Rock Springs, Wyoming 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

836
FXUS65 KRIW 131050
AFDRIW

Area Forecast Discussion
National Weather Service Riverton WY
450 AM MDT Wed Aug 13 2025

.KEY MESSAGES...

- Critical fire weather today as a result of dry and warm air,
  as well as gusty afternoon winds and thunderstorm chances.
  Red Flag Warnings are in effect.

- Elevated to critical fire weather conditions remain for
  Thursday, especially across southwest and central Wyoming.

- Increasing moisture brings daily rain chances through the
  weekend, with the highest chances over southwest Wyoming.

&&

.DISCUSSION...
Issued at 1230 AM MDT Wed Aug 13 2025

The focus for today is on fire weather, which consists of low
relative humidities (RH), gusty winds, and shower/thunderstorm
chances. Starting with RH. The axis of high pressure moves over
today, and with it, the warmest and driest air compared to the past
few days. Afternoon minimum RHs will generally be around or under 25
percent for all locations (both higher and lower elevations) today.
Most low elevations will be under 15 percent. Driest locations will
be in central and southern Wyoming, with RHs down into the single
digits. High temperatures today will be in the upper 80s to mid-90s,
which are a bit above normal for mid-August.

Next element is gusty winds. A shortwave moving through northern
Wyoming, in combination with an approaching low system tightening
the pressure gradient, afternoon, synoptic winds increase. Gusts 25
mph or greater should occur across much of central and southern
Wyoming. In addition, the higher elevations, namely the western
mountains, will see gusts over 35 mph. The least windy spots will be
the Bighorn Basin and northern Johnson County. The other wind factor
comes from thunderstorms chances.

Showers and thunderstorms are possible (at least 15 percent) across
the entire area today. Hi-res models show convection developing over
the far western mountains as early as about 9am MDT, though would be
more likely with typical diurnal trends starting 11am to 1pm.
Chances than become very difficult to pinpoint. Each model has
differing locations and timings of showers and storms through the
afternoon and evening. Have blended them altogether for the
forecast, and "broad-brushed" to give the entire area at least a 15
percent chance. Not everywhere will get a shower or storm, but given
the widespread coverage models depict, there is at least a chance
everywhere. The main hazard with the showers/storms is wind in the
form of localized outflow gusts. Given dew points, gusts over 40 mph
are very possible, with the HRRR producing some gusts over 50 mph.

Combining the previous paragraphs` weather elements, elevated to
critical fire weather is in place today. Red Flag Warnings are in
effect for much of the area, where the synoptic winds, low RHs, and
thunderstorms chances best align. RH recovery is fairly poor
Wednesday night, especially across central and southern portions of
the area, and with winds increasing again Thursday, Red Flags
continue for some locations (fire zones 279, 280, 289, 300) into
Thursday.

On Thursday, moisture increase for the area as the high shifts east
and advects moisture from the south. RHs begin to improve a little,
especially across western Wyoming where moisture gets to first. This
also brings the chances of showers and thunderstorms, primarily for
southwest Wyoming, though there are still some chances into central
and northern Wyoming. The monsoonal moisture push keeps daily rain
chances into the weekend. Temperatures remain very similar through
the rest of the week as well. The upper-level pattern remains messy
through the weekend, with long range models showing the ridge
building back into the start of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 450 AM MDT Wed Aug 13 2025

VFR conditions throughout the period for all TAF sites. Light
winds and mainly clear skies to start the period this Wednesday
morning. Winds increase west of the Divide, as well as CPR/COD,
after 18-20Z with gusts up to 25kts at most of these locations.
These winds last through 02-04Z through peak heating of the
afternoon and strongest mixing. Increasing mid to upper level
clouds during the afternoon hours as well but start to lift and
scatter out after 06Z. Chances for storms east of the Divide
between 20-24Z with PROB30 groups, except at CPR with VCSH as
less confidence that far east. As always, lightning and gusty
outflow winds the main concerns at that time.

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


&&

.FIRE WEATHER...
Issued at 1230 AM MDT Wed Aug 13 2025

Winds increase late morning today, with critical RHs in the
afternoon. Therefore, Red Flag Warnings are in effect across
portions of southwest and central WY today. Across Fire Zones 277,
278, 279, 280, 283, 289, and 300, RHs as low as 8 to 12 percent,
coupled with west winds 10 to 15 mph gusting 25 to 30 mph in the
afternoon, will result in critical fire weather conditions. Notably
for zones 279, 280, 289, and 300, similar conditions will return
Thursday afternoon, so Red Flag Warnings for those zones are in
effect through 8 PM Thursday. Conditions are expected to improve
Wednesday night with winds decreasing to mostly light and variable,
however, overnight recoveries will be fairly poor, with RHs only
recovering to around 30 to 45 percent.

Across mountain zones in western and northern WY, including zones
414, 415, and 416 along with 286 and 288, RHs will be much more
marginal, generally 14 to 16 percent in the valleys and around 20
percent across higher elevations. Despite this, winds gusting 30 to
40 mph across higher terrain and the thunderstorm threat (20 to 40
percent chances) across those regions this afternoon necessitated
the issuance of Red Flag Warnings for those zones. In particular,
there is increased concern for new fire starts and erratic fire
behavior with any new starts, given the thunderstorm chances. Though
there should be some rain with any thunderstorms, precipitation will
not be enough to extinguish any lightning starts that may occur, as
wetting rain chances remain near zero. Thursday, the thunderstorm
threat shifts to southwest WY, but storms should have more notable
moisture with them on Thursday as monsoonal flow begins to become
more dominant.

&&

.RIW WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning from noon today to 8 PM MDT this evening for
WYZ277-278-283-286-288-414>416.

Red Flag Warning from noon today to 8 PM MDT Thursday for
WYZ279-280-289-300.

&&

$$

DISCUSSION...Wittmann
AVIATION...Lowe
FIRE WEATHER...Hensley/Wittmann