293
FXUS65 KRIW 122056
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
256 PM MDT Fri Jul 12 2024

.KEY MESSAGES...

- Mid-summer near-record heat through Sunday. Afternoon
  temperatures in the 90s to low 100s will be common.

- Isolated showers and thunderstorms will cause brief erratic
  wind gusts in the 45 to 60 mph range.

- Distant wildfires across the western US will continue adding
  smoke to the stagnant air mass, leading to thickening smoke
  over much of Wyoming.

- The dry air mass and breezy afternoon winds will lead to
  elevated fire weather danger today and into the weekend.

- Temperatures moderate slightly but remain above average next
  week.

&&

.DISCUSSION...
Issued at 245 PM MDT Fri Jul 12 2024

The mid-summer and near-record heat will continue through this
weekend as an amplified ridge remains firmly in place over the
Northern Rockies. Several sites broke daily high temperatures
records yesterday, and this trend is likely to continue for the
next few days. A Heat Advisory is in effect east of the
Continental Divide where temperatures will be hottest.

Several distant wildfires throughout the Rockies and West Coast
have slowly been adding smoke to the atmosphere, and given the
stable and stagnant ridging pattern, smoke is likely to thicken
over the weekend.

The extreme heat is leading to low relative humidities, and
combined with the typical afternoon breezes in the 10 to 20 mph
range, there are elevated concerns for fire weather. Along with
the dry heat combined with daytime breezes, there will again be
a small chance (10 to 20% chance) for isolated showers and
thunderstorms this afternoon and evening. Not much
precipitation is expected from most of this convection, but
outflow winds will likely be strong in the immediate vicinity of
any downdrafts, with wind gusts on the order of 45 to 60 mph,
which is enough to cause isolated damage and blown objects. The
storms with appreciable precipitation will be across the far
northern counties of Wyoming where higher dew points show a
greater moisture availability. Across the western southwestern
and south central portions of the state, any lightning could be
outside of the wetting rain potion of storms, leading to some
concern for dry lightning. These same concerns are in play for
afternoons and evenings this weekend.

On Monday, a slight flattening of the ridge will lead to
moderating temperatures, however, daytime 90s will still be
common, and temperatures remain 5 degrees or so above normal,
increasing to about 10 degrees above normal for the second half
of the week. So although the near-record temperatures will
abate next week, the stagnant warm pattern is likely to continue
for the foreseeable future.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1145 AM MDT Fri Jul 12 2024

VFR conditions are at all TAF sites to start out the afternoon
under mostly clear skies, although slowly increasing smoke from
the west is starting to obscure the mountains/longer distances.
Breezy and gusty west-northwest winds are expected this
afternoon at most sites, with gusts around 20 kts. North winds
should continue in the Bighorn Basin. The best chances for late
afternoon and evening convection will be across northern WY,
primarily impacting KCOD from about 13/00-05Z. Gusty outflow
winds over 40 kts are possible at KCOD, as well as KWRL as
storms to the north push winds to the south. Feel that KCOD also
has the best shot for precipitation due to the storms, and thus
MVFR conditions could occur during the evening. Winds will
decrease around sunset generally and mid-level clouds will
linger across north-central WY into Saturday morning. Afternoon
cumulus fields should also diminish across the rest of the
forecast area overnight, though mid-level clouds will increase
from the SW to NE into western WY Saturday morning as moisture
from the Great Basin rotates into Wyoming. Breezy and gusty
winds should then occur again on Saturday with isolated showers
and thunderstorms returning to western WY and the mountain
areas as moisture in the mid-levels increases.

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

&&

.FIRE WEATHER...
Issued at 245 PM MDT Fri Jul 12 2024

Hot and mostly dry conditions this afternoon and through the
weekend will lead to elevated fire weather conditions over the
next few days. Afternoon relative humidities drop into the 10
to 15 percent range for most lower elevations through Sunday.
This combined with westerly and northwesterly sustained winds in
the 10 to 20 mph range will lead to elevated fire weather
conditions. There is a small chance (10 to 20% chance) of an
isolated shower or thunderstorm causing 45 to 60 mph brief
erratic wind gusts this evening. Across the western,
southwestern, and south central portions of the state, any
lightning could be outside of the wetting rain potion of
storms, leading to some concern for dry lightning. RH recoveries
in the terrain will again be poor (in the 25 to 40 percent
range) tonight for the midslopes due to thermal belts. This
weather pattern persists through at least Sunday, and
conditions currently don`t look to change much for next week
either.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 10 PM MDT Sunday for WYZ004>006-010-011-
017-018-020.

&&

$$

DISCUSSION...VandenBoogart
AVIATION...McDonald
FIRE WEATHER...VandenBoogart