048
FXUS65 KRIW 240349
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
949 PM MDT Mon Sep 23 2024

.KEY MESSAGES...

- Slightly above normal temperatures Monday and Tuesday with
  partly cloudy skies becoming mostly sunny along with some
  gusty north winds east of the Divide.

- High pressure strengthens Tuesday night into Wednesday,
  bringing well above normal afternoon temperatures and gusty
  southwest wind for elevated fire weather conditions.

- Similar situation creates elevated fire weather conditions on
  Thursday with gusty west winds and partly cloudy skies across
  northern Wyoming.

- Dry and very warm conditions continue Friday and Saturday,
  with the next chance (20-30 percent) of precipitation Sunday
  afternoon and evening into Monday as a disturbance moves
  through the northern Rockies.

&&

.DISCUSSION...
Issued at 113 PM MDT Mon Sep 23 2024

Dry northwest flow continues over western and central WY today
as a low pressure system moves out of southern Canada into the
Northern Plains. High-level clouds have increased today with a
northerly component, and some mid-level wave clouds have also
developed in response to the increase in moisture. One or two
high- resolution models are showing a 5-10% chance of showers
over the east-central Bighorn Mountains late this afternoon and
early evening, but feel that the better chance is well to the
northeast. Near the surface across north-central WY, winds are
generally from the NW to N and are gusty, especially around
Buffalo. In response to the "boundary", gusty west- southwest
winds continue today from southwest WY into central WY, though
central WY should see some north winds this evening. With 700 mb
temps around +6 to +8 C today and tomorrow, max temps will be
about 3-6 degrees above normal in the 70s to around 80. Upper-
level high pressure is expected to move from OR to the northern
Intermountain West overnight, and then over northern UT Tuesday
afternoon. Skies will thus clear from west to east on Tuesday,
and the surface pressure gradient will weaken to bring
relatively light winds for an amazing fall day across the state.

Wednesday will see the ridge axis move over WY during the morning
and then eastward through the day.  A lee-side low is expected to
develop over eastern MT, strengthening the gradient across the
forecast area, and increasing southwest winds during the
afternoon. Skies will still remain mostly clear, but surface
temperatures will increase in response to 700mb temps also
increasing to +12 to +15 C. Expected max temps will be from the
high 70s to around 90, which is 14-16 degrees above normal for
Sept. 25. Models are showing drier air moving in Wednesday
afternoon as well with min RH values dropping to around 15
percent, to create elevated fire weather conditions during the
afternoon and early evening. The shortwave trough over the PACNW
then moves into MT on Thursday with no precipitation expected
across northern WY. Dry and very warm air continues over the
forecast area as winds shift from southwest to west and remain
gusty. Again, elevated fire weather conditions are expected. As
the trough moves eastward across MT, a weak surface cool front
then shifts the winds to the north across north- central and
northeast WY Thursday afternoon.

Weak mid-level southwest flow will return to WY Friday and
Saturday as the pressure gradient weakens. Temperatures will
cool slightly to the mid 70s to mid 80s, but still remain 10-12
degrees above normal for late September. Skies should remain
mostly clear until late Saturday night as a shortwave trough
moves from the West Coast toward the MT/WY area. Winds and
clouds will increase Sunday morning with the advance of a strong
cold front and some showers and thunderstorms are possible (25
percent) through the day. The north- south uncertainty with this
wave though is likely to bring a better chance of storminess to
northern WY, with considerable cooling behind the system. Ahead
of the front in central WY, gusty southwest winds and dry
conditions will again elevated fire weather concerns. Hopefully
a better picture will develop over the coming days, as well as
some autumn precipitation to keep drought categories from
worsening.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 945 PM MDT Mon Sep 23 2024

High clouds will continue to exit to the southeast, with SKC
skies across the forecast area by 16Z. Winds will remain light
(11 kt or less) through the TAF period, along with dry
conditions.

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...McDonald
AVIATION...LaVoie