633
FXUS65 KRIW 200412
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1012 PM MDT Thu Sep 19 2024

.KEY MESSAGES...

- Dry and seasonal today and tomorrow.

- A weak cold front moves through Friday evening, bringing a
  cool north wind shift.

- Cool to seasonal through the weekend, with isolated (20%) rain chances
  for portions of southern Wyoming.

&&

.DISCUSSION...
Issued at 1238 PM MDT Thu Sep 19 2024

A very seasonal day today. Highs are in the 60s to mid-70s across
the area this afternoon. Winds will be light, with gusts around 20
mph for the Wind Corridor (approx. South Pass through Casper). Some
low clouds have hung around portions of northwest Wyoming. Of note
is Jackson Valley, where mid-level clouds have kept the eroding
sunshine from breaking up the lower clouds. Models have been
struggling to resolve this. Would expect these lower clouds to erode
by mid-afternoon as the sun becomes stronger.

For Friday, temperatures increase a little, with highs in the 70s
for most of the area. Not expecting any precipitation. Afternoon
winds do increase, with 20 to 30 mph gusts for the Wind Corridor and
portions of northwest Wyoming. Elevated fire conditions may occur
for the Wind Corridor, but winds will be marginal, and critical RHs
may not be widespread enough to warrant any highlights. A weak cold
front pushes through in the evening. This shifts winds to the north
and northeast, with a slight breeze and cooler temperatures.

The cold front leaves Saturday cooler, with highs in the 60s. No
strong signals for precipitation chances, but an approaching low to
the south could bring an isolated (20%) shower for southern Wyoming
areas. This low also brings a tighter pressure gradient, so gusty
winds across the Wind Corridor of 20 to 35 mph. Models still track
this low southeast of the CWA, so its impacts will be minimal to
none through the weekend -cooler temperatures and isolated (20%)
rain chances for southern areas. Sunday morning looks to have the
coldest temperatures through the next week. Even so, Sunday morning
lows look to remain in the middle 30s to around 40 degrees for lower
elevation locations that have yet to hit freezing (mainly east of
the Divide locations). The HREF has less than 10% chances for 32F or
less Sunday morning.

The low exits to the east Monday, allowing another trough to dip
down into the state. There is some uncertainty with this low. The
ECMWF brings a closed upper-level low, while the GFS keeps it an
open trough as it passes through Wyoming. Continued cool
temperatures and some precipitation chances are the main result in
either case.

High pressure looks to make a return for the middle and end of next
week. This would favor warmer temperatures and less precipitation
chances. Long range models are keeping these conditions until the
start of October.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1010 PM MDT Thu Sep 19 2024

Light winds and mostly clear skies prevail overnight into Friday
morning. During the early afternoon hours on Friday, typical 15
to 25 kt breezes will develop for many TAF locations.

A cold front will push in from the north during the evening and
early overnight, causing winds to shift to northerly and become
gusty (see TAFs for more precise timing). An hour or two of 20
to 30 kt gusts are likely (60% chance) at sites east of the
Continental Divide as the front passes, then decreasing to
lighter northerly flow overnight into Saturday morning.

&&

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

&&

$$

DISCUSSION...Wittmann
AVIATION...VandenBoogart