Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 021758
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1058 AM MST MON MAR 2 2015

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 224 AM MST MON MAR 2 2015

POTENT WINTER STORM SYSTEM TAKING SHAPE ACROSS THE
WESTERN CONUS AS A STRONG PAC NW IMPULSE WILL PARTIALLY MERGE WITH
AN EJECTING SW CONUS UPPER TROUGH. THIS WILL SET THE STAGE FOR
SNOW/WIND/AND ARCTIC AIR FOR THE REGION...WITH POTENTIALLY DANGEROUS
TRAVEL CONDS TUE MORNING ACROSS MUCH OF THE SD PLAINS. WEAK WAA
ONGOING ACROSS THE REGION AHEAD OF THE ADVANCING UPPER WAVES. LLJ
WILL INTENSIFY THIS MORNING...SUPPORTING GUSTY SOUTHERLY WINDS ON THE
SD PLAINS...ESP OVER SCENTRAL SOUTH DAKOTA. INCREASING CLOUDS
EXPECTED ACROSS THE SOUTHERN HALF...WHICH MAY HAMPER TEMP
POTENTIALS. HAVE SIDED ON THE COOL SIDE OF GUIDANCE FOR THIS...BUT
STILL A MUCH WARMER DAY THAN COMPARED TO THE PREVIOUS FEW. ATTENTION
TURNS TOWARD THE MERGING AFOREMENTIONED TROUGHS. LSA/UVM WILL
SPREAD OVER THE SW HALF OF THE FA THIS EVENING...WITH SNOW
DEVELOPING PER THE ADVANCING SOUTHERN STREAM SYSTEM. SNOW WILL
DEVELOP/OVERSPREAD THE SOUTHERN 2/3 AS FGEN/UPGLIDE PROCESSES ENSUE.
NEARLY ALL MODEL GUIDANCE SUGGEST A CONCENTRATED BAND OF HEAVIER
SNOWFALL ACROSS SCENTRAL SD. THE NAM REMAINS THE FURTHEST NW WITH
THE BAND PLACEMENT IN ADDITION TO BEING THE MOST AGGRESSIVE WITH
QPF. FEEL THE NW PLACEMENT IS POSSIBLE IF PHASING OF THE TWO UPPER
WAVES IS MORE COMPLETE...SUPPORTING A NW TILT TO THE HEIGHT FIELDS.
IN ADDITION...STRONG DYNAMICS COULD SUPPORT A PERIOD OF HEAVIER SNOW
MORE IN LINE WITH THE NAM. SOMETHING THE DAY SHIFT CAN ASSESS.
GENERALLY 2 TO 5 INCHES OF SNOW CAN BE EXPECTED ALONG AND SOUTH OF
I90...WITH HIGHEST AMOUNTS CONCENTRATED IN THE EXPECTED BAND ACROSS
SOUTHERN SD AND IN THE NORTHERN BLACK HILLS PER UPSLOPE. STEEP LL
LAPSE RATES/INCREASING LL FLOW/AND DEEPER INVERSION HEIGHTS WILL
SUPPORT A PERIOD OF STRONG UPSLOPE IN THE NORTHERN BLACK HILLS.
CURRENT THINKING IS WIDESPREAD 3 TO 5 WITH LOCALLY HIGHER AMOUNTS
EXPECTED. MEANWHILE THE STRONGER NW FLOW IMPULSE WILL QUICKLY SHIFT
SE INTO THE REGION...SUPPORTING A STRONG COLD FRONT INTO THE AREA.
STAUNCH PRESSURE RISES IN VERY STRONG CAA WILL SUPPORT INCREASING
NORTHERLY WINDS ON THE SD PLAINS...WITH WINDS INCREASING TO 20 TO 30
MPH WITH GUSTS IN THE 40S.  THIS WILL SUPPORT DANGEROUS TRAVEL CONDS
WHERE PERSISTENT SNOWFALL IS FORECAST. GIVEN ABOVE CONCERNS...HAVE
RETAINED THE WINTER STORM WATCH...DEFERRING HAZARD TYPE TO THE DAY
SHIFT WHEN A BETTER HANDLE ON SNOW AMOUNTS WILL BE ESTABLISHED. DID
PULL THE WATCH BACK TO THE EASTERN BH FOOTHILLS GIVEN CONCERNS ON
POTENTIALLY HIGHER SNOW AMOUNTS WITH WIND. OTHERWISE...ISSUED A
WINTER WX ADV FOR NE WY/THE BH/AND SW SD WHERE GENERALLY 2-5 INCHES
CAN BE EXPECTED. FURTHER NORTH ACROSS THE NW SD ZONES...MINIMAL SNOW
IS EXPECTED WITH WIND BEING THE PRIMARY HAZARD. A WIND ADV MAY BE
NEEDED THERE. SNOW WILL END TUE AFTERNOON AS AN ARCTIC HIGH BUILDS
INTO THE REGION. UPSLOPE SNOWS MAY LINGER INTO THE EVENING.
HOWEVER...DRYING BL CONDS WILL LIKELY SUPPORT A HEAVY WANE. A WEAK
UPSLOPE RESPONSE LOOKS POSSIBLE ONCE AGAIN LATE TUE NIGHT OVER THE
NORTHERN HILLS WITH THE MAIN UPPER WAVE PASSING OVERHEAD. HAVE
RETAINED LOW POPS FOR THIS. COLD CONDS EXPECTED TUE WITH TEMPS
FALLING THROUGH THE DAY INTO THE NIGHT...WITH SUBZERO CONDS ON TRACK
FOR TUE NIGHT...POTENTIALLY NECESSITATING THE NEED FOR WINDCHILL
HEADLINES.

