Ellis, Idaho Weather Forecast Discussion

190
FXUS65 KMSO 261858
AFDMSO
Area Forecast Discussion
National Weather Service Missoula MT
1258 PM MDT Fri Sep 26 2025
.DISCUSSION...
KEY MESSAGES:
-  A ridge builds back over the region for the weekend with
   unseasonably warm daytime temperatures returning.
-  High confidence in cooler and wetter weather next week with
   lower confidence in precipitation amounts for western Montana.
Cool and breezy conditions today with wildfire smoke decreasing
in concentration from north to south in the wake of a dry cold
front that moved through overnight. Fire behavior remained active
late into last evening and overnight due to poor RH recoveries
and continued gusty west winds. This afternoon, gusts of 15-25
mph will be commonplace again across much of the region which
will likely reinvigorate fire and smoke plume behavior into the
late evening despite the cooler temperatures and resultant higher
relative humidities.
An upper-level ridge will begin to move over the northern Rockies
this weekend leading to large-scale descent, unseasonably warm
daytime temperatures, and dry conditions. Temperatures climb to
between 8-15 degrees above normal for this time of year with low
80s in valley locations of western Montana, and low 90s in the
lower river valleys of north-central Idaho by the hottest day of
the next several, which is expected to be Sunday.
Confidence is very high for a significant shift in the upcoming
weather pattern for next week. A cool and wet Pacific trough will
begin to replace the weekend ridge by Monday leading to increasing
moisture, out of the south and west, and subsequent chances for
showers and thunderstorms. As moist air is pulled in from a North
American Monsoonal surge and the Pacific low, it begins to
displace our dry air from the top down on Monday afternoon.
Thunderstorms, under this setup, could generate strong outflow
winds of 40-45 mph, primarily in north-central Idaho and west-
central Montana south of I-90.
The atmosphere begins to moisten much more sufficiently by Tuesday
reducing the threat for gusty outflow but increasing the threat
for more numerous and efficient rain showers with embedded
thunderstorms. The highest confidence in beneficial, wetting rains
remains over north-central Idaho and the mountains of western
Montana. Valleys in western Montana, especially south of I-90,
currently have a 55-75% chance to receive a cumulative total of
0.20" of rain from Monday through Wednesday evening. Risks exist for
locally-heavy rainfall intensities in north-central Idaho and the
southern Bitterroot/Sapphire mountains during this time period
which could lead to excessive runoff or flash flooding of burn
scars, in steep terrain, and/or ponding of low-lying areas.
The evolution of the forecast into the last half of the week
remains uncertain dependent on the track of the main upper-level
low moving onshore and into the interior. Current modeling
suggests a 50% chance for the low to fill and lift into Canada
through Thursday into Friday becoming replaced by a ridge or even
purely zonal flow. The other 50% of global modeling suggests a
reinforcing trough digging down the backside of the main low
keeping conditions unsettled and cool through at least next
Saturday, if not longer.
&&
.AVIATION...Gusty west winds of 15-25 knot range are possible this
afternoon and early evening before calming overnight. Patchy
wildfire smoke may continue to reduce visibilities at times to
near 6 statute miles. Broken mid-high level clouds will move into
areas north of I-90 by Saturday morning, but otherwise, VFR and
MVFR weather conditions will be present through the weekend.
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&
$$

NWS MSO Office Area Forecast Discussion