000
FXUS63 KUNR 011020
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
320 AM MST SUN DEC 1 2013

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 320 AM MST SUN DEC 1 2013

CURRENT SURFACE ANALYSIS SHOWS A FRONTAL BOUNDARY/WARM FRONT
STRETCHING FROM NORTHEASTERN MT TO FAR WESTERN ND TO NORTHERN AND
EASTERN SD. UPPER LEVEL ANALYSIS SHOWS WEST-NORTHWEST FLOW OVER
THE REGION WITH IMBEDDED WEAK DISTURBANCES. STRONG UPPER JET IS IN
PLACE FROM THE NORTHERN PACIFIC OCEAN THROUGH THE PACIFIC NW...TO
THE SOUTH OF A LOW OVER THE AK PANHANDLE. SKIES ARE MOSTLY CLOUDY
ACROSS MUCH OF THE AREA...WITH THE MOST CLEARING ACROSS THE FAR
SOUTHERN CWA. REGIONAL RADARS ARE SHOWING MOSTLY WEAK RETURNS FROM
EASTERN MT THROUGH CENTRAL WY...ASSOCIATED WITH A WEAK DISTURBANCE
ALOFT. THIS WAVE WILL MOVE EAST ACROSS THE AREA THIS
MORNING...WITH A FEW AREAS OF LIGHT RAIN...LIGHT FREEZING
RAIN...OR SNOW POSSIBLE. TEMPERATURES ARE MOSTLY IN THE UPPER 20S
AND 30S...EXCEPT FOR SOME COLDER TEMPS OVER FAR SOUTHERN SD IN THE
CLEARING. WINDS ARE MOSTLY LIGHT FROM THE SOUTH TO SOUTHWEST.

MILD WEATHER WILL CONTINUE THROUGH MONDAY WITH HIGHS IN THE 40S AND
50S EACH DAY. WEAK UPPER LEVEL DISTURBANCES IN THE FLOW WILL
CONTINUE TO BRING CLOUDS AND A FEW AREAS OF LIGHT PCPN THROUGH THE
PERIOD...MAINLY ACROSS FAR NORTHEASTERN.WY...THE BLACK HILLS...AND
NORTHWESTERN SD. WEST-SOUTHWEST WINDS WILL INCREASE ACROSS
NORTHEASTERN WY AND INTO THE BLACK HILLS THIS EVENING INTO
MONDAY...BECOMING BREEZY TO WINDY...AS PRESSURE GRADIENT TIGHTENS
AHEAD OF AN ARCTIC COLD FRONT.

THE ARCTIC FRONT WILL PUSH THROUGH THE AREA MONDAY NIGHT...WITH
STRONG COLD AIR ADVECTION AND TIGHTENING PRESSURE GRADIENT BEHIND IT
BRINGING GUSTY WINDS AND BITTERLY COLD AIR FOR THE REST OF THE WEEK.
MEDIUM RANGE MODELS ARE STILL HAVING DIFFICULTIES HANDLING THE UPPER
LEVEL SYSTEM THAT WILL SLIDE SOUTH AND EAST ACROSS THE PACIFIC NW
AND EVENTUALLY ACROSS THE NORTHERN ROCKIES AND PLAINS TUESDAY AND
WEDNESDAY. THE ECMWF HAS BEEN THE MOST CONSISTENT OF THE MODELS
OVER THE LAST FEW DAYS...BUT EVEN IT HAS SOME DIFFENECES FROM RUN
TO RUN THAT WOULD AFFECT SNOWFALL POTENTIAL ACROSS OUR AREA FROM
LATER MONDAY NIGHT THROUGH TUESDAY NIGHT. SOME KIND OF WINTER
WEATHER/WIND HEADLINES WILL LIKELY BE NEEDED FOR THIS SYSTEM...BUT
OUR CONFIDENCE IN WHERE AND WHAT THE MAIN IMPACTS WILL BE ACROSS
THE CWA REMAIN LOW AT THIS TIME.

&&

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 320 AM MST SUN DEC 1 2013

MODELS CONTINUE TO SHOW NOTABLE DIFFERENCES IN THE TRACK OF THE
AFOREMENTIONED STORM SYSTEM. NAM HAS THE UPPER LOW MOVING ACROSS
ND...THE GFS ACROSS SOUTHERN SD...AND THE ECMWF SPLITTING THE
DIFFERENCE. GFS MOST FAVORABLE FOR HEAVY SNOW ACROSS THE FAR
NORTHERN PORTIONS OF THE CWA...WITH THE NAM/ECMWF SHOWING A FEW
INCHES OF SNOW...ESPECIALLY ACROSS NORTHWEST SD AND NORTHEAST WY.

TUESDAY...ROBUST COLD AIR ADVECTION EXPECTED WITH TIGHT GRADIENT
CAUSING GUSTY NORTHWEST WINDS. STRONG BAND OF SURFACE-700MB
FRONTOGENESIS WILL BE MAIN FORCING MECHANISM FOR SNOW ACROSS THE
CWA...WITH THE BAND MOVING SLOWLY SOUTHEAST THROUGH THE DAY.
ADDITIONAL FORCING WILL ARRIVE IN THE FAR WEST LATER TUESDAY
NIGHT...DEPENDING ON WHAT GUIDANCE YOU BELIEVE. TEMPERATURES WILL BE
STEADY OR SLOWLY FALLING. GIVEN LOW CONFIDENCE IN POSITION OF HEAVY
SNOW AXIS AND PERIOD 4/5 EVENT...WILL HOLD OFF ON ANY WINTER STORM
WATCHES FOR THE TIME BEING. SOME SORT OF HEADLINES FOR SNOW/COLD
WILL LIKELY BE NEEDED BY THE TIME ALL IS SAID AND DONE.

WEDNESDAY...-SN WILL CONTINUE WITH BEST POTENTIAL FOR ACCUMULATION
OVER NORTHEAST WY/BLACK HILLS AS SECONDARY UPPER LOW/SHORTWAVE DROPS
INTO THE ROCKIES AND CENTRAL PLAINS AND THEN CONSOLIDATES WITH MAIN
UPPER LOW OVER THE NORTHERN PLAINS. GUSTY NORTHWEST WINDS WILL
CONTINUE.

THURSDAY THROUGH SUNDAY...ARCTIC AIR WILL REMAIN ENTRENCHED OVER THE
CWA WITH MASSIVE UPPER TROUGH OVER CENTRAL NORTH AMERICA AND CROSS
POLAR FLOW. SHOULD BE MAINLY DRY GIVEN SUBSIDENCE/LACK OF MOISTURE
BUT WEAK WARM AIR ADVECTION ON SUNDAY MAY BRING SOME -SN TO THE AREA.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING
ISSUED AT 320 AM MST SUN DEC 1 2013

VFR CONDITIONS WILL DOMINATE THROUGH THE PERIOD. A WEAK
SHORTWAVE MAY BRING LIGHT PRECIPITATION AND LOCAL MVFR/IFR CIGS FOR
THE BLACK HILLS/NORTHWEST SD EARLY THIS MORNING. ADDITIONAL
PRECIPITATION MAY DEVELOP LATER TONIGHT INTO MONDAY AS ANOTHER
SHORTWAVE MOVES THROUGH.

&&

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

$$

SHORT TERM...26
LONG TERM...HELGESON
AVIATION...HELGESON