Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 220552
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1152 PM MDT THU APR 21 2016

.UPDATE...ADDED 06Z AVIATION DISCUSSION.

&&

.AVIATION.../06Z ISSUANCE/

VFR CONDITIONS WILL PREVAIL THROUGH THE PERIOD.  SOUTH TO SOUTHWEST
SFC WINDS WILL INCREASE TO 10-20KTS ACROSS MUCH OF THE AREA FRIDAY
AFTERNOON.  ISOLD TO WDLY SCT SHRA/TSRA ARE EXPECTED TO DEVELOP
AFTER 20Z IN THE VCNTY OF THE DIVIDE...MAINLY ALONG A VCNTY KJAC-
KCOD ROUTE ADN ALSO ISOLD TSRA/SHRA MAY DEVELOP OFF THE UINTA RANGE
AND MOVE NORTH BTWN KEVW-KRKS.  MOST OF THIS ACTIVITY WILL DISSIPATE
AFTER SUNSET.  AN INCREASING SOUTHERLY FLOW AHEAD OF AN APPROACHING
COLD FRONT WILL BRING AREAS OF LLWS VCNTY AND WEST OF THE DIVIDE 8Z-
12Z SATURDAY.

&&

.PREV DISCUSSION... /ISSUED 217 PM MDT THU APR 21 2016/

SHORT TERM...TONIGHT THROUGH FRIDAY

IMAGERY SHOWS LARGE AMPLIFIED RIDGE ACROSS THE INTERMOUNTAIN
WEST...WITH AN UPSTREAM EMBEDDED SW OVR CNTRL CA/WRN NV AND LARGE
TROF COMING INTO THE WCST JUST NOW AFFECTING NRN CA/OR/WA. SFC HAS
BASICALLY HIGH P ACROSS THE REGION WITH A WEAK BACKDOOR COLD FRONT
OVER FAR NERN WY. SKIES ARE CURRENTLY MOSTLY CLEAR WITH NO AREAS OF
CLOUD OR PRECIP ANYWHERE TO BE FOUND.

LATE THIS AFTERNOON AND EARLY EVENING OVER THE HIGHER MOUNTAINS OF
THE WEST...A FEW SHOWERS COULD MANIFEST WHERE THE BUBBLE CAN BE
BURST. THESE SHOWERS...WITH ONLY A SLIGHT POSSIBILITY FOR
THUNDER...WILL BE OF LITTLE OVERALL CONSEQUENCE OTHER THAN PUTTING
DOWN A 25KT GUST HERE AND THERE. TONIGHT...CONVECTIVE CLOUDS WILL
CLEAR ACROSS THE WEST AS SUNDOWN NEARS...REMAINING CLEAR MOST OTHER
LOCATIONS.

FRIDAY...RIDGE TRANSLATES EWD AND BEGINS TO BREAK DOWN SLIGHTLY
ACROSS WRN WY THRU THE DAY. RIDGE AND SFC HIGH P WILL KEEP A LID ON
THINGS E OF THE DIVIDE. WHILE SOME WEAK INSTABILITY WILL REMAIN
ACROSS WEST...RESULTING IN LATE AFTERNOON ISO/WDLY SCTD
SHOWERS/THUNDER...THERE WILL BE LESS MOISTURE TO WORK. MANY OF THESE
SHOWERS ETC WILL BE OF LITTLE ACTUAL PRECIP...MOSTLY VIRGA...AND
REALLY ONLY PRODUCING ISOLATED GUSTY WINDS 25 TO 45 MPH. FIRE DANGER
WILL START TO ELEVATE IN THE AFTERNOON...WITH A COUPLE HRS OF NEAR
BORDERLINE RED-FLAG CONDITIONS LATE IN THE AFTERNOON ACROSS ERN
FREMONT OR NATRONA COUNTIES.

LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

QUITE AN ACTIVE PERIOD SHAPING UP THROUGH THE LONG TERM. AND IN THE
SPIRIT OF SESAME STREET...THIS FORECAST IS BROUGHT TO YOU BY THE
LETTERS C AND W...AS IN COOL AND WET. AFTER A MAINLY DRY FRIDAY
NIGHT...THE FIRST IN A SERIES OF SYSTEMS MOVES IN FROM THE WEST AND
SPREADS PRECIPITATION ACROSS THE WEST LATER SATURDAY MORNING AND
CONTINUING INTO THE NIGHT. TEMPERATURES WILL START OUT WARM...BUT AS
COLD ADVECTION MOVES IN BEHIND THE FRONT...SNOW LEVELS WILL BEGIN TO
DROP. AT THIS POINT...DOWN TO AROUND 7500 FEET BY SATURDAY EVENING
AND POSSIBLY AS LOW AS 6500 FEET BY SUNDAY MORNING. AS A
RESULT...SEVERAL INCHES OF SNOW WILL BE POSSIBLE BY SUNDAY MORNING
ACROSS THE MOUNTAINS. MEANWHILE...EAST OF THE DIVIDE MOST AREAS
SHOULD SQUEEZE IN ONE MORE MAINLY DRY AND WARM DAY SINCE DOWNSLOPING
SHOULD KEEP THINGS MAINLY DRY FOR A VAST MAJORITY OF THE DAY.
HOWEVER...IT WILL BE BREEZY TO WINDY FOR MANY AREAS. THE CHANCE OF
SHOWERS AND THUNDERSTORMS WILL MOVE IN SATURDAY BUT PROBABLY NOT
UNTIL LATER IN THE AFTERNOON AND EVENING. THE MAIN THREAT FROM THE
STORMS WOULD BE STRONG WINDS WITH STRONG WINDS ALOFT MIXING TO THE
GROUND.

