Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 050941
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
241 AM MST FRI FEB 5 2016

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT

IMAGERY SHOWS BROAD UPR TROF ACROSS THE ERN 80 PERCENT OF THE CONUS
WITH A SW RIDGE THRU THE CNTRL CONUS AND A LARGER RIDGE ACROSS THE
WRN 20 PERCENT. WY CONTINUES UNDER NW FLOW WITH MINOR SW PUSHING
ACROSS THE FA...SUPPORTING A FEW LIGHT SNOW SHOWERS/FLURRIES OVR
PORTION OF THE NRN AND WRN FA. UPSTREAM...SW TROF NOW MOVING
INTO/THU THE WRN PORTION OF THE RIDGE. SFC HAS GENERAL HIGH P WEST
OF WY ACROSS THE GREAT BASIN WITH LOWERING P TO THE NORTHEAST AND A
SLOWLY STRENGTHENING P GRAD DEVELOPING IN BETWEEN.

TODAY...THE UPR SYSTEM AND ASSOCIATED CLIPPER TYPE FRONT BRUSHING
THE ERN FA MOVE OUT OF THE ERN FA THIS MORNING WITH CLEARING SKIES
ACROSS CENTRAL AND ERN WY...AND HIGH P IN CONTROL OF THE FA AND ONLY
LINGERING ISOLATED -SHSN/FLURRIES REMAINING ACROSS PORTIONS OF THE W
CNTRL/NWRN MOUNTAINS. LATE THIS AFTERNOON...UPR LVL NW FLOW RETURNS
ALONG WITH GOOD RIDGE TOP STABILITY...AND A LEE SIDE SFC TROF IN THE
BIG HORN BASIN...WITH AN INCREASING THERMAL/OMEGA GRAD ACROSS THE
CODY FOOTHILLS ONCE AGAIN TONIGHT. ALONG WITH RENEWED MOUNTAIN WAVE
ACTIVITY OVERNIGHT THRU SAT MORNING...ANOTHER CHANCE FOR LOCALLY
HIGH WIND WILL BE POSSIBLE. ADDITIONALLY...AS THE NEXT UPPER LEVEL
SW/JET STREAK MOVES THRU THE AREA SATURDAY...AND THE P GRAD
CURRENTLY IN PLACE WILL STRENGTHEN TO DELTA 8 TO 9 MB BETWEEN ERN
SWEETWATER AND CNTRL NATRONA COUNTIES...WITH A RATHER STRONG
ELEVATED INVERSION HELPING TO SQUEEZE AND ACCELERATE THE WINDS AND
KEEP THEM NEAR SFC. A HIGH WIND WATCH HAS BEEN POSTED TO REFLECT
THIS SCENARIO ACROSS ZONES 19 AND 20 SATURDAY/SAT EVE.

ALSO ON SATURDAY...AS THE FLOW FLATTENS WITH THE APPROACH AND
PASSING OF THE UPR SW...MORE EPAC MOISTURE WILL BE DIRECTED INTO THE
WRN FA...WITH LIGHT TO OCCASIONALLY MODERATE SNOWFALL POSSIBLE THRU
SUNDAY MORNING. SNOWFALL ACCUMULATION WILL BE RATHER LIGHT WITH 30
HR TOTALS BETWEEN MIDNIGHT TONIGHT AND SUNDAY MORNING RANGING FROM 2
TO 6 INCHES IN THE MOUNTAINS...AND FROM A TENTH OF AN INCH TO
PERHAPS AN INCH AND A HALF AT ISOLATED LOCATIONS. THE REST OF THE
DAY SUNDAY WILL SEE ONLY ISOLATED/DECREASING SNOW SHOWERS LINGERING
OVR THE MOUNTAINS...RELATIVELY LIGHT WINDS AND CLEARING SKIES.

.LONG TERM...MONDAY THROUGH FRIDAY

SYNOPSIS...AMPLIFIED UPPER RIDGE ALONG THE WEST COAST WILL GRADUALLY
SHIFT EAST ACROSS THE INTERMOUNTAIN WEST THROUGH THE WEEK BRINGING
UNSEASONABLY WARM TEMPERATURES TO THE MOUNTAINS AND SNOW-FREE
NORTHERN BASINS WHILE SNOW COVERED WESTERN VALLEYS AND THE WIND
RIVER BASIN WILL REMAIN COLDER WITH PATCHY MORNING FOG UNDER STEEP
INVERSIONS THROUGH AT LEAST WEDNESDAY.

