393
FXUS65 KRIW 131848
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
1248 PM MDT Sun Jul 13 2025

.KEY MESSAGES...

- Another pleasant, sunny, warm, and dry July day across the
  Cowboy State today.

- Warm temperatures and dry conditions persist into Monday with increased
  chances for elevated to near critical fire weather
  conditions.

- A frontal passage with introduce chances for showers and
  thunderstorms on Tuesday and Wednesday.

&&

.UPDATE...
Issued at 1247 PM MDT Sun Jul 13 2025

Little change in regard to the upcoming forecast. Warm summer-like
temperatures return to much of the Cowboy State today. Highs range
from the upper 80s west of the Continental Divide to the mid to
upper 90s east of the Divide. Skies remain mostly clear allowing for
plenty of sunshine along with dry conditions. Minimum RH values are
expected to be near critical values for portions of the state.
However, marginal winds should limit any elevated fire weather
concerns. While nearly all of the area will remain dry there is
still a small chance (~10%) for a very isolated virga shower.
Overall a fairly typical mid July day is expected.

A cold front is expected to approach the state Monday, but will
remain just out of reach. This allows temperatures to stay warm for
another day. Highs Monday are expected to be similar to Sunday with
temperatures in the upper 80s west of the Divide and mid to upper
90s east of the Divide. The approaching front creates some scattered
showers and thunderstorms mainly across northern Wyoming. Dewpoint
depressions will range from 40 to 50 degrees, which may generate
isolated strong gusty outflow winds in association with any showers
that develop. The front will bring increased winds with a westerly
breeze developing during the afternoon. Winds range from 10 to 15
mph with periodic gusts of 15 to 25 mph. These winds combined with
low minimum RH values produce elevated fire weather conditions,
especially over southern Wyoming. However, with winds remaining
mostly marginal the concern for widespread near critical fire
weather conditions looks to be low at this time.

Tuesday continues to look active as much of the state will see
increased chances for showers and thunderstorms. The aforementioned
cold front moves across the state Tuesday, gradually trekking south
during the day. The best chances for precipitation will be east of
the Divide, especially across northern Wyoming. Models do show these
showers spreading south into central Wyoming and eventually across
the south. However, just how far into southern Wyoming is still to
be seen, as there remains some discrepancies among models at this
time. Above normal PWATs will move into the area along with the
frontal passage. This could create the chance for isolated heavy
downpours as showers and thunderstorms develop and move across the
state. There does look to be the potential for a few strong storms
on Tuesday. Abundant moisture streams into the state with some
locations seeing dewpoints in the 50s. Depending on how much
sunlight can break through during the first half of the day, CAPE
values could reach of 500 to 1000 J/kg if not slightly more. This
combines with favorable shear as northeasterly surface flow
interacts with upper-level southwesterly flow. Overall, the area of
concern looks to be across central and eastern Wyoming where the
greatest instability is expected to develop. The strongest storms
may be capable of producing strong gusty winds, hail, and heavy
downpours. Showers and thunderstorms linger into the late evening
hours before gradually dissipating early Wednesday.

Cooler temperatures settle over the region Wednesday with highs in
the low to mid 80s west of the Divide and the 70s east of the
Divide. Warmer temperatures return for the second half of the week
as a broad area of ridging tries to build back in. There may be some
chances for showers and thunderstorms even with this ridging
developing but coverage will be isolated. Warm and mostly dry
conditions look to return and persist into next weekend.

&&

.DISCUSSION...
Issued at 306 AM MDT Sun Jul 13 2025

All in all, the reasoning in the forecast has changes little from
yesterday. Northwest flow will continue to dominate today.
Thicknesses continue to climb today though, so it will be a rather
hot day today with widespread 90s in the lower elevations East of
the Divide. Almost all areas will be dry as well. However, notice
the modifier, almost. There will be a very subtle shortwave moving
across the area this evening. And this may be just enough to bring
an isolated shower or thunderstorm in and near the northern
mountains. The chance is very small though, small with a capital S.
We have some slight POPs in spots but the chance is at most 1 out of
6 with the vast majority of locations seeing nothing.

Things start turning more active next week. A cold front will start
approaching the area from the north. It will remain north of the
area though, so it will be another hot day with temperature fairly
similar to todays. We have two concerns. And it reminds me of one of
my favorite songs from the 70s, Fire and Rain by James Taylor.
Although starting Monday will should not see sunny days we thought
would never end. We will start with fire. With the approaching
cold front, the pressure gradient will tighten ahead of it and
bring some breezy conditions. Humidity will be very low on this
day, falling as low as 10 percent. This brings the possibility
of elevated to critical weather into the forecast. Wind looks
borderline though. The most likely place to see it would be
across portions of Sweetwater, Sublette and Fremont counties in
the afternoon. At this time, it is uncertain if we will get 3
hours of wind gusts past 25 mph for Red Flag criteria though.
So, we will let the day shift take another look to see if any
watches are needed and then we can upgrade tomorrow night if
needed.

Now for the rain, or more specifically thunderstorm part. Chances of
storms will increase but mainly across the northern portions of the
state. Chances here range anywhere from 1 in 5 in the lower
elevations to 1 in 3 in the mountains. There is not a lot of upper
forcing with on this day. However, what we do have are very large
dew point depressions (as high as 60 degrees) and inverted V
soundings with any afternoon convection being high based, strong
wind gusts are possible with any shower or storm, although many may
end up bring rain free. The chance of rain increases in the evening
and at night as temperatures cool and the atmosphere moistens
somewhat.

Tuesday and Wednesday still look like the most active days. The
models do agree on the northwestern half of the area and areas East
of the Divide seeing the best chance of seeing showers and storms,
with tapering chances further south. There are still disagreements
though on the timing and rainfall amounts of the storms each day,
with some models showing Tuesday as the most active day with the
system more progressive. Others have it on Wednesday with a slower
progression. So, there is still little confidence in the details at
this time. Temperatures will be substantially cooler though,
especially in northern Wyoming. Some guidance shows Buffalo
remaining in the 50s on Wednesday. Don`t know if I believe that with
it being the middle of July though. Some areas will be around 30
degrees cooler on Tuesday or Wednesday when compared to Sunday and
Monday.

Flat ridging should then control the weather for Thursday through
Friday and bring near normal temperatures. A few storms may be
around each afternoon but most areas should be dry. Above normal
temperatures are then favored to return for next weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1110 AM MDT Sun Jul 13 2025

Afternoon cumulus develop over mainly the Absaroka and Wind River
Range and adjacent areas Sunday afternoon and linger into the
evening. Isolated showers or virga clip the northwest corner of
the state late Sunday evening. Otherwise, VFR conditions prevail
through the period. Surface wind speeds to be westerly around
10kts at terminals west of the Continental Divide from
20Z/Sunday until 02Z/Monday.

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 1247 PM MDT Sun Jul 13 2025

Elevated to near critical fire weather conditions will be possible
across portions of the state Monday. Minimum RH will be 10 to 15%
for much of the region with higher values over northern Wyoming.
Winds look to be the main limiting factor with periodic gusts of 20
to 25 mph, but not consistent enough to warrant a Fire Weather Watch
at this time. Increasing chances for showers and thunderstorms
arrive Tuesday with higher minimum RH values and cooler
temperatures.

&&

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

&&

$$

UPDATE...Dziewaltowski
DISCUSSION...Hattings
AVIATION...CNJ
FIRE WEATHER...Dziewaltowski