Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 180016
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
516 PM MST WED DEC 17 2014

.SHORT TERM...THIS EVENING THROUGH THURSDAY NIGHT
ISSUED AT 248 PM MST WED DEC 17 2014

UPPER LEVEL ANALYSIS HAS SHORTWAVE LIFTING THROUGH EASTERN MONTANA
WITH WEAK SOUTHWEST FLOW ACROSS THE NORTHERN PLAINS. SKIES ARE
MOSTLY CLOUDY ACROSS THE SOUTH DAKOTA PLAINS...WITH SOME FOG STILL
IN PLACE ALONG THE FOOTHILLS OF THE BLACK HILLS. SKIES ARE SUNNY
ACROSS PARTS OF NORTHEAST WYOMING AND THE HIGHER ELEVATIONS OF THE
BLACK HILLS. AT THE SURFACE...HIGH PRESSURE RESIDES ACROSS THE
EASTERN DAKOTAS WITH WEAK LOW PRESSURE ACROSS THE ROCKIES. WEAK
EAST TO SOUTHEAST UPSLOPE FLOW CONTINUES...AND IS THE MAIN
CONTRIBUTING FACTOR FOR THE LOW CLOUDS AND FOG. TEMPERATURES AT
3PM ARE MAINLY IN THE TEENS AND 20S...WITH 30S IN THE BLACK
HILLS.

TONIGHT...UPPER LEVEL SHORTWAVE WILL SLIDE INTO CENTRAL NORTH
DAKOTA AS FLOW ALOFT REMAINS WEAK OUT OF THE WEST. SURFACE HIGH
PRESSURE SHIFTS EAST WITH SOUTHEAST BOUNDARY LAYER FLOW
CONTINUING. THIS WILL KEEP LOW CLOUD DECK/FOG AROUND THE SOUTH
DAKOTA PLAINS FOR MUCH OF THE NIGHT. LOW TEMPERATURES WILL FALL
INTO THE 10 TO 20 DEGREE RANGE.

ON THURSDAY...UPPER TROF SHIFTS EAST OF THE DAKOTAS AS RIDGE
BUILDS INTO THE WEST COAST. SURFACE HIGH SHIFTS INTO THE GREAT
LAKES AS LOW PRESSURE TROF STRENGTHENS ACROSS MONTANA AND WYOMING.
WINDS WILL SHIFT TO THE SOUTHWEST AS THE SURFACE TROUGH PASSES
THROUGH...AND CLOUDS WILL SLOWLY BE PUSHED OUT OF THE CWA FROM
WEST TO EAST. HIGHS WILL WARM INTO THE 30S...WITH SOME LOWER 40S
POSSIBLE ACROSS THE EASTERN FOOTHILLS. SKIES WILL BE PARTLY CLOUDY
THURSDAY NIGHT...WITH LOW TEMPERATURES FALLING INTO THE TEENS TO
MID 20S.

.LONG TERM...FRIDAY THROUGH WEDNESDAY
ISSUED AT 248 PM MST WED DEC 17 2014

EXTENDED MODEL SOLUTIONS REMAIN SIMILAR WITH THE LARGER SCALE
FEATURES THROUGH THE WEEKEND INTO EARLY NEXT WEEK...SHOWING A
RIDGE BUILDING ALONG THE PACIFIC COAST AND A DOWNSTREAM TROF
DIGGING ACROSS THE UPPER MIDWEST/GREAT LAKES. THIS PATTERN WILL
RESULT IN NORTHWEST FLOW ALOFT OVER THE NORTHERN PLAINS...WITH
SERIES OF SHORTWAVES TRACKING ACROSS THE AREA. DRY WEATHER IS
STILL EXPECTED FRIDAY AND SATURDAY WITH TEMPERATURES NEAR AVERAGE.
A SHORTWAVE WILL AFFECT THE FORECAST AREA LATE SUNDAY AND ON
MONDAY AS A LOW LEVEL BAROCLINIC ZONE SLIPS INTO THE AREA. THERMAL
PROFILES SUPPORT SOME RAIN/SNOW. INCREASING NORTHWEST BL-850MB
FLOW WILL LEAD TO UPSLOPE ENHANCEMENT ACROSS THE NRN BLKHLS. AS
THE DEEP UPPER TROF MOVES EASTWARD MID-WEEK...THE SIGNIFICANT WEST
COAST TROF STARTS DIGGING THROUGH PACIFIC NORTHWEST INTO THE GREAT
BASIN. ECMWF/GFS DIFFER SOME IN STRENGTH AND TRACK...BUT BOTH
OFFER UP POTENTIAL FOR SNOW ON CHRISTMAS DAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 510 PM MST WED DEC 17 2014

FOR THE 18Z TAFS THROUGH 18Z THURSDAY
ISSUED AT 248 PM MST WED DEC 17 2014

CURRENT IR SATELLITE AND OBS SHOW MUCH OF WESTERN SD AND PARTS OF
NORTHEASTERN WY IN LOW STRATUS AND FOG WITH IFR/LIFR CIGS AND
VSBYS. MODEL SOUNDINGS KEEP THE LOW LEVEL MOISTURE LOCKED INTO
WESTERN SD... INCLUDING KRAP...AND SURFACE WINDS MAINTAIN AN
EASTERLY COMPONENT THROUGH THURSDAY MORNING. A SURFACE TROF WILL
SLOWLY SHIFT OUT OF NORTHEAST WYOMING INTO WESTERN SOUTH DAKOTA
THURSDAY MORNING...PUSHING THE LOW STRATUS DECK EAST THROUGH THE
DAY. VFR CONDITIONS ARE NOT EXPECTED AT KRAP UNTIL AT LEAST MID
MORNING ON THURSDAY.

MEANWHILE...NORTHEAST WY WILL SEE MAINLY VFR CONDITIONS EXCEPT FOR
LOW CLOUDS/STRATUS/AND FOG IN THE VICINITY OF THE BLACK HILLS. WHILE
PATCHY FOG/STRATUS COULD DEVELOP OVERNIGHT ACROSS THE WYOMING
PLAINS...DO NOT EXPECT IT TO BE WIDESPREAD...AND HAVE LEFT IT OUT
OF KGCC TAF FOR THE CURRENT TIME.

&&

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

$$

SHORT TERM...15
LONG TERM...10
AVIATION...15





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