Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 061734
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1034 AM MST SAT FEB 6 2016

.SHORT TERM...TODAY THROUGH MONDAY NIGHT

IMAGERY SHOWS AMPLIFYING TROF ACROSS THE ERN HALF OF THE CONUS WITH
BROAD RIDGING OVR THE WRN HALF. UPSTREAM...A WEAK SW NOW PUSHING
THRU ID WITH A MORE VIGOROUS SW TROF/JET CURRENTLY MOVING INTO/THRU
THE PAC NW. SFC HAS STRENGTHENING HIGH P ACROSS THE GREAT BASIN INTO
WR/SWRN WY...WITH LOWER P OFF TO THE NE...WITH A MESOSCALE LEE SIDE
TROF DEVELOPING ACROSS THE BIGHORN BASIN. ISOLATED LIGHT
SNOW/FLURRIES MOVING INTO THE FAR WRN FA.

THIS MORNING...FLAT NW FLOW WITH GOOD RIDGE TOP STABILITY...AND A
LEE SIDE SFC TROF IN THE BIG HORN BASIN...WITH A STRONG
THERMAL/OMEGA GRAD ACROSS THE CODY FOOTHILLS ALONG WITH RENEWED
MOUNTAIN WAVE ACTIVITY WILL KEEP LOCALLY HIGH WINDS ACROSS THIS
AREA...SUPPORTING A HIGH WIND WARNING THAT HAS BEEN EXTENDED TO
UNTIL AROUND 1 PM. ADDITIONALLY...AS THE NEXT UPPER LEVEL SW/JET
STREAK MOVES THRU THE AREA TODAY...THE P GRAD CURRENTLY IN PLACE
WILL STRENGTHEN BETWEEN ERN SWEETWATER AND ERN NATRONA
COUNTIES...WITH A RATHER STRONG ELEVATED INVERSION HELPING TO
SQUEEZE AND ACCELERATE THE WINDS AND KEEP THEM NEAR SFC. A HIGH WIND
WARNING ALSO REFLECTS THIS SCENARIO ACROSS BOTH ZONES 19 AND 20
TODAY. ALSO...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 24
HR TOTALS BETWEEN THIS MORNING AND SUNDAY MORNING RANGING FROM 1.5
TO 4 INCHES IN THE MOUNTAINS...AND FROM A TRACE TO PERHAPS AN INCH
OVER THE VALLEYS. THIS EVENING...CLIPPER FRONT MOVES THRU ERN
WY...WITH GUSTY NW SFC WINDS PICKING UP ACROSS THE ERN
FA...PARTICULARLY OVR JOHNSON COUNTY. THESE WINDS HOWEVER SHOULD
REMAIN BELOW WARNING CRITERIA. FROM THIS EVENING THRU THE DAY
SUNDAY. ELSEWHERE AND OTHERWISE...SUNDAY WILL SEE ONLY
ISOLATED/DECREASING SNOW SHOWERS LINGERING OVR THE WRN/NRN
MOUNTAINS...WITH RELATIVELY LIGHT WINDS AND CLEAR TO PARTLY CLOUDY
SKIES...MORE CLOUD ACROSS THE FAR WEST. THESE CONDITIONS WILL
GENERALLY PERSIST THRU THE END OF THE FCST PERIOD.

.LONG TERM...TUESDAY THROUGH SATURDAY

SYNOPSIS...A RIDGE OF HIGH PRESSURE WILL PREVAIL OVER THE AREA
THROUGH FRIDAY BRINGING DRY WEATHER WITH UNSEASONABLY WARM
TEMPERATURES ACROSS SNOW FREE AREAS ACROSS NORTHERN WYOMING WITH
MORE GRADUAL MODERATION OF TEMPERATURES ACROSS SNOW-COVERED AREAS OF
SOUTHERN WYOMING.  COLDER TEMPERATURES AND PATCHY MORNING FOG WILL
BE THE RULE UNDER STEEPER INVERSIONS ACROSS FAR WEST VALLEYS AND THE
LOWER WIND RIVER BASIN.

