Basin, Montana Weather Forecast Discussion

174
FXUS65 KTFX 100524
AFDTFX
Area Forecast Discussion
National Weather Service Great Falls MT
1124 PM MDT Tue Sep 9 2025
Aviation Section Updated.
.KEY MESSAGES...
- Hazy skies will continue across portions of north-central
   Montana through Wednesday afternoon.
- Isolated to scattered showers expected through the rest of the
   evening into tomorrow.
- More widespread chances for showers Thursday through Sunday.
&&
.UPDATE...
/Issued 828 PM MDT Tue Sep 9 2025/
Showers and a few thunderstorms continue to track north across the
area this evening as the initial energy associated with a larger
scale upper trough along the west coast lifts into the area. There
was enough low level dry air in place across southwest MT for some
localized stronger wind gusts associated with this activity there, though
the risk of stronger winds will decrease through the rest of this
evening. Shortwave energy lifting out of central ID will support
additional showers and thunderstorms across western portions of
central/north-central MT later this evening through the early
overnight period and pops/weather have been adjusted in line with
this. Hoenisch
&&
.DISCUSSION...
/Issued 828 PM MDT Tue Sep 9 2025/
- Meteorological Overview:
Today an upper-level ridge is over North-central, Central, and
Southwestern Montana with an upper-level trough approaching the
area. As a result it will be another warm day today. Due to the
southwest flow aloft combined with monsoonal moisture, there will be
isolated showers and thunderstorms this afternoon and evening across
North-central, Central, and Southwestern Montana. The strongest
thunderstorms will produce strong wind gusts, frequent lightning,
and a brief heavy downpour. On Wednesday the upper-level ridge
begins to shift eastward and the upper-level trough approaches
Montana. On Wednesday it will be another warm day with isolated
showers and thunderstorms across North-central, Central, and
Southwestern Montana due to the upper-level ridge and approaching
trough combined with monsoonal moisture. Today and Wednesday due to
the Southwest flow aloft there will be hazy skies from regional
wildfires across North-central, Central, and Southwestern Montana.
On Thursday the upper-level trough moves over North-central,
Central, and Southwestern Montana. This will cool temperatures down
and bring another round of showers and thunderstorms to the area.
The strongest thunderstorms will produce strong winds, frequent
lightning, and a brief heavy downpour. On Friday the upper-level
trough remains over North-central, Central, and Southwestern
Montana. This will cool temperatures down to near seasonal averages
across the area and bring showers to the area. Saturday through
Monday generally an upper-level trough persists with a few upper-
level shortwaves. This will keep temperatures at about seasonal
averages with daily chances for showers across North-central,
Central, and Southwestern Montana Saturday through Monday.  -IG
- Forecast Confidence & Scenarios:
Showers/Thunderstorms Today through Thursday:
Coverage through this evening and tomorrow afternoon will be
isolated to scattered. In general, these storms are expected to
stay far below severe thresholds although a couple stronger storms
could produce locally heavy downpours.
The bigger concern is for what occurs Thursday afternoon across
north-central Montana. Looking at all the parameters for
instability, the potential exists for stronger storms to develop
along the Hi-Line with higher probabilities of severe weather
further east of the region. The uncertainty in this set up is in
how the cold front progresses and what timeframe it arrives in
central Montana. Variations between model runs have made it
difficult to pin down exactly what the threat level will be for
Thursday. But there is enough of a concern for what might unfold
that this will be something to watch with future updates.
Rainfall Amounts:
Thursday through Sunday, across north-central and central Montana
there is a greater than 75% chance of at least 0.25", a 50-70%
chance of at least 0.5", and a 30-50% chance of at least 0.75".
Across southwest Montana Thursday through Sunday there is a
40-60% chance of at least 0.25" and a 20-40% chance of at least
0.5".
Thus the takeaway for now is that most locations will see some
measurable rain through the weekend. Some heavier amounts are
possible but it is more likely that the heavy amounts will be
local to where the stronger storms develop. In general, the Hi-
Line has the highest probabilities of seeing these higher amounts.
-thor
&&
.AVIATION...
10/06Z TAF Period
VFR conditions will prevail across all terminals during this TAF
Period outside of during any thunderstorms.  At the KGTF and KHLN
terminals for the first three hours of this TAF period there is a
20 - 40% chance for rain showers and between 11/00Z and 11/06Z
there is a 15 - 30% chance for showers and thunderstorms. At the
KCTB, KHVR, and KLWT terminals there is a 20 - 40% chance for
showers between now and 10/18Z. At the KCTB terminal between
10/21Z and the end of this TAF Period there is a 15 - 25% chance
for showers and thunderstorms. All thunderstorms will produce
frequent lightning, a brief heavy downpour, and gusty, erratic
winds. During any thunderstorm there will be mountain obscuration. -IG
Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF  53  82  53  75 /  60  10  20  50
CTB  49  79  51  74 /  60  40  20  40
HLN  52  83  53  78 /  50  20  30  60
BZN  47  83  50  78 /  50  10  20  60
WYS  37  73  39  67 /  50  20  30  60
DLN  45  78  46  73 /  40  30  10  40
HVR  54  85  55  79 /  40  40  20  40
LWT  52  82  54  74 /  20  20  20  60
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
http://www.weather.gov/greatfalls

NWS TFX Office Area Forecast Discussion