Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 220450
AFDRIW

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RIVERTON WY
1050 PM MDT TUE APR 21 2015

.SHORT TERM...TONIGHT THROUGH WEDNESDAY (ISSUED AT 211 PM MDT)

WEAK SHOWERS DEVELOPING OVER THE MOUNTAINS AND UPPER WIND RIVER
BASIN FOOTHILLS EARLY THIS AFTERNOON. THESE SHOWERS AND PERHAPS A
TSTM OR TWO WILL CONTINUE TO DEVELOP BEFORE DYING OFF THIS EVENING.
WEAK FRONTAL BOUNDARY IS PUSHING SOUTH THRU OUR NRN AND ERN ZONES
AND WILL CONTINUE PUSHING S AND SW INTO THIS EVENING BEFORE STALLING
OUT SOMEWHERE IN THE UPPER GREEN MOST LIKELY. FRONTAL BOUNDARY MAY
HELP FOCUS A FEW CELLS ALONG IT INTO THE EVENING. THE FRONTAL
BOUNDARY WILL LIKELY ERODE SOME ON WEDNESDAY AND BE CENTERED MORE
OVER THE NE HALF FROM NEAR COD TO CPR. WEAK DISTURBANCE IN THE NW
FLOW IS BRINGING A FEW WEAK SHOWERS TO THE NRN BIGHORNS. WEAK
DISTURBANCE IN THE NW FLOW MOVING TOWARDS NWRN WYO IS EXPECTED TO
DROP SE TONIGHT AND THEN GET LOST IN THE WEAK FLOW AS WE TRANSITION
FROM A NW TO SW FLOW. PRETTY WEAK FEATURE SO NOT SURE IF IT WILL
HELP THAT MUCH WITH CONVECTION TOMORROW. SOUNDINGS ARE JUST NOT THAT
EXCITING WITH WEAK WINDS AND VERY LIMITED INSTABILITY OF 100-200J/KG
AT MOST. SURFACE DEW POINTS AND PW VALUES WILL REMAIN QUITE LOW
THROUGH THE PERIOD. STILL COOL IN THE MID LEVELS SO AFTERNOON
HEATING WILL FIRE SOME SHOWERS ONCE AGAIN WITH A FEW TSTMS
POSSIBLE...MAINLY ALONG AND WEST OF THE DIVIDE.

.LONG TERM...WEDNESDAY NIGHT THROUGH TUESDAY

BEGINNING OF FCST THRU FRI NIGHT...RIDGING AND WEAK FLOW ALOFT.
UNSTABLE THOUGH...ESPECIALLY AFTERNOONS AND EVENINGS...WITH MODERATE
TO DRY LAPSE RATES RANGING BETWEEN 8.5 AND 10.5 AND CAPE VALUES
MAXING OUT BETWEEN 100 AND 450 J/JG EAST TO WEST. WED NIGHT...MAINLY
MOUNTAIN SHOWERS AND ISOLATED THUNDER WITH ADDITIONAL CHANCES FOR
CONVECTION OCCURRING NEAR/ALONG FRONT ACROSS SRN WY. THU AND THU
NIGHT...DEVELOPING LOW OVR CNTRL THEN LEE SIDE ERN WY BY AFTERNOON
WITH MOUNTAIN SHOWER AND THUNDER ONCE AGAIN...AND ALSO ALONG/NEAR
WEAKLY DEVELOPING FRONT STRETCHING FROM SOUTH PASS...E INTO NATRONA
COUNTY AND WRAPPED INTO/AROUND LOW STRETCHING N THRU JOHNSON COUNTY.
A LITTLE BETTER MOISTURE BEGINS TO MAKE ITS WAY INTO SWRN/WRN FA THU
NIGHT THRU FRI MORNING...WITH BETTER MOUNTAIN WRN MOUNTAIN SHOWERS
IN ADDITION TO LL FORCING ALONG NEAR STATIONARY FRONT OVR
SWRN/SCNTRL WY. THE CONVECTIVE NATURE OF THIS PRECIPITATION WILL
ALLOW FOR LOCALIZED ISOLATED AREAS TO RECEIVE A FEW TENTHS/TO A
COUPLE IN INCHES OF SNOW (HIGH MOUNTAINS/OVERNIGHT) IN SHORT
ORDER....BUT RATHER HARD IN PINNING DOWN JUST ONE LOCATION. THE
SALTS/WYOMING AND WIND RIVER RANGES WOULD CERTAINLY BE FAVORED IN
THIS SCENARIO.

