707
FXUS65 KRIW 171053
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
453 AM MDT Tue Sep 17 2024

.KEY MESSAGES...

- Widely scattered rain showers and thunderstorms this morning
  west of the Divide that will spread east in the afternoon.

- A cold front pushes through west to east from late morning
  through mid afternoon with gusty west to north of westerly
  winds behind it, some of which could be high wind warning
  criteria.

- Cooler temperatures for the rest of the week and into the
  weekend with continued precipitation chances throughout as
  well.

&&

.DISCUSSION...
Issued at 122 AM MDT Tue Sep 17 2024

IR currently depicts some dry air intrusion across the CWA ahead
of the main upper level low pushing across Nevada. Any rain
shower activity has dissipated and pushed into Montana out of
the Bighorn Basin. An upper level shortwave will begin to push
out of northern Utah/eastern Idaho by mid morning that will
spark some widely scattered rain showers and isolated
thunderstorms west of the Divide. Another area of note will be
from Sweetwater County up to Natrona with an area of surface
convergence ahead of the cold front. This will all spread north
and east into the afternoon hours becoming more numerous with
daytime heating. Hi-Res models are picking up on leeside
cyclogenesis along the triple point off the Bighorns that will
strengthen these aforementioned thunderstorms along the I-25
corridor by 3-4PM before exiting to the east in a short hour or
two. Main concerns will be with damaging winds as the main
threat with the support a strong mid level jet over 50kts that
will aid in mixing to the surface in this area of Johnson County
east of the interstate. Otherwise, the bulk of the main energy
will be well east of the CWA where more ample CAPE and steeper
lapse rates will be.

The main concern outside of precipitation activity will be with
FROPA and wind shifting out of the west to north of west. Timing
is more aligned with the models improving confidence of pushing
out of Idaho by late morning and progressing east through the
afternoon hours exiting east by 4-5PM. On the backside of the
low, moisture will wrap back into northwestern portions of the
state with the occlusion emphasizing the stronger winds with
CAA. Wind gusts up to 50-60 mph are possible in some areas of
the Cody Foothills (funneling) and into eastern parts of Fremont
County and Natrona County as well. Other areas will see winds
up to 40-50 mph, staying below any high wind thresholds.
Precipitation will be for the northern third of the CWA with
mountain snow likely for elevations of the Winds, Tetons, and
Absarokas over around 8kft as the cold air pushes in behind the
aforementioned cold front. Nothing significant in accumulations
but a decent amount as the first bigger snow of the season.
Lower elevations will see rain showers progress east into the
Bighorn Basin after midnight and into Wednesday morning.

Precipitation will linger in these areas into the afternoon as
winds decrease by late morning and into the afternoon with a
diminishing gradient behind the occlusion. A more stratiform
type event through the afternoon and evening with the cooler
air making its way across the CWA. Afternoon high temperatures
will be in the 50s and 60s for points west of the Divide (and
some even cooler), with 60s to low 70s to the east for the
remainder of the week and into the weekend. Induced upper level
ridging ahead of another deepening low making its way down the
west coast for Thursday the the CWA remaining mostly dry for
most. The EC has the low cutting off well to the south pushing
across the Four Corner Region late week with the bulk of the
greater impacts out of the state. Regardless, continued cooler
temperatures and unsettled weather with daily precipitation
chances to include snow in the higher elevations into the
weekend and the extended forecast.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 433 AM MDT Tue Sep 17 2024

VFR conditions to start the period for all TAF sites with
scattered mid level clouds and light varying winds through mid
to late morning. Rain showers and possible thunderstorms after
15Z at JAC spreading east with time after 16Z for RKS, 17Z for
BPI/PNA, 19Z for CPR, RIW, and LND, and 21Z at COD and WRL.
These will last for several hours as winds increase with an
approaching cold front before turning more westerly after around
21-01Z west to east. Winds will be reinforced at RKS, COD, and
LND on the backside of the low with additional rain showers for
JAC, COD, and WRL after 04-06Z through the end of the period.
Points south will remain dry overnight into Wednesday morning
with winds eventually diminishing after sunrise and into the
morning hours. Confidence at a medium level with precipitation
timing but still a bit of uncertainty with models and the
overall widespread sporadic nature of coverage.

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

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from late tonight through Wednesday morning
for WYZ003-019-020.

&&

$$

DISCUSSION...Lowe
AVIATION...Lowe