207
FXUS65 KRIW 171622
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1022 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 northwest winds
  behind it. There is a small window for strong to severe storms
  this afternoon in the vicinity of Natrona County.

- Winds will remain gusty tonight, increasing after midnight off
  the east slopes of the central and northern mountains, as well
  as southern portions of Fremont and Natrona Counties. A High
  Wind Warning is likely for these areas though Wednesday
  morning.

- Cooler and seasonal temperatures for the rest of the week and
  into the weekend with dry conditions as well.

&&

.DISCUSSION...
Issued at 1008 AM MDT Tue Sep 17 2024

An active day of weather on tap today. Showers and isolated
thunderstorms are ongoing over far western portions of the CWA this
morning, with a few thunderstorms moving northward over Sweetwater
County. These look to be forming along the cold front that is
expected to progress eastward through the day today. The overall
pattern is a bit messy this morning, with the dominant features well-
defined later this afternoon into the evening. The overall forecast
remains unchanged: the showers over the far west will spread across
eastward through the morning as the upper low moves eastward over
eastern ID, while showers and thunderstorms develop over eastern
portions of Sweetwater County and Carbon County and push northward
into Natrona and Johnson counties this afternoon. There is a brief
time frame where the storms in the latter area become strong to
severe before moving out of the CWA and into UNR and CYS areas.
Strong to severe wind gusts will be the main threat, but hail up to
1" cannot be ruled out. Some showers and thunderstorms could occur
through the day across the central basins as well.

The focus of the precipitation will shift to western portions and
eventually northwestern portions after 00Z, as the upper low moves
over MT. A moist, upslope flow will occur on the backside of the low
keeping the showers going tonight. These showers will spread
eastward through the overnight hours and continue through the day
Wednesday, before gradually ending late Wednesday night. The
gradient will remain tight tonight and Wednesday, as the low bottoms
out over eastern MT. 700mb winds will increase through the night,
with 50 kt occurring by 09Z Wednesday over southern portions of
Fremont and Natrona counties, as well as the Cody Foothills. The NAM
is depicting 700mb temperatures warming along the east slopes of the
Absaroka Mountains, indicative of a downsloping signature. Will
upgrade the High Wind Watch to a Warning as a result, but will push
the timing forward. Winds will remain strong through the rest of the
day Wednesday, with gusts of 45 to 55 mph in these areas. Wind gusts
of 25 to 40 mph will be common across the rest of the forecast area.
Otherwise, temperatures will be seasonal to slightly below
normal in the wake of the cold front.

An induced ridge will develop over he Cowboy State Thursday, as
another closed low moves over central/southern CA. This will keep
conditions dry, temperatures seasonal and winds relatively
light. This low will track over the Four Corners Friday, while a
trough tracks over Canada. Neither of these features will have
a direct impact on the forecast area, but winds over the Wind
Corridor could be slightly stronger with gusts of 25-30 mph in
the afternoon. Dry and seasonal conditions will continue through
the rest of the weekend.

&&

.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.

&&

.FIRE WEATHER...
Issued at 1008 AM MDT Tue Sep 17 2024

Gusty winds of 30 to 40 mph will occur outside of showers and
thunderstorms across all, but northwestern portions this
afternoon. Stronger gusts of 50-60 mph will be possible, as
thunderstorms develop and move over portions of zones 280, 281
and 289 for a few hours this afternoon. Winds will remain gusty
tonight into Wednesday morning, especially over zones 276, 280,
286, 288 and 289. Wind gusts will approach 60 mph in these zones
late tonight into Wednesday morning, gradually decreasing and
spreading across areas east of the Divide with gusts of 45 to 55
mph. winds will be slightly lower at 25 to 35 mph across the
rest of the forecast area. RH values will stay above critical
thresholds this afternoon and Wednesday, but the winds will
remain the bigger threat.

&&

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

&&

$$

DISCUSSION...LaVoie
AVIATION...Lowe
FIRE WEATHER...LaVoie