Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 201627
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
927 AM MST SAT DEC 20 2014

.UPDATE...
ISSUED AT 926 AM MST SAT DEC 20 2014

CURRENT SURFACE ANALYSIS SHOWS WARM FRONT JUST TO THE EAST OF THE
FORECAST AREA. UPPER LEVEL ANALYSIS DEPICTS NEAR ZONAL FLOW
ACROSS THE REGION. WATER VAPOR IMAGERY SHOWS A WEAK SHORTWAVE
MOVING ACROSS WESTERN SD NOW...WITH CLOUDS AND AREAS OF LIGHT PCPN
OVER NORTHWESTERN SD. THE PCPN IS MOSTLY IN THE FORM OF LIGHT
RAIN...WITH TEMPERATURES STILL COLD ENOUGH RIGHT NOW IN A FEW
AREAS FOR LIGHT FREEZING RAIN OVER PORTIONS OF PERKINS...NORTHERN
MEADE...AND ZIEBACH COUNTIES. TEMPS WILL WARM ABOVE FREEZING LATE
THIS MORNING AS PCPN MOVES OUT. TEMPS AT THIS HOUR ACROSS THE CWA
ARE MOSTLY IN THE 30S AND LOWER 40S WITH LIGHT WINDS.

HAVE UPDATED TO REMOVE POPS OVER WESTERN AREAS AND KEEP RELATIVELY LOW
CHANCES ACROSS THE NORTHEASTERN CWA THROUGH MIDDAY. PCPN SHOULD
MOVE OUT OF THE AREA BY EARLY AFTERNOON WITH SOME CLEARING FROM
WEST TO EAST. ALSO RAISED HIGH TEMPERATURES 1 TO 3 DEGREES ACROSS
MOST OF THE AREA WITH MORE SUNSHINE EXPECTED IN THE AFTERNOON AND
WESTERLY WINDS IN MOST AREAS. HIGHS WILL BE IN THE UPPER 30S AND
40S THIS AFTERNOON.

&&

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 332 AM MST SAT DEC 20 2014

ZONAL WESTERLY UPPER LEVEL FLOW CONTINUES ACROSS THE WESTERN
CONUS WITH SEVERAL EMBEDDED SHORTWAVES CROSSING THE PACIFIC NW TO
THE NRN PLAINS. THE NEXT WAVE IS CROSSING CNTRL/ERN MT ATTM
PRODUCING HARDLY ANY PRECIP. SURFACE OBS SHOW TEMPS IN THE 20S TO
MID 30S ACROSS THE AREA. EARLY MORNING FOG IS AGAIN STAYING EAST
OF THE CWA OVER THE ERN HALF OF SD. UPPER WAVE WILL QUICKLY PUSH
THROUGH WRN ND AND NW SD PRODUCING MAINLY MID LEVEL CLOUD COVER.
SOME VERY LIGHT PRECIP MAY MAKE IT TO THE GROUND...AND IF ANY
PRECIP DOES FALL...SOME OF IT COULD BE IN THE FORM OF FREEZING
RAIN VERY EARLY THIS MORNING BEFORE TEMPS RISE ABOVE FREEZING. NO
IMPACTS ARE EXPECTED. TEMPS WILL RISE THIS AFTERNOON INTO THE MID
30S TO MID 40S.

A WEAK UPPER TROUGH WILL PUSH INTO THE CWA LATER TONIGHT/EARLY
SUNDAY AHEAD OF A JET STREAK OVER THE PACIFIC NW/NRN ROCKIES...AND
DEEPEN THROUGH THE DAY SUNDAY INTO SUNDAY NIGHT. SURFACE LOW WILL
CROSS ERN MT SUNDAY AND THE DAKOTAS SUNDAY NIGHT. PRECIP WILL
DEVELOP FROM WEST TO EAST THROUGH THE DAY. TEMPS WILL BE MOSTLY IN
THE 40S...SO PRECIP WILL BE RAIN EXCEPT THE HIGHEST ELEVATIONS OF
THE BLACK HILLS. AS THE SURFACE LOW CROSSES THE DAKOTAS SUNDAY
NIGHT...COOLER AIR WILL PUSH IN WITH TEMPS DROPPING ENOUGH FOR
PRECIP TO CHANGE TO SNOW OVERNIGHT. UPSLOPE CONDITIONS WILL DEVELOP
OVER THE NRN BLKHLS WITH SNOW DEVELOPING. THIS IS LIKELY TO
INITIALLY PRODUCE LIGHT SNOW ACCUMULATIONS THROUGH THE NIGHT.

