Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 010459
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1059 PM MDT WED AUG 31 2016

.SHORT TERM...Tonight Through Saturday

Weak ripple moving into se Idaho looks like it will clip the nw
corner this evening helping with a few showers and gusty
thunderstorms. The next one with a little more punch is over nwrn
Nevada and this one looks to arrive in the west late tonight into
Thursday morning with a few showers. Moisture is drawn nnewd
ahead of this feature with increasing mid and even low level
moisture in the west overnight into Thursday. With reasonably
moist mid levels and daytime heating, most of the soundings around
the forecast area are showing some weak instability with cape of a
couple hundred or so in many spots. Scattered showers and
isold/wdly sct tstms over the west will move east of the divide
thru the afternoon and eventually the ern zones by evening. Models
vary but it looks like some mid level moisture will linger
overnight Thursday which may keep a few showers going around the
area. On Friday our front approaches the west and it looks a
little faster than yesterday with the leading edge hitting the
west in the afternoon. Winds will be increasing across most of the
area with critical fire weather conditions quite possible east of
the divide and in the south. The west still looks like it will
have enough low level moisture around to keep min rh`s above 15
percent (more like 20-25 percent). With that said, we`ll have to
watch YNP as there is some hint of drying behind the front late in
the day Friday and if that occurs with the wind, we`ll have more
critical fire weather conditions. Storms look limited on Friday to
mainly the sern corner as the Thu/Thu ngt plume gets shunted se. A
weak ripple may lift ne into central Wyo early Saturday with a few
light showers for the central and nrn/nern zones. Front will
likely hang over the north half through Saturday with a few
showers around. Maybe a few storms in the sern corner with the
plume/moisture streaming ne out of CO and off the higher terrain
down there. Quite warm to hot ahead of this cold front with only
the moisture and clouds trying to hold the west down a little
Thursday and Friday while east of the divide it continues quite
warm to hot until fropa (so cooler Saturday).

.LONG TERM...Saturday Night Through Wednesday

A disturbance moving through the area will leave fairly widespread
showers and thunderstorms across the area on Saturday evening. The
bulk of moisture associated with this feature will quickly move to
the northeast, leaving cooler temperatures across central and
western Wyoming.

Another trough will move over the intermountain west by Sunday
afternoon leaving a moist southwest flow over the state. Expect
showers and thunderstorms to again be present, especially across the
northwestern half of the state. This surge of moisture will move
through by Monday morning, but another fast developing wave will
almost immediately take its place over the intermountain west and
into the desert southwest. Southwest flow will consequently
continue, though models start to lose agreement with the moisture
amounts associated with this continued flow pattern. The ECMWF
indicates the opportunity for another round of fairly widespread
showers and thunderstorms by Tuesday afternoon, while the GFS keeps
dry conditions over the area with a slower movement of the system.
Showers have been included with the current forecast package, though
confidence in this more aggressive solution is not as strong.

Regardless to solution, temperatures will remain cooler than normal
through the middle portion of next week.

&&

.AVIATION.../06Z Issuance/

Very light showers still showing up on radar over far west
Wyoming late Wednesday evening. A few thunderstorms farther
west over Idaho where better moisture axis stretches from
central Nevada to southwest Montana. This axis may just
nip the northwest corner late tonight, but no impacts to
terminals which will be VFR through the forecast period.
Mid-level moisture and instability will increase Thursday
afternoon, generally after 20Z/Thu. Have VCTS west of a
KCOD-KLND-KBPI line with VCSH at KRIW and KRKS. Surface
wind will increase Thursday afternoon at many terminals
with KCPR, KRKS, and KJAC all 10-20kts until 00Z-02Z/Fri.
Showers and isolated thunderstorms will move northeast
across the valleys/basins through about the same time.
Surface moisture is limited and forecast soundings most
certainly favor gusty outflow wind to around 40kts as
the main hazard. Shear is limited and mid-level wind is
10-15kts at best, so 40kt max could be overdone.

&&

.FIRE WEATHER...

...RED FLAG WARNING FOR THE SOUTHWEST CORNER OF WYOMING...FROM 12
PM THURSDAY TO 10 PM FRIDAY...

...FIRE WEATHER WATCH FOR MUCH OF CENTRAL...NORTHERN...AND
SOUTHERN WYOMING...INCLUDING YELLOWSTONE NATIONAL PARK...FROM 12
PM TO 10 PM FRIDAY...

Dry and warm into the evening with isolated showers/storms possible
over the west, central and northern mountains...with possible
localized outflow gusts to 45 mph with stronger convection. Thursday
should generally see an increase in moisture across most of the
forecast area, yet still remain quite dry for most lower elevations
east of the divide. The southwest corner looks like the best chance
for critical fire weather conditions with min rh`s around 15 percent
and southwest wind increasing to 10 to 20 mph with gusts around 25-
28 mph. Further north, moisture levels look like they`ll rise
with our approaching disturbance keeping rh`s in the upper teens
to mid 20s. East of the divide, it will be very dry but winds will
generally be 5 to 15 mph with local gusts 20-25. Right now, Friday
looks to have the best overall potential for producing critical
fire weather conditions .

&&

.RIW Watches/Warnings/Advisories...
Fire Weather Watch from Friday afternoon through Friday evening
for WYZ140-275-276-278>283-285-287-289-300.

Red Flag Warning from noon Thursday to 10 PM MDT Friday for
WYZ277.

&&

$$

SHORT TERM...Skrbac
LONG TERM...Branham
AVIATION...CNJ
FIRE WEATHER...Braun



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