SAT THRU THE END OF THE FCST...UPSTREAM TROF...CURRENTLY ASSOCIATED
WITH DEEP GULF OF ALASKA LOW...WILL MOVE INTO AND THRU THE FA
BETWEEN SAT AND SUN MORNING...WITH WEAK LEE TROFFING GOING ON AT THE
SFC. TRACK AND BETTER MOISTURE ASSOCIATED WITH THIS FEATURE SHOULD
BRING A WIDER AREA OF SHOWERS/ISO THUNDER TO THE REGION FROM SAT
AFTERNOON THRU AT LEAST SUN MORNING...POSSIBLY DRAGGING INTO SUN
AFTERNOON BEFORE ALL IS SAID AND DONE. FOR MONDAY AND TUE...POST UPR
TROF/SFC FRONTAL AND MODEST RIDGING RETURNING WILL KEEP THE FA ON
THE DRY SIDE WITH ONLY LOW END CHCS FOR SHRA AFTERNOON/EVES...MAINLY
ACROSS THE NRN CWA ...FOLLOWING THE STORM/MOISTURE TRACK
TOWARDS/INTO SRN CANADA.

&&

.AVIATION.../06Z ISSUANCE/

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

SCATTERED SHOWERS AND ISOLATED STORMS WILL DEVELOP AFTER 19Z WED
OVER OR ALONG THE ABSAROKA AND WIND RIVER MOUNTAINS. SHOWERS WILL BE
MORE ISOLATED OVER THE BIGHORN MOUNTAINS. SOME OF THE SHOWER
ACTIVITY WILL DRIFT OFF THE MOUNTAINS AND IMPACT THE LOWER
ELEVATIONS. NOT ALL TERMINAL SITES WILL SEE SHOWERS AND VCSH WILL
APPEAR IN SOME TERMINAL FORECASTS. EXPECT OCCASIONAL MOUNTAIN
OBSCURATION THIS AFTERNOON INTO THE EVENING. MOST OF THE SHOWERS
WILL DISSIPATE BY 06Z THURSDAY. VFR CONDITIONS WILL PREVAIL AT THE
TERMINAL SITES THROUGH THE PERIOD. THERE MAY BE LOCAL MVFR
CONDITIONS OVER AND NEAR THE MOUNTAINS.

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

SCATTERED SHOWERS WILL DEVELOP OVER THE WESTERN MOUNTAINS AFTER 19Z
WED WITH ISOLATED THUNDERSTORMS. THE ACTIVITY WILL DECREASE AFTER
03Z THURSDAY. TERMINAL SITES MAY SEE SHOWERS AT TIMES FROM 21Z WED
UNTIL 03Z THURSDAY. MOST TERMINAL FORECASTS WILL HAVE VCSH FOR NOW.
EXPECT OCCASIONAL MOUNTAIN OBSCURATION THIS AFTERNOON INTO THE
EVENING. VFR CONDITIONS WILL PREVAIL AT THE TERMINAL SITES THROUGH
THE PERIOD. THERE MAY BE LOCAL MVFR CONDITIONS OVER AND NEAR THE
MOUNTAINS.

&&

.FIRE WEATHER...

TODAY LOOKS LIKE THE DRIEST AND MOST STABLE DAY OF THE WEEK WITH
ONLY ISOLATED AFTERNOON SHOWERS AND THUNDERSTORMS IN THE MOUNTAINS.
OTHERWISE...THERE WILL BE A CHANCE FOR SHOWERS OFF AND
ON...ESPECIALLY AFTER WEDNESDAY BUT WITH A LOW CHANCE OF ANY WETTING
RAIN UNTIL LATE IN THE WEEK. OTHERWISE THERE ARE NO MAJOR WIND
EVENTS OR SIGNIFICANT LIGHTNING EPISODES ON THE HORIZON.

&&

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

&&

$$

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










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