Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 192202
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
302 PM MST FRI DEC 19 2014

.SHORT TERM...THIS EVENING THROUGH SATURDAY NIGHT
ISSUED AT 300 PM MST FRI DEC 19 2014

CURRENT SURFACE ANALYSIS SHOWS WARM FRONT OVER CENTRAL SD. UPPER
LEVEL ANALYSIS SHOWS SHORTWAVE RIDGE OVER THE ROCKIES... WITH
ANOTHER LOW PRESSURE SYSTEM MOVING ONTO THE PACIFIC NW COAST.
SKIES ARE VARIABLY CLOUDY ACROSS THE AREA...WITH THE MOST CLOUDS
OVER THE BLACK HILLS AND WEST CENTRAL SD PLAINS. KUDX RADAR EVEN
HAS SHOWN A FEW SPRINKLES OVER WEST CENTRAL SD. TEMPS ARE
MILD...UPPER 30S TO UPPER 40S. WINDS ARE MOSTLY FROM THE WEST TO
SOUTHWEST AT 5 TO 15 MPH.

MILDER WEATHER WILL PERSIST INTO THE WEEKEND AS THE RIDGE TO THE
WEST FLATTENS OUT AS IT MOVES OVER THE PLAINS BY EARLY SATURDAY.
ZONAL FLOW BEHIND THE RIDGE WILL BRING A WEAK AND QUICK MOVING
DISTURBANCE THROUGH THE AREA DURING THE MORNING AND EARLY AFTERNOON
HOURS. CLOUDS AND SOME AREAS OF LIGHT MIXED PCPN ARE POSSIBLE AS IT
MOVES THROUGH.

FOR TONIGHT...SKIES WILL BE MOSTLY CLEAR TO PARTLY CLOUDY AS THE
FRONT MOVES EAST OF THE FORECAST AREA. LOWS WILL BE IN THE 20S
ACROSS NORTHEAST WY...THE BLACK HILLS AREA...AND MUCH OF NORTHWEST
SD AS CLOUDS INCREASE OVERNIGHT. PATCHY FOG DOES LOOK POSSIBLE
LATE TONIGHT TO THE SOUTH AND EAST OF THE BLACK HILLS AS LIGHT WINDS
AND MOSTLY CLEAR SKIES ALLOW TEMPS TO DROP INTO THE TEENS.

UPPER LEVEL DISTURBANCE WILL APPROACH WESTERN PORTIONS OF THE CWA
LATE TONIGHT AND MOVE QUICKLY EAST ACROSS THE AREA DURING THE
MORNING HOURS. PCPN WITH THIS SYSTEM WILL BE MINIMAL...SO WILL KEEP
CHANCES IN THE 20 TO 30 PERCENT RANGE FOR MOST AREAS. FORECAST
SOUNDINGS SUGGEST A MIX OF PCPN IF ANY DOES FALL...INCLUDING THE
POTENTIAL FOR LIGHT FREEZING RAIN. THIS DISTURBANCE WILL MOVE
QUICKLY OUT OF THE AREA BY EARLY AFTERNOON...WITH SOME CLEARING
BEHIND IT. MILD TEMPS WILL PERSIST...WITH HIGHS MOSTLY IN THE UPPER
30S AND 40S AGAIN...AS WESTERLY WINDS CONTINUE IN MOST AREAS. LOWS
SATURDAY NIGHT WILL MOSTLY BE IN THE 20S UNDER MOSTLY CLEAR TO
PARTLY CLOUDY SKIES.

.LONG TERM...SUNDAY THROUGH FRIDAY
ISSUED AT 300 PM MST FRI DEC 19 2014

EXTENDED MODELS REMAIN IN RELATIVELY GOOD AGREEMENT WITH THE
LARGE SCALE FEATURES FOR SUNDAY THROUGH TUESDAY...SHOWING A HIGH
AMPLITUDE RIDGE BUILDING OVER THE PACIFIC COAST AND A BROAD
TROUGH/UPPER LOW CLOSING OVER THE UPPER MIDWEST. THE ECMWF KEEPS
AN OPEN WAVE AS THE TROUGH CROSSES THE FORECAST AREA WHILE THE 12Z
GFS IS NOW SHOWING A CLOSED UPPER LOW DEVELOPING OVER WESTERN
NORTH DAKOTA ON SUNDAY NIGHT...DROPPING SOUTHWARD TO OVER
SOUTHEASTERN SOUTH DAKOTA MONDAY EVENING...COMING BACK INTO LINE
WITH THE ECMWF AT THAT POINT. THE MAIN SHORTWAVE RESPONSIBLE FOR
THE UPPER LOW CLOSING OFF WILL CROSS THE DAKOTAS LATE SUNDAY AND
MONDAY BRINGING A CHANCE OF RAIN AND SNOW. POPS WOULD BE SLIGHTLY
HIGHER WITH THE GFS SOLUTION COMPARED TO THE ECMWF. TEMPERATURES
WILL REMAIN SLIGHTLY WARMER THAN AVERAGE FOR SUNDAY WITH COOLER
AIR FLOWING INTO THE REGION BEHIND A COLD FRONT ON SUNDAY NIGHT
AND MONDAY WITH GUSTY NORTHWEST WINDS. FAST NORTHWEST FLOW ALOFT
WILL BE LOCATED OVER THE NORTHERN PLAINS MID WEEK...WITH SERIES OF
WEAK SHORTWAVES. MAINLY DRY WEATHER IS EXPECTED BUT THE EXCEPTION
WOULD BE OVER THE NORTHERN BLACK HILLS...WHERE STEEP LOW LEVEL
LAPSE RATES AND MARGINAL 0-2KM RELATIVE HUMIDITY COULD RESULT IN
SOME LIGHT UPSLOPE SNOW. EXTENDED MODELS SEEM TO BE TRANSITIONING
BETWEEN SOLUTIONS FOR THE WEEKEND. WHERE THE PREVIOUS RUNS WERE
SHOWING THE POTENTIAL FOR SIGNIFICANT SNOW ACROSS NEBRASKA INTO
THE SOUTHERN PARTS OF THE FORECAST AREA FROM FRIDAY THROUGH THE
WEEKEND...THE LATEST GFS IS SHOWING A MUCH DIFFERENT PATTERN WITH
ONLY LIGHT SNOW POSSIBLE ACROSS THE FORECAST AREA. EXPECT LATER
RUNS TO COME INTO MUCH BETTER AGREEMENT WITH A SOLUTION.

&&

.AVIATION...FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING
ISSUED AT 300 PM MST FRI DEC 19 2014

VFR CONDITIONS WILL CONTINUE TROUGH TONIGHT. MVFR CIGS
WITH A SLIGHT CHANCE OF -SN WILL MOVE INTO NORTHWESTERN SOUTH DAKOTA
AND PARTS OF NORTHEASTERN WYOMING LATE SATURDAY MORNING.

&&

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

$$

SHORT TERM...26
LONG TERM...10
AVIATION...10






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