607
FXUS65 KRIW 300839
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
239 AM MDT Mon Sep 30 2024

.KEY MESSAGES...

- Elevated to critical fire weather likely today in central and
  southern Wyoming with gusty wind and low humidity.

- High temperatures today averaging anywhere from 15 to as much
  as 35 degrees cooler than yesterday. A freeze is possible
  tonight.

- Tuesday into the weekend looks warm and dry with further
  chances of elevated to possibly critical fire weather.

&&

.DISCUSSION...
Issued at 227 AM MDT Mon Sep 30 2024

The main concern today and probably for the next several days will
be fire weather. A cold front is currently moving through the area
and will clear most of the area by sunrise. The effect will be much
cooler temperatures. Every of our official climate sites set record
high temperatures, with 4 locations seeing the latest 90 degree high
on record. It will certainly feel cooler today, especially East of
the Divide, here high temperatures will generally be anywhere from
25 to 35 degrees below normal. Things will be cooler to the west as
well, but only by around 10 to 20 degrees.
As
for fire weather, the cooler temperatures should keep humidity high
enough to prevent widespread critical fire weather. There will
continue to be elevated fire weather so we have issued Fire Danger
Statements for many areas with the gusty northwest wind behind the
front with the cold advection. With lower humidity and warmer
temperatures across the south, we will continue the Red Flag
Warnings there. And speaking of the wind, there  are some strong
winds ongoing across the favored areas across northern
Wyoming, where Buffalo and Greybull have seen gusts to around 50
mph. These should continue into the morning before decreasing in the
afternoon as the cold advection wanes and the pressure gradient
lessens.

Wind should decrease tonight. And this will bring in another
concern, a possible freeze. We will have a few ingredients for a
freeze, one will be a much cooler airmass in place. The second will
be longer nights, as we will be entering October. The third will be
a mainly clear sky, allowing for good radiational cooling. The
fourth ingredient is a little more in question, is calm wind. There
should be some decoupling of the wind after sunset. Chances are
greater around the lower elevations of the Bighorn Basin, where the
chance is as high as 1 out of 2 in a place like Worland. In the Wind
River Basin, it is around 1 out of 3. With that, we have issued
freeze watches for these areas. It is far from a slam dunk though.

The near normal temperatures (yes, the highs today are only near
normal), will not last long as flow turns southwest and allows for
another rise in temperatures, back to around 5 to 10 degrees above
normal. There is a concern for fire weather again though, but it
would be restricted largely from Rock Springs to Casper. It is
borderline though. For now, we will not issue any highlights but the
chance is around 2 out 5 some would be needed for Tuesday. It would
probably to go straight to a warning since duplicate headlines
(watch and warning) can cause confusion.

Dry weather will continue through most of the period. October looks
like another very warm day, with many of the population centers
seeing at least a 1 out of 2 chance of seeing highs rise into the
80s. Another shortwave and dry cold front moving through the area
will bring gusty wind and possibly more fire weather concerns. This
will knock temperatures down around 10 degrees. Following that,
ridging should bring a return of warmer temperatures and less wind
for Thursday and Friday. Another front may approach for the weekend,
but like the previous couple, it will be dry and largely only have
wind with it and no precipitation. And with it, possible more fire
weather concerns for next weekend. So, the pattern of above normal
temperatures and below normal precipitation will likely continue
into the first week of October.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1043 PM MDT Sun Sep 29 2024

A dry cold front tracks southward to start the TAF period, moving
from northern Wyoming southward. KCOD is the first to be impacted at
the very start of the period. Gusty winds 20 to 30 knots accompany
the initial passage of the front. These winds decrease within a
couple hours of frontal passage. The front moves through other sites
through the TAF period, shifting winds to a northerly/northeasterly
direction, excluding western-most sites (KBPI, KJAC, and KPNA).
Winds will be strongest for more northern sites, with lesser gusty
wind impacts the further south the front travels. KJAC and KRIW
could see a few gusts up to 20 knots Monday afternoon, but not
expecting it to be frequent, so have left out of the TAFs. A few
high clouds may accompany the front, but the sky should otherwise
remain clear to mostly clear.

The front also pushes the smoke from the Pack Trail fire southward.
This should move the thicker smoke out of the vicinity of KWRL near
the start of the period. However, the smoke begins to filter into
central Wyoming, including KCPR, KLND, and KRIW Monday morning.
Smoke should increase towards the afternoon as instability allows
greater smoke production. These central sites could see some
visibility reductions with the smoke, especially KRIW due to its
proximity to the fire. Have kept any mention out of the TAFs for now
due to lower confidence at this range (main smoke impacts look to
begin after 21Z/Mon). Will need to re-evaluate for future issuances.

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 227 AM MDT Mon Sep 30 2024

A cold front will be through the area by sunrise, bring much cooler
temperatures, especially East of the Divide. However, a gusty wind
will continue, with gusts to 40 to 50 mph this morning across the
north and to 30 mph across southern Wyoming today. Across southern
Wyoming, relative humidity will fall to under 15 percent and
combined with the wind, will lead to another day of critical fire
weather. In areas East of the Divide, somewhat higher humidity and
cooler temperatures should prevent widespread critical fire weather.
However, elevated fire weather is still likely across much of this
area. Mixing and smoke dispersal will be generally good to very good
across the area.

On Tuesday, elevated to possibly critical fire weather remains
possible largely from around Rock Springs northeastward to Casper.
Still some uncertainty though so we will hold off on any further
highlights. Elevated fire weather is possible again on Wednesday
before conditions should improve somewhat on Thursday and Friday.


&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Freeze Watch from late tonight through Tuesday morning for
WYZ004>006-016>018-020.

Red Flag Warning until 7 PM MDT this evening for WYZ277>279-
289.

&&

$$

DISCUSSION...Hattings
AVIATION...Wittmann
FIRE WEATHER...Hattings