Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 210521

Area Forecast Discussion
National Weather Service Riverton WY
1121 PM MDT Sun Aug 20 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 415 PM MDT Sun Aug 20 2017

Isolated gusty showers/storms will continue over Sweetwater County
into the early evening with a few forming further east across
southeast Fremont and Natrona Counties into early evening. Strong
outflow winds and and lightning strikes will be the main hazard.
Northern shortwave will push another front southward tonight with
potential for concentrated smoke along and behind it. This smoke
may limit visibility from Riverton to Casper on Monday morning
possibly hampering or at least changing the look of the sky around
the eclipse. One other feature to watch is thinning band of
higher clouds that is forecast by some of the guidance to be
between the Wind River Basin and Casper around totality time. It
may be clearing the Wind River Basin/Riverton vicinity in time and
then possibly affect the Casper area between 11 and noon. May be
a rather narrow band then but there could be some concern for
viewing in this narrow cloud feature. Otherwise, just smoky/hazy
and mostly sunny. Isolated storms possible in swrn Sweetwater
only. About the same for Tuesday. On Wednesday, ridge builds back
in from the south and flow around that and the offshore SOCAL low
will bring another bout of mainly mid level moisture into swrn WY
leading to an increasing chance of showers/storms near and west of
the divide Wednesday afternoon and evening. A few gusty
outflows/storms may also sneak east of the divide by the evening
hours. Continued quite warm through the period with just the
shallow front cooling some of the northern and central sections a
couple degrees Monday and the southwest half Wednesday. Otherwise,
mainly upper 70s to upper 80s lower elevations with 60s and 70s
high country. A few lower 90s in the Big Horn Basin Tuesday and

.LONG TERM...(Wednesday night through Sunday)
Issued at 415 PM MDT Sun Aug 20 2017

On Wednesday night the ridge axis will begin to slide off to the
east of the area. Monsoon moisture will then stream northeast toward
Wyoming as some desert southwest troughiness sends the moisture up
our way. Also, the next well defined shortwave will be tracking east
across the Pacific Northwest with heights beginning to fall over our
area. As a result, temperatures will cool off a few degrees east of
the divide and continue to cool off in the far west Thursday.
Isolated to scattered late day thunderstorms will erupt as a result
Thursday along with a repeat of late day storms Friday and Saturday.
Then by Sunday, the long wave ridge will reestablish itself with
warming temperatures once again by Sunday. The Canadian appears
to be a tad slower in bringing Sundays ridge back in.


.AVIATION...(For the 06Z TAFS through 06Z Monday evening)
Issued at 1121 PM MDT Sun Aug 20 2017

All terminals to be VFR through the forecast period. Surface smoke
does not look as pesky as Saturday night despite weak frontal
boundary that has pushed into central Wyoming. 05Z/Mon IR satellite
imagery showing mid-high clouds, generally around 20K MSL, pushing
into northern Wyoming from Montana. Trends have been for warming
cloud tops and some thinning as the clouds drop farther south. Looks
like the tail end of these clouds will lay west-to-east across
central Wyoming by late Monday morning. However, current trends
indicate these clouds will be thinning late tonight and Monday
morning. As for wind, diurnally driven west-northwest wind at KBPI,
KPNA, and KRKS Monday afternoon with speeds generally 10-12kts.
Eastern terminals will see a weak north to northeast flow with
speeds mainly 7-10kts. Only chance for convection would be in
extreme southwest Sweetwater County near the Uinta Mountains late
Monday afternoon, and that chance is slim.


Issued AT 415 PM MDT Sun Aug 20 2017

...Elevated Fire Weather Concerns Through Tuesday Due To Very Dry
and Warm Conditions with Locally Breezy Areas...

Fuels at critical levels for most of the low elevation forecast
zones in addition to a few mountain zones above 8000 feet across
western Wyoming. (Please see the Fire Weather Forecast product for
more information). Elevated fire weather concerns continue for the
entire forecast through early this week due to low RH values during
the afternoon and evening hours along with wind gusts between 15 and
20 mph at times along and west of the Continental Divide. Wind gusts
over 25 mph can still be expected into early this evening. Very dry
conditions continue with minimum RH values in the teens to around 20
percent Monday and teens Tuesday.





LONG TERM...Lipson
FIRE WEATHER...Skrbac is the U.S. government's official web portal to all federal, state and local government web resources and services.