Simms, Montana Weather Forecast Discussion

029
FXUS65 KTFX 101104
AFDTFX
Area Forecast Discussion
National Weather Service Great Falls MT
504 AM MDT Wed Sep 10 2025
Aviation Section Updated.
.KEY MESSAGES...
- Periodic showers and thunderstorms are expected today and
  Thursday, with a few storms being capable of producing gusty
  winds, locally heavy downpours, and small hail.
- Precipitation coverage increases to more scattered to
  widespread Thursday through Saturday.
- A cooldown is expected during the latter half of the week and
  into next week.
&&
.DISCUSSION...
/Issued 250 AM MDT Wed Sep 10 2025/
- Meteorological Overview:
With that trough axis continuing to move east across the Western
U.S, increasing moisture and forcing will allow for periodic
precipitation today and Thursday. Showers and a rogue thunderstorm
this morning will continue to lift north across North-Central MT.
There will be a lull in precipitation before another wave of
showers and thunderstorms arrive Wednesday afternoon and evening.
Clearing skies from the morning precipitation will allow for about
~500 J/kg of CAPE to build in. This combined with dry air at the
low levels of the atmosphere will allow for a few storms to
produce gusty winds in addition to brief heavy downpours.
Thursday, better forcing and moisture advects into the region. This
will increase coverage of precipitation starting in the
afternoon. Scattered to widespread showers and thunderstorms will
lift north from Southwest MT through North-Central MT. Deep layer
shear of 30- 40kts will allow for some stronger thunderstorms to
develop if the region builds in enough instability. If it does,
then gusty winds, locally heavy rainfall, and small hail will be a
concern.
Models hint at a closed low forming heading into the weekend. This
will keep periods of scattered to widespread precipitation Friday
and Saturday. This will also bring cooler temperatures. Heading
into next week, the ensembles begin to diverge noticeably on the
evolution of the next trough building along the Pacific coast.
Though, an active pattern continues, but details are murky.
- Forecast Confidence & Scenarios:
Thermodynamics today don`t look overall impressive for severe
thunderstorms. However, I can`t rule out a stronger storm or two
from dry low levels and 30-40kts of deep layer shear. Thunderstorm
strength remains a little uncertain on Thursday. This is due cloud
cover from morning precipitation. Given the time of year, surface
heating isn`t as strong like in the summer time. If the region can
get some periods of sun through the scattered to broken cloud deck,
then some stronger storms to low end severe will be possible mainly
towards Central MT. If cloud cover limits instability development,
then the threat diminishes.
There remains uncertainty in where the corridor of heavier
 sets up and how much rain falls through the weekend. Models
still vary in solutions. The 25th percentile NBM (lower end
amounts) shows the wetter corridor of precipitation ranging from
0.3-0.6" and the 75th percentile (higher end amounts) ranging
from 1-2". Overall, expect a wetter next few days albeit the
uncertainty in amounts. -Wilson
&&
.AVIATION...
10/12Z TAF Period
VFR conditions will prevail across all terminals during this TAF
Period outside of during any thunderstorms. At the KGTF and KHLN
terminals between 11/00Z and the 11/06Z there is a 15 - 30% chance
for showers and thunderstorms. At the KHVR and KLWT terminals
there is a 15 - 20% chance for showers between 11/00Z and 11/07Z.
At the KCTB terminal during there majority of this TAF Period
there is a 10 - 20% chance for showers and thunderstorms. At the
KHVR terminal there is a 15% chance for showers and thunderstorms
between now and 10/18Z. All thunderstorms will produce frequent
lightning, a brief heavy downpour, and gusty, erratic winds.
During any thunderstorm there will be a brief period of mountain
obscuration. -IG
Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF  82  52  76  53 /  10  20  50  60
CTB  78  50  76  51 /  30  20  50  60
HLN  82  53  76  51 /  20  30  70  50
BZN  82  50  76  45 /  10  10  60  30
WYS  74  39  67  33 /  10  20  70  20
DLN  78  46  73  43 /  20  20  50  20
HVR  83  53  78  54 /  20  20  50  70
LWT  81  54  73  49 /  10  20  80  60
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
http://www.weather.gov/greatfalls

NWS TFX Office Area Forecast Discussion