428
FXUS65 KTFX 181705
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1105 AM MDT Sat Jul 18 2026

Aviation Section Updated.

.KEY MESSAGES...

- Another round of scattered showers and thunderstorms will move
  in a southwest to northeast fashion this afternoon and tonight.

- Thunderstorm hazards will include strong, gusty winds, hail,
  and heavy downpours capable of producing isolated instances of
  localized flooding.

- Sunday will be breezy and dry with continued very warm to hot
  temperatures.

- After a brief cooldown Monday, summer heat and daily rounds
  of storms return heading towards the middle of next week.

&&

.DISCUSSION...
/Issued 522 AM MDT Sat Jul 18 2026/

Lingering shower and thunderstorm activity from last night has
mostly diminished and ended while some patchy areas of low stratus
and fog develop over portions of central and southwest MT this
morning. This should clear out by mid- morning with the focus
turning to another shortwave passing through an unstable
southwesterly flow aloft and bringing another round of scattered
showers thunderstorms this afternoon and evening. Similar to
yesterday, this activity will initialize over west and
southwestern MT early in the afternoon before moving northeastward
over the plains and valleys later in the afternoon and evening.

Model guidance has ramped up today`s ML CAPE values to around 800
to 1,500 J/kg, resulting in more widespread convective activity
than what was anticipated 24 hours ago. Drier surface conditions
suggest that instances of localized strong wind gusts over 60 mph
will be more pronounced while shear above 25 kts will be
marginally supportive of hail events. These storms will also be
capable of producing isolated flooding of sensitive burn scars and
urban areas, although PWATS look to drop off some compered to the
last few days. Given slightly lower moisture levels and more
progressive storm motion, I decided to hold off on flash flood
products for now.

Today`s showers and storms should wind down by late this evening
with increased westerly flow aloft bringing drier, breezy, and
continued hot conditions on Sunday. Deep layer mixing and H700
flow approaching 30 to 35 kts will keep the windiest conditions
along the Rocky Mountain Front and the plains. Any shower or
thunderstorm activity will be isolated and mostly confined to the
higher terrain of southwest MT. A Canadian surface front will
bring a northerly wind shift and a brief cooldown on Monday before
ridging aloft strengthens and brings a return to hot conditions
heading towards the middle of next week. Passing shortwaves
interacting with monsoon moisture will also increase daily shower
and thunderstorm activity. - RCG

&&

.AVIATION...
18/18Z TAF Period

Initial concern this TAF period will be for development of showers
and thunderstorms this afternoon and evening, capable of producing
strong winds gusts, small hail, and lightning. Should any of these
showers or thunderstorms produce briefly heavy rain, there will be
the risk for some fog by Sunday morning. The confidence in this
occurring was too low to warrant mention in any TAF at this point,
however. Looking ahead toward Sunday during the day, breezy west
to northwest winds look to develop in most areas by late morning. -AM

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  61  95  59  84 /  30   0   0   0
CTB  57  87  55  79 /  20   0   0   0
HLN  61  94  59  87 /  50  10   0   0
BZN  57  93  56  90 /  30  10  10   0
WYS  48  86  48  87 /  20   0   0   0
DLN  55  90  55  87 /  30   0   0   0
HVR  63  95  58  86 /  30   0   0   0
LWT  57  90  54  82 /  40  20  10   0

&&

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

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