368
FXUS65 KRIW 051826
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1226 PM MDT Sun May 5 2024

.KEY MESSAGES...

- Showers develop across western WY this morning and gradually spread
  east as a cold front moves through the state this
  afternoon/evening.

- High elevation snow will be possible after the frontal passage with
  chances for light snow in western valleys.

- Winds will be gusty late this morning through the evening with many
  seeing gusts of 30+ mph. Parts of Sweetwater, Fremont, and
  Natrona Counties likely see gusts exceeding 55 mph.

- The first half of the week looks to be unsettled with chance
  for precipitation, breezy winds, and below normal
  temperatures.

&&

.DISCUSSION...
Issued at 332 AM MDT Sun May 5 2024

Saturday saw pleasant and sunny weather across the Cowboy State.
Unfortunately change is around the corner, as a potent upper-level
Pacific low is currently making its way across the Great Basin this
morning. This low will bring gusty winds, chances for precipitation
and cooler temperatures over the next couple of days. Temperatures
do make a brief rebound ahead of the FROPA today, with highs west of
the Divide in the 50s/60s and highs east of the Divide reaching the
70s.

Today will be the start of an unsettled weather pattern, with the
main culprit behind this pattern change being a deep Pacific low.
The low continues to near the state during the morning and impacts
look to begin to ramp up around the same time. There are two parts
of this upcoming system. The first will be winds which are going to
be the main concern, as a strong 100+ knot jet sets up over the
region by the afternoon. Southerly winds begin to increase shortly
after sunrise, with the first impacts seen across the southern CWA
before gradually spreading north through the early afternoon. Gusts
of 30+ mph will be widespread with a (70-90%) chance across most of
CWA during the afternoon and evening. Stronger gusts of 50+ mph are
likely (50-80%) in parts of Sweetwater, Fremont, and Natrona
Counties. Models continue to indicate these strong wind gusts and
due to that, the High Wind Watches have been upgraded to High Wind
Warnings. Winds have slightly decrease for the Lander Foothills and
much of Natrona County. So, the High Wind Watches for these areas
have been cancelled. Winds look to decrease Sunday night and then
once again increase after sunrise Monday. For this reason these
Warnings will be in effect from Sunday afternoon through Monday
evening. Some areas of concern will be along the I-80 corridor and
South Pass. Gusts in these areas likely exceed 60+ mph on Sunday and
Monday which may make travel difficult, especially for high profile
vehicles.

West of the Divide...

Precipitation arrives this morning across western WY and will
gradually spread eastward throughout the day. Showers will be
periodic with steady precipitation not arriving over this area until
Monday morning. Temperatures on Sunday look to be too warm to
support snow even at high elevations, with snow levels during the
day exceeding 10,000 feet. However, snow levels look to quickly drop
this afternoon/evening as a cold front sweeps across the state.
After the front pushes through the heaviest snowfall is expected to
fall over western mountains with snowfall rates nearing 1 inch per
hour. Snow is expected to continue across western ranges through
Monday into Tuesday evening. Snow accumulation will mainly be
limited to the higher elevations with totals ranging from 6 inches
to over 2 feet. A Winter Storm Warning has been issued for the high
elevations of the Tetons and Gros Ventre ranges as they look to see
1 to 2 feet of snow. Winter Weather Advisories have been issued for
the remaining western ranges including the Wind Rivers as they will
likely see snow totals of 6 to 12 inches. Lower elevation valleys in
western WY will likely have a period of snowfall starting early
Monday morning. Periodic snow showers look to fall through Tuesday
evening, with snow totals ranging from 2-4 inches in parts of
Jackson Hole and Star Valley. One thing to keep in mind is that the
snow will likely have difficulty accumulating on surfaces due to the
strong Sun angle. There is a good chance that some of the snow in
lower elevations will melt in between showers, leading to lower
amounts.

East of the Divide...

Most of the CWA east of the Divide looks to remain dry for much of
today. The best chance for precipitation comes with the nearing
FROPA during the late afternoon and evening. Central portions of the
CWA such as most of Fremont, Natrona and the Bighorn Basin will see
little QPF as a result of the FROPA. Monday will be a slightly
different story, as the low begins to shift northward due to a
persist area of ridging over the central CONUS. As the low tracks
north winds will shift to the NW, leading to enhanced upsloping for
portions of the eastern Bighorn Basin. Natrona and Johnson Counties
will also have a good chance seeing some showers during this time
with a (40-70%) of seeing at least 0.20 inches of QPF by Monday
night. Daily showers will be possible over the Bighorn Basin and the
eastern portion of the CWA through midweek as the low wobbles around
Montana.

Remainder of the week...

Uncertainty remains in regards to the impacts the low will have on
the CWA as it moves over Montana during the first half of the week.
The best chances of precipitation do look to remain across western
and northern Wyoming, as flow and proximity to the low will be the
most favorable. Overall, most of the state will continue to see
breezy winds, below normal temperatures, and chances for
precipitation through at least the first half of the upcoming
week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1225 PM MDT Sun May 5 2024

Scattered showers and thunderstorms will continue across western and
southern Wyoming through this evening, at times impacting KJAC,
KBPI, KPNA, and KRKS. This activity will also spill east of the
Divide this afternoon, though most terminals here will not see
impacts until around or after sunset. Precipitation chances will
then become fairly widespread through Monday morning as a low
pressure system passes over Wyoming. Confidence is low on specific
timing of impacts; MVFR to brief IFR conditions can be expected with
any precipitation impacting terminals. Otherwise, this system will
also bring strong wind to central and southern terminals this
afternoon, decreasing this evening. Wind will increase again by 12Z
Monday. Frequent mountain obscurations are expected across western
Wyoming through the period.

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 Weather Advisory from 11 PM this evening to 6 PM MDT
Tuesday for WYZ001.

Winter Storm Watch from Monday morning through Tuesday morning
for WYZ008-009.

Winter Storm Warning from 6 PM this evening to 11 PM MDT
Tuesday for WYZ012.

Winter Weather Advisory from 6 PM this evening to 6 PM MDT
Monday for WYZ014-015.

High Wind Warning until 9 PM MDT Monday for WYZ019-028>030.

High Wind Watch from Monday morning through Monday evening for
WYZ020.

Winter Weather Advisory from 11 PM this evening to 6 PM MDT
Monday for WYZ024.

&&

$$

DISCUSSION...Dziewaltowski
AVIATION...Myers