Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 270630
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1128 PM MST WED NOV 26 2014

UPDATE...UPDATED TO ADD 06Z AVIATION DISCUSSION.

.SHORT TERM...TONIGHT THROUGH THURSDAY (ISSUED AT 245 PM MST)

LIGHT SNOW WILL DECREASE OVER THE NORTHERN MOUNTAINS...THE
NORTHERN BIGHORN BASIN AND NORTHERN JOHNSON COUNTY TONIGHT WITH
WIDELY SCATTERED SHOWERS LINGERING OVER THE NORTHWEST THROUGH
THURSDAY. TEMPERATURES WILL WARM AS WEST WINDS INCREASE ACROSS THE
AREA. HIGH WINDS WILL BECOME A THREAT EAST OF THE CONTINENTAL
DIVIDE...ESPECIALLY IN THE ABSAROKA MOUNTAINS INTO THE CODY
FOOTHILLS. PLEASE REFER TO THE HIGH WIND WATCH FOR MORE DETAILS.
IN THE VALLEYS AND BASINS ALONG RIVERS AND LAKES... AREAS OF FOG
MAY DEVELOP TONIGHT AND REMAIN INTO THURSDAY MORNING BEFORE
DISSIPATING.

.LONG TERM...THURSDAY NIGHT THROUGH WEDNESDAY

BEGINNING OF FCST...WRN CONUS UPR LVL RIDGE PUSHING INTO AND
FLATTENING ACROSS THE FA. SFC SHOWS GENERAL HI P WEST WITH LOWERING
PRESSURE EAST OF THE BIGHORN MOUNTAINS ACROSS ERN WY. TIGHTENING
THERMAL AND PRESSURE GRAD ALONG/OVR/NEAR ABSAROKA MOUNTAINS IN
ADDITION TO INCREASING WINDS ALOFT BECOMING MORE FAVORABLY ORIENTED
IN ALL DIRECTIONS WITH RESPECT TO THE MOUNTAIN RIDGELINES FOR
EXCELLENT MOUNTAIN WAVE PRODUCTION...GIVING AN EXTENDED PERIOD OF
STRONG...POSSIBLY DAMAGING...WINDS ACROSS THE ABSAROKAS AND ADJACENT
CODY FOOTHILLS. THIS SET-UP WILL LAST FROM LATER IN THE DAY
THANKSGIVING THRU THE DAY ON SATURDAY. AN NPW FOR A HIGH WIND WATCH
HAS BEEN ISSUED.

THE RIDGE CONTINUES TO FLATTEN THROUGH THE DAY ON FRIDAY WITH THE
APPROACH OF THE NEXT SW TROF AND ASSOCIATED JET. A SRN STREAM OF
MODEST MOISTURE WILL CONTINUE TO STREAM INTO NWRN WY THRU THE DAY ON
FRIDAY OFFERING LOW END CHCS FOR OROGRAPHICALLY FORCED SNOW ACROSS
THE MOUNTAINS OF MAINLY YELLOWSTONE THE WAY IT LOOKS ATTM.
HOWEVER...FCST EPV FIELDS SHOW MAJOR CYCLO/FRONTO-GENESIS ALSO
BEGINNING DURING THE DAY OVR THE NWRN CONUS...CONTINUING INTO THE NRN
ROCKIES THRU THE REST OF THE DAY AND BECOMING A MAJOR PLAYER ACROSS
THE WRN FA BY SAT AS MORE PAC MOISTURE ALSO SINKS INTO THE REGION
BEGINNING LATER FRI NIGHT. THROUGH THE DAY SAT...STRONG SFC TO UPR LVL
FORCING WILL COME TOGETHER ALONG WITH THE INCREASING AVAILABLE
MOISTURE AND TERRAIN FORCING TO GIVE A GOOD PERIOD...18 TO 24
HRS...OF MODERATE TO HEAVY SNOWFALL OVR THE WRN MOUNTAINS. WITH
SNOWFALL RATES INCREASING AND FCST TO AVG AROUND AN INCH/HR AT
TIMES...TOTAL SNOW FALL OF 12 -16 INCHES IN THE MOUNTAINS WILL NOT
BE OUT OF THE ORDINARY...WITH 4 TO 8 ACROSS THE VALLEYS. WILL WATCH
THE EVOLUTION OF THE STORM FOR CONSISTENCY WITH RESPECT TO POSITION
AND INTENSITY OVR THE NEXT 24 HRS BEFORE DECIDING THE EXACT
HIGHLIGHTS NEEDED OUT WEST. THEN...IT DOES LOOK LIKE THIS STORM WILL
AFFECT MOST OF THE REST OF THE CWA ON SUNDAY AS...WHAT LOOKS TO BE A
WELL FORMED FRONT PUSHES SOUTH ACROSS THE FA GIVING AT LEAST A SHORT
PERIOD OF DECENT UPSLOPE FLOW OVR THE CNTRL BASINS AS WELL THE ERN
ZONES. BEST OVERALL FORCING E OF THE DIVIDE LOOKS TO SET-UP FROM
JOHNSON AND NATRONA COUNTIES...TO ERN FREMONT AND TOWARD THE SOUTH
PASS AREA. THIS SITUATION COULD PRODUCE GOOD AMOUNTS OF SNOW
PARTICULARLY ACROSS THE SRN HALF OF NATRONA COUNTY WHERE DEEP
FORCING AND MOISTURE WILL BE MAXIMIZED FOR A 6 TO 9 HR PERIOD. WILL
CONTINUE TO MONITOR THIS AREA FOR FUTURE HIGHLIGHTS.

