638
FXUS65 KRIW 091742
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1142 AM MDT Thu May 9 2024

.KEY MESSAGES...

- Rain chances today and tomorrow (20% to 60%), mainly east of
  the Continental Divide and over Sweetwater County. Some
  thunder is possible.

- Warmer this weekend, with less rain chances.

&&

.DISCUSSION...
Issued at 1111 AM MDT Thu May 9 2024

That low pressure system that has brought gusty winds, rain, snow,
and cloudy days has finally weakened and is moving eastward today.
As its influence weakens over Wyoming, precipitation chances will be
on the downward trend. Today, some lingering showers from overnight
and this morning continue to move through the area. Showers are also
favored to develop this afternoon in northeast flow. Rain chances of
20% to 60% occur through the day east of the Continental Divide. For
west locations, chances (30% to 50%) will generally be confined to
the higher terrain, with a few showers moving off the mountains to
the nearby lower elevations. A rumble of thunder is possible today.

A Winter Storm Warning continues for the eastern Wind River
Mountains through this evening as favored flow continues. Snow rates
should decrease through the afternoon. Snow showers this afternoon
may bring localized moderate snow rates, while other locations
receive lesser amounts. A couple inches are possible late this
evening into the early overnight hours, but the main impacts should
be ending through this afternoon.

A cutoff low develops to our southwest (Utah area) today as well.
This should keep the northeast-to-east flow going tonight and into
tomorrow. The main impacts of this low remain to our south, but some
moisture continues rain chances (15%-30%) overnight for east of the
Divide locations, mainly for the mountains, and near Lander and
Casper where favored upslope occurs. Fog is also possible (30%)
overnight into Friday morning, especially for locations with recent
rainfall, such as the Wind River Basin and Johnson/Natrona Counties.

Rain chances will be less during the day Friday, generally 15% to
25% chances, mainly across Fremont, Natrona, and Sweetwater
Counties. A rumble of thunder is also possible with these shower
chances Friday afternoon. After sunset Friday, rain chances quickly
drop off across the area, with less than 10% chances across the
entire area.

Ridging sets up for this weekend. Peak heating during the day
Saturday, in combination with the cut off low moving eastward, could
bring some afternoon showers/thunderstorms for the southern half of
the area, mainly Sweetwater County. These decrease after sunset.
Temperatures Saturday peak near, to a little above, normal. Highs in
the 60s to low 70s are expected. Sunday is similar, with slightly
warmer temperatures and afternoon showers possible.

A slightly bigger weather system is projected by models for Monday
into Tuesday. Overall, it does not appear very impactful at this
time, but could bring some gusty winds and rain chances. Uncertainty
towards the end of next week, with some models showing a stronger
ridge building in.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1111 AM MDT Thu May 9 2024

The large upper level circulation continues to bring a series of weak
shortwaves to the region. These will promote northeast flow,
scattered showers, and widespread mountain obscurations through the
period. KJAC is the only terminal to see VFR conditions and mostly
clear skies prevail through the period. MVFR conditions to
occasional IFR conditions are possible at all other terminals. Other
west of the Divide terminals, particularly KBPI and KPNA will see
the lowest chance for MVFR, and thus are expected to remain VFR
through the period, with BKN cigs hovering around FL035. KRKS has a
30% chance of seeing MVFR conditions linger through the first hour
or so of the period, then prevail VFR through the rest of the
period. Low clouds will prevail through much of the period east of
the Divide, with lowest cigs at KCPR and KLND. Other east of the
Divide terminals (KCOD, KRIW, and KWRL) will see occasional VFR,
especially at KCOD and KWRL overnight, but otherwise will also
generally see prevailing MVFR conditions. TEMPO and PROB30 groups
have been included to highlight most likely periods of prevailing
-RA and/or IFR conditions.

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...
Winter Storm Warning until 6 PM MDT this evening for WYZ015.

&&

$$

DISCUSSION...Wittmann
AVIATION...Hensley