MORNING...STRONGEST
ACROSS NORTHWESTERN SD...AS SURFACE LOW MOVES SLOWLY EAST-
SOUTHEAST ACROSS SOUTHERN MT. CHANCES FOR SHOWERS AND
THUNDERSTORMS WILL INCREASE ACROSS NORTHERN WY AND EASTERN MT AS
THE AFTERNOON GOES ON. THIS IS WHERE INSTABILITY WILL BE
GREATEST...WITH CAPE OF 500 TO 1000 J/KG PROGGED BY LATE
AFTERNOON. SHEAR WILL BE MARGINALLY STRONG BY LATE AFTERNOON
ACROSS THESE AREAS. THE THREAT FOR SEVERE STORMS LOOKS
MINIMAL...BUT GUSTY WINDS AND HAIL WOULD BE POSSIBLE WITH ANY
STRONGER STORMS INTO THE EVENING HOURS.

CHANCES FOR SHOWERS AND STORMS WILL INCREASE FURTHER FRIDAY NIGHT
AND SPREAD EAST ACROSS MOST OF THE CWA OVERNIGHT. THE BETTER
CHANCES LOOK TO BE FROM NORTHEASTERN WY INTO THE BLACK HILLS AND
NORTHWESTERN SD AS LOW MOVES INTO SOUTHEASTERN MT. TEMPS WILL
DROP INTO THE MID 50S TO MID 60S WITH BREEZY WINDS LINGERING IN SOME
AREAS...ESPECIALLY OVER THE SD PLAINS AS LOW LEVEL JET INTENSIFIES
OVERNIGHT. 

SURFACE LOW IS PROGGED TO TRACK ACROSS THE CWA ON SATURDAY...WITH
A GOOD CHANCE FOR SHOWERS AND THUNDERSTORMS ALONG AND AHEAD OF THE
FRONT AS IT MOVES ACROSS THE AREA. THE BETTER CHANCES WILL REMAIN
ACROSS NORTHERN SD INTO ND...TO THE NORTH AND EAST OF THE LOW AND
CLOSER TO MAIN SHORTWAVE TRACK. THE BETTER CHANCES FOR STRONGER
STORMS WOULD BE MAINLY SOUTH AND EAST OF THE BLACK HILLS AS
FRONTAL PASSAGE OCCURS THERE DURING THE MIDDAY AND AFTERNOON
HOURS. HOWEVER...THOSE CHANCES WILL REMAIN FAIRLY LOW AS
AVAILABLE INSTABILITY AND LOW LEVEL MOISTURE WILL BE RELATIVELY
WEAK. HIGH TEMP FORECAST WILL BE TRICKY WITH FRONTAL PASSAGE AND
VARYING AMOUNTS OF CLOUDINESS AND SHOWERS AROUND. WILL GO WITH HIGHS
RANGING FROM THE 70S OVER THE BLACK HILLS AND FAR NORTHWESTERN
SD...TO AROUND 90 ACROSS FAR SOUTHWESTERN SD. GUSTY NORTHWESTERLY
WINDS WILL LIKELY DEVELOP IN THE AFTERNOON ACROSS PORTIONS OF THE
WESTERN SD PLAINS AND LINGER INTO THE EVENING.

SHOWERS WILL EXIT EASTERN PORTIONS OF THE CWA SATURDAY NIGHT AS
SYSTEM MOVES SOUTH AND EAST OF THE CWA. SUNDAY WILL CLEARLY BE THE
BETTER OF THE WEEKEND DAYS FOR OUTDOOR ACTIVITIES...WITH MAINLY
SUNNY SKIES AND HIGHS IN THE 80S AND LOWER 90S. BREEZY NORTH-
NORTHWEST WINDS WILL DEVELOP ACROSS MUCH OF THE SD PLAINS DURING
THE LATE MORNING AND AFTERNOON HOURS IN THE WAKE OF EXITING SYSTEM.

