Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 231855
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1255 PM MDT THU APR 23 2015

.SHORT TERM...TONIGHT THROUGH FRIDAY

REMNANT CIRCULATION THAT WAS ON TOP OF OUR DEFORMATION AXIS TO OUR
SOUTH YESTERDAY IS NOW OVER SWRN WYO WITH CONVECTION FORMING AROUND
IT AS IT MOVES NE. IT LOOKS LIKE IT WILL MOVE SLOWLY NE AND END UP
IN NRN NATRONA OR SRN JOHNSON COUNTY EARLY THIS EVENING AND HANG OUT
THE REMAINDER OF THE NIGHT IN THIS GENERAL AREA. SURFACE LOW
STRENGTHENING OVER NRN NATRONA COUNTY WILL AIDING IN FAVORABLE
UPSLOPE FLOW ALONG THE SRN BIG HORNS WHERE A TSTM DEVELOPED BEFORE
NOON. THIS AREA WILL BE FAVORABLE DUE TO THE AVAILABLE CAPES OF
400-600 J/KG AND CONVERGENCE/UPSLOPE SUPPORT ALONG THE BIGHORNS.
ANOTHER AREA OF BUILDING CAPE IS ALONG THE CODY FOOTHILLS WHERE
MORNING SOUNDING ANALYSIS PRODUCED UP TO 600 J/KG WITH TEMPS IN THE
UPPER 50S AND DP IN THE MID TO UPPER 30S. OTHERWISE...GENERAL
CONVECTION WITH ENOUGH T/DP SPREAD FOR GUSTY WIND. SMALL HAIL IN THE
FAVORABLE AREAS ARE CERTAINLY POSSIBLE. EXCEPT FOR THE NERN
ZONES...SHOWERS ALL BUT END OR RETREAT TO THE PICKS BY LATER THIS
EVENING. NEXT TROUGH CURRENTLY MOVING INTO THE PACNW WILL MOVE
TOWARDS THE WEST/SW LATE FRIDAY AFTERNOON WITH AN INCREASING CHANCE
OF SHOWERS AND ISOLD TSTMS. UPPER CIRCULATION/CONVERGENCE ZONE MAY
LINGER CLOSE ENOUGH TO THE ERN BORDER AREAS TO KEEP SOME SHOWERS
AROUND THERE INTO THE MORNING HOURS BEFORE SOME AFTERNOON CONVECTION
FORMS. CENTRAL PARTS LOOK DRY UNTIL A FEW SHOWERS/ISOLD TSTMS TRY TO
MOVE OFF THE MTNS AFTER 21Z.

.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY

BEGINNING OF FCST...FLAT RIDGING EAST W/ TROF APPROACHING AND
KNOCKING ON THE WRN FA`S DOORSTEP. BETTER MOISTURE AND INSTABILITY
W/ FALLING TEMPS ALOFT MAKES IT BACK INTO SWRN/WRN FA WITH INCREASED
TERRAIN FORCED PRECIP COUPLED WITH CONVECTIVE SHOWERS OVR THE WRN
MOUNTAINS AND ALONG/NEAR STATIONARY BOUNDARY OVR SWRN/SCNTRL WY. THE
CONVECTIVE NATURE OF THIS PRECIPITATION WILL ALLOW FOR LOCALIZED
AREAS...ESPECIALLY OVR THE HIGHER MOUNTAINS...TO RECEIVE A FEW
TENTHS OF AN INCH LIQUID...EQUATING TO 1 TO 3 INCHES OF SNOW (HIGH
MOUNTAINS/OVERNIGHT) IN THE SALTS/WYOMING/TETON AND WRN WIND RIVER
RANGES.

SAT THRU SUNDAY NIGHT...DIFFERENCES AGAIN SHOWING WITH THE APPROACH
OF THE UPSTREAM TROF...STILL ASSOCIATED WITH GULF OF ALASKA LOW
CURRENTLY MOVING DOWN THE COAST...AS IT IS FCST TO PLUNGE MUCH
FURTHER S BECOMING NEGATIVELY TILTED BEFORE CLOSING OFF AND SLOWING
DOWN OVR THE FOUR CORNERS. THIS AGAIN WILL KEEP THE JET WEST AND
FORCED WELL SOUTH UNDER THE DEVELOPING LOW...BUT WITH MORE MOISTURE
AND INSTABILITY ROTATING IN TO WY FROM THE SE/E AND STICKING AROUND
LONGER. PRECIP CHCS AGAIN HAVE BEEN RAISED AND EXTEND A BIT BEFORE THE
TROF AXIS FINALLY BURSTS THRU THE CWA MONDAY
AFTERNOON/EVE...SCOURING THINGS (MOSTLY) OUT BY MON NIGHT. WHILE H7
TEMPS RANGE FROM -2 TO -6 FROM SE TO NW...SNOW ELEVATIONS WILL FALL
FROM AROUND 9.5K FT SAT NIGHT TO START WITH...TO AROUND 7K FT
SUNDAY...THEN MIXING WITH RAIN AND EVENTUALLY TURNING TO ALL SNOW
AT/NEAR BASIN/VALLEY FLOOR LATER SUN AFTERNOON ACROSS THE
NORTH...TRACKING SWD OVERNIGHT REACHING POSSIBLY INTO SWEETWATER
COUNTY AND THE I80 CORRIDOR THRU MON MORNING. WHILE QPF VALUES LOOK
DECENT ENOUGH...HEAVIER SNOWFALL SHOULD BE CONFINED TO THE MOSTLY TO
THE HIGHER MOUNTAINS OF CENTRAL AND NORTHERN WY WHERE THE MOISTURE
WILL BE MAXIMIZED AND PROLONGED. HIGHER MOUNTAIN TWO DAY SNOWFALL
FROM SATURDAY THRU SUNDAY COULD RANGE FROM 4 TO 6 INCHES EACH
DAY...LOCALLY/ISOLATED TO 8 INCHES EACH DAY OVR THE HIGHEST
PEAKS/RIDGES OF CENTRAL AND NORTHERN WY. GRANITE PASS AND TOGWOTEE
PASS LOOK TO BE THE MOST IMPACTED ATTM. ADDITIONALLY...AS AN
ASSOCIATED COLD FRONT MOVES S AND THRU THE FA SUNDAY...GUSTY NORTH
WIND MAY COMBINE WITH WET SLUSHY SNOW TO CAUSE SOME PERIODS OF
HAZARDOUS TRAVEL EAST OF THE DIVIDE AT LOWER ELEVATIONS...REGARDLESS
OF THE AMOUNT OF SNOW THAT STICKS TO THE ROADWAY. WILL MONITOR FOR
CHANGES IN ORIENTATION AND QPF WITH THIS SYSTEM.

