445
FXUS65 KRIW 011715
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1115 AM MDT Sat Jun 1 2024

.KEY MESSAGES...

- Isolated thunderstorms return to southern and western areas
  this afternoon and evening.

- Monday and Monday night will be the most active day, with the
  best chance of showers and storms along with strong wind.

- The warmest weather of the year moves in later next week,
  especially on Friday when the first 90 degree highs may occur.

&&

.DISCUSSION...
Issued at 256 AM MDT Sat Jun 1 2024

I would like to welcome you to June today. And, welcome you to the
start of meteorological summer, which runs through August. And we
are only 19 days from the start of astronomical summer, which begins
on the June 20th, which is when the summer solstice occurs. And for
the next week, we will have things that are found in a Wyoming
summer, rather warm temperatures and a scattering of thunderstorms.

The day will start dry today, although there could be some
virga over southern Wyoming this morning. A few showers and
storms will likely return to the area today, mainly over the
western and southern half of the state this afternoon as a
subtle shortwave moves through and a bit of mid level moisture
creeps into the area. The chance of an afternoon or evening
storm is small though, with a 1 out of 4 chance at the most. The
main and probably only threat from any storm or shower would be
strong wind gusts, given the inverted V sounding across the
area. This could end up being a "Little Green Blob" day, with
innocent looking showers producing strong wind gusts.
Temperatures should be comfortably warm, averaging near to about
5 degrees above normal.

A second shortwave then approaches for Sunday. With this one,
the best forcing looks to be across northern Wyoming so the best
chance of showers will be found here. Again, not a ton of
moisture to work with, so coverage will be small again,
generally around a 1 out of 3 chance in the mountains and 1 out
of 5 in the lower elevations. And again, strong wind gusts will
be the main threat with any shower or storm. This looks to be an
earlier show though, with most convection out of the area by
around 6 pm.

The third and final wave will approach for Monday. This waves looks
somewhat more potent, as it has a bit more moisture to work with and
also better upper level support as an 120 knot jet will be
associated with it. Chances for stronger storms look limited at this
time though. There will be decent cloud cover across the area,
limiting instability. The timing of the system is not ideal either
for strong convection. The best upper level forcing also waits until
nighttime to move through the area. With this though, we have kept
the chance of thunder in the forecast through the night on Monday
night. The main concern could end up being strong wind. This will be
in the usual areas, mainly ahead of the system in the southwest flow
areas like Casper and Rock Springs on Monday and Monday evening, and
then switching to areas favored by northwest flow later Monday night
and Tuesday like Greybull and Buffalo. The 700 millibar winds don`t
look sufficient for high winds, but there is a 3 in 4 chance of wind
gusts past 40 mph. As for fire weather concerns, humidity does not
look that low, and green up should keep things from being too bad.

Any lingering showers should end Tuesday morning. Following that,
ridging should build in from the south and bring the warmest weather
so far this year. Temperatures will rise on Wednesday and Thursday
but the warmest day will be Friday when some of the warmer locations
could see their first 90 degree highs of the year. The next chance
of convection may move in for Friday, with some moisture and a spoke
of energy in the form of a shortwave moves toward the area. Details
on placement of the convection is obviously uncertain this far out.
So, it looks like summer will arrive to the Cowboy State over the
next several days.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1112 AM MDT Sat Jun 1 2024

Prevailing VFR conditions through the TAF period. Isolated showers
and thunderstorms will be around this afternoon and early evening.
The best chances (30% to 50%) occur at KLND and KRKS. Lesser chances
(15% or less) occur at most other sites though. Given the lower
chances, other sites do not have rain chance mentioned in TAFs. KCPR
would be the most likely, with about 15% to 20% chances between
roughly 23Z/Sat and 03Z/Sun. High-resolution models are very
inconsistent with rain placement, so confidence is low at this time.
These showers, especially in the vicinity of KCPR and KRKS (but
could occur at most sites this afternoon) could bring strong
outflows, the highest potential gusts being 40 to 50 mph. These
winds will be the biggest threat through this evening.

Some low rain chances (15% to 30%) move into western Wyoming between
06Z/Sun and 12Z/Sun, with KJAC being the potential impacted terminal
there.

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