Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 310205
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
805 PM MDT SUN AUG 30 2015

.UPDATE...
ISSUED AT 802 PM MDT SUN AUG 30 2015

01Z SURFACE ANALYSIS HAD FRONTAL BOUNDARY FROM CENTRAL ND INTO
CENTRAL WY WITH PREFRONTAL TROUGH FROM CENTRAL ND INTO WESTERN NE.
DEEP DAYTIME MIXING ALONG WITH INCREASE IN MID-LEVEL MOISTURE PER
WATER VAPOUR RESULTED IN MAINLY HIGH-BASED -SHRA/-TSRA ALONG THE
FRONTAL BOUNDARY THIS EVENING...WHICH ARE NOW MOVING NORTHEAST
UNDER MEAN FLOW ALOFT. ACTIVITY WILL SLOWLY WANE OVERNIGHT. UPDATE
TO ADDRESS LATEST TRENDS IN TIMING.

&&

.SHORT TERM...THIS EVENING THROUGH MONDAY NIGHT
ISSUED AT 300 PM MDT SUN AUG 30 2015

CURRENT SURFACE ANALYSIS SHOWS SLOW MOVING COLD FRONT FROM FAR
EASTERN MT THROUGH NORTHEAST INTO CENTRAL WY. UPPER LEVEL ANALYSIS
SHOWS POSITIVELY TILTED RIDGE FROM THE SOUTHERN ROCKIES INTO
EASTERN PORTIONS OF THE NORTHERN PLAINS. SOUTHWEST FLOW ALOFT
BEHIND THE RIDGE FROM THE GREAT BASIN TO THE NORTHERN HIGH PLAINS.
SKIES ARE MOSTLY SUNNY ACROSS EASTERN PORTIONS OF THE CWA...PARTLY
CLOUDY OVER NORTHEAST WY. REGIONAL RADARS SHOW BULK OF SHOWER AND
THUNDERSTORM ACTIVITY OVER NORTHEAST MT INTO NORTHWEST ND NEAR THE
FRONT...AS WELL AS OVER THE HIGHER TERRAIN OF CENTRAL WY. A FEW
SHOWERS AND STORMS ARE NOW DEVELOPING NEAR AND AHEAD OF THE FRONT
OVER NORTHEAST WY. TEMPS ARE IN THE 90S OVER MUCH OF THE
AREA...WITH SOME 80S OVER THE BLACK HILLS. WINDS ARE FROM THE
SOUTH TO SOUTHWEST... BREEZY OVER SOUTH CENTRAL SD AS WELL AS
PORTIONS OF NORTHEAST WY.

COLD FRONT WILL EVER SO SLOWLY CROSS THE FORECAST AREA LATE TODAY
AND TONIGHT...WEAKENING SOME AS IT REACHES SOUTH CENTRAL SD MONDAY
MORNING. MOSTLY ISOLATED SHOWERS AND THUNDERSTORMS CAN BE EXPECTED
WITH THE FRONTAL PASSAGE TONIGHT. THE BEST CHANCES WILL LIKELY BE
OVER FAR NORTHWEST SD THIS EVENING. THE THREAT FOR ANY STRONGER
STORMS WILL BE MINIMAL THROUGH THE EVENING AS CAPE VALUES REMAIN
RELATIVELY LOW ACROSS THE AREA...BUT SOME GUSTY WINDS ARE POSSIBLE.
WINDS WILL SWITCH TO THE WEST AND NORTHWEST BEHIND THE
FRONT...BECOMING BREEZY LATER TONIGHT AND EARLY MONDAY OVER MUCH OF
THE PLAINS. AHEAD OF THE FRONT...WINDS WILL REMAIN BREEZY FROM THE
SOUTH OVER SOUTH CENTRAL SD. LOWS WILL RANGE FROM THE 50S OVER
NORTHEAST WY AND THE BLACK HILLS TO AROUND 70 OVER SOUTH CENTRAL SD.