AS COLDER AIR MOVES IN BEHIND THE FRONT...THE POTENTIAL FOR HEAVIER
SNOW WILL MOVE IN FOR THE BIG HORN RANGE AS FAVORABLE NORTHWEST FLOW
DEVELOPS. ON SUNDAY...BOTH MODELS ARE SHOWING A DECENT SLUG OF QPF
MOVING ACROSS EASTERN PORTIONS OF THE AREA. THE EXACT LOCATION OF
THE HEAVIEST PRECIPITATION IS STILL IN DOUBT...BUT SUNDAY EAST OF
THE DIVIDE WILL BE A MUCH COOLER DAY WITH CLOUD COVER ALONG WITH
SOME PRECIPITATION. IN THE LOWER ELEVATIONS...TEMPERATURES SHOULD
REMAIN WARM ENOUGH FOR RAIN. ACROSS THE WEST...EXPECT SHOWERY
WEATHER BUT LIKELY NO ORGANIZED RAIN OR SNOW.

THINGS THEN SETTLE A BUT SUNDAY NIGHT INTO MONDAY MORNING...NOT
REALLY STOP BUT MORE OF A LULL. THE SECOND SYSTEM THEN MOVES INTO
THE WEST MONDAY AFTERNOON AND SPREADS ACROSS THE ENTIRE STATE MONDAY
NIGHT INTO TUESDAY. THE MODELS ARE IN FAIR AGREEMENT WITH THIS
SYSTEM AS WELL AS A 500 MILLIBAR LOW MOVES OVER OR JUST SOUTH OF
WYOMING. THIS MEANS ANOTHER WET DAY FOR MANY AREAS. THIS SYSTEM DOES
LOOK COOLER AS WELL WITH 700 MILLIBAR TEMPERATURES FALLING AS LOW AS
MINUS 6 WHICH COULD BRING SNOW DOWN TO THE BASIN FLOORS...ESPECIALLY
IF THE PRECIPITATION RATE IS HEAVY. THIS SYSTEM THEN EXITS STAGE
EAST LATER TUESDAY NIGHT. ANOTHER SYSTEM MAY THEN APPROACH FOR THE
MIDDLE OF THE WEEK BUT THE MODELS ARE MORE SPLIT ON THIS ONE AND
GIVEN ALL THE CONCERNS EARLIER...WE MADE FEW CHANGES BEYOND TUESDAY
NIGHT.&&

AVIATION.../00Z ISSUANCE/

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

VFR CONDITIONS TO PREVAIL THROUGH THE FORECAST PERIOD. ISOLATED
SHOWERS WITH GUSTY WINDS AND OCCASIONAL THUNDER WILL BE POSSIBLE
OVER THE WESTERN MOUNTAINS EARLY THIS EVENING...AND AGAIN
LATER FRIDAY AFTERNOON.

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

VFR CONDITIONS TO PREVAIL THROUGH THE FORECAST PERIOD. ISOLATED
SHOWERS WITH GUSTY WINDS WILL BE POSSIBLE OVER THE MOUNTAINS NEAR
THE DIVIDE EARLY THIS EVENING...AND AGAIN LATER FRIDAY AFTERNOON.

FIRE WEATHER...

TODAY...LOW FIRE DANGER ALL LOCATIONS WITH LIGHT WIND AND RH VALUES
BOTTOMING OUT IN THE MID 20S TO MID 30S (PERCENT). VERY SMALL CHANCE
FOR AN ISOLATED SHOWER OR THUNDERSTORM ACROSS THE SW MOUNTAINS LATE
THIS AFTERNOON/EARLY EVENING. FRIDAY...FIRE DANGER ENHANCED ACROSS
PORTIONS OF CENTRAL AND NORTHERN WYOMING AS WARM AND DRY CONDITIONS
WITH INCREASING SOUTH TO SOUTHWEST WIND...GUSTING 15 TO 30 MPH AT
TIMES...MIX WITH RH VALUES DROPPING INTO THE MID AND UPPER TEENS AND
LOWER 20S. A FEW ISOLATED GUSTY LOW PRECIPITATION SHOWERS OR
THUNDERSTORMS WILL BE FOUND ACROSS THE WESTERN MOUNTAINS.


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

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



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