Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 161223
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
523 AM MST SUN NOV 16 2014

.UPDATE...ADDED THE UPPER WIND RIVER BASIN TO THE WINTER WEATHER
ADVISORIES FOR BLOWING SNOW.

&&

.PREV DISCUSSION... /ISSUED 334 AM MST SUN NOV 16 2014/

SHORT TERM...TODAY THROUGH TUESDAY NIGHT

LARGE UPPER LOW STILL ROTATING AROUND IN NCNTRL CANADA WITH SW TROFS
EXTENDING DOWN INTO NCNTRL CONUS AND ON TO THE SW THRU THE CNTRL
PLAINS...HIGH PLAINS AND THEN ACROSS THE CNTRL GREAT BASIN. ANOTHER
SW/JET STREAK IS CURRENTLY LOCATED OVR SCNTRL CA...AND WILL HAVE
SOME EFFECT ON THE FCST OVR THE NEXT 24 HRS. CURRENT SFC SHOWS
EXTENDED HIGH PRESSURE ACROSS THE REGION STRETCHING FROM FROM WRN NE
TO CNTRL ID. COLD FRONT WELL TO THE NORTH ACROSS SRN CANADA. VERY
COLD SFC TEMPS ACROSS WY E OF THE DIVIDE...NOT QUITE AS COLD TO THE
WEST.

TODAY...BOTH CANADIAN UPPER SW/JET STREAK (100KT) AND ASSOCIATED SFC
FRONT MOVE SOUTH QUICKLY ACTING AS A CLIPPER SYSTEM...BRINGING SOME
INCREASE IN CLOUDS/MOISTURE TO THE NRN/NERN FA...ALONG WITH VERY LOW
CHCS FOR NEW PRECIP/SNOW CHANCES...AND EVEN THEN MAINLY OVR THE
BIGHORN MOUNTAINS. HOWEVER...THE MAIN EVENT WILL BE ASSOCIATED WITH
INCREASED BRISK NW WINDS... OFFERING NEARLY WHITE-OUT CONDITIONS AT
TIMES AND LOW WIND CHILL TEMPS. WSW WILL BE ISSUED FOR JOHNSON AND
MUCH OF NATRONA COUNTY ALONG WITH THE BIGHORN MOUNTAINS...CODY
FOOTHILLS AND THE ABSAROKA MOUNTAINS THIS MORNING AND LAST THRU THE
EVENING PERIOD.

AFTER THIS CLIPPER SYSTEM MOVES THRU...SKIES WILL DRY/CLEAR
OUT...HEIGHTS WILL RISE AND SFC TEMPS WILL BEGIN RISING. ANOTHER
CLIPPER FRONT WILL AGAIN BRUSH THE NE/E FA ON TUE...INCREASING NW
WINDS ONCE AGAIN ACROSS JOHNSON COUNTY AND THE BIGHORNS...AND
PERHAPS GETTING INTO NATRONA COUNTY. NOT MUCH IN THE WAY OF
SIGNIFICANT MOISTURE WILL ACCOMPANY THIS WX MAKER HOWEVER...WITH
ONLY SLIGHT CHC POPS OVR THE BIGHORN MOUNTAINS WITH PERHAPS A SKIFF
OF NEW SNOWFALL EXPECTED. TEMPS SHOULD ALSO BE WARM ENOUGH AT THIS
POINT TO KEEP WIND CHILL VALUES WELL ABOVE WARNING CRITERIA.

LONG TERM...WEDNESDAY THROUGH SUNDAY

SYNOPSIS...A TRANSITION TO A MILDER PACIFIC FLOW OCCURS WEDNESDAY
THROUGH THE WEEKEND WITH A SERIES OF PACIFIC SYSTEMS BRINGING
CHANCES OF LIGHT SNOW MAINLY TO THE WEST.