FRONT WILL SLOWLY SAG SOUTH AND EAST OF THE AREA ON MONDAY AND
FURTHER WEAKEN. WOULD NOT BE SURPRISED TO SEE A SHOWER OR
THUNDERSTORM OVER FAR SOUTHERN SD ON MONDAY IN CLOSER VICINITY TO
THE FRONT...ESPECIALLY SOUTH CENTRAL SD...BUT CHANCES LOOK BELOW 15
PERCENT SO WILL LEAVE FORECAST DRY. SOME COOLER AIR WILL BUILD INTO
THE AREA...WITH HIGHS IN THE 80S ACROSS THE PLAINS...70S IN THE
BLACK HILLS. BRISK NORTHWEST WINDS CAN BE EXPECTED ACROSS THE SD
PLAINS DURING THE DAY. MOSTLY CLEAR MONDAY NIGHT WITH LOWS NEAR OR
SLIGHTLY ABOVE SEASONAL AVERAGES.

.LONG TERM...TUESDAY THROUGH SUNDAY
ISSUED AT 300 PM MDT SUN AUG 30 2015

LONG WAVE TROUGH OVER WESTERN NOAM WILL REMAIN THROUGH
MID WEEK...WITH EVENTUAL BREAKDOWN PER AN ADVECTING STRONG NORTHERN
PAC IMPULSE. THIS WILL SUPPORT VERY WARM TEMPS THROUGH THURS. STRONG
SUPPORT AMONG DETERMINISTIC AND ENSEMBLE MODEL RUNS FOR A STRONG
COLD FRONT TO ADVECT TROUGH THE REGION NEXT WEEKEND AS THE PAC NW
UPPER TROUGH MERGES WITH A STRONG CENTRAL CANADIAN TROUGH.
HOWEVER...PRECIP CHANCES STILL LOOK LOW GIVEN LACK OF SUFFICIENT
MOISTURE WITH THE BULK OF LSA SHIFTING NORTH OF THE AREA. MUCH
COOLER TEMPS LOOK MORE LIKELY BY SUN-MON NEXT WEEK WITH HIGHS IN THE
50S-60S POSSIBLE BY THEN. MEANWHILE...DRY WEATHER IS EXPECTED TUE-
THUR...ALTHOUGH A WEAK SIGNAL REMAINS OVER SCENTRAL SD TUES WHERE A
LL TROUGH AND MOISTURE ADV ARE PROGGED. DID BUMPS TEMPS UP TUE-THUR
GIVEN WARM-DRY SW FLOW WITH WARMER TEMPS NOW PROGGED IN CONSENSUS
BLENDS. OTHERWISE...COOLER CONDS WILL ARRIVE FRI-SAT...HOW COOL WILL
DEPEND ON THE PROGRESSIVE NATURE OF THE UPPER TROUGH...WHICH IS A
LITTLE SLOWER IN THE ECMWF. MUCH COOLER CONDS EXPECTED BY EARLY NEXT
WEEK...ALONG WITH ISOLD-SCT SHRA.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 520 PM MDT SUN AUG 30 2015

A COOL FRONT WILL SLOWLY SLIDE SOUTHEAST THROUGH THE CWA TONIGHT
INTO MONDAY MORNING. GUSTY SOUTHERLY WINDS ARE EXPECTED AHEAD OF
IT WITH GUSTY NORTHWEST WINDS BEHIND IT. ISOLATED HIGH BASED -TSRA
ARE POSSIBLE NEAR THE FRONT TONIGHT WITH ISOLATED WIND GUSTS
AROUND 40KTS. VFR CIGS/VSBYS ARE EXPECTED THROUGH THE PERIOD.

&&

.FIRE WEATHER...
ISSUED AT 300 PM MDT SUN AUG 30 2015

WARM AND DRY CONDITIONS WILL PERSIST ACROSS NE WY THIS
AFTERNOON...WITH RELATIVE HUMIDITY AROUND 15 PERCENT AND GUSTY
WESTERLY WINDS OF 20 TO 30 MPH. A FEW ISOLD TS ARE ALSO POSSIBLE
WITH DRY LIGHTNING AND GUSTY WINDS LIKELY WITH ANY TS. A COLD
FRONT WILL CROSS THE AREA TONIGHT WITH WINDS SHIFTING NW AND
REMAINING GUSTY FOR A FEW HOURS.

&&

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

$$

UPDATE...HELGESON
SHORT TERM...26
LONG TERM...JC
AVIATION...HELGESON
FIRE WEATHER...JC


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