EXTENDED...DISTURBED WNW MID LEVEL FLOW WILL BE IN PLACE AT THE 
START OF THE PERIOD...SUPPORTING PERIODIC LOW AMPLITUDE IMPULSES 
THROUGH THE REGION THROUGH MID WEEK. THE FOCUS THEN BECOMES THE 
ADVECTION OF A DEEP LONG WAVE NORTHERN STREAM TROUGH INTO THE 
NORTHERN TIER. FORECAST MODELS CONTINUE TO SUPPORT PHASING OF A NE 
PAC UPPER LEVEL DISTURBANCE WITH A SOUTHERN PERIPHERY POLAR LOW 
IMPULSE...WITH LONG TRAJECTORY CAA UNDER THE MID LEVEL TROUGH. END 
RESULT LOOKS TO BE A SIG NEGATIVE INFLUENCE TO THE THICKNESS OVER 
THE NORTHERN PLAINS BEHIND A COLD FRONT WED...WITH AN APPRECIABLE 
COOL DOWN LOOKING MORE LIKELY THUR-FRI. GROWING INDICATIONS FOR 
DOWNSTREAM BLOCKING OVER THE WESTERN ATLANTIC MAY SUPPORT COOL TEMPS 
INTO NEXT WEEKEND...ESP IF SECONDARY IMPULSES ROTATE AROUND THE 
BACKSIDE OF THE EXPECTED MASSIVE CENTRAL/EASTERN NOAM UPPER TROUGH. 

RETAINED POPS IN THE MONDAY AFTERNOON/MON NIGHT PERIODS FOR A 
CONTINUED PROGGED LOW AMPLITUDE IMPULSE. LL MOISTURE CERTAINLY 
LACKING. HOWEVER...STRONG HEATING WITH SUBTLE LARGE SCALE ASCENT 
WOULD BE MORE THAN ENOUGH TO SUPPORT DIURNAL 
CONVECTION...TRANSITIONING TO HIGH CENTERED THETA-E ADV OVERNIGHT. ALSO 
RETAINED POPS TUES NIGHT THROUGH WED NIGHT WITH AN EXPECTED THETA-E 
RISE/FALL COUPLET ASSOCIATED WITH THE DEEP NORTHERN STREAM UPPER 
TROUGH. FORECAST MODELS CERTAINLY DONT SEEM TO SUPPORT MUCH PRECIP 
DEVELOPMENT WITH THIS SYSTEM...GIVEN LACK OF SIG DEEP MOISTURE AND 
LIKELY CAPPING AHEAD OF THE COLD FRONT. HOWEVER...GIVEN THE 
INTENSITY OF THE UPPER TROUGH...CERTAINLY DONT SEE ANY REASON TO 
REMOVE/ADJUST POPS IN THIS PERIOD UNTIL WAVE TIMING BECOMES BETTER 
ESTABLISHED. RETAINED SMALL CHANCES FOR TS OVER THE BH THUR GIVEN 
SIG MID LEVEL COOLING WITH STEEP AFTERNOON LL LAPSE RATES...IN 
ADDITION TO CONCERN FOR A POSSIBLE SOUTHERN PERIPHERY LOW AMPLITUDE 
IMPULSE.

AS FOR TEMPS...RETAINED WARM READINGS MON-TUE...WITH A DOWN TREND IN 
HIGHS/LOWS WED /WESTERN AREAS/ THROUGH FRIDAY. GEFS CONTINUES TO PROG 
H7 TEMPS 1-2 STANDARD DEVIATION BELOW CLIMO THUR-FRI...WITH SIG H85 
COOLING IN ECMWF/GFS SOLUTIONS.

&&

.AVIATION...06Z TAFS
VFR CONDITIONS EXPECTED OVERNIGHT. THETA-E ADV AOA H7 WILL SUPPORT 
HIGH BASED SHRA/TS OVER THE SD PLAINS THROUGH MID MORNING. A BETTER 
CHANCE FOR THUNDERSTORMS EXPECTED FRIDAY AFTERNOON ACROSS NERN WY 
AND FAR WRN SD...ALTHOUGH FLIGHT RESTRICTIONS WILL BE VERY ISOLATED 
FROM CONVECTION.

&&

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

$$

SHORT TERM...26
LONG TERM....JC
AVIATION...JC