082
FXUS65 KRIW 050423
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1023 PM MDT Fri Oct 4 2024

.KEY MESSAGES...

- Very warm, dry, and windy conditions this afternoon and
  evening will bring critical fire weather conditions across
  western and central Wyoming, along with likely wind gusts
  above 50 mph in some areas. Virga showers are also possible
  (10%) over the northwest mountains this evening.

- Cooler yet near normal temperatures expected Saturday with
  gusty west winds across southern WY after a cold front drops
  south out of Montana Saturday morning.

- Above normal temperatures and dry conditions are expected
  through at least Friday next week, with a very small chance of
  showers late Monday and Tuesday evening.

- A strong low pressure system is possible next weekend, with
  much uncertainty at this time on strength and timing.

&&

.DISCUSSION...
Issued at 100 PM MDT Fri Oct 4 2024

With mostly clear skies over western and central Wyoming this
morning (though there are pockets of pooled smoke), the upper-level
ridge axis will be sliding eastward over the forecast area today. A
fast-moving shortwave trough over the Pacific Northwest is
strengthening the gradients across northern Rockies and Great Basin
today, increasing mid-level and surface winds this afternoon and
overnight, as well as bringing continued very dry air.  As a result
of frequent wind gusts over 25 mph and RH values dropping below 15%
(yet again), critical fire weather conditions are expected this
afternoon and into the evening hours.  This afternoon`s high
temperatures will again be well above normal with a few areas
reaching record high temps, such as Riverton and Rock Springs. 700mb
wind speeds over northwest and northern WY will be increasing from
30 kts this afternoon to 45-50 kts just after midnight due to the
shortwave trough quickly moving into Montana. Thus, some mountain
areas over northwest WY should see 60+ mph wind gusts overnight.  As
the shortwave trough passes through the forecast area between
midnight and 6am, winds will shift from southwest to the west, then
WNW later in the morning.  A surface cold front will also move
southward from Montana into northern WY, bringing gusty north winds
to the Bighorn Basin and Johnson County between 3 and 6 am. The
north winds will move south through the morning and stall out in the
southern Bighorn Basin to around Casper as moderate WNW flow
continues across western and southern WY.  Temperatures Saturday
will be 8-10 degrees cooler than today, though elevated fire weather
conditions will continue from west-central into southwest and
southern WY.  Saturday evening will see the NNE winds move into
central WY as the gradient relaxes and weak high pressures develops
just to the west of Wyoming.

Weak high pressure with mild upper-level westerly flow then sets up
Monday and Tuesday.  There will be a noticeable decrease in winds
these days as high temperatures remain in the 70s.  Models are
indicating a couple of weak shortwaves in the flow both Monday and
Tuesday afternoon.  Clouds will increase during the afternoons due
to the moisture and slight instability, with virga showers likely
late Monday.  The wave on Tuesday appears to be a bit stronger, for
a slightly better chance of showers, though still very little
precipitation is expected. Instead, gusty outflow winds are the more
likely outcome Tuesday evening into Wednesday afternoon.  Dry
southwest flow sets up again Thursday as weak high pressure returns
with a strong trough along the west coast.  Clouds will increase
Friday as the trough approaches, though details are uncertain at
this time given the differences in storm movement and intensity. The
GFS has a solution that will bring quite the storm to WY late
Saturday into Sunday, but the ECMWF is much slower and weaker with
no real relief for the fires.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1020 PM MDT Fri Oct 4 2024

Winds have been able to slacken off briefly this evening with a
gap between todays` gusty winds and the approaching cold front.
This front is expected to jump winds back up overnight at all
sites, and is expected between 06Z and 08Z. Winds will stay
elevated and gusty through the night and most of the day
Saturday, before finally decreasing late afternoon Saturday. One
area of clouds is stretching across western WY currently, but
will remain SCT or better, and will not cross east of the
Divide. Most of the day Saturday will be SKC.

&&

.FIRE WEATHER...
Issued at 100 PM MDT Fri Oct 4 2024

Red flag warnings are in effect from 12pm today through 7pm Saturday
evening for much of the forecast area due to well above normal
temperatures, very dry humidities, and very strong winds.  Zone 140
will only go through 12pm Saturday, and parts of southern WY will
continue to 9pm Saturday.  These conditions are bringing critical
fire weather conditions to much of the state for the next 30-26
hours. High pressure over the area today will give way to dry windy
southwest flow as a low pressure system from the Pacific Northwest
moves toward Montana tonight.  Winds will not only be strong this
afternoon and evening ahead of the cold front, but moderate and
gusty behind the cold front on Saturday as well. Southwest winds are
already increasing across southern into central WY late in the
morning, and will increase further this afternoon over the rest of
western and central WY.  Due to strengthening surface gradients and
increasing mid-level winds, winds will remain strong overnight, with
the strongest winds over the southern Absarokas expected to be 60+
mph around 0000 tonight.  Temperatures will cool on Saturday, with a
surface cold front entering northern WY around midnight and pushing
south.  It will stall however from the southern Bighorn Basin to
Casper during the day as gusty WNW winds continue on Saturday south
of the boundary. Winds will gradually decrease across northern WY
Saturday afternoon, and then across southern WY around sunset
Saturday. Dry near normal conditions are expected on Sunday with
much lighter winds.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until noon MDT Saturday for WYZ140.

Red Flag Warning until 7 PM MDT Saturday for WYZ275>277-
280>283-285>287-300-414-415.

Air Quality Alert until 1 PM MDT Monday for WYZ010-016>018.

Red Flag Warning until 9 PM MDT Saturday for WYZ278-279-288-
289-416.

&&

$$

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