DISCUSSION...MEDIUM-RANGE MODELS IN GOOD OVERALL AGREEMENT WITH
UPPER RIDGE ALONG THE WEST COAST PROGRESSING EASTWARD WITH GRADUAL
DEAMPLIFICATION MONDAY THROUGH THURSDAY.  BY FRIDAY...ECMWF AND GFS
HAVE BEEN SHOWING POOR RUN TO RUN CONSISTENCY ON PACIFIC SHORTWAVE
INTERACTION WITH RIDGE AS IT PUSHES ONTO WEST COAST.  THE ENSEMBLE
MEANS FAVOR SLOWER PROGRESSION OF THIS PACIFIC ENERGY...LESS
FLATTENING OF RIDGE OVER THE ROCKIES.  THE MAIN FORECAST CHALLENGE
DURING THIS PERIOD CONTINUES TO BE PINPOINTING AREAS THAT WILL BE
NEAR 15F ABOVE NORMAL TUESDAY AND WEDNESDAY...WHILE COLDEST AREAS
UNDER STEEP INVERSIONS WILL LIKELY REMAIN NEAR OR BELOW FREEZING. ON
THE WARM END WILL BE THE CODY FOOTHILLS AND EASTERN JOHNSON COUNTY
WHERE HIGHS WILL BE IN THE 50S ON TUESDAY AND WEDNESDAY.  COLDEST
AREAS WILL BE THE JACKSON HOLE AND STAR VALLEYS AND LOWER WIND RIVER
BASIN WHERE HIGHS WILL LIKELY BE IN THE 25-35F RANGE TUESDAY AND
WEDNESDAY.  CLIPPER SYSTEM FLATTENING RIDGE AND DIVING INTO THE
NORTHERN PLAINS ON THURSDAY MAY PROVIDE BETTER MIXING AND MODERATION
OF TEMPERATURES IN THE WIND RIVER BASIN ON THURSDAY.  LEE SIDE
SURFACE TROUGH WILL RESULT IN GUSTY SW WINDS IN THE WIND CORRIDOR
FROM ROCK SPRINGS TO CASPER BEGINNING LATE MONDAY AND CONTINUING
THROUGH THE WEEK.  ALSO KEPT TEMPERATURES ON THE COOL SIDE IN THESE
AREAS WHERE THERE IS EXTENSIVE SNOWPACK THAT WILL NEED TO MELT OFF
BEFORE THIS WIND CORRIDOR CAN FULLY PARTAKE IN THE WARMTH.  AFTER A
DRY WEEK UNDER THE RIDGE...INTRODUCED SLIGHT CHANCES OF SNOW SHOWERS
IN THE NW MTNS ON FRIDAY AS NEXT PACIFIC SYSTEM SPLITS ALONG THE
WEST COAST.


&&

.AVIATION.../12Z ISSUANCE/

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

TERMINAL FORECASTS IN SW WY WILL SEE VFR CONDITIONS PREVAILING
THROUGH TONIGHT. GUSTY WIND AT KRKS AIRPORT TODAY INTO TONIGHT.

LOWER CLOUDS WILL OCCUR FROM YELLOWSTONE NATIONAL PARK SOUTH TO
KEMMERER THROUGH TONIGHT. AREAS OF MFVR CONDITIONS ALONG WITH SOME
LIGHT SNOW AT TIMES. THIS INCLUDES THE JACKSON AIRPORT WHERE MVFR
CIGS ARE TO PREVAIL FOR MOST OF THE FORECAST PERIOD WITH LIGHT SNOW
IN THE NEARBY TETONS AT TIMES. MOUNTAINS TO BE OBSCURED AT TIMES.

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

SCATTERED SNOW SHOWERS THROUGH 15Z FROM KBYG TO KCPR. LOCAL MVFR
CONDITIONS WILL OCCUR WITH MOUNTAIN OBSCURATION IN THE BIGHORN
MOUNTAINS AND AROUND CASPER MOUNTAIN. AFTER 15Z VFR CONDITIONS WILL
PREVAIL. ELSEWHERE VFR CONDITIONS WILL OCCUR THROUGH TONIGHT.
WINDY AT KCPR AIRPORT THIS AFTERNOON THROUGH TONIGHT.

&&

.FIRE WEATHER...

FIRE DANGER REMAINS LOW ACROSS THE FORECAST AREA THROUGH THE WEEKEND
WITH SEASONALLY COLD TEMPERATURES...SNOW COVERING MOST
SURFACES....AND A NEW WINTER WEATHER SYSTEM ROLLING THROUGH THE
FORECAST AREA SATURDAY. WINDS...HOWEVER...WILL BE QUITE GUSTY AT
TIMES LATER TODAY...FRIDAY NIGHT AND SATURDAY ACROSS THE USUAL WIND
PRONE AREAS OF NORTHERN AND CENTRAL WYOMING. MOST AFTERNOONS ACROSS
WYOMING SHOULD SEE FAIR TO GOOD SMOKE DISPERSION THROUGH THIS SAME
PERIOD.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WATCH FROM LATE TONIGHT THROUGH SATURDAY EVENING FOR
WYZ019-020.

HIGH WIND WATCH FROM THIS AFTERNOON THROUGH SATURDAY MORNING FOR
WYZ003.

&&

$$

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


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