THE FRONT PASSES THRU THE CWA MON NIGHT WITH MOSTLY FAIR/COLD
CONDITIONS MON AHEAD OF ANOTHER GOOD UPR LVL SITUATION LEADING FROM
LEE TROFFING TO EVENTUALLY LEE SIDE CYCLOGENESIS ACROSS THE HIGH
PLAINS OF WY/CO THRU THE DAY TUE. BY LATER MON NIGHT...TERRAIN
FORCED SNOW LOOKS PROMISING ONCE AGAIN IN THE NW MOUNTAINS BEFORE
WRAP-AROUND FORCING FROM THE LEE CYCLOGENESIS ALLOWS FOR INCREASING
POPS ACROSS THE SRN HALF OF THE FA FROM WEST TO EAST LATER TUE INTO
WED.

&&

.AVIATION.../06Z ISSUANCE/

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

AREAS OF IFR/LIFR FOG OR LIFR CIGS WILL PERSIST ACROSS THE BIGHORN
BASIN OVERNIGHT WELL INTO THURSDAY MORNING.  THERE SHOULD BE SOME
EROSION OF THE FOG BANK ON THE WEST END...VCNTY AND WEST KCOD...AS
STRONGER DOWNSLOPE WINDS MIX DOWN.

OTHERWISE VFR CONDITIONS WILL PREVAIL ACROSS THE REST OF THE AREA
WITH MUCH MORE PATCHY FOG PARTIALLY OBSCURING LOWER RIVER VALLEYS
THROUGH 18Z.  AREAS OF LLWS WILL BE ENCOUNTERED THROUGH THE
PERIOD...ESPECIALLY ALONG THE EAST SLOPES OF THE DIVIDE...VCNTY
KLND-KCOD...WHERE WINDS IN THE FL080-100 LAYER WILL BE
270/50-60KTS.  SOME OF THESE STRONGER WINDS WILL PUSH DOWN THE
FOOTHILLS INTO VCNTY KCOD-KDUB BY 00Z FRIDAY.

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

WINDS AT MOUNTAIN TOP LEVEL WILL INCREASE TO BETWEEN 50-60 KTS BY
12Z THURSDAY...RESULTING IN INCREASING TURBULENCE THROUGH THE REST
OF THE PERIOD.  THIS STRONG WESTERLY FLOW WILL ALSO KEEP SOME HIGHER
MTNS OBSCURED IN -SN WITH SOME LCL MVFR CIGS VCNTY KJAC.

&&

.FIRE WEATHER...

LIGHT SNOW WILL DECREASE OVER THE NORTHERN MOUNTAINS...THE
NORTHERN BIGHORN BASIN AND NORTHERN JOHNSON COUNTY TONIGHT WITH
WIDELY SCATTERED SHOWERS LINGERING OVER THE NORTHWEST THROUGH
THURSDAY. TEMPERATURES WILL WARM AS WEST WINDS INCREASE ACROSS THE
AREA. HIGH WINDS WILL BECOME A THREAT EAST OF THE CONTINENTAL
DIVIDE...ESPECIALLY IN THE ABSAROKA MOUNTAINS INTO THE CODY
FOOTHILLS. IN THE VALLEYS AND BASINS ALONG RIVERS AND LAKES...
AREAS OF FOG MAY DEVELOP TONIGHT AND REMAIN INTO THURSDAY MORNING
BEFORE DISSIPATING. SNOW COVER WILL REMAIN WIDESPREAD OVER MOST OF
THE AREA WITH LOW FIRE WEATHER CONCERNS.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM THURSDAY AFTERNOON THROUGH SATURDAY
AFTERNOON WYZ002-003.

&&

$$

SHORT TERM...C.BAKER
LONG TERM...BRAUN
AVIATION...AEM
FIRE WEATHER...C.BAKER












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