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000
FXUS65 KRIW 280832
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
232 AM MDT Sun Apr 28 2024

.KEY MESSAGES...

- Remaining unsettled today and Monday with a scattering of
  showers and thunderstorms.

- Windy conditions likely Monday and especially Tuesday with
  elevated fire weather possible.

- Remaining unsettled through much of the work week. Potential
  for some accumulating snow Wednesday night and Thursday
  morning.

&&

.DISCUSSION...
Issued at 227 AM MDT Sun Apr 28 2024

Steady precipitation has ended across the area as the low that was
moving across colorado as pulled into the Plains states, the trigger
for the severe weather outbreak across the central and southern
Plains states. The weather looks to remain unsettled through most of
the period, but some details are still in flux, especially further
out in the forecast period. To sum the pattern up, I will a Sesame
Street reference, as I heard the song Rubber Ducky earlier today,
sparking some memories from my young childhood many years ago
when big collars and bell bottoms were in style. It also got
the creative juices flowing. So, this forecast is brought to you
by the letters Z (Zonal flow) and U (Unsettled) and the number
4 (the number of waves that will likely impact the area through
the week).

We continue to have some showers across western Wyoming as a
shortwave moves in from Idaho and slowly crosses the state, bringing
a chance of showers and thunderstorms, anytime in the west and
mainly afternoon East of the Divide. Many places won`t see one
though in the lower elevations, the chance is generally 1 in 3 or
less at any point and less than 1 in 5 for a thunderstorm. Gusty
wind will be possible with any storm, and with low wet bulb zero
levels, small hail will also be a possibility. This could also be a
day of self-destructive sunshine, when a clear sky will lead to more
clouds through the day with the unstable atmosphere (lifted indices
fall to around minus 1). Temperatures will be warmer than yesterday,
but still averaging around 5 degrees below normal. Showers should
end around midnight as the trough moves away.

After a brief break from late tonight through Monday morning, the
next Pacific shortwave and weak cold front will swing across the
state. With the later arrival, temperatures should be warmer than
today, rising to near to slightly above normals levels. We have two
concerns for Monday. The first is for the potential of elevated fire
weather. The tightening pressure gradient ahead of the system will
increase southwest flow and tighten the pressure gradient ahead of
the front. This will lead to some gusty wind. The 700 millibar wind
does not look sufficient for high wind though (only around 40
knots), there is a greater than 1 in 2 chance of a few wind gusts
past 40 mph. Relative humidity will be rather low as well, falling
to around 20 percent. The main area of concern would be Johnson and
Natrona Counties, which did not receive the soaking rain of further
west. The second concern is convective wind gusts. There will be
some dry air ahead of the front. This will likely lead to some high
based convection. Model soundings are showing the tell tale inverted
V signature that leads to dry downbursts. With dew point depressions
approaching 50 degrees in the afternoon, there is a 1 in 2 chance of
a wind gust of around 50 mph with any thunderstorms or shower. This
could be out first "Little Green Blob" day of the season.

Tuesday looks drier as we will be in between systems with zonal
flow with somewhat cooler temperatures behind the front.
Coverage of showers should be less than 20 percent. the main
concern will again be fire weather and possibly strong to high
wind. A rather potent 120 knot jet will be crossing the area,
with the core coinciding with maximum heating and mixing. The
main of concern will be across the southern two thirds of the
state, which has the best possibility to be in the right front
quadrant of the jet, helping to enhance downward momentum. There
is greater than a 1 in 2 chance of wind gusts past 45 mph in
these areas. And with this, the air will be very dry, with dew
points falling in the single digits, pushing relative humidity
into the teens. This could, again, bring a day of elevated to
near critical fire weather.

Models continue to trend southward with the Wednesday system, bring
a better chance of precipitation to the area. There are still large
differences in placement of the eventually developing upper level
low though, so confidence in details remains low. Of particular
interest is Wednesday night, as we could have a north to northeast
upslope pattern developing that could bring some mountain snow to
areas like the Absarokas, Wind Rivers and Casper Mountain during
this timeframe. And, with low temperatures falling to around
freezing and 700 millibar temperatures falling to around minus 8,
snow levels could lower to around 4500 feet, bringing the chance of
accumulating snow to the populated areas as well. This is still
uncertain though, as it all depends on the eventual track of
the low pressure area, but we will have to watch this carefully.
Transitory ridging should bring mainly dry weather for Thursday
before another wave possibly approaches for Friday with another
chance of showers.
&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 951 PM MDT Sat Apr 27 2024

Main impacts through the TAF period comes from a passing, weak
weather system Sunday. Rain chances move from west to east starting
around the beginning of the TAF period, with precipitation chances
moving east of the Divide Sunday afternoon. Current rain chances are
generally 20% to 60% for sites. Models are showing scattered
showers, so looking to be another hit-or-miss day, similar to the
past couple days. Winds also increase, with gusts 20 to 25 knots for
some sites. Other sites see sustained wind near 10 knots, but some
gusts are possible, especially given nearby showers.

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...Hattings
AVIATION...Wittmann