860
FXUS65 KRIW 271734
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1134 AM MDT Thu Jun 27 2024

.KEY MESSAGES...

- Strong to severe storms today, the main threat being damaging
  wind, though large hail may also occur.

- Elevated fire weather conditions Friday through Sunday. Sunday looks
  to be the windiest and driest of those days. Hot Sunday.

- Weather system moves through late Sunday through Monday,
  bringing cooler temperatures and precipitation chances, though
  mainly across northern Wyoming.

&&

.DISCUSSION...
Issued at 119 AM MDT Thu Jun 27 2024

The main weather story for today is the scattered thunderstorm
chances, with strong to severe storms. An upper-level trough moving
eastward over the Washington/Canada border brings a cold front
through the area today. This feature brings good CAPE values (up to
1000 J/kg) as well as decent shear (pockets of 30 to 45 kt 1-6km and
20 to 30 kt 0-1km) ahead of it. The high that has been sitting south
of the state continues to rotate moisture around it, with morning
and afternoon dewpoints in the upper 40s to lower 50s. All these
factors favor strong to severe thunderstorms this afternoon across
much of the area. Generally, the main threat occurs between 11am and
8pm MDT, with the strongest storm potential in the afternoon as peak
heating takes place. The main threat is damaging outflow winds,
though large hail is also possible with stronger storms. High-
resolution models are supporting discrete cells, with supercells
possible. A tornado cannot be ruled out, with the most favored area
being southern Sweetwater County and areas east-northeast of our
CWA. Well-above average precipitable water (PWAT) values means heavy
rain can occur with any storm. Good upper level flow should keep
storms moving, though training of storms would be the main flooding
risk; models again show this threat to mainly occur south of I-80 in
Sweetwater County. The Storm Prediction Center (SPC) has all but far
western portions of the area in a slight risk (2 of 5) today, with
wind being the main threat, though also highlighting a hail threat.
Storms come to an end this evening.

Friday looks dry for most. Some lingering moisture brings isolated
(15% to 30%) shower and thunderstorm chances across southern
Sweetwater County to near Casper Mountain and across the northern
mountains. High temperatures are a bit cooler in the wake of the
front, with highs in the middle to upper 70s for most, or cooler
than average for late June. Relative humidity (RH) values drop near,
to below, 15% Friday afternoon. A tight pressure gradient brings
afternoon winds gusting 25 to 25 mph for many. As a result, elevated
fire weather conditions occur.

Dry conditions continue Saturday, with elevated fire weather
conditions continuing, though will be more marginal as winds are
expected to be less. Sunday ramps up the fire concerns, however. An
approaching system increases winds once again, with gusts over 30
mph for many locations. Very dry air brings RHs under 15% for most
of the area, with under 10% for many locations. Temperatures will
also be hot, being about 8 to 15 degrees above average. Rain chances
pick up, mainly over the northwest mountains as the system
approaches Sunday afternoon and evening.

Monday looks cooler as the associated front passes through Sunday
night. Shower and storm chances also continue through the day;
current model projections favors these chances across northern
Wyoming. Past Monday, temperatures look to be a bit above average
through the end of the workweek, with little in the way of rain
chances as a high builds over the western U.S.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1134 AM MDT Thu Jun 27 2024

Showers have begun to re-ignite over the Wind River Range and along
the ID/WY border late Thursday morning as mid-level clouds have
cleared and surface heating has increased. The overall trend will be
toward scattered showers and isolated thunderstorms across west-
central and southwest Wyoming by 21Z/Thursday, eventually
shifting to KCPR around 23Z. Gusty outflow wind around 40kts
will be the primary hazard. Additionally, westerly surface wind
of 15-30kts will be common for most terminals by 20Z. The
prevailing surface wind and scattered convection persist until
02Z-03Z/Friday. VFR and quiet conditions anticipated after that
time through the remainder of the forecast period.

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...Wittmann
AVIATION...CNJ