Area Forecast Discussion
Issued by NWS Riverton, WY

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463
FXUS65 KRIW 261937
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
137 PM MDT Tue Sep 26 2017

.SHORT TERM...(This evening through Friday)
Issued at 136 PM MDT Tue Sep 26 2017

Cold high pressure will bring stable dry weather with
clearing through Wednesday.  Some valley fog is expected
to develop in the western valleys tonight and Wednesday
morning.  Isolated mountain snow showers may occur with
little if any accumulations.  Freezing temperatures will
occur across the west and southwest and mountains, with
mid to upper 30s expected across the lower elevations
east of the continental divide.  A cut off upper low
pressure system over the Desert Southwest and southern
Great Basin will begin to eject northeast towards southwest
Wyoming Wednesday night with some light sowers moving into
extreme southern Wyoming late Wednesday night and Thursday
morning.  As the low moves into northeast Utah south of the
Uinta mountains on Thursday, moisture and instability will
increase across the southwest moving into central Wyoming
through Thursday with isolated thunderstorms embedded in
the increasing area of showers.  The threat of precipitation
is expected to make it north into the southern Absaroka,
Owl Creek and Bighorn mountains Thursday night.  The low
will make it into central Wyoming on Friday with showers
spreading into the northern mountains.  Temperatures will
be on the cool side but cloud cover will decrease the
coverage of freezing temperatures at night Wednesday night
and Thursday night.  Snow levels are expected to remain
around 7500 to 8000 feet.

.LONG TERM...(Friday night through Tuesday)
Issued at 136 PM MDT Tue Sep 26 2017

Tail end of our nwd moving upper low will continue to affect the
area at least into the evening hours, especially the north half with
some showers/higher elevation snow and isolated thunder potential
before it exits stage north. Not much break as the next system(s)
approaches late Saturday/Sat evening in the far west and then moves
across the area Saturday night into Sunday morning. This system is
currently  moving towards the central Aleutians attm and as our mean
ridge weakens and transitions to a mean trough, this system will dig
into the Pacific Northwest Friday night into Saturday. The system
will strengthen and approach the west late Saturday into Saturday
evening with an increasing chance of showers and a few thunderstorms
along with increasing wind for most of the area. The cold front
moves through the west Saturday night with lowering snow levels to
near at or at the valley floor with a swath/period of decent
precipitation. The front could be supported by active cyclonic nose
of encroaching jet. New guidance has backed off on a stronger
dynamic front east of the divide (for late Sat ngt and Sun mrng)
diminishing the chances of a good swath of pcpn but confidence low
with model trends past 36 hours. Either way, a good shot of wind
should occur ahead of, with fropa and behind it. The new GFS has now
joined the old Euro in building in a shortwave ridge Monday as a new
trough develops near the west coast. The new Euro brings the next
front into the west already on Monday with a good chance of more
widespread pcpn into the nw mtns Monday into Tuesday. Models have
been struggling mightily with the pattern change once again so low
confidence the last couple days of the extended as the GFS 5-wave is
now developing the mean trough further west along the coast early
next week (about 8 degrees further west than the past couple runs).

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday)
Issued at 136 PM MDT Tue Sep 26 2017

Dry with VFR conds through Wednesday. A few showers are expected in
and near the the northwest mountains through early this evening.
There could still be a few patches of fog again early Wednesday in
low lying areas and near area rivers/streams.

&&

.FIRE WEATHER...
Issued AT 136 PM MDT Tue Sep 26 2017

Cold high pressure will bring stable dry weather with
clearing through Wednesday.  Some valley fog is expected
to develop in the western valleys tonight and Wednesday
morning.  Isolated mountain snow showers may occur with
little if any accumulations.  Freezing temperatures will
occur across the west and southwest and mountains, with
mid to upper 30s expected across the lower elevations
east of the continental divide.  A cut off upper low
pressure system over the Desert Southwest and southern
Great Basin will begin to eject northeast towards southwest
Wyoming Wednesday night with some light sowers moving into
extreme southern Wyoming late Wednesday night and Thursday
morning.  As the low moves into northeast Utah south of the
Uinta mountains on Thursday, moisture and instability will
increase across the southwest moving into central Wyoming
through Thursday with isolated thunderstorms embedded in
the increasing area of showers.  The threat of precipitation
is expected to make it north into the southern Absaroka,
Owl Creek and Bighorn mountains Thursday night.  The low
will make it into central Wyoming on Friday with showers
spreading into the northern mountains.  Temperatures will
be on the cool side but cloud cover will decrease the
coverage of freezing temperatures at night Wednesday night
and Thursday night.  Snow levels are expected to remain
around 7500 to 8000 feet.  Mixing heights will be rather
low with light transport winds.  More sunny areas with
heating can expect fair to low end good smoke dispersal
Wednesday and Thursday afternoons.  Cloudy areas with
precipitation will have poor to locally fair smoke
dispersal.

&&

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

&&

$$

SHORT TERM...Baker
LONG TERM...Skrbac
AVIATION...Skrbac
FIRE WEATHER...Baker



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