DISCUSSION...POLAR JET AXIS WILL SHIFT EAST OF THE AREA WEDNESDAY AS
UPPER RIDGE ALONG THE WEST COAST GETS SHOVED INTO THE INTERMOUNTAIN
WEST.  HOWEVER...ONCE LAST GLANCING BLOW OF MODIFIED ARCTIC AIR IS
POSSIBLE ON THURSDAY ACROSS THE NORTH AND EAST AS VORT LOBE ROUNDS
THE BACK SIDE OF HUDSON BAY LOW...DIVING INTO THE NORTHERN PLAINS ON
THURSDAY.  THIS WILL DRIVE A SHALLOW COLD FRONT MAINLY ALONG THE
EAST SLOPES OF THE BIGHORN RANGE INTO NATRONA COUNTY ON THURSDAY
MORNING.  THE FRONT WILL BE DRY WITH POSSIBLY SOME LOW STRATUS
FILLING IN BEHIND THE FRONT DURING THE MORNING AND EARLY
AFTERNOON.   STRENGTHENING 160+ ZONAL JET STREAM FORECAST TO PUSH
ACROSS THE CENTRAL AND EASTERN PACIFIC ALONG 40N WEDNESDAY AND
THURSDAY...NOSING INTO NORTHERN CALIFORNIA BY SATURDAY MORNING.  A
FEW WEAK SPLITTING SYSTEMS WILL PUSH ACROSS THE WESTERN U.S. AND
ROCKIES...THE ECMWF SHOWING THE FIRST OF THESE SYSTEMS DAMPENING OUT
INTO THE FOUR CORNERS AREA THURSDAY MORNING AS IT RUNS INTO
CONFLUENT FLOW DOWNSTREAM WITH LITTLE IMPACT ON THE AREA.  THE
SECOND SYSTEM IS FORECAST TO SPLIT ACROSS THE NORTHERN ROCKIES AND
SOUTH OF THE FOUR CORNERS AREA LATE FRIDAY AND SATURDAY MORNING.
FORECAST BRINGS SOME CHANCES OF SNOW ACROSS THE WEST AND FAR NORTH
WITH THIS SYSTEM...THOUGH MODELS ARE TYPICALLY OVERLY GENEROUS
FILLING IN QPF BETWEEN THE SPLIT SYSTEMS.  INCOMING PACIFIC JET IS
EXPECTED TO DIG A COLDER...BROADER UPPER TROUGH ACROSS THE
ROCKIES LATE SATURDAY AND SUNDAY WITH MOST OF THE ENERGY HEADED
INTO THE FOUR CORNERS REGION AND INTO THE SOUTHERN PLAINS.
HOWEVER...ATMOSPHERE WILL BECOME INCREASINGLY BAROCLINIC OVER
WYOMING SATURDAY NIGHT WITH INCREASING CHANCES OF SNOW IN THE WEST
WITH SOME SNOW SHOWER ACTIVITY BREAKING OUT EAST OF THE DIVIDE.
LEE SURFACE CYCLOGENESIS IS FORECAST IN THE SOUTHERN HIGH PLAINS
SUNDAY MORNING WITH SFC WINDS TURNING NORTHERLY ACROSS CENTRAL AND
EASTERN WYOMING...A PATTERN MOST FAVORABLE FOR THE CASPER AREA FOR
SNOW...BUT NOT QUITE CONFIDENT ENOUGH EIGHT DAYS OUT TO GO
ANYTHING BEYOND LOW CHANCES.

AVIATION.../12Z ISSUANCE/

EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES

VFR CONDITIONS WILL OCCUR THROUGH 12Z MONDAY OVER THE REGION.
ISOLATED SNOW SHOWERS WILL OCCUR IN THE NORTHERN BIGHORN MOUNTAINS
FROM 12Z THROUGH 21Z WITH LOCAL MVFR CONDITIONS. THE WIND WILL BE
GUSTY AROUND THE BIGHORN MOUNTAINS AND AT BUFFALO TODAY INTO THIS
EVENING. WINDY CONDITIONS WILL ALSO OCCUR AT CASPER TODAY AS WELL.
SEE INDIVIDUAL TERMINAL FORECASTS FOR MORE DETAILS.

WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES

AREAS OF LOW CLOUDS AND LIGHT SNOW WILL LINGER IN THE SOUTHWEST
UNTIL 15Z WITH LOCAL MVFR CONDITIONS. AREAS OF FOG MAY OCCUR IN THE
JACKSON VALLEY AND STAR VALLEY UNTIL 17Z WITH LOCAL IFR CONDITIONS.
VFR CONDITIONS WILL PREVAIL AFTER 18Z THROUGH 12Z MONDAY.
SEE INDIVIDUAL TERMINAL FORECASTS FOR MORE DETAILS.

FIRE WEATHER...

FIRE DANGER LOW AND REMAINING LOW THROUGH THE REST OF THE WORK WEEK
AS SNOW COVER OR MINIMUM RH VALUES STAY WELL ABOVE CRITICAL LEVELS
EVEN WITH BOUTS OF BRISK WEST TO NORTHWEST WINDS TODAY AND AGAIN ON
TUESDAY MAINLY EAST OF THE DIVIDE.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING
WYZ002-003-008>011-020.

WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING WYZ016.

&&

$$

UPDATE...AEM
SHORT TERM...BRAUN
LONG TERM...AEM
AVIATION...AR
FIRE WEATHER...BRAUN





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