595
FXUS65 KRIW 120431
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1031 PM MDT Tue Jun 11 2024

.KEY MESSAGES...

- Dry, breezy, and very warm conditions are expected through
  Thursday. Elevated fire weather conditions will occur as a
  result for the basins and valleys and into the foothills.

- The above normal temperatures are continuing mountain snowmelt
  and keeping river and stream levels elevated for the next few
  days. Water levels should decrease toward the end of the week.

- Isolated thunderstorms are possible this afternoon across far
  northern Wyoming, with isolated showers and thunderstorms
  across northern WY and far southern WY Wednesday afternoon and
  early evening. Isolated showers and thunderstorms are expected
  over some mountain areas Thursday, with higher chances on
  Friday.

&&

.DISCUSSION...
Issued at 1230 PM MDT Tue Jun 11 2024

Weak ridging over the Great Basin with zonal flow over the
northern Rockies has brought mostly clear skies to western and
central Wyoming today, along with above normal temperatures in
the 70s and 80s. This pattern will also continue breezy and
gusty WSW winds for much of the area this afternoon and early
evening before decreasing around sunset. Models are showing a
low chance (10-15%) of showers and thunderstorms over the
northern portions of Yellowstone and the Absarokas as well as
the Bighorn mountains late this afternoon as a weak shortwave
trough moves eastward through Montana. Drier mid-level flow then
pushes eastward in the zonal flow on Wednesday. WSW winds should
be a bit stronger tomorrow with some areas gusting 25-40 mph
during the afternoon. Lingering moisture around NW WY could
develop some showers and thunderstorms (15-20%) during the
afternoon. A weak trough moving from northern UT into northern
Colorado should also bring a slight chance of showers and
thunderstorms (15-25%) to southern Sweetwater County
(developing off the Uintas). Outflow wind gusts from the storms
could reach 50 mph. Afternoon max temperatures should be
increase a couple of degrees Wednesday to range from around 80
to the low 90s.

A similar pattern continues on Thursday though winds will not be
as strong as the previous day. Models are showing a very weak
boundary moving north-south during the afternoon into central
WY. Around this boundary from west-central WY toward Casper,
there may be a few showers and thunderstorms during the late
afternoon and evening. Better chances are around southern
Natrona County. With the large-scale high over SE CO, some
moisture is finally brought northward from eastern UT to keep a
slight chance of showers across southern and central WY through
the night into Friday morning. Models are indicating a shortwave
trough moving from the PacNW into Montana on Friday as well. The
resulting pattern is likely to bring modest chance of the
showers and thunderstorms (40-60%) to both the northwest and
southern into central parts of the state. Temperatures should
drop a few degrees on Friday with the increased cloud cover and
precipitation.

Saturday looks to be a little cooler but still above normal,
along with breezy to windy west winds in the post-storm
environment. A few showers are possible over northern WY during
the late afternoon and evening. Indications at this time are for
a much colder system to move into the PacNW on Sunday, which
will bring 700-mb temps below 10C to the forecast area. Sunday
and Monday should then be near normal for temperatures. The
strong system then moves westward on Tuesday, warming
temperatures and increasing the south-southwest wind. There are
some timing issues with model forecasts with the ECMWF being
18-24 hours faster than the GFS. However, it appears that this
system will bring a cold front to western WY and some showers
and thunderstorms to the northern half of the forecast area.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1028 PM MDT Tue Jun 11 2024

Winds have decreased this evening at all sites, and should stay
L/V through sunrise Wednesday. Winds will again ramp up tomorrow
morning, with all sites noting wind gusts of 25 to 35kts in the
afternoon. Winds will again decrease between 01Z and 03Z/13.
Cigs and vis remain VFR through the next 24 hours, but note some
light smoke starting to drift in from the east may slightly
obscure approach angles late afternoon.

&&

.FIRE WEATHER...
Issued at 1240 PM MDT Tue Jun 11 2024

West to southwest winds with gusts of 25-30 mph and RH values
in the teens will result in elevated to near- critical fire
weather conditions today and Wednesday. High temperatures in the
90s will be much more widespread east of the divide Wednesday
with RH values in the teens, along with wingspread wind gusts
up to 30-50 mph. These conditions will once again result in
elevated to near-critical fire weather conditions. Agricultural
burning of any kind is highly discouraged today and Wednesday.
Although temperatures will still be above normal on Thursday,
winds will be weaker and RH values in the teens will be pushed
south to southwest and southern WY.

&&

.HYDROLOGY...
Issued at 1250 PM MDT Mon Jun 10 2024

Rivers and creeks will continue to run high at or just below action
stage, but remain steady for the next 24-26 hours. Snow Water
Equivalent (SWE) at SnoTel sites continues to fall, with most
remaining locations at 5 inches or less. A couple of notable
exceptions, Grand Targhee in the Tetons and Two Ocean Plateau in
southern portions of Yellowstone NP, still have 30 and 20
inches, respectively. It looks like any widespread flooding
threat is diminishing and will likely only impact localized
areas, if at all. Water levels are expected to decrease quite a
bit by the weekend.

&&

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

&&

$$

DISCUSSION...McDonald
AVIATION...Straub
FIRE WEATHER...McDonald
HYDROLOGY...McDonald