462
FXUS65 KRIW 160715
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
115 AM MDT Mon Sep 16 2024

.KEY MESSAGES...

- More active weather Monday as an upper level system pushes
  closer to the area with widely scattered rain showers and a
  few isolated thunderstorms.

- A cold front pushes through Tuesday with more scattered rain
  showers and isolated thunderstorms. Severe wind gusts are
  possible across eastern counties east of the Bighorns.

- Cooler temperatures and continued unsettled weather through
  the rest of the week and into the weekend with another
  system.


&&

.DISCUSSION...
Issued at 1250 AM MDT Mon Sep 16 2024

IR currently depicts ample cloud cover across much of the area
west of the Divide. Radar shows some light rain showers pushing
north off the Winds that short term models have it slowly
dissipating with its progression through the Absarokas. The main
upper level low will continue to slowly progress eastward over
the Sierra Nevada deepening with increasing divergence aloft.
This has allowed for ample diffluence over the CWA, especially
west of the Divide where stronger PVA is expected. A shortwave
will kick off the low up the ridge through the CWA through the
late morning to afternoon and evening hours. More widely
scattered rain showers and a few isolated thunderstorms are
expected west of the Divide by mid afternoon after 2PM. The ARW
was best throughout the activity Sunday and is also more aligned
with the FV3 in coverage as the HRRR is heavily over doing it
with more east of the Divide. A further eastward wave will clip
Natrona County and Casper towards late afternoon after 5-6PM but
with much of the activity further east into Cheyenne`s area with
better ingredients for any severe convective activity.

Otherwise, shower activity will continue overnight into Tuesday
off and on west of the Divide as the aforementioned low nears
from the southwest. More widespread activity once again,
spreading east of the Divide through the afternoon hours. A cold
front associated with the low will push through from around noon
in the west to 5-6PM to the east across the CWA. Winds will turn
westerly with initial gusts over 30-35mph in some areas before
subsiding into the overnight hours. Severe activity could occur
along the triple point area as the front moves over the Bighorns
across the I-25 corridor and points east. Wind gusts up to 50-60
mph the main threat as the low becomes more progressive the
further east it gets. Mountain snow is likely for much of the
higher terrain areas of the CWA with the Winds and Tetons seeing
the most but still only light in nature for a couple inches or
so.

As the low kicks off to the northeast and opens back into a
wave, the jet digs another low off the Pacific northwest coast
through the Sierra Nevadas in similar fashion. Models are in
some disagreement on how far south this one goes but will be
closed off and deepening with its slow eastward progression. The
further south it digs, the less of an impact to the CWA it will
be. Regardless, an unsettled pattern will continue through the
entirety of the week and into next weekend as well. The EC
usually handles these longer term outlooks better and has it
more south than others as the main PFJ remains north to support
it as a weaker finger to the south keeps it south. Time will
tell, but what can be had will be cooler and more seasonable
temperatures for the long term forecast with 50s west of the
Divide and 60s to low 70s to the east.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1008 PM MDT Sun Sep 15 2024

An active weather pattern means more chances for rain showers,
thunderstorms, and strong outflow boundaries on Monday. Tonight a
few rain showers will pass through western WY, with a TEMPO for -
SHRA at KJAC from 07-11Z. Other terminals should stay dry and VFR
tonight into Monday morning. Southerly flow will increase on Monday
as an approaching upper-low moves into the region. Sustained wind
will average 10-20 knots, with gusts of 20-30 knots. Convection will
develop in the afternoon, with the best chances for terminals west
of the Continental Divide and KCPR. All terminals have a good chance
(50%) of strong outflows/downdrafts during the afternoon/evening
hours.

Monday evening into Monday night convection will hang around the
low, so KJAC/KBPI/KPNA may have rain showers and thunderstorms
continue. Wind will decrease substantially around sunset
(01-02Z) for all terminals, but will remain around 7-12 knots
through the evening hours. Conditions will remain VFR for all
terminals through the TAF period, with the exception being
if/when thunderstorms directly impact a terminal. If/when this
occurs brief reductions in VIS to MVFR/IFR will result.

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 1250 AM MDT Mon Sep 16 2024

Elevated fire weather conditions Monday with southerly gusts up
to 25-30 mph for much of Sweetwater County and across the
Rattlesnakes as well. Higher low level moisture content expected
in this area with increasing shower activity seeing relative
humidity values in the 25 to 35 percent range. Areas of lower
humidity in the 15-20 percent range along the I-25 corridor will
see wind speeds below 15-20 mph. Otherwise, less fire weather
concerns the remainder of the week with more unsettled weather
and cooler temperatures. The only thing of note will be a shift
in winds out of the west to north of west behind a cold front
that will push through Tuesday afternoon.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Lowe
AVIATION...Rowe
FIRE WEATHER...Lowe