Area Forecast Discussion
Issued by NWS Riverton, WY

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000
FXUS65 KRIW 281726
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1126 AM MDT Thu Mar 28 2024

.KEY MESSAGES...

- Moderate snow expected for the western mountains today.

- Strong wind likely this afternoon from Muddy Gap through
  Casper and possibly around Lander.

- Cool and unsettled weather is expected for Easter weekend.
  Confidence in placement and timing of the heaviest
  precipitation remains low.

&&

.DISCUSSION...
Issued at 227 AM MDT Thu Mar 28 2024

Well, I hope you enjoyed the day of reasonably quiet weather
yesterday because we will be entering a period of rather
unsettled and active weather into the Easter weekend. Radar
shows things are fairly quiet as I write this, but moisture is
gathering to the west and will begin moving into western Wyoming
before sunrise. All in all, things look fairly similar to the
thinking yesterday at this time. The heaviest snow is expected
to fall between 9 am to 3 pm today as the trough axis swings
through the area and snowfall rates are enhanced by a 90 knot
jet streak moving into the area. The steady snow may end before
11 pm, but we will leave highlights alone as we can just cancel
them early if needed. There remains a greater than 3 in 4
chance of exceedance of 6 inches of snow in the mountains.
Chance of advisory amounts in the western valleys are low
though, generally less than 1 in 10. There will be some snow
here, but most accumulation would be on non paved surfaces due
to the warm ground and high sun angle. Highlights will be
maintained as is.

Meanwhile, the main story east of the Divide will be wind. This
will be especially the case in areas favored by southwest flow,
meaning the Green Mountain/Rattlesnake Range, Natrona County
and possibly Lander. The reasoning here remains the same as
well, with 700 millibar winds topping out at around 40 knots.
This is generally not sufficient for widespread high wind. We
could see an isolated gust to around 60 mph in a place like
Wyoming Boulevard on the south side of Casper though. We will
issue a Special Weather Statement to account for this. Wind
should decrease tonight after the cold front passage and a
decoupling of the wind as the mixing decreases after sunset. As
for precipitation east of the Divide, there will be a few
showers scattered around late today and this evening, but
nothing substantial. A few inches of snow may fall in the
Bighorns, but nothing highlight worthy. In addition, there is
the potential for snow in Sweetwater County late today and this
evening. Temperatures are borderline though, so it could end up
being rain. This area is known for snow squalls though and
there could be one late today with the frontal passage.

There will be a lull in precipitation with weak ridging over the
area on Friday. A few showers will be around, mainly in the
north with a weak shortwave riding over the top of the ridge and
the extreme south with some jet energy. Any amounts would be
light.

Unfortunately, we have the same situation with confidence of
the period from Friday night into Easter Sunday. We still have a
good amount of moisture moving into the area, moving in from
the southwest courtesy of an upper level low moving onshore in
southern California. There is a bit more agreement in showing
that, especially Saturday night and Sunday, look rather damp
with precipitation through the area. However, there is still a
wide range of solutions in regards to the placement of the
heaviest precipitation and timing of the individual shortwaves.
And since flow will be southwest and the air will be from the
Pacific, temperatures are also on the borderline for rain vs
snow. On Saturday night, 700 millibar temperatures range from
minus 7C in the north to minus 3C in the north, which would put
snow levels from roughly 5000 feet in the north to 7000 feet in
the south. During the day Sunday, the temperatures rise a bit,
which could lead to mainly rain, especially if precipitation
rates are light. Accumulations during the day Sunday would
likely be restricted to non paved surfaces, with the borderline
temperatures and almost April sun angle. The main travel
concerns would be at night. In addition, we also have around a
12 to 18 hour difference in end time of the precipitation, from
before sunrise Monday to Monday night. So, we continue to have
high confidence in unsettled weather into the weekend. However,
the details, especially in placement of the heaviest
precipitation, remains in flux. Drier weather should then return
Tuesday into Wednesday as ridging folds over the area.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1125 AM MDT Thu Mar 28 2024

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

The current weather system is continuing snow over the western
WY mountains this afternoon, obscuring the higher terrain
through at least 29/06Z. Moderate snow will continue at KJAC
through about 28/21Z with IFR ceilings/vsby before slowly
improving to MVFR by sunset. Snow showers are already impacting
KBPI/KPNA as well, and models are showing a 3-4 hours period
from about 28/21Z-29/01Z of IFR conditions under moderate snow.
KRKS should also have MVFR/IFR conditions during the same time
frame with a slight chance of thundersnow as well. All sites are
seeing breezy wind of 10-15 kts with gusts around 25 kts. These
will decrease after about 29/03Z as the wave moves eastward.
With winds decreasing overnight, can`t rule out lingering low
clouds through Friday morning and localized fog. Thus, MVFR
conditions are possible at these sites overnight, but if not,
VFR will prevail. Light mountain showers are expected to return
Friday afternoon, with little impact at the TAF sites, and winds
will not be nearly as strong Friday.

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

As the current weather system pushes into western WY and brings
snow along and west of the divide, east of the divide is seeing
increased winds, with KCPR/KLND already observing gusts 30-35
kts. The other sites are expected to have these wind gusts
later in the afternoon. Each site will have a slight chance of
showers late in the afternoon/early in the evening as the axis
of the wave moves eastward. Winds will continue to be moderate
to strong as well as see a wind shift to the northwest. VFR
should dominate though brief MVFR conditions are possible. The
higher terrain will be obscured through 29/06Z. Breezy winds of
10-15 kts are likely overnight at some sites. Winds are expected
to shift to the NNE at KCOD/KWRL between 29/06-09Z as a weak
cool front pushes south and brings low clouds. Friday should be
less windy with VFR conditions generally. KCOD will have a
20-30 percent chance of showers Friday afternoon.

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 until 11 PM MDT this evening for
WYZ001-012-014-015-024.

&&

$$

DISCUSSION...Hattings
AVIATION...McDonald


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