Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 201722
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1122 AM MDT MON APR 20 2015

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 317 AM MDT MON APR 20 2015

CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE WELL EAST OF THE
REGION THIS MORNING...WITH A WEAKENING COLD FRONT OVER NORTHERN MN
AND ND. UPPER LEVEL ANALYSIS SHOWS LARGE TROF OVER THE UPPER
MIDWEST AND MS RIVER VALLEY...WITH REMNANTS OF UPPER LOW OVER
SOUTHERN IL. NORTH-NORTHWEST FLOW IN PLACE OVER THE NORTHERN
PLAINS...WITH DRY AND COOL AIRMASS SLIDING SOUTH OUT OF CANADA.
SKIES ARE MOSTLY CLEAR TO THE NORTH AND EAST OF THE BLACK
HILLS...WITH MORE CLOUDINESS OVER NORTHEAST WY. WINDS HAVE
DIMINISHED TO 5 TO 15 MPH FROM THE WEST AND NORTHWEST OVERNIGHT.
TEMPS ARE MOSTLY IN THE MID 20S TO LOWER 30S...WITH SOME VALLEY
AREAS EVEN COOLER.

THE RELATIVELY COOL AND DRY WX WILL CONTINUE EARLY THIS WEEK...WITH
A BIT OF WARMUP TO NEAR OR SLIGHTLY ABOVE AVERAGE TEMPERATURES ON
TUESDAY AND WEDNESDAY AS A RIDGE SLOWLY MOVES EAST INTO THE
INTERMOUNTAIN WEST. THE NORTHWEST FLOW WILL ALLOW FOR DEEP MIXING
AND BRISK WINDS TO DEVELOP ACROSS MUCH OF THE AREA TODAY...THOUGH
NOT AS STRONG AS YESTERDAY. NORTHWESTERLY WINDS LATE THIS MORNING
AND AFTERNOON WILL RANGE FROM 10 TO 20 MPH OVER NORTHEAST WY AND
THE BLACK HILLS...TO 20 TO 30 MPH AND GUSTS TO AROUND 40 MPH OVER
CENTRAL SD. SKIES WILL GENERALLY BE PARTLY CLOUDY ACROSS THE AREA
AS A WEAK DISTURBANCE IN THE FLOW MOVES ACROSS...THOUGH SOME AREAS
COULD BECOME RATHER CLOUDY FOR PARTS OF THE AFTERNOON. A FEW LIGHT
SHOWERS MAY TRY TO DEVELOP IN THE AFTERNOON...BUT DRY LOW LEVELS
SHOULD GENERALLY KEEP PCPN FROM REACHING THE GROUND. HOWEVER...WOULD
NOT BE TOO SURPRISED TO SEE A FEW SPRINKLES REACH THE GROUND OVER
WESTERN SD. HIGHS WILL BE IN THE 50S ACROSS THE PLAINS...WITH 40S
OVER MUCH OF THE BLACK HILLS. DRY AIRMASS IN PLACE...ESPECIALLY
OVER THE CENTRAL AND EASTERN DAKOTAS...WILL ALLOW RELATIVE
HUMIDITIES TO DROP TO AROUND 20 PERCENT THIS AFTERNOON FROM
NORTHWEST INTO SOUTH CENTRAL SD.

WINDS WILL DECREASE AGAIN TOWARD SUNSET AND SKIES WILL BE PARTLY
CLOUDY OVERNIGHT. WITH LIGHT WINDS AND DRY AIRMASS IN PLACE...TEMPS
WILL AGAIN DROP INTO THE 20S AND LOWER 30S BY MORNING. MILDER AIR
WILL BEGIN TO MOVE INTO THE AREA LATE TONIGHT AND TUESDAY...WITH
HIGHS EXPECTED TO BE 5 TO 10 DEGREES WARMER IN MOST AREAS. WINDS
WILL GENERALLY REMAIN FROM THE NORTH OR NORTHWEST...INCREASING TO
10 TO 20 MPH BY THE AFTERNOON. WEAK ENERGY ENERGY ALOFT AND MID
LEVEL MOISTURE WILL KEEP SOME CLOUDS AROUND...BUT SKIES SHOULD BE
MOSTLY SUNNY TO PARTLY CLOUDY THROUGH THE DAY. LOWS TUESDAY NIGHT
WILL BE IN THE MID 20S TO MID 30S.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 317 AM MDT MON APR 20 2015

DEEP EASTERN NOAM UPPER TROUGH WILL SUPPORT BLOCKED DOWNSTREAM
FLOW...AS COMPLICATED FAST FLOW OVER THE PAC SUPPORTS SPLIT FLOW
LOCALLY. LARGE SCALE UPPER LOW OVER THE EASTERN PAC WILL ALLOW A
SOUTHERN PERIPHERY VORTEX INTO THE SW CONUS BY MID WEEK WITH
ANTECEDENT DOWNSTREAM RIDGING. DRY CONDS WILL PREVAIL UNTIL THE
END OF THE WEEK...AT WHICH TIME WESTERN ATLANTIC BLOCKING LOOKS TO
DIMINISH...SUPPORTING AN EASTWARD SHIFT AND BREAKDOWN OF THE
WESTERN NOAM RIDGE AND THE EVENTUAL EJECTION OF THE SW CONUS UPPER
LOW...WITH NW FLOW IMPULSES. THE GFS CONTINUES TO STRUGGLE WITH
THIS SCENARIO WITH WAVE PHASING ISSUES OVER CENTRAL CANADA AS WELL
AS IT/S USUAL FAST BIAS EJECTION OF THE SW UPPER LOW...WHILE THE
ECMWF/GEM AND GEFS REMAIN CLOSE IN THEIR SOLUTIONS INCREASING
CONFIDENCE IN THEIR DIRECTION. THE TRACK OF THE SW CONUS UPPER LOW
REMAINS THROUGH THE CENTRAL/SOUTHERN PLAINS...WITH MOST LSA
PASSING SOUTH OF THE FA. HOWEVER...POS THETA-E ADV NORTH INTO THE
REGION FROM THIS SYSTEM WILL ALLOW ANY NW FLOW IMPULSES TO HAVE
PLENTY OF MOISTURE TO WORK WITH. RETAINED LOW CHANCE POPS THUR
THROUGH THE WEEKEND WITH WAVE TIMING/STRENGTH STILL IN QUESTION.

TEMPS ARE EXPECTED TO BE NEAR SEASONAL NORMS IN THE MAJORITY OF THE
PERIOD...WITH AN INFLUENCE FROM THE EASTERN CONUS UPPER LOW. HIGHS
WILL GENERALLY BE IN THE 50S AND 60S WITH LOWS IN THE 30S/40S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z TUESDAY)
ISSUED AT 1121 AM MDT MON APR 20 2015

VFR CONDITIONS EXPECTED THROUGH THE PERIOD.

&&

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

$$

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



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