695
FXUS65 KRIW 161715
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1115 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 /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1112 AM MDT Mon Sep 16 2024

VFR conditions are expected to prevail across mostly all terminals
through the TAF period. Winds will gradually increase for all sites
during the afternoon today. Gusts of 15 to 25 knots will be frequent
through the afternoon and evening. A shortwave approaches the area
from the southwest, which will increase chances for showers and
thunderstorms mainly for KJAC/KRKS/KBPI/KPNA/KCPR this
afternoon and evening. However, overall confidence in any
showers or thunderstorms impacting terminals remains low. The
main concern today will be strong gusty outflows created by any
nearby developing showers and storms. Erratic outflows exceeding
40 knots are possible this afternoon and evening as convection
increases. Winds are expected to remain breezy through much of
the overnight into the early morning hours Tuesday. This looks
to be the case especially at KLND/KRKS/KCPR with KRIW possibly
seeing a light breeze linger into Tuesday morning. A cold front
will move into the state Tuesday bringing with it gusty winds
and chances for showers and thunderstorms. Shower and
thunderstorm groups have already been put into the TAFS for
KRKS/KJAC for the end of the TAF period. Confidence in the
timing of the fronts arrival still remains low at this time. Due
to this uncertainty, the remaining TAF sites will likely see
PROB30 groups be added in for the next TAF issuance.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on smoke, 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...Dziewaltowski
FIRE WEATHER...Lowe