Lewistown, Montana 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

093
FXUS65 KTFX 160223
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
823 PM MDT Fri May 15 2026

.KEY MESSAGES...

 - Breezy through the remainder of the day in most areas.

 - Locally breezy conditions develop Saturday ahead of a colder
   Spring system moving in late Saturday into Sunday.

 - Mountain snow, with a mix of lower elevation rain and snow
   Saturday night into Sunday.

&&

.UPDATE...

Moisture within continued westerly flow aloft increases tonight as
upper level troughing digs into the NW US. An initial shortwave
disturbance ejecting out of the broader trough lifts across NW MT
late tonight with showers developing along the continental divide
after midnight. A Pacific cold front crosses the continental
divide Saturday morning and slows as the mid-upper level flow
turns more southwesterly. Showers are likely to increase along
this boundary Saturday morning, affecting areas from Helena to
Great Falls, with precipitation shifting south and eastward
through Saturday afternoon. Hoenisch

&&

.DISCUSSION...
/Issued 558 PM MDT Fri May 15 2026/

 - Meteorological Overview:

Zonal flow aloft continues across the region this afternoon into
tonight, with a small shortwave ridge moving through tonight
ahead of a robust Pacific trough near the pacific NW coast
arriving this weekend with active weather. Sufficient instability
has developed to result in some showers near the Canadian border
east of I-15/. THis activity, along with breezy winds, continues
through the early evening before subsiding.

Aforementioned troughing begins to move in tomorrow, which will
combine with sufficient daytime heating and cool air aloft to result
in lower elevation showers and mountain snow showers, primarily from
late morning through early evening. As orographic forcing takes over
and snow levels fall tomorrow afternoon and evening as the core of
the upper trough arrives, a stretch of more impactful snow
develops south of I-90 and east of I-15, primarily in the terrain
through Sunday morning.

Meanwhile, surface low pressure being carved out in Wyoming and
southeast Montana through the day Saturday will result in a
northerly winds developing, initially over the plains late afternoon
into the evening hours Saturday. These northerly winds, which
will be gusty at times, usher in cooler air from north to south
across the region Saturday night into Sunday. The cooler air
moving in will coincide with the best orographic and dynamical
forcing, which will yield at least a brief opportunity for some
lower elevation snow Sunday. The coldest night looks to be Sunday
night, which will feature lows into the 20s for many areas.

Attempts are made at a ridge building in early next week, though
embedded waves in the building northwest flow aloft will keep
conditions unsettled and on the cooler side to open the week. This
theme more or less persists through the remainder of the week, which
will keep daily opportunities for showers around. -AM

 - Forecast Confidence & Scenarios:

Snow levels Saturday afternoon and evening in SW MT:

Present timing of falling snow levels Saturday afternoon and evening
results in snow beginning to mix in just after sunset at Bozeman and
Ennis and adjacent areas. Should this transition be quicker with an
overall cooler solution, some minor impacts from snow would develop
in the Gallatin Valley and Madison River Valley.

At this time the timing of snow levels keeps impacts from the snow
confined to higher elevation areas across SW MT, particularly the
northern end of the Madison and Gallatin Ranges, where upslope
enhancement will occur. Overall snowfall amount and duration
appears to be lighter/more brief in nature for the Big Belts and
Bridgers through the night Saturday, but trends will be monitored
for changes in thinking.

Snow Sunday:

As better orographic left and synoptic forcing arrives late
Saturday night into Sunday, additional periods of snow develop
(Some rain does look to mix in at times at lower elevations).
Areas where confidence is greatest in impactful snow is in the
Little Belts and near Glacier NP, though there still remains
uncertainty in overall amounts and timing. Should snow fall at
night, there would be greater confidence in impacts, and vice
versa. -AM

&&

.AVIATION...
16/00Z TAF Period

VFR conditions will prevail at all terminals during this TAF
period. The exception is KLWT, where MVFR conditions are possible
towards the end of this TAF period. Light rain showers are
expected to occur beginning around 19Z 5/16 for KBZN, KEKS, and
KLWT, with a change to a rain/snow mix around 03Z 5/17 for KBZN.
For KHLN and KGTF, these light rain showers are expected to occur
closer to 14Z 5/16. -Dzomba

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  57  34  44 /  10  40  40  80
CTB  34  55  29  43 /   0  10  70  70
HLN  39  54  34  46 /  10  60  30  80
BZN  36  59  29  45 /  10  70  90  70
WYS  30  55  25  42 /   0  20  70  60
DLN  37  58  27  46 /  10  20  60  60
HVR  38  62  33  47 /  10  30  40  80
LWT  38  56  30  41 /  10  70  90  90

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 5 PM Saturday to 6 AM MDT Sunday
for Gallatin and Madison County Mountains and Centennial
Mountains.

&&

$$
http://www.weather.gov/greatfalls