000
FXUS65 KRIW 032315
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
515 PM MDT Fri May 3 2024

.KEY MESSAGES...

- Snow ends this afternoon, with a clearing sky overnight.
  Patchy fog is possible (20%) for basins and near Casper due to
  recent moisture (snow).

- High pressure Saturday brings warmer temperatures and dry
  weather. Warmer Sunday.

- Gusty south wind Sunday. Gusts 30 to 50 mph for most of the
  area. Strongest winds over southern Sweetwater County, with
  high winds (gusts greater than 58mph) likely (80%). Impacts to
  I-80 and South Pass due to strong crosswinds.

- Precipitation moves in Sunday, with widespread precipitation
  Monday. Snow levels drop to around 6000 feet. Cool and
  unsettled weather pattern through next week.

&&

.DISCUSSION...
Issued at 1238 PM MDT Fri May 3 2024

Snow has been falling across the area this morning as a cold front
passes through. As the sun rises through the afternoon, any snow
that has accumulated on grass should melt quickly. Clouds linger
through the rest of the day, limiting high temperatures today. Many
places peak in the upper 40s today, with the Bighorn Basin seeing a
few places hit 50. These temperatures are roughly 10 degrees below
normal. Any remaining precipitation comes to an end by around 03Z
(9pm).

As the trough moves eastward tonight, transitory ridging builds in
for the weekend. Starting with Saturday, the day brings warm
temperatures and a mainly clear sky (a stark difference from today).
High temperatures for many reach the mid-to-upper 60s, with a few
places hitting 70. A slight breeze develops in the afternoon (10-25
mph gusts), but should otherwise be a good day for any outdoor
activities or chores.

The high pressure shifts eastward for Sunday as a potent upper-level
low swings into the northern California area. This brings a tight
pressure gradient, as well as a 100 knot jet positioned into
southern Sweetwater County. A strong south wind develops after
sunrise, and especially for the afternoon and evening across
Sweetwater County, northward into most of the CWA (exception being
far northwest Wyoming). Where the exit region of the jet is
(southern Sweetwater County), gusts up to 70 mph are possible if the
upper levels are able to fully mix down. Shift of tails highlights
this area in the 90th percentile. Elsewhere, widespread gusts 35 to
50 mph occur. Being a south wind, roads like I-80, South Pass/Red
Canyon, and US-26 will be impacted as strong crosswinds occur.

Precipitation chances move into western Wyoming Sunday morning,
spreading east of the Divide for the afternoon and evening, with
about a 20% chance of thunderstorms. Snow levels begin around 9000
feet Sunday, but drop to roughly 6000 feet through Monday morning.
Therefore, lower elevations are expected to receive mostly rain from
this system. That upper-level low moves into the Utah/Idaho/Wyoming
area Sunday night and into Monday. Winds begin to shift to a more
southwesterly direction, decreasing the gusts some from the day, but
gusty winds continue through the night, especially from Sweetwater
County up through Natrona County.

For Monday, the center of the low is projected to move across
Wyoming, then traveling northeastward near the Montana/North Dakota
border. The GFS and ECMWF vary a bit in placement on this.
Widespread precipitation occurs Monday. The heaviest precipitation
will be where favored upslope occurs. Currently, this would be for
the Bighorn Mountains and Johnson County, but as mentioned, there is
still some uncertainty in exact storm track, which could alter where
the best precipitation totals are favored. Will need to watch
closely the next few days on where models agree on the storm track.

The low is slow to move, as ridge over the eastern half of the
country keeps it mostly in place. This would keep precipitation
chances over the area Tuesday, especially over the northern
half of Wyoming. Currently, models are keeping the influence of
the low through Friday, so a cool, cloudy, and unsettled next
week is in store.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 515 PM MDT Fri May 3 2024

West of the Divide...KBPI/KJAC/KPNA/KRKS Terminals.

VFR to prevail at all terminals through 00Z/Sunday. Mid-cloud cover
gives way to a clearing sky early Friday evening as an upper low
tracks southeast of the forecast area. Mainly high clouds and a few
cumulus over the higher terrain Saturday. Gusty west to northwest
wind 15-25kts on the backside of the upper low Friday afternoon
decreases between 01Z-03Z/Saturday. Southerly wind around 10kts
increases late Saturday morning and early afternoon. Mountain tops
occasionally obscured above 10K feet MSL until 02Z/Saturday.

East of the Divide...KCOD/KCPR/KLND/KRIW/KWRL Terminals.

Mid-cloud decks gradually diminish between 00Z-02Z Friday evening,
leaving a clearing sky overnight. Boundary layer moisture is
sufficient to at least generate patchy fog at KCPR, KRIW, and
possibly KLND between 10Z-15Z/Saturday. The best chance for MVFR fog
comes at KCPR during this window, as the late clearing, lack of
wind, and abundant low-level moisture favor formation. The fog
clears between 14Z-16Z/Saturday, leaving only high clouds and a few
mountain cumulus through Saturday afternoon. Mountain tops obscured
until 02Z/Saturday.

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...
None.

&&

$$

DISCUSSION...Wittmann
AVIATION...Jones