FOR MONDAY NIGHT THRU THURSDAY...POST UPR TROF/SFC FRONT WITH
RIDGING RETURNING FROM THE WEST WILL KEEP THE FA MOSTLY DRY THROUGH
AT LEAST MID-DAY THURSDAY AS THE MOISTURE/STORM TRACK WILL PUSH WELL
NORTH. LR MDLS DIVERGE WIDELY BY THE END OF THE FCST...WITH THE GFS
KEEPING A GOOD RIDGE OVR THE FA WHILE THE EURO FLATTENS AND ALLOWS A
DISTURBANCE TO ROLL THROUGH. AS A DEFINITE SOLUTION IS FAR FROM
BEING DETERMINED...AM LEANING TOWARD THE GFS SOLUTION W/ WARM DRY
RIDGE PERSISTING LONGER BEFORE BREAKING DOWN BY THE END OF THE WEEK.
HAVE THEREFORE TAKEN A 70/30 GFS/EURO APPROACH FOR LATE THURSDAY.

&&

.AVIATION.../00Z ISSUANCE/

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

SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS OVER AND NEAR THE
MOUNTAINS WILL GRADUALLY SPREAD OVER THE LOWER ELEVATIONS AND
CONTINUE THROUGH 06Z. TERMINAL SITES MAY BE IMPACTED BY SHOWERS AND
OUTFLOW WIND GUSTS AROUND 35 KNOTS. SMALL HAIL IS EVEN POSSIBLE
AROUND KCOD AND KCPR. ISOLATED SHOWERS WILL OCCUR THROUGH 10Z
FRIDAY. VFR CONDITIONS WILL PREVAIL TODAY AND TONIGHT WITH LOCAL
MVFR CONDITIONS ASSOCIATED WITH HEAVIER SHOWERS OR STORMS. EXPECT
OCCASIONAL MOUNTAIN OBSCURATION DURING THE AFTERNOON AND EVENING
HOURS. SHOWERS WILL DEVELOP AGAIN OVER THE MOUNTAINS FRIDAY WITH
MORE ISOLATED COVERAGE ACROSS THE LOWER ELEVATIONS LATE FRIDAY.

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

SCATTERED SHOWERS AND ISOLD THUNDERSTORMS WILL CONTINUE THROUGH AT
LEAST 03Z THIS EVENING. TERMINAL SITES MAY BE IMPACTED BY SHOWERS OR
STORMS ALONG WITH OUTFLOW WIND GUSTS AROUND 30 KNOTS. ISOLATED
SHOWERS WILL OCCUR THROUGH 10Z FRIDAY. EXPECT OCCASIONAL MOUNTAIN
OBSCURATION THIS AFTERNOON AND EVENING. VFR CONDITIONS WILL PREVAIL
AT THE TERMINAL SITES THROUGH THE PERIOD. THERE MAY BE LOCAL MVFR
CONDITIONS OVER AND NEAR THE MOUNTAINS DURING THE AFTERNOON AND
EVENING HOURS. SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS WILL
MOVE BACK INTO THE WEST FRIDAY AFTERNOON WITH ISOLATED SHOWERS
POSSIBLE IN THE SOUTHWEST FRIDAY MORNING.

&&

.FIRE WEATHER...

AN UPPER LEVEL DISTURBANCE WILL CONTINUE MOVING NE ACROSS THE AREA
TODAY WHILE ENOUGH MOISTURE EXISTS TO PRODUCE SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS THROUGH THE EVENING. EXPECT ANOTHER CHANCE
FOR FRIDAY...ESPECIALLY WEST OF THE DIVIDE. A SLOW MOVING LOW
PRESSURE AREA COULD BRING A WETTING RAIN FOR SOME AREAS FOR SATURDAY
NIGHT AND SUNDAY BUT PINPOINTING THE AREA IS DIFFICULT AT THIS POINT.

&&

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

&&

$$

SHORT TERM...PS
LONG TERM...BRAUN
AVIATION...PS
FIRE WEATHER...PS






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