254
FXUS65 KRIW 091108
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
508 AM MDT Sun Jun 9 2024

.KEY MESSAGES...

- Showers and thunderstorms will move over western portions by
  midday, becoming widespread through the afternoon. Stronger
  thunderstorms could produce strong to severe wind gusts and
  large hail.

- Isolated to scattered (20-30%) thunderstorms will remain
  possible across the CWA Monday, but are not expected to be as
  strong.

- Dry conditions return Tuesday with temperatures remaining
  above normal. Widespread showers and thunderstorms could
  return by Friday.

&&

.DISCUSSION...
Issued at 214 AM MDT Sun Jun 9 2024

An upper level ridge will shift eastward over western portions of
the CWA this morning. A shortwave trough is also already moving
onshore over OR/CA this morning. These features will allow an area
of subtropical moisture, currently over the Great Basin and marked
by showers as of 130 am, to reach western portions by 18Z.
Precipitable water (PW) values will increase across the CWA today,
ranging between 0.6 and 1.0 inches, with the lower end of these
values staying over southern portions. This is still within the 90th
percentile (0.66"), with 0.9" as the daily max for June 9th. Gulf
moisture (from the Gulf of Mexico) will also add to this moist
environment, advecting into eastern portions through the afternoon.
This will culminate in dewpoints in the low to mid 50s for most
areas east of the Divide, CAPE values of 1000 to 1500 J/kg and LI`s
of minus 4 to minus 6 across much of the CWA. SPC has kept the
northern half of the Cowboy State under a Marginal Risk for severe
thunderstorms today. Strong to severe wind gusts and large hail will
be the main threats from the stronger thunderstorms, with locally
heavy rain being a threat as well due to the abnormally high PWs.
Thunderstorms will continue through the evening becoming more
isolated after midnight, with showers remaining possible through the
night along and north of an Afton-Riverton-Kaycee line as the trough
begins to move over western WY Monday morning.

Temperatures west of the Divide will be about 5 degrees cooler
Monday. with isolated to scattered thunderstorms remaining possible
across much of the CWA. Strong to severe storms are not expected, as
the trough keep the most unstable elements over eastern portions of
the state. Gusty west-northwest winds will be widespread across the
forecast area, due to the resulting pressure gradient from the
passing trough.

Dry conditions will return Tuesday, as a transitory ridge moves over
the region. A more zonal flow pattern will be in place Wednesday,
before a ridge, from a strong high center over AZ/NM, rebuilds over
the Northern Rockies Thursday into Friday. Showers and thunderstorms
could return to the area Friday, as an upper level low from the
Desert Southwest surges northward.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 507 AM MDT Sun Jun 9 2024

A difficult forecast for precision. Scattered showers and
thunderstorms develop this afternoon in response to a passing
shortwave. Each high-resolution model has varying timings and
locations of thunderstorms, making it difficult to know if a
terminal will be impacted or not; have gone with PROB30 groups
for the afternoon. These storms bring variable and gusty winds,
possibly up to around 50 knots for the strongest outflows.
Heavy downpours are also possible, meaning short duration drops
in categories if a storm directly passes over a terminal. Hail
is also possible, more favored towards KCPR.

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

&&

.HYDROLOGY...
Issued at 214 AM MDT Sun Jun 9 2024

Rivers and creeks will remain on the high side today at Action Stage
or below, but look to remain steady for now. SnoTel sites above 9000
ft remain below 10 inches of SWE and continue to drop. At this rate,
the remaining snow at these sites could be gone in the next couple
of days. The notable exception is sites in the Tetons and portions
of Yellowstone NP, where 20-30 inches remain on the ground.

&&

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

&&

$$

DISCUSSION...LaVoie
AVIATION...Wittmann
HYDROLOGY...LaVoie