Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 241602
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
902 AM MST WED DEC 24 2014

.UPDATE...
ISSUED AT 852 AM MST WED DEC 24 2014

SURFACE MAP SHOWS LOW OVER SOUTHEAST MT...WHILE BOWMAN RADAR
INDICATES SOME LIGHT ECHOES ACROSS FAR NORTHWESTERN SD. ADDED SOME
ISOLATED MORNING SNOW SHOWERS/FREEZING RAIN THERE. SATELLITE
DEPICTS MID/HIGH CLOUDS STREAMING IN FROM THE NORTHWEST...WITH FOG
COVERING MUCH OF EASTERN SD...SO TWEAKED SKY GRIDS A BIT. WINDS
ARE GENERALLY FROM THE SOUTHWEST. INCREASED HIGHS A FEW DEGREES
TODAY TO ALIGN WITH LATEST MOS GUIDANCE.

&&

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT
ISSUED AT 313 AM MST WED DEC 24 2014

WATER VAPOR IMAGERY SHOWS BROAD UPPER RIDGING STRETCHING FROM THE
PACIFIC GULF COAST TO THE HIGH PLAINS...WITH A WEAK RIDGING RIDING
SHORTWAVE CROSSING CNTRL MT. REGIONAL RADAR SHOWS LIGHT SHOWERS
FALLING IN A N-S LINE OVER CNTRL MT MOVING EAST. LOW CIGS ARE
AFFECTING THE ERN HALF OF SD...ONLY AFFECTING THE TRIPP COUNTY
PORTION OF THE CWA. RIDGING WILL PROGRESS TODAY ACROSS THE PLAINS
STATES INTO THE MIDWEST WHILE THE NEXT TROUGH DIGS INTO THE PACIFIC
COAST. SHOWERS OVER CNTRL MT WILL DISSIPATE BEFORE REACHING THE CWA
BORDER. DRY WEATHER IS EXPECTED TODAY WITH INCREASING CLOUDS AND
HIGHS IN THE MID 30S TO MID 40S.

THE UPPER TROUGH WILL STRENGTHEN AND CUT OFF TONIGHT INTO CHRISTMAS.
STRONG UPPER DIFFLUENT FLOW WILL COMBINE WITH 750MB FRONTOGENESIS
TO PRODUCE SNOW ACROSS THE AREA DURING THE DAY. THE BEST FORCING
WITH THIS SYSTEM AS IT SWINGS TO THE FOUR CORNERS AREA WILL STAY
SOUTH OF THE CWA. OVERALL IT LOOKS LIKE AREAS WILL SEE ANYWHERE
FROM 1 TO 4 INCHES OVER THE COURSE OF 24 HOURS. COOLER AIR WILL
ADVECT IN FROM THE NORTHWEST...BUT OVERALL WINDS WILL BE IN THE 15
TO 20 KT RANGE...NOT ENOUGH TO MAKE BLOWING SNOW A SIGNIFICANT
CONCERN. THE NAM IS SHOWING HIGHER SNOWFALL AMOUNTS OF 4 TO 7
INCHES ACROSS THE NORTHERN BLACK HILLS AS UPSLOPING DEVELOPS...BUT
UPSLOPE WILL BE ON THE WEAK SIDE SO THESE AMOUNTS MAY BE OVERDONE.
WILL LET THE DAY SHIFT TAKE A LOOK AT THE 12Z RUNS TO SEE IF ANY
ADVISORIES WILL BE NEEDED...BUT MOST AREAS ARE EXPECTED TO STAY
BELOW ADVISORY CRITERIA.

.LONG TERM...FRIDAY THROUGH TUESDAY
ISSUED AT 313 AM MST WED DEC 24 2014

DEVELOPING BLOCKING PATTERN PER APPRECIABLE HEIGHT RISES OVER
GREENLAND...COUPLED WITH MASSIVE WESTERN NOAM RIDGING WILL
EVENTUALLY SUPPORT ARCTIC AIR SOUTH INTO THE CONUS BY EARLY NEXT
WEEK. THE ARCTIC AIR WILL ARRIVE VIA ANOTHER STRONG NW FLOW
IMPULSE...WITH SNOW EXPECTED SUNDAY ACROSS THE AREA ONCE AGAIN.
DETERMINISTIC RUNS OF THE ECMWF AND GFS ARE IN GOOD AGREEMENT WITH
BRINGING SOME VERY COLD AIR INTO THE REGION...WITH -26C NOTED AT
H85. HOWEVER...SOME PERTURBATIONS OF THE NAEFS AND GEFS OFFER A
MORE SUBDUED STAY OF ARCTIC AIR...WITH QUICK RESURGENCE OF THE
WESTERN NOAM RIDGE EAST. THIS WOULD PUSH THE BULK OF THE ARCTIC
AIR EAST OF THE REGION. HENCE...DID TREND MUCH COLDER EARLY NEXT
WEEK...BUT NOT TO THE DEGREE OF DETERMINISTIC SOLUTIONS.

SAVE FOR POSSIBLE LINGERING SNOWS OVER THE SE FA FRIDAY...MAINLY DRY
WEATHER EXPECTED THROUGH SAT...BEFORE THE NEXT SYSTEM DIVES SE
ACROSS THE ROCKIES SUNDAY. THERE IS THE POTENTIAL FOR SOME ISOLATED
SNOW SHOWER OVER THE BH FRIDAY AFTERNOON AND EVENING WITH A WEAK
BACKSIDE IMPULSE...NOTHING OF MUCH CONCERN THOUGH. ANOTHER FGEN
RESPONSE LOOKS LIKELY SUNDAY WHICH WILL SUPPORT SNOW CHANCES ACROSS
THE AREA ONCE AGAIN. KEPT CLOSE TO PREVIOUS POP NUMBERS...ALTHOUGH
DID INDUCE A SMALL UPTICK SUNDAY NIGHT. LONG MERIDIONAL FLOW
TRAJECTORIES WITH THIS SYSTEM CONTINUE TO SUPPORT AN ARCTIC FRONT
INTO THE REGION SUNDAY NIGHT INTO MONDAY. MODELS HAVE BEEN
CONSISTENTLY PROGGING THIS FEATURE...WHICH MAKES SENSE GIVEN WEAK
BLOCKING PATTERN...RAISING CONFIDENCE OF OCCURRENCE.
HENCE...CONTINUED TO TREND COOLER. IF THIS ARCTIC OUTBREAK DOES
MATERIALIZE TO THE DEGREE OF THE DETERMINISTIC ECMWF/GFS...TEMPS
WOULD NEED TO BE CUT EVEN MORE EARLY NEXT WEEK...ESP WITH EXPECTED
SNOW COVER.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING)
ISSUED AT 416 AM MST WED DEC 24 2014

LINGERING MVFR CONDS FROM KMBG TO KPIR TO KICR WILL SHIFT EAST
THIS MORNING. VFR CONDITIONS WILL PREVAIL ELSEWHERE THROUGH THE
DAY WITH INCREASING MID/HIGH CLOUDS. ANOTHER STORM SYSTEM WILL
BRING SNOW TO WESTERN AREAS LATE IN THE PERIOD...WITH IFR CONDS
EXPECTED AT KGCC BY EARLY MORNING THURSDAY.


&&

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

$$

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






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