DISCUSSION...MEDIUM-RANGE MODELS SHOW AN OVERALL TREND TOWARD A MORE
PERSISTENT RIDGE OVER THE WESTERN U.S. WITH A GRADUAL PROGRESSION
INTO THE ROCKIES BY THE END OF THE WEEK.  PREVIOUS ECMWF RUNS WERE
QUICKER TO BRING PACIFIC ENERGY THROUGH THE RIDGE INTO WESTERN
WYOMING AS SOON AS THURSDAY. ALL THE LATEST GUIDANCE HOLD NEXT
SIGNIFICANT PACIFIC TROUGH OFF THE WEST COAST THROUGH AT LEAST 00Z
SAT WITH THIS ENERGY EXPECTED TO SPLIT INTO THE INTERMOUNTAIN WEST
ON SATURDAY. THUS...FORECAST KEPT DRY EXCEPT FOR SOME SLIGHT
CHANCE POPS IN THE NW MTNS TOWARD THE END OF THE PERIOD. THE MAIN
FORECAST CHALLENGE CONTINUES TO BE AREAS THAT WILL MOSTLY PARTAKE
IN THE WARM UP UNDER THE RIDGE SUCH AS SNOW-FREE AREAS ACROSS THE
NORTHERN BASINS WHERE THE WARMEST HIGHS WILL BE IN 50S AROUND CODY
AND BUFFALO TUESDAY THROUGH FRIDAY...VERSUS SNOW-COVERED WESTERN
VALLEYS AND MUCH OF SOUTHERN WYOMING. LEE SIDE SURFACE TROUGH AND
PERSISTENT GUSTY SW WINDS WILL EAT AWAY AT SNOWPACK ACROSS EASTERN
SWEETWATER AND NATRONA COUNTIES. STEEP INVERSIONS SHOULD HOLD OVER
THE JACKSON AND STAR VALLEYS THROUGH FRIDAY WHERE LOWS WILL BE IN
THE SINGLE DIGITS AND HIGHS NEAR OR A FEW DEGREES BELOW FREEZING.
THE BIGGEST QUESTION MARK FOR TEMPERATURES WILL BE THE WIND RIVER
BASIN. FEBRUARY SUN AND WINDY CONDITIONS IN THE SHORT-TERM SHOULD
CONTINUE TO DEPLETE THE SNOWPACK. WE CURRENTLY HAVE A SLOW WARMING
TREND WITH TEMPERATURES PUSHING UP INTO THE 40S IN THE WIND RIVER
BASIN BY FRIDAY...THE WARM-UP COULD HAPPEN EARLIER BUT THAT IS
USUALLY A LOSING BET FORECAST-WISE.

&&

.AVIATION.../18Z ISSUANCE/

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

PERIODS OF LIGHT SNOW MAY BRING INSTANCES OF MVFR CONDITIONS TO
KJAC THROUGH 07Z THIS EVENING. OTHERWISE...THE WESTERN MOUNTAINS
WILL CONTINUE TO SEE LIGHT SNOWFALL THROUGH THE PERIOD WITH
ANTICIPATED MOUNTAIN TOP OBSCURATIONS. OTHER TERMINALS ACROSS THE
AREA WILL GENERALLY REMAIN VFR...THOUGH PERIODS OF GUSTY WIND WILL
BE NOTED ACROSS THE AREA. THE STRONGEST WIND LOOKS TO IMPACT KRKS
THROUGH AROUND 03Z THIS EVENING.

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

STRONG WIND WILL BE FOUND ACROSS THE AREA TODAY...ESPECIALLY
IMPACTING KCPR AND AREAS AROUND THE KCPR TERMINAL. WIND GUSTS TO
50KT MAY BE POSSIBLE AT TIMES...ESPECIALLY CLOSER TO CASPER
MOUNTAIN. ELSEWHERE GUSTY WIND WILL BE FOUND ACROSS KBYG THROUGH
THE AFTERNOON...WITH OTHER TERMINALS REMAINING GENERALLY LIGHT.
CONDITIONS TO REMAIN VFR AS SNOWFALL REMAINS MOSTLY WEST OF THE
CONTINENTAL DIVIDE. ADJACENT MOUNTAINS COULD SEE SOME LIGHT
SNOWFALL WITH OBSCURED MOUNTAIN TOPS THROUGH THE AFTERNOON AND
EVENING.


&&

.FIRE WEATHER...

FIRE DANGER REMAINS LOW ACROSS THE FORECAST AREA THROUGH THE WEEKEND
WITH SEASONAL TEMPERATURES...SNOW COVERING MANY SURFACES....AND A
NEW WINTER WEATHER SYSTEM ROLLING THROUGH THE FORECAST AREA TODAY.
WINDS...HOWEVER...WILL BE QUITE GUSTY AT TIMES TODAY 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 WARNING UNTIL 11 PM MST THIS EVENING FOR WYZ019-020.

HIGH WIND WARNING UNTIL 1 PM MST THIS AFTERNOON FOR WYZ003.

&&

$$

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


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