885
FXUS65 KTFX 301813
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1213 PM MDT Sat May 30 2026

Aviation Section Updated.

.KEY MESSAGES...

 - Widespread rainfall and light snowfall in the higher terrain today
   through Monday.

 - Flooding due to heavy rainfall are possible for areas near and
   west of the I-15 corridor across North-Central MT.

 - Temperatures gradually warm up next week, with daily chances
   for scattered showers and thunderstorms.

&&

.UPDATE...
/Issued 858 AM MDT Sat May 30 2026/

Satellite imagery this morning shows the mid-upper level
circulation center lifting from UT into southern WY with plumes of
deep moisture originating from both the Gulf of Mexico and eastern
Pacific being pulled northward across the US plains and up across
MT into AB. Favorable placement of upper jet energy both NW of
the area and also moving northwest out of the circulation over WY
is already providing enough lift for an increasing coverage of
showers this morning with precipitation coverage and intensity on
track to increase further this afternoon as the upper level
circulation lifts north and an inverted surface trough deepens
across eastern MT. Period of heavier precipitation are most
likely to develop this afternoon, initially from convective
elements across eastern portions of central and southwest MT with
a transition to a more widespread frontogenetic forced area of
precipitation enhanced by upslope flow as a TROWAL feature
develops from the inverted trough and circulates precipitation
westward across north-central MT through the overnight period.
Hoenisch

&&

.DISCUSSION...
/Issued 858 AM MDT Sat May 30 2026/

 - Meteorological Overview:

An upper level trough with a negative tilt centered over Utah
moves northward into Montana this weekend, bringing widespread
precipitation across the region. The heaviest rainfall will likely
be in Central MT and along and west of the I-15 corridor in
North-Central MT. There will be enough instability present to
where a rumble of thunder or isolated lightning strike is not out
of the question Saturday. Snow levels will decrease, but remain
above pass levels, allowing for the possibility of light, slushy
accumulations near 7,000 ft. The low-level jet strengthens over
North-Central MT and along the Hi-Line on Sunday morning, creating
breezy conditions throughout the day. Winds for the most part
will stay below High Wind Warning criteria, but the combination of
the east/northeast winds and heavy rainfall threat can loosen
trees up better, causing them to fall and cause tree damage/power
outages. By late Sunday night, the upper level trough turns into
a closed low and moves northwest. As the system moves out of the
CWA on Monday, precipitation chances decrease. However, they do
not fully dissipate, and there will be lingering chances of
showers and thunderstorms throughout next week. Temperatures will
gradually increase, as ridging aloft begins to build over the
region Thursday night. -Dzomba

 - Forecast Confidence & Scenarios:

Confidence has been increasing for the risk of 1 to 3 inches of
rainfall across the region. The low end amount, which has a 90%
chance of occurring, shows between 0.75" to 1.5" across the CWA.
The high end amount, which has a 10% chance of occurring, shows
between 3.5" to 4" for areas along and west of the I-15 corridor
across North- Central MT. There may be some enhanced impacts to
rivers and creeks due to snowmelt runoff depending on how quickly
the cold air comes in. As a result, a Flood Watch has been issued
Saturday through Monday (see Hydrology for more info). Where the
corridor of best moisture/low level convergence sets up is
ultimately where the heaviest precipitation will fall.

The colder air is not as cold/deep as previous forecasts.
Therefore, impacts are expected to be limited to slushy
accumulations mostly above 7,000ft. We will closely monitor for
any additional impacts in case the trend changes. -Wilson/Dzomba


&&

.AVIATION...
30/18Z TAF Period

Showers will continue to fill in across the region today, leading
to widespread coverage by the evening. Weak instability this
afternoon will allow for some moderate to heavy showers/isolated
thunderstorms to develop. However, the thunderstorm risk is more
likely towards Central MT (by KLWT). Rain will turn more
stratiformlater this evening through Sunday. MVFR to IFR
visibilities are expected at times throughout the TAF period from
ceilings and visibility. Breezy west/northwest winds pick up late
Saturday/Sunday morning, with the highest winds expected along
the Hi-line. Cloud obscuration will be persistent through the TAF
period from precipitation and low ceilings. -Wilson

&&

.HYDROLOGY...

Widespread rainfall will affect the CWA this weekend. In looking
at NOAA Atlas 14, 2 inch rainfalls in a 2 day period happen about
every 2 to 5 years in the Great Falls area. For areas west of
Augusta, a 3 inch rainfall in a 2 day period also happens about
every 2 to 5 years. Thus the spring storm that we are forecasting
this weekend is on par for a fairly common spring storm...it is
just that we have not had a storm like this in a few years.

Current river forecasts for Saint Mary, and the Sun River are
forecasted to go into flood stage late Sunday into Monday. This
forecast is heavily dependent on the precipitation amounts and
could change in the coming day(s). Many mountains have melted out
the snowpack for the season, but a few areas along the divide do
have snow, especially Glacier Park. This will add to run off
concerns for rivers like the Sun River, Badger Creek, and the St
Mary`s River.

Additionally, areal QPF of 1 to 2 inches is possible over the
western half of North Central MT. Overall, much of the area should
be able to handle the first few inches. Recent model runs have an
isolated (10% chance) for 3" of rainfall. The combination of
heavy rainfall and impacts from river/creek flooding has resulted
in a Flood Watch being issued for North-Central MT along and west
of the I-15 corridor. Another impact with be rural, dirt roads
could become washed out if the higher end amounts end up
happening. Depending on how the rivers respond, additional or
extensions of flood products may be needed.

-Brusda/Wilson

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  46  53  42  58 / 100 100  80  40
CTB  41  51  37  52 / 100 100  80  70
HLN  44  57  43  63 / 100  80  50  50
BZN  40  56  37  64 /  90  80  20  40
WYS  35  55  30  62 /  60  60  30  20
DLN  41  60  37  64 /  90  50  20  50
HVR  45  58  39  59 /  80  80  70  50
LWT  42  52  38  58 /  80  90  60  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Monday afternoon for Cascade County below
5000ft-East Glacier Park Region-Eastern Glacier, Western Toole,
and Central Pondera-Eastern Pondera and Eastern Teton-Gates of
the Mountains-Northern High Plains-Southern High Plains-Southern
Rocky Mountain Front.

&&

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