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 224 AM MST MON MAR 2 2015

UPPER TROF AXIS SWINGS THROUGH THE NORTHERN PLAINS FOR WEDNESDAY AS
ARCTIC SURFACE HIGH SETTLES IN ACROSS THE DAKOTAS. DRY CONDITIONS
ARE EXPECTED WITH HIGH TEMPERATURES WELL BELOW AVERAGE...MAINLY IN
THE TEENS.

FOR THURSDAY THROUGH EARLY NEXT WEEK...GFS/ECMWF SHOWING UPPER TROF
SHIFTING QUICKLY EAST WITH FAST NORTHWEST FLOW ACROSS THE NORTHERN
PLAINS...AND RIDGING ACROSS THE FAR WESTERN CONUS. DRY CONDITIONS
EXPECTED THROUGH THE EXTENDED PERIOD WITH TEMPERATURES NEAR TO
SLIGHTLY ABOVE AVERAGE.

&&

.AVIATION...FOR THE 18Z TAFS THROUGH 18Z TUESDAY
ISSUED AT 1057 AM MST MON MAR 2 2015

VFR CONDITIONS ARE EXPECTED THROUGH THE AFTERNOON IN MOST AREAS. A
STRONG WEATHER DISTURBANCE WILL MOVE INTO NORTHEAST WYOMING AND
SOUTHWEST SOUTH DAKOTA AROUND OR SHORTLY AFTER 00Z...WITH FLIGHT
CONDITIONS DETERIORATING QUICKLY TO IFR/LIFR IN SNOW BY MID EVENING
ACROSS THESE AREAS. SNOW AND IFR/LIFR CONDITIONS WILL SPREAD NORTH
AND EAST ACROSS MOST OF THE CWA OVERNIGHT...WITH THE HEAVIEST
SNOWFALL GENERALLY EXPECTED ACROSS PORTIONS OF THE BLACK HILLS AND
FAR SOUTHWEST SD...TO SOUTH CENTRAL SD. SNOW SHOULD TAPER OFF
QUICKLY IN MOST AREAS EARLY TUESDAY MORNING.

A STRONG ARCTIC FRONT WILL ALSO DROP SOUTH THROUGH THE FORECAST AREA
THIS EVENING...INCREASING NORTH WINDS TO 20 TO 35 MPH WITH HIGHER
GUSTS THROUGH TUESDAY MORNING...PRODUCING BLOWING SNOW AND REDUCED
VISIBILITIES.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 5 PM MST
     TUESDAY FOR SDZ024-025-027>029-041-072.

     WINTER STORM WATCH FROM THIS EVENING THROUGH TUESDAY AFTERNOON
     FOR SDZ026-030>032-042>044-046-047-049-073-074.

WY...WINTER WEATHER ADVISORY FROM 8 PM THIS EVENING TO 5 PM MST
     TUESDAY FOR WYZ054>058-071.

&&

$$

SHORT TERM...JC
LONG TERM...15
AVIATION...26





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