842
FXUS65 KRIW 031745
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1145 AM MDT Mon Jun 3 2024

.KEY MESSAGES...

- A good rain expected for the west today, with scattered
  convection East of the Divide this afternoon and tonight.

- Breezy to windy conditions are likely at times from later
  today through Wednesday.

- The warmest weather of the year is likely later this week.
  This brings the chance of rising rivers and possible minor
  flooding.

&&

.DISCUSSION...
Issued at 259 AM MDT Mon Jun 3 2024

It looks like one more active day before quieter weather returns for
the middle of the week. Things are fairly quiet right now but radar
is showing some showers across Idaho and these will move into
western Wyoming shortly after sunrise. There is a decent amount of
moisture with this system, with precipitable water values averaging
around 125 to 150 percent of normal depending on what model you
believe. This all adds up to a decent rain event across the west.
With at least a 1 in 2 chance of a half an inch or rain or more in
our western valley locations. I do think the NBM QPF amounts in the
mountains were a bit too high though. They have been running hot the
past few systems. Think there is too much orographic enhancement in
the high resolution models. Anyway, think a widespread half to
inch of rain in the western mountains is at least a 2 out of 3
chance, but over an inch is less than 1 in 4. This will fall
around an 18 hour period, but the steadiest would be between 12
pm and 8 pm with lighter rain persisting into the night. Areas
East of the Divide will see more scattered activity, with most
holding off until later today or tonight as the trough moves
eastward and some jet energy gets involved. Things look more
showery and harder to pinpoint here though. The best chance
looks to be across the northern areas. Precipitation chances
should decrease late tonight. Wind will also be an issue. The
strongest wind will occur today in areas favored by southwest
flow, like Casper. The strongest wind then shifts to the areas
favored by northwest flow tonight as the low pressure area moves
to the east. This means places like Johnson County. The 700
millibar winds do not look sufficient for high wind, but gusts
over 40 mph are greater than a 3 out of 4 possibility. The
strongest wind may end up bring tonight with the additional
downward forcing of the right front quadrant of the jet.

Any showers will end early on Tuesday as ridging builds into the
area. Concerns shift to wind on Tuesday and even Wednesday as we
will have a good height gradient between the low pressure over
Saskatchewan and Manitoba and the building ridge of the desert
southwest. Again, high wind is not expected, but it will be windy at
times, especially in the favored locations. This could lead to
elevated fire weather at times. However, most fuels are still in
green up and this should mitigate the danger somewhat.

Gusty wind could linger into Wednesday as well. Ridging should then
build over the area and shut off the wind machine for Thursday. And
this brings in the next threat, possible flooding. Temperatures stay
mild for Tuesday but will rise to above normal levels starting
Wednesday and continuing into next weekend. Friday and Saturday look
to be the warmest days with some of the warmer locations, like
Worland or Greybull, possibly seeing the first 90 degree highs of
the year. This will lead to high elevation snow melt and possible
rising rivers and minor flooding. Areas West of the Divide look to
most likely at this time as there is more snowpack there. Areas East
of the Divide have less and we have more room in the rivers. Rapid
snow melt could overcome this though. Stay tuned.

Some mid level moisture may return for Friday along with a couple of
shortwaves that could bring the chance of high based convection for
the end of the week. There is still a spread in timing of the waves
though, so details are still difficult to hash out at this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1145 AM MDT Mon Jun 3 2024

A shortwave trough is moving from the Pacific Northwest toward
the northern Rockies today, increasing moisture from the WSW
into western Wyoming. Light rain continues across much of
western WY this afternoon, with periods of moderate rain
possible, especially on the west slopes of the mountains.
General VFR conditions will become MVFR at KJAC/KBPI/KPNA from
about 03/20Z to 04/02Z due to the precipitation and lowered
ceilings and visibilities. KCOD/KLND/KRKS also have a chance of
showers at varied periods this afternoon and evening, though
chances are less than the western WY sites. The mountains across
western WY will be obscured through 04/12Z as the trough moves
eastward into the northern plains. Winds will be 15-20 kts at
all TAF sites today, with gusts 25-35 kts. They will somewhat
decrease after sunset, but some sites will see breezy and gusty
winds through the night. Behind the trough passage Tuesday
morning, WNW surface winds will again increase and be gusty from
04/15Z into the afternoon as isolated showers are only expected
over far northern WY.

Models are showing some indications of mountain wave activity
along the east slopes of the Wind Rivers and Absarokas from
04/00Z to 04/15Z. This pattern could create increased winds over
the foothills but at elevations of 3-8K feet above the ground.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on smoke, icing, and turbulence forecasts.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...None.

&&

$$

DISCUSSION...Hattings
AVIATION...McDonald