671
FXUS65 KTFX 130506
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1106 PM MDT Sat Jul 12 2025

Aviation Section Updated.

.KEY MESSAGES...

- Dry with temperatures above normal through Monday.

- A low chance for thunderstorms along the Hi Line and Southwest
  Montana Sunday evening.

- A cold front Monday will bring precipitation and cooler weather
  through Wednesday.


&&

.UPDATE...
/Issued 824 PM MDT Sat Jul 12 2025/

Satellite imagery this evening shows the few areas of afternoon cumulus
from earlier today dissipating, leaving mainly clear skies for
the region through the rest of tonight as broad upper level
ridging maintains a dry west-northwest flow aloft across the
Northern Rockies and MT. Somewhat breezy northwest surface winds
have also decreased with overall dry and mild conditions tonight
leading into a very warm day tomorrow. Hoenisch

&&

.DISCUSSION...
/Issued 824 PM MDT Sat Jul 12 2025/

 - Meteorological Overview:

High pressure in place today will keep the area dry and warmer
again. Heading into Sunday, most of the region will still remain
dry, with a weak disturbance in southern Canada and ID will try
to clip a few showers and thunderstorms into the region along the
ID and Canadian border. Storms that move south out of the
Canadian border will have the potential to become strong,
producing strong wind gusts and smaller hail.

The main system holds off until Monday. Looks like the current cold
front will bring down the main wave of precipitation Monday, with
the timings a little uncertain still. A little bit of
precipitation will develop Monday afternoon/evening ahead of the
main wave, but widespread looks to arrive later in the
evening/overnight. Models hint at a weak disturbance along the
ID/MT border and tries to initiate a few thunderstorms Monday
afternoon/evening. Low CAPE in North-Central MT should keep
convection weaker. Down in Southwest MT, sounding profiles have
more drier air and CAPE, which will bring a concern for a few
stronger storms. The same case is for Tuesday, where a wave from
ID move through Southwest MT can bring a few more stronger storms
to the region, where drier air in place will help keep storms
from being `water-logged` as opposed to North-Central MT. The
500mb trough closes off Tuesday, which will help precipitation
linger through the evening and overnight hours. There remains
inconsistencies with end timing, with some modeling having
precipitation lingering through the morning hours Wednesday. This
system will also bring in cooler air Tuesday and Wednesday, where
some locations can experience a 15-20 degree drop in the high
temperatures from Monday to Tuesday.

After this system exists, we will transition to a weak northwest/
zonal flow aloft pattern through next weekend. Although the
forecast looks to be drier through next weekend, a few weak
disturbances will keep low end chances for precipitation in the
forecast in the meantime for the second half of next week. Most
of what happens later in the week will be dependent on how this
system plays out at the beginning of the week. A gradual warm up
to near to slightly above normal also looks to trend through next
weekend.


 - Forecast Confidence & Scenarios:

Sunday looks to be a `hit or miss` kind of day with precipitation
near the border of Canada and ID (meaning, there is a low end
chance for a few shower and thunderstorms to clip the region from
ID and Canada). Deep inverted V`s and decent lapse rates also
indicate the potential for a few stronger storms towards the
Canadian border.

There remains some inconsistencies in model guidance for timing
and how much precipitation falls during this time period (though
the agreement in the 12z runs did agree better than yesterday).
The NAM is the more progressive solution in the cold front
passage earlier in the day Monday. It look likes the recent runs
do agree to close off that upperr-level wave Tuesday, which will
help keep precipitation around later (with the GFS keeping rain
all the way through the morning Wednesday). However, I would like
to see more run to run consistency before hopping on any train.
Current rain amounts still remain uncertain. The current NBM gives
a 40-70% chance of 0.5" inches of rain, the GFS still is a high
end solution (likely due to the later end timing in
precipitation), giving close to or just above 1" of rain in
North- Central MT. The 25th percentile for lower end amounts give
0.15-0.3" and the 75th percentile for higher amounts give
0.8-1.25" in Central MT. The middle of road solution give
0.4-0.6".

A later arrival and weaker time of precipitation in the evening
Monday will keep thunderstorms weak in Central MT. Though, any
faster progression of the front will increase thunderstorm
chances. Tuesday will have embedded thunderstorms with widespread
precipitation, but saturated low to mid levels of the atmosphere
will keep thunderstorms weak overall. Across Southwest MT, there
is drier air. This will help bring the potential for a few
stronger wind gusts Monday with deep inverted V soundings. Tuesday
has a slight increase in elevated CAPE towards the Continental
Divide, where it can bring a low end potential for hail if this
keeps trending. -Wilson

&&

.AVIATION...
13/06Z TAF Period

VFR conditions prevail at all terminals through the period. Light
and variable winds will continue through the overnight before
pickup up to around 10kts in the afternoon. Mid-level clouds will
filter into the Hi-Line by the afternoon ahead of a cold front
with around a 15-20% chance for isolated afternoon showers and
thunderstorms, particularly for KHVR.  -thor

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  60  94  58  89 /   0   0  10  20
CTB  57  87  55  72 /   0  10  20  40
HLN  59  93  61  93 /   0   0   0  10
BZN  53  92  56  94 /   0   0  10  10
WYS  41  84  45  83 /   0   0  10  20
DLN  50  90  53  90 /   0   0  10  10
HVR  58  93  58  83 /   0   0  20  30
LWT  55  88  56  86 /   0   0  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

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