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 332 AM MST SAT DEC 20 2014

FAST PROGRESSIVE WESTERLY FLOW WILL BE INTERRUPTED BY TWO
AMPLIFIED TROUGHS IN THE PERIOD...SUPPORTING COLDER WEATHER AND
CHANCES FOR SNOW. THE FIRST OF THIS WAVE SERIES WILL ARRIVE
MONDAY...AND WILL SUPPORT SFC CYCLOGENESIS OVER THE MIDWEST AND
EASTERN PLAINS. A PERIOD OF RIDGING WILL FOLLOW MID WEEK BEFORE
THE NEXT LONG WAVE TROUGH ARRIVES NEAR THE END OF THE WEEK. THE
LATTER TROUGH/S DETAILS STILL REMAIN SKETCHY ATTM...WITH SOME
POTENTIAL LOOMING FOR A LARGE PORTION OF THE MID LEVEL VORT MAX TO
DIG WELL SOUTH OF THE REGION. HAVE ADJUSTED POPS AND TEMPS IN THE
PERIOD...RAISING POPS MONDAY /MAINLY OVER THE WESTERN AND NORTHERN
HILLS/ WITH A SLIGHT DOWNTREND IN TEMPS MOST OF THE WEEK.

MONDAY...WIDESPREAD LSA/MOIST NW FLOW/AND INCREASING MOMENTUM WILL
SUPPORT PRECIP CHANCES OVER MUCH OF THE AREA...ESP WHEN COUPLED WITH
A STRONG UPPER LEVEL JET STREAK. A GOOD SETUP IS IN THE WORKS FOR A
PERIOD OF UPSLOPE SNOW IN THE WESTERN AND NORTHERN BLACK HILLS.
PLENTY OF LINGERING PAC MOISTURE WILL BE IN PLACE WITH STEEP LL
LAPSE RATES AND INCREASING DEEP LAYER FLOW. WINDS WILL HAVE MORE OF
A WESTERLY COMPONENT MONDAY...WITH VEERING PROFILES INTO MONDAY
NIGHT. THIS WILL FAVOR BEST SNOWS MORE SO TOWARD THE FOUR
CORNERS-BUCKHORN AREA AT FIRST...TRENDING INTO THE NORTHERN HILLS AS
POSSIBLY FAR NORTH AS DEADWOOD AND LEAD. CURRENT PROGS SUGGEST 6+
INCHES WITH LOCALLY HIGHER AMOUNTS CERTAINLY POSSIBLE. HAVE RAISED
POPS IN THESE AREAS. OUTSIDE OF THE HILLS A MIX OF FGEN AND
CONVECTIVELY INDUCED SHRA WILL BE POSSIBLE...WITH BETTER
FGEN/DEFORMATION TYPE LIFT OVER EASTERN AREAS INCLUDING SCENTRAL SD
MONDAY NIGHT. DEPENDING ON THE LOW TRACK...A PERIOD OF SNOW ACCUMS
WILL BE POSSIBLE THERE. FURTHER WEST ACROSS THE SD PLAINS LIGHTER
AMOUNTS OF SNOW ARE EXPECTED ATTM...LEAST IN THE LEE OF THE BH WHERE
DOWNSLOPE SHADOWING WILL BE IN PLACE...ESP FROM RAPID CITY SOUTH.
THE OTHER STORY WILL BE THE WIND. ONGOING PRESSURE FALLS EAST OF THE
FA IN A CAA REGIME WILL SUPPORT INCREASING LL FLOW...INDICATED WELL
IN MODEL SOUNDING PROGS. WIND ADV CONDS CAN BE EXPECTED ACROSS MUCH
OF WESTERN SD...ESP FROM 2WX TO RAP.

TUE-WED...MAINLY DRY WEATHER EXPECTED SAVE FOR SOME LINGERING
MORNING SNOW SHOWERS OVER THE BH AND FAR SCENTRAL. COLDER CONDS
EXPECTED TUE...ALTHOUGH SHORTWAVE RIDGING MAY BE STRONG ENOUGH TO
SUPPORT A DECENT DAY WED.

THUR-FRI...THE NEXT LONGWAVE TROUGH WILL AFFECT THE WESTERN CONUS.
HAVE RETAINED CHANCES POPS ALL PLACES UNTIL TRENDS IN WAVE
STRENGTH/TRACK CAN BE ATTAINED. DID OPT FOR THE COOL SIDE OF GUIDANCE
GIVEN POTENTIAL DOWNSTREAM BLOCKING FROM THE EARLY WEEK WAVE...WHICH
WOULD ALLOW A STRONGER MERIDIONAL COMPONENT TO THE FLOW LOCALLY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 412 AM MST SAT DEC 20 2014

MAINLY VFR CONDITIONS THROUGH THE PERIOD. A FEW MVFR CIGS WITH A
SLIGHT CHANCE OF RAIN/SNOW ARE POSSIBLE ACROSS FAR NORTHWESTERN
SOUTH DAKOTA/THE NORTHERN-CENTRAL BLACK HILLS/AND PARTS OF
NORTHEASTERN WYOMING THIS MORNING WITH A FAST MOVING TROUGH.
HOWEVER...PROBS FOR CIG RESTRICTIONS ARE LOW..


&&

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

$$

UPDATE...26
SHORT TERM...13
LONG TERM...JC
AVIATION...JC






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