Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 310413
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
913 PM MST FRI JAN 30 2015

.UPDATE...
ISSUED AT 907 PM MST FRI JAN 30 2015

LATEST 11U-3.9U SATELLITE LOOP SHOWED ST DECK MAKING STEADY
PROGRESS SOUTH AND WEST THIS EVENING ACROSS THE NORTHEAST 2/3RDS
OF ND. DECK SHOULD CONTINUE SOUTHWEST OVERNIGHT PER LATEST
GUIDANCE AND EXTRAPOLATION...PUSHING INTO THE BLACK HILLS EARLY
SATURDAY MORNING. GIVEN BOUNDARY LAYER WINDS TURNING WEAK
UPSLOPE...THERE IS A SMALL SIGNAL FOR SOME FOG ALONG THE EASTERN
FOOTHILLS. MAY NEED TO INTRODUCE TO PUBLIC FORECASTS LATER DEPENDING
ON HOW FAR ST INFILTRATES THE REGION.

&&

.SHORT TERM...THIS EVENING THROUGH SATURDAY NIGHT
ISSUED AT 151 PM MST FRI JAN 30 2015

WESTERN CONUS RIDGE WILL WEAKEN IN THE PERIOD...WITH A STRONG NW
FLOW IMPULSE FORCING AN ARCTIC FRONT THROUGH THE REGION SATURDAY.
THIS FEATURE WITH AN ASSOCIATED STRONG JET STREAK WILL FORCE A
PERIOD OF LIGHT SNOW OVER THE AREA MAINLY SAT NIGHT. IN
ADDITION...A SW CONUS UPPER LOW AND ITS ASSOCIATED DEEP MOISTURE
WILL SKIRT THE CENTRAL PLAINS...HELPING TO PIVOT THE LL BAROCLINIC
ZONE NEAR SCENTRAL SD...SUPPORTING A SEPARATE AREA OF SNOW.
OVERALL...SNOW TOTALS WILL BE LIGHT...IN THE 1-2 INCH
RANGE...HIGHEST ACROSS NW SD AND THE NORTHERN BH FOOTHILLS.

MILD CONDS IN PLACE ACROSS THE FA THIS AFTERNOON. HOWEVER...A
PASSING SHORTWAVE ACROSS THE SOUTHERN PRAIRIE PROVINCES OF CANADA IS
FORCING A COLD FRONT SOUTH INTO ND. THIS FRONT WILL PUSH SSW ACROSS
THE DAKOTAS...INCLUDING THE NORTHERN PORTION OF THE FA
TONIGHT...STALLING OVER THE BLACK HILLS SAT. A POTENT IMPULSE NOW
OVER SOUTHERN BC WILL QUICKLY ADVECT SE INTO THE REGION
SAT...SUPPORTING INCREASING LSA. THIS SYSTEM WILL BE ASSOCIATED WITH
A 120 KNOT JET STREAK...WITH THE LEFT EXIT REGION SPREADING OVER THE
FA. STRONG CONVERGENCE ASSOCIATED WITH AN EXPECTED ARCTIC
SURGE/STRONG LSA/AND ENHANCED LEFT EXIT FORCING WILL PRODUCE AMPLE
UVM...SUPPORTING SNOWS LATE SAT AFTERNOON INTO SATURDAY NIGHT. SNOW
WILL SPREAD SW ACROSS THE FA...WITH NW SD SEEING THE BEST
COLLOCATION OF THE AFOREMENTIONED FEATURES. ADDITIONAL UPSLOPE
ENHANCEMENT EXPECTED OVER THE NORTHERN BLACK HILLS FOOTHILLS. THESE
AREAS ARE EXPECTED TO SEE 1-2 INCHES WITH LOCALLY 3 POSSIBLE WHERE
FORCING PERSIST LONGEST. ADDITIONAL AND SEPARATE SNOWS LIKELY ACROSS
FAR EASTERN SCENTRAL SD WITH ENHANCEMENT FROM THE SKIRTING SOUTHERN
PLAINS SYSTEM MOISTURE PLUME. COLD AIR WILL SPREAD SOUTH INTO THE
REGION WITH TONIGHT/S FIRST FRONT...STALLING OVER THE BH SAT. THIS
WILL SUPPORT A LARGE TEMP SPREAD ACROSS THE FA SAT WITH 40S EXPECTED
OVER NE WY TO UPPER 20S ACROSS FAR NE PORTIONS OF THE FA. MODIFIED
ARCTIC AIR WILL SPREAD SOUTH INTO THE REGION SAT NIGHT WITH LOWS IN
THE SINGLE DIGITS MOST AREAS.

.LONG TERM...SUNDAY THROUGH FRIDAY
ISSUED AT 151 PM MST FRI JAN 30 2015

SHORTWAVE ENERGY WILL CROSS THE NORTHERN PLAINS IN NORTHWEST
FLOW...BRINGING LIGHT SNOW TO PARTS OF THE AREA MONDAY INTO
TUESDAY. AN UPPER RIDGE IS PROGGED TO BUILD ACROSS THE ROCKIES
LATE NEXT WEEK...WITH DRY WEATHER EXPECTED.

THE TEMPERATURE FORECAST FOR NEXT WEEK REMAINS TRICKY AS SURFACE
FRONTAL BOUNDARY MEANDERS ACROSS THE CWA AT TIMES. UNDER A COLDER
AIRMASS...TEMPS ON SUNDAY WILL BE 10-20 DEGREES BELOW AVERAGE. FOR
THE REST OF THE EXTENDED...THE LATEST MODEL RUNS HAVE MUCH WARMER
TEMPS THAN PREVIOUSLY. THERE ARE STILL SOME TIMING ISSUES WITH THE
NEXT COLD FRONT THAT DIVES SOUTH TUESDAY...BUT THE GFS AND ECMWF
CONTINUE TO SHOW WARMER AIR MOVING BACK INTO THE REGION TOWARDS THE
END OF NEXT WEEK. WITH LOW CONFIDENCE IN MODEL TEMP
FORECASTS...COOLED TEMPS A BIT MONDAY THROUGH WEDNESDAY NIGHT TO
CURTAIL SUCH A DRASTIC CHANGE.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 907 PM MST FRI JAN 30 2015

VFR CONDITIONS ARE EXPECTED TONIGHT THROUGH 09Z. AN AREA OF
IFR/MVFR ST OVER ND WILL INVADE NORTHWEST SD AFTER 09Z AND MAKE
IT TO THE BLACK HILLS AROUND 15Z AND THEN SINK SOUTH/WEST THROUGH
SATURDAY EVENING. LOCAL IFR VSBYS POSSIBLE AS ST INTERSECTS HIGHER
TERRAIN. A STORM SYSTEM WILL CREATE AN AREA OF -SN LATER SATURDAY
AFTERNOON OVER FAR NORTHWEST SD WITH IFR CIGS/VSBYS MOVING ACROSS
ENTIRE AREA SATURDAY EVENING.

&&

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

$$

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




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