807
FXUS65 KTFX 181706
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1106 AM MDT Mon Aug 18 2025

Aviation Section Updated.

.KEY MESSAGES...

 - Isolated to scattered showers and thunderstorms are expected
   this afternoon, with gusty winds and lightning being the main
   concerns.

 - Warmer temperatures expected on Tuesday and Wednesday with
   Tuesday expected to be the warmest day.

 - Mostly dry conditions are expected through the rest of the week
   with the exception of a cold front that is expected to move
   through and bring a chance for rain Wednesday and Thursday.

&&

.UPDATE...
/Issued 1002 AM MDT Mon Aug 18 2025/

The only change this morning was to increase the PoPs in
Jefferson county and vicinity. A few showers and a thunderstorm or
two have continued northeastward after forming in Idaho early this
morning. The thinking is that these showers slowly diminish late
this morning, though with increased daytime heating, the window
for them to diminish is becoming more and more narrow.

Additional showers and thunderstorms look to develop this
afternoon, initially in Beaverhead county and vicinity. These
showers and thunderstorms shifts northeastward through the
afternoon and evening, eventually making their way onto the
plains. Gusty winds and lightning are the primary concerns with
the stronger thunderstorms that form today. -AM

&&

.DISCUSSION...
/Issued 1002 AM MDT Mon Aug 18 2025/

 - Meteorological Overview:

Unstable southwest flow will continue today allowing for another
round of showers and thunderstorms this afternoon. Overall these
thunderstorms are expected to be on the drier side compared to
previous days which will increase fire weather concerns with
gusty, erratic winds and lightning as the main hazards.

Upper level ridging will continue to build on Tuesday allowing for
temperatures to get into the mid to upper 90s across the plains
and valleys of central and southwest Montana. By Wednesday evening
into Thursday the ridge starts to flatten out as a trough comes
down across central and southern Canada. Depending on the timing
of the cold front, afternoon showers and thunderstorms may be
possible on Wednesday but the main benefit will be cooler
temperatures that will last through the remainder of the work
week.


 - Forecast Confidence & Scenarios:

Thunderstorms Today:

Yet another round of afternoon showers and thunderstorms is
expected this afternoon. Inverted-v soundings and DCAPE over 1000
J/kg in the models point towards another day of strong gusty
winds out of any thunderstorm that develops with an isolated
chance for severe wind gusts out of stronger downbursts.

One of the big concerns for this afternoon is that these storms
will trend on the drier side particularly across southwest
Montana. The potential for frequent lightning along with gusty
winds will raise fire weather concerns through the afternoon. North
of I-90 PWAT values start increasing which will allow for some
wetter thunderstorms to develop across central Montana through the
early evening hours. Compared to yesterday the track and coverage
of storms is expected to be fairly similar.


Heat Tuesday and Wednesday:

When looking at the HeatRisk, there are areas across Fergus and
Blaine counties that touch the major category on Tuesday and there
is some justification for a heat advisory based on Tuesday`s high
temperatures and dewpoints. However, temperatures cool off into the
low to mid 60s overnight and while Wednesday is expected to reach
the 90s again, overall, temperatures are expected stay below
critical thresholds. Because the main threat seems to be only
Tuesday afternoon, for now, the decision was made to hold off on
issuing a heat advisory. However, this is a developing situation and
if updated model guidance trends warmer for Wednesday it is possible
an advisory may be needed.


Late Wednesday and Beyond:

The latest model guidance shows the ridge flattening out as a trough
moves across central and southern Canada. Currently the best
estimate for timing between Wednesday afternoon and early
Thursday morning. There remains some uncertainty with how this
event will play out with even minor changes in the track and
timing potentially having a significant impact. If the associated
cold front arrives earlier on Wednesday it may become a concern
for severe weather along the Hi-Line and if the trough is able to
make it farther south it may be able to impact more of the
region. Right now those are the two main questions that have yet
to receive a definitive answer but will be monitored closely with
future updates.  -thor


&&

.AVIATION...

18/18Z TAF Period

Primary concern this TAF period will be for scattered showers and
thunderstorms developing early this afternoon across Southwest
Montana, shifting northeastward through the afternoon and evening
into Central Montana. Gusty and erratic winds and lightning are the
primary concerns with thunderstorms.

Otherwise impacts from regional wildfires will continue to result in
localized reduction to surface visibility, with more widespread
slant-range visibility reductions. -AM

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

&&

.FIRE WEATHER...

Elevated fire weather conditions are expected to continue through
today. A mix of wet and dry showers/thunderstorms can produce
strong erratic wind gusts and frequent lightning. This can
lead to new lightning starts and easier fire spread with gusty
outflow winds and lower minimum humidities. -Wilson

Fire weather concerns will continue through Tuesday and Wednesday
with highs in the 90s expected across the plains and valleys across
the region. Minimum RH values will range from the single digits to
the mid teens with Tuesday expected to be the warmest and driest day
of the week. Winds are less of a concern these days, however, an
isolated afternoon dry thunderstorm cannot be ruled out which will
keep fire weather concerns elevated until a cold front passes
through late Wednesday into Thursday. -thor

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  89  59  96  60 /  10  20   0  10
CTB  84  54  91  59 /   0  20   0  10
HLN  89  58  96  59 /  20  50   0   0
BZN  89  53  96  55 /  20  20   0   0
WYS  82  40  86  43 /  20  10   0   0
DLN  86  49  93  52 /  20  20   0   0
HVR  90  60  96  61 /   0  10   0  10
LWT  85  58  93  59 /  10  20   0   0

&&

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

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