Rock Springs, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

612
FXUS65 KRIW 112330
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
530 PM MDT Fri Apr 11 2025

.KEY MESSAGES...

- Breezy and warm today with record high temperatures and
  elevated fire weather concerns likely.

- A cold front brings showers and thunderstorms and strong wind
  on Saturday to mainly northern Wyoming. Some thunderstorms may
  be accompanied by gusty winds.

- Remaining windy and much cooler for Sunday.

&&

.UPDATE...
Issued at 309 PM MDT Fri Apr 11 2025

The cold front is still on pace to move into northern WY later
Saturday afternoon. With CAPE values approaching 500 and
inverted-V soundings during peak heating, some thunderstorms
along the WY/MT border could get strong, with gusty winds being
the threat. Most precipitation should be limited to the Bighorn
Basin and Johnson County, but a few rumbles of thunder may be
noted in the Wind River Basin before sunset decreases the
instability.

&&

.DISCUSSION...
Issued at 223 AM MDT Fri Apr 11 2025

We are have a few concerns today, but nothing earth shattering.
Probably on the order of getting a mosquito bite vs a bee sting.
Things looks dry for today. However, we do have a concern, and that
is elevated fire weather. A Pacific weather system will be
approaching the area, and as it does, it will begin to tighten up
the pressure gradient, leading to breezy conditions developing
over much of the area this afternoon. These breezes, combined
with humidity falling to or under 15 percent, will bring
elevated fire weather to much of the area. This would be
critical criteria, but many fuels are in green up and are not
deem critical. The other thing of note is possible record high
temperatures. Many of the lower elevations, especially in the
warmer spots like from Greybull to Thermopolis, have at least a
1 in 2 chance of reaching 80 degrees. The more interesting
locations though are Riverton, Lander and Casper, which could
have their earliest 80 degree temperatures in station history.
NBM ensemble guidance gives the chances of at least 1 in 2 for
those locations. As for tonight, a few showers may occur in the
western mountains, but a vast majority of these would be after
midnight and nothing heavy is expected. There is still a small
risk of minor flooding in the Star Valley, but it would likely
be of the minor and overland variety.

Things get more active on Saturday as the front moves across the
area. The deepest moisture looks to remain across Montana. However,
it will be close enough to bring some showers to the area, with the
greatest concentration across northern Wyoming and the highest
potential amounts across the Absarokas and Yellowstone. For most
locations, this looks to be largely rain. Almost all locations
will maintain 700 millibar temperatures above minus 1C, which
would put snow levels at 8000 feet or higher, with morning
levels closer to 9000 feet. Even in areas that receive snow,
amounts would not be that impactful. There is at most a 1 in 6
chance of 6 inches of snow or more, and that would be across the
highest peaks where impacts are few. In addition, with the vast
majority of precipitation expected to fall during the day, any
road impacts would be minimal to none. There is some instability
with the system as well, with lifted indices falling as low as
minus 2 and as much as 500 J/Kg of CAPE in the afternoon. That
will likely lead to a scattering of showers and thunderstorms,
especially across northern Wyoming. The main threat of a
thunderstorm or even a shower would be strong wind gusts, given
a lot of the convection may be higher cloud bases and models
are showing inverted V signatures. Wind will also be rather
strong as the front approaches. The initial locations would be the
favored west to southwest flow locations, mainly from Muddy Gap
through Casper and in the Cody Foothills. It is still
questionable for high wind though. Probabilistic guidance gives
around 1 in 3 chance of wind gusts over 50 mph near Cody,
elsewhere it is less than 1 out of 5. The 700 millibar winds
only top out around 40 to 45 knots and I would like to see 50 to
55 knots. So, no high wind highlights at this time.
Temperatures will remain warm, but cooler than today.

Things remain somewhat active on Sunday, but the big story would be
the slap in the face that the much cooler temperatures will be. Many
locations east of the Divide will see temperatures as much as
30 to 35 degrees colder on Sunday versus this afternoon. The
other concern will be high wind. Concerns on this day shift to
areas favored by cold advection / northwest flow, especially the
northern Bighorn Basin and Johnson County. Guidance is showing
some 50 to 55 knot wind barbs at 700 millibars, with MOS
guidance showing as much as 40 knots sustained. This does tend
to be a bit overdone this far out though. Probabilistic guidance
gives around a 1 in 3 chance of wind gusts past 50 mph at the
Buffalo airport. It is too far out for highlights but we will
watch it. One change is that model consensus is showing that
the upper level low causing this is expected to remain over
Montana and not drop into Wyoming. As a result, PoPS were cut
back and amounts would be negligible. Most of these showers
should end by sunset on Sunday.

Things look quieter for the rest of the period as ridging begins to
build into the area. Temperatures will remain cool on Monday
then warm again to above normal starting Tuesday and lasting
much of next week. A shortwave brushing by to the north may
bring some showers on Wednesday, but nothing substantial. The
overall trend heading into late April looks to be above normal
temperatures and below normal precipitation.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 530 PM MDT Fri Apr 11 2025

High clouds (FL150-200) will increase overnight tonight. Conditions
will remain VFR through the TAF period. Wind will taper off at most
terminals this evening around 01-02Z.

A weather system will approach the area tonight into Saturday
morning, with a strong cold front pushing through the area late
Saturday. A line of showers is likely (70%) to push into
northwestern Wyoming early Saturday morning sliding east toward KCOD
and KJAC late Saturday morning. For now confidence is low this line
of showers will actually reach the ground and cause impacts at these
terminals, with only about a 10-20% this would occur.

Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.

&&

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

&&

$$

UPDATE...
DISCUSSION...Hattings
AVIATION...Rowe