856
FXUS65 KRIW 221930
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
130 PM MDT Sat Jun 22 2024

.KEY MESSAGES...

- A very warm and dry west-southwest pattern expected from this
  afternoon through Tuesday. Temperatures will climb to the 80s
  and 90s Sunday through Tuesday in the lower elevations, with
  possibly 100 in the lower-elevations of the Bighorn Basin.

- Isolated showers and thunderstorms are expected across far
  southern and far northern WY this afternoon. Sunday will also
  see isolated showers and thunderstorms over the same areas,
  plus the northern Wind Rivers into the SW Bighorn Basin.

- Hot, dry, breezy, and gusty conditions will create elevated
  fire weather conditions over the next few days.

- Moisture returns to western and central WY Wednesday and
  Thursday for increased chances of scattered showers and
  thunderstorms. Thursday afternoon could see some strong storms
  over central WY.

&&

.DISCUSSION...
Issued at 1230 PM MDT Sat Jun 22 2024

Yesterday`s storm system has moved off into the northern plains,
leaving a fairly dry and stable air mass over western and
central WY with moderate zonal flow in the mid-levels. Isolated
thunderstorms have already initiated over the northern slopes
of the Uintas late in the morning though as increased moisture
remains over the central Rockies along with increasing
instability to the south. This afternoon could also see some
very isolated showers and storms over the WY/MT border as
lingering moisture and instability over MT interacts with the
west flow over the terrain. Across the middle of the state will
be very warm and dry as west flow dries out the boundary layer
through the afternoon and humidities drop to the 20s and teens
in the lower elevations and along the east slopes of the
mountains. Some areas are already seeing winds of 10-15 mph with
gusts 20-30 mph, and breezy gusty winds should increase in
coverage through the afternoon as temperatures climb to the 80s
across the lower-elevations.

Sunday will see the somewhat flattened ridge axis align north-
south over WY in the morning and move eastward during the
afternoon and evening. West-southwest winds should increase
Sunday compared to Saturday as temperatures climb 4-8 degrees to
the mid 80s to upper 90s. The lower elevations of the Bighorn
Basin around Basin and Greybull have a decent shot of seeing 100
degrees - which is 12-15 degrees above normal. Once again,
isolated showers and thunderstorms are possible over far
southern WY as well as far northern WY. A few high-res models
are indicating some storm development over the northern Wind
Rivers and southern Absarokas, which then move into the SW
Bighorn Basin. The hot and dry conditions Sunday will create
elevated to near critical fire weather conditions, but fuels are
still deemed non- critical. Caution should still be used with
fires given the dryness in most areas of western and northwest
WY.

The same pattern continues on Monday, with similar temperatures
and winds, though a weak shortwave trough should move from
northern Utah through far southern WY to bring showers and
thunderstorms to southwest and southern WY through the day.
Temperatures remain well above normal, but should cool by 2-3
degrees over Sunday for most of the area. Amazingly, the same
pattern continues on Tuesday with isolated showers and
thunderstorms across southern WY during the afternoon and
increased clouds along the WY/MT border. Hot and dry will
persist through the center sections of the state. As a trough
digs along the west coast of the US on Wednesday, the flow
pattern becomes more southwesterly on Wednesday, advecting
moisture from the Great Basin and Four Corners areas over
Wyoming. While temperatures remain very warm, cloud cover will
make a difference and help temperatures decrease a few degrees.
Initial indications are for the best chances of storminess over
southwest and southern WY, as well as the northwest mountains. A
shortwave trough is then expected to move from WA to MT on
Thursday, with a mid-level front interacting with moisture from
the south. The result should be more widespread showers and
thunderstorms Thursday afternoon, with another shot at severe
storms, much like Friday June 21. Cooler air moves in late
Thursday into Friday to bring temperatures back to normal, or
even below, especially east of the divide as northerly flow
drops down. Western WY on Friday should again be dry and windy.
Next Saturday then appears to be mostly clear with no
precipitation and light winds as high pressure starts to build
again over the Great Basin.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1114 AM MDT Sat Jun 22 2024

VFR conditions will prevail through the TAF period. A light west to
northwest breeze will develop at most terminals this afternoon, with
gusts around 20 to 25kts. Have left the wind at KCOD as a TEMPO for
now, as there is low confidence in enough mixing to develop a
northwesterly wind there before the nocturnal northerly flow sets
back in, so gusty winds there this afternoon will be brief if the
occur at all (40% chance). Skies will remain mostly clear with
possibly a few fair weather cumulus developing this afternoon across
the region. This evening, winds will decrease to mostly light and
variable after 03Z and skies will remain mostly clear through the
night. A few terminals (KRKS and KCPR) should see west-
southwest winds start to increase again late in the period (70%
chance).

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

&&

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

&&

$$

DISCUSSION...McDonald
AVIATION...Hensley