Area Forecast Discussion
Issued by NWS Riverton, WY

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FXUS65 KRIW 170431
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1031 PM MDT Wed Aug 16 2017

.SHORT TERM...(This evening through Thursday)
Issued at 230 PM MDT Wed Aug 16 2017

Dry with a warming trend sums up the short term. Limited instability
exists around the central and northern sections with isold
showers/tstms expected into early this evening, mainly mtns and far
north. Thursday will see a warmup of 3-5 degrees east of the divide
with little change west. A shortwave will clip the nern zones with a
shallow cold front, brief gusty wind and isold afternoon
showers/storms but with limited instability and upper support.
Friday will see another 3-5 degree warmup for all areas as shortwave
ridging moves in with a dry day. On Saturday, the ridge flattens and
upper low starts to develop along the CA coast. Temps will be
similar to Friday with a couple degrees of warming in the central
zones east of the divide. The far swrn sections will see the
beginnings of sw flow and limited moisture return possibly resulting
in a few late day storms off the Uintas.

.LONG TERM...(Saturday night through Wednesday)
Issued at 230 PM MDT Wed Aug 16 2017

Overview...For Monday, Eclipse Day, the 12z model runs still
indicate that a weak surface cold front is progged to move into
the northwest portion of Wyoming and will bring with it some mid
to high clouds into the region during the morning. The models seem
to indicate that the frontal boundary should weaken and become
diffuse during the day as it attempts to move southeast into the
state. The low level southwest flow ahead of the boundary should
also result in more low/mid level moisture and partly to mostly
cloudy conditions expected across the forecast area from the
morning into the afternoon. It is expected that there should be
some isolated showers/storms over the western mountains due to
expected slight instability.

For the weekend leading up to eclipse day, we are expecting that most
areas will be mainly dry with near normal temperatures. Will
continue with just slight chance pops for showers/storms across
the south and northwest areas. With a continued slight southwest
low level flow expected on Tuesday and Wednesday, there will be
slight chances of showers and thunderstorms.

Discussion...Initially by Saturday night, the monsoonal flow will
be kept mainly south of the forecast area with just southern
Wyoming feeling the effects of the developing southwest flow. By
Sunday and into Monday, the GFS and ECMWF models continue by
varying degrees to build a ridge across the northwest U.S. with an
accompanying clipper system expected to move southeast. An
adjoining cold front will be further moving into the northwest
portion of Wyoming by Monday morning. Based upon 12z model
solutions from the GFS and ECMWF models, both still indicate that
scattered to broken mid and high clouds are possible along and
south of the path of eclipse totality. The southwest low level
flow will also result in some slight instability along and west of
the Divide, that will lead to some cumulus buildups over the
mountains by 11 am. With this in mind, it is expected that partly
cloudy conditions at best are expected on eclipse day.

At the end of the extended forecast period on Tuesday and
Wednesday, the models are in general agreement involving building
an upper level ridge over the Rockies. This should result in
increased monsoonal moisture moving northward across the forecast
area. Will continue with slight chances for mainly afternoon
showers/storms.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday)
Issued at 1030 PM MDT Wed Aug 16 2017

VFR conditions will occur at the terminal sites through the period.
Isolated showers and thunderstorms will occur after 20Z Thurs in the
northern WY mountains until 03Z Friday. Northern Johnson county may
also see isolated showers or a storm from 21Z Thurs until 03Z
Friday. Expect brief mountain obscuration at times.

&&

.FIRE WEATHER...
Issued AT 230 PM MDT Wed Aug 16 2017

Dry for most areas with a warming trend the next few days. Isolated
showers and thunderstorms be confined to central and northern
mountains and far north into this evening. Lower elevation min rh`s
will be rather low Thursday and Friday with mid teens to around 20
percent late in the day. A general west wind will develop across the
south and west on Thursday afternoon at 10 to 20 mph which will
elevate the fire danger across the lower elevations and foothill
areas when combined with min rh`s in the mid teens to lower 20s.

&&

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

&&

$$

SHORT TERM...Skrbac
LONG TERM...Troutman
AVIATION...AR
FIRE WEATHER...Skrbac



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