Helena, Montana Weather Forecast Discussion

948
FXUS65 KTFX 061923
AFDTFX
Area Forecast Discussion
National Weather Service Great Falls MT
Issued by National Weather Service Missoula MT
123 PM MDT Sat Sep 6 2025
.KEY MESSAGES...
-  Above average temperatures over the next few days trend closer
   to average toward the middle to late portions of this week.
-  Scattered showers and thunderstorms the remainder of the
   weekend, largely across Southwest Montana and along the
   Continental Divide.
-  Showers and thunderstorms become more
   numerous after Monday.
&&
.DISCUSSION...
/Issued Issued by National Weather Service Missoula MT/
- Meteorological Overview:
High amplitude upper level ridging across the western CONUS, with
ridge axis extending well north into BC/AB will begin to weaken
and shift eastward through the remainder of the weekend. An upper
level trough well off the Pacific NW coast nudges slowly eastward
through the weekend into early next week, which will begin to
transition flow aloft from the northwest to be more southwesterly
by Sunday afternoon. Showers and thunderstorms will increase in
spatial extent as the troughing gets closer, though Monday does
look to feature a bit of a lull in the increase in coverage. Given
all the wildfire activity off to the southwest, this switch in
flow aloft does look to reintroduce smoke to the remainder of the
region heading into Sunday and beyond.
Movement of the troughing approaching the Pacific NW slows to a
crawl early next week as it moves just onshore. Persistent south
to southwest flow aloft, with embedded waves ejecting from the
troughing, will allow for a several day stretch of scattered
afternoon and evening showers and thunderstorms across most if not
all of the region. At this point Wednesday and Thursday
afternoons look to feature the best combination of instability and
shear. EFI values for cape-shear are in the 0.7-0.8 range in the
Hill/Blaine county areas for late Wednesday through Thursday
afternoon timeframe, with a shift of tails of 0. This area will
need to be monitored for a more organized severe weather threat.
Heading toward the weekend deterministic models have been flip
flopping with the progression of upper troughing. Ensembles are a
bit more steady offering opportunities for precipitation, but
there will almost certainly be dry periods, even if there is a
trend toward a wetter solution. At this point the main takeaway
for Friday into the weekend is for opportunities for additional
rain. -AM
- Forecast Confidence & Scenarios:
The greatest source of uncertainty in the near term will be for
nocturnal showers tonight lifting from Southwest Montana into
Central Montana Sunday morning. Most of the latest high resolution
guidance does lift light showers across the aforementioned areas,
but is much less bullish on precipitation actually accumulating
(Producing 0.01 or more).
Looking further ahead, there remains uncertainty on location where
the best instability will set up in the afternoon in the middle
of next week. These details are not likely to be fully resolved
til the day prior to each round of showers and thunderstorms.
Confidence in specifics decreases further toward Friday and next
weekend. Several rounds of rain appear to be in the cards, but
will be heavily reliant on the timing of troughing and embedded
waves, which will take some time to resolve. -AM
&&
.AVIATION...
06/18Z TAF Period
VFR conditions will predominately prevail throughout the
0618/0718 TAF period as upper level ridging remains in place over
the Northern Rockies; however, regional wildfire smoke may bring
periods of mainly low-VFR VIS to the KHLN, KBZN, KEKS, and KWYS
terminals. Additionally, monsoonal moisture lifting northeastward
beneath the ridge will bring increasing mid- and upper level
cloudiness to Southwest and into portions of Central Montana
through the afternoon and evening hours. While isolated showers
and thunderstorms are possible beyond 00z Sunday along and south
of the I-90 corridor in Southwest Montana the probability of any
one shower or storm directly impacting the KWYS, KEKS, or KBZN
terminals was too low to mention at this time. -AM
Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF  50  86  55  83 /   0  10  10  10
CTB  45  83  52  80 /   0  10  10  20
HLN  55  83  53  83 /   0  20  20  10
BZN  50  83  48  81 /   0  20  20  10
WYS  42  73  37  72 /  10  60  40   0
DLN  50  80  45  80 /  10  30  20   0
HVR  44  83  56  83 /   0   0  10  10
LWT  49  82  53  80 /   0  20  10  20
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
http://www.weather.gov/greatfalls

NWS TFX Office Area Forecast Discussion