760
FXUS65 KRIW 270721
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
121 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 /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1045 PM MDT Wed Jun 26 2024

Isolated rain showers and thunderstorms continue through the
overnight hours. Convective activity will end early Thursday morning
with clear skies paving the way for more convection Thursday
afternoon. A low pressure system will slide southeast into Wyoming
Thursday afternoon, which will lead to the development of scattered
rain showers and thunderstorms. Some of the thunderstorms will be
strong. As it stands right now KRKS has the best chance of
prevailing TSRA Thursday afternoon, but not a high enough chance to
add it to this issuance of the TAFs. There`s a slight chance (20-
30%) of thunderstorms at all terminals Thursday afternoon. Wind will
increase Thursday morning and continue into the afternoon. Wind
gusts of 20-30 knots will be prevalent across the area. Higher gusts
are likely (70%) with thunderstorm downdrafts/outflows. There will
be prevailing VFR conditions, with temporary drops to MVFR/IFR if a
thunderstorm moves directly over the terminal.

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...Wittmann
AVIATION...Rowe