000
FXUS65 KRIW 300351
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
951 PM MDT Fri Sep 29 2023

.DISCUSSION...(This evening through Friday)
Issued at 134 PM MDT Fri Sep 29 2023

Another warm and mostly sunny day across the area this afternoon as
a dry southwest flow continues. As has been the case lately, it will
be breezy again, especially across southern and eastern Sweetwater
County. Elevated to near-critical fire weather conditions are likely
there through the afternoon given the winds and low humidity.
Otherwise, temperatures will peak 5 to 10 degrees above normal. A
few showers across the northwest are possible this evening as a
weak disturbance moves through the flow, but dry conditions will
continue for the majority of the area through tonight.

On Saturday a trough will deepen across the western Great Basin.
This will cause southerly flow to increase across Wyoming.
Widespread windy conditions are expected as this occurs, especially
across southern Wyoming where gusts of 35 to 45 mph are likely.
This flow will also advect in warm and dry air, bringing humidity
values to near or below 15 percent for much of central and
southern Wyoming. Accordingly, widespread elevated to critical
fire weather conditions are expected through the afternoon; fire
weather highlights have been issued for zones with cured fuels as
appropriate. That being said, a few showers appear possible across
western areas as a bit of divergence aloft passes over; have
added some light PoPs during the afternoon to account for this.
The majority of locations will remain dry through the day,
however.

By Saturday evening, we will start to see chances increase as the
trough and now closed low approach. However, the continued forecast
trend of a slower progression of these features will keep chances
mainly limited to far western Wyoming through around sunrise Sunday
morning. Chances will then increase through Sunday for the rest of
the area, with widely scattered showers and thunderstorms, as well
as mountain snow, moving north to northeast through the area.
However, moisture with this system is not overly impressive (PWAT
values around a half inch for most of the area), and it`s likely
that much of the area misses the precipitation and remains dry as
the primary low pulls north through Sunday evening. Additionally for
Sunday, guidance is trending up on wind potential as a passing jet
streak brings downsloping conditions for much of central and
southern areas. Wind gusts over 40 mph look plausible at the moment.
Otherwise, Sunday will be cooler, with humidity elevated to over 25
percent.

A secondary low looks to pull north with the primary trough axis on
Monday. This will bring another round of precipitation chances, as
well as cooler temperatures, through Tuesday. Again, some of this
will fall as snow in the mountains with snow levels dropping to
around 8,500 feet Monday night. Further ahead, guidance favors mild
and generally drier weather through much of next week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 950 PM MDT Fri Sep 29 2023

VFR conditions through the TAF period. Relatively light winds
persist overnight. Gusty, southerly winds expected Saturday
afternoon thanks to an approaching weather system. Gusts to 30 knots
are possible; KRKS could see some gusts to 40 knots. Gusty winds
decrease after sunset, but may continue to be around 10 knots
through Saturday night.

Recent model runs are showing drier conditions than previously, so
have removed VCSH from most sites Saturday afternoon. KJAC could see
a nearby shower, but chances are low enough to not mention in TAF.
Better moisture, and thus rain chances, look better towards the end
of the TAF period and beyond.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

.FIRE WEATHER...
Issued at 134 PM MDT Fri Sep 29 2023

Elevated to near-critical fire weather conditions will continue this
afternoon for much of central and southern Wyoming. Mainly dry
conditions expected overnight, though with a shower or two across
northwestern areas. Saturday will see widespread windy conditions as
a trough approaches. Combined with a dry airmass, elevated to
critical fire weather conditions are expected again across central
and southern portions. Precipitation chances increase Saturday night
across the west, spreading rain and mountain snow potential to
the rest of the area Sunday through Tuesday. Cooler temperatures
are also expected with this system, as well as gusty wind on
Sunday.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from 1 PM to 7 PM MDT Saturday for WYZ283-289.

&&

$$

DISCUSSION...Myers
AVIATION...Wittmann
FIRE WEATHER...Myers