629
FXUS65 KRIW 121903
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
103 PM MDT Sun May 12 2024

.KEY MESSAGES...

- An unsettled weather pattern sets up thanks to weak ridging
  and northwest flow, but temperatures remain above normal
  through Tuesday.

- Shower and thunderstorm chances increase through the next
  several days. Best chances for showers and thunderstorms will
  be across areas east of the Divide Tuesday and Wednesday
  afternoons.

- Ridging redevelops for the later half of the week, decreasing
  shower and thunderstorm chances and allowing temps to rise
  back to above normal values through the weekend.

&&

.DISCUSSION...
Issued at 101 PM MDT Sun May 12 2024

A generally unsettled weather pattern begins to set up today, but we
really won`t start to see the impacts of the unsettled pattern until
tomorrow. That leaves today to be a relatively quiet day. Light
winds exist across the CWA, with the exception of the northwest
favored locations (mainly the Green River Basin and northeast Johnson
County). Even across those locations, wind gusts will still
generally remain less than 20 to 25 mph through the afternoon. Winds
will be a tad stronger tomorrow afternoon, but only by 5 to 10 mph.

As of noon, some terrain enhanced showers have developed along the
Bighorn Mountains. These will continue through the afternoon. Some
locations along the Bighorns could see up to 0.1" of rainfall out of
these showers, with less than 10% chance of seeing more than 0.25".
A few very isolated showers will also develop along the Absarokas
and Owl Creeks, but these will be few and far between and dissolve
just as quickly as they developed. Dewpoint depressions across lower
elevations are 30 to 35 degrees this afternoon, so as showers slide
off the mountains, they will quickly dry and dissolve. Hi-res
models, such as the HRRR, hint at some outflows as a result of the
dissolving showers across the Bighorn Basin and across Natrona and
Johnson Counties. If outflows do develop, they are not expected to
be more than 30 to 35 mph or to sustain themselves for any
significant distance from the dissolving storm. Shower activity will
end around sunset.

Showers and thunderstorms will become more prevalent tomorrow
afternoon, as well as Tuesday and Wednesday afternoons. Passing
shortwaves in prevailing unsettled northwest flow will enhance
instability, particularly across northern portions of the CWA. SPC
continues with only a general thunder outlook for both Monday and
Tuesday and CAPE will be weak (<500J/kg). Dewpoint depressions also
will continue to be in the 30 to 40 degree range, so getting long-
lived thunderstorms will be very difficult. Showers and weak
thunderstorms are certainly possible though. Most northern areas
have a 30 to 40% chance of rain Monday afternoon through the
evening. Another, stronger shortwave will pass through on Tuesday
and Wednesday. More showers and thunderstorms are expected, again,
mainly focused across the north, especially east of the Divide.
Details are lacking due to the inherently convective and chaotic
nature of the showers and thunderstorms. We will continue to monitor
and as we get more high-res model input over the next days, we will
be able to narrow down timing and favored locations a bit better. At
this time though, strong long-lived thunderstorms are not looking
likely.

After the passage of the shortwave Wednesday, which will cool temps
back to near seasonal normals, Thursday will see temperatures will
start to climb back above normal. Models are progging zonal flow
through the weekend, but as of the latest runs, are suggesting the
flow will be mostly dry. That is not to say that we won`t see
afternoon showers and thunderstorms through next weekend, as
confidence remains low in the pattern beyond Wednesday`s
shortwave.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1029 AM MDT Sun May 12 2024

VFR conditions expected at all TAF sites through the entirety of
the period. Light winds for most with some breezy gusts up to
18kts at PNA, BPI, and RKS after 19Z through sunset around 03Z
during peak heating. Otherwise, a few to scattered upper level
clouds with any rain shower/thunderstorm activity north and
northeast of CPR. No other weather elements are expected at
this time.

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.

&&

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

&&

$$

DISCUSSION...Hensley
AVIATION...Lowe