961
FXUS65 KTFX 132100
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
300 PM MDT Sat Jul 13 2024

.SYNOPSIS...

Critical fire weather conditions across much of southwestern and
central Montana will continue through the rest of the afternoon
and early evening. Further north, the threat of severe weather
will continue through the evening hours before tapering off.
Winds and storms will decrease overnight, but another hot and dry
day is forecasted on Sunday.

&&

.DISCUSSION...

Today and Tonight... Thunderstorms are already underway along Hill
and Blaine counties. The severe weather threat for these two
counties is higher with up to 2 inch hail and over 60 mph gusts
possible. These storms will continue to push east with more storms
coming down from Canada over the next few hours. The thunderstorm
threat is expected to diminish after 7 PM.

The other main threat for this afternoon will be critical fire
weather conditions in southwestern Montana with gusty winds and
low relative humidity that will make fires hard to contain. The
winds will start to taper off after sunset but poor recovery
overnight will lead to near-critical fire weather conditions
tomorrow afternoon. Despite the near-critical environment, the
duration of the highest winds is quite narrow and winds are
generally expected to be lighter Sunday than today. However, it
will be something to watch in case conditions deteriorated
further. -thor

Sunday through Monday... A high pressure ridge is forecast to
build back into the forecast area on Sunday, maintaining the hot
and dry conditions. However, it will also help decrease winds
aloft, which will in turn keep winds from becoming quite as strong
as those today. Weak energy in the resulting flow aloft may bring
a few weak thunderstorms to the Hi-Line and to the Southwest
Montana mountains once again during the afternoon. A shortwave
trough is then forecast to move southeast on the leading edge of
the ridge across southern Saskatchewan Sunday night through
Monday, which will swing a Canadian cold front south over at
least the plains of Montana. An overall lack of moisture will
limit the possibility of thunderstorm activity, but a few storms
cannot be ruled out. The main impact of this frontal passage will
be to cool temperatures back closer to seasonal averages with a
shift to more northerly winds, at least over the plains.

Tuesday through next Saturday... The ridge is forecast to remain
unusually strong over the Western United States through this
period, as indicated by good agreement among model ensemble
clusters. This will likely result in a return to widespread much
above normal temperatures through this period, with most lower
elevations continuing to have high temperatures in the 90s and
possibly over 100 degrees. The chance for afternoon and evening
thunderstorms will mainly be focused over the mountainous area of
Southwest Montana. However, the heat will likely be the greater
threat, so prepare for it now if you need to. -Coulston

&&

.AVIATION...
13/18Z TAF Period

VFR conditions will prevail throughout the 1318/1418 TAF period;
however, monsoonal moisture lifting northeast from the Great Basin
and towards the Northern Rockies this evening will overspread
Southwest Montana by Sunday morning and bring increasing mid- to
upper level cloudiness to the KWYS, KEKS, and KBZN terminals. Smoke
from wildfires burning across the Western US will also lead to hazy
skies across much of Southwest Montana (i.e. KWYS, KEKS, and KBZN
terminals) through the early evening hours tonight, mainly reducing
slantwise visibility on approach. At the KHLN terminal, west to
northwest winds will keep most of the smoke and haze from the Horse
Gulch fire west of the terminal through this evening, but decreasing
winds overnight may allow for reductions in slantwise visibility
through the morning hours on Sunday at the terminal. Finally,
temperatures in excess of 90 degrees across all terminals this
afternoon will lead to density altitude concerns.

A weak disturbance moving over Southeast Alberta/Southwest
Saskatchewan this afternoon and through the early evening hours will
help to initiate isolated to scattered thunderstorms near and east
of the KHVR terminal in North Central Montana. The best chance,
approximately 30-40%, for any thunderstorms impacting the KHVR here
appears to be between 19-23z this afternoon; but may linger as late
as 04z this evening. Main threat from any thunderstorm, especially
east of the KHVR terminal over Blaine County, would be a period of
heavy rain, hail, and strong outflow winds.

An isolated thunderstorm or two can`t be ruled out across Southwest
Montana near the KEKS and KWYS terminals this afternoon and evening,
mainly between 18z and 00z, but the probability for said activity is
less than a 20% chance. Should any storm develop the main threat to
terminal operations would be gusty and erratic outflow winds. -
Moldan/Coulston

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

&&

.FIRE WEATHER...

The Red Flag Warning remains in effect from 2 pm today through
midnight tonight for Fire Weather Zones 117 and 118 due to hot
temperatures, low humidity, and gusty winds.

The forecast remains on track with keeping the main focus for
critical fire weather conditions today over portions of Southwest
and Central Montana (including Fire Weather Zones 117 and 118).
Significantly dry fuels will combine with increasing westerly
winds (gusting mostly to 35 mph at times) and continued low
afternoon humidity (as low as 10 percent). The area of most
concern in Zone 117 is Meagher County, as fuels in areas farther
north in the Zone (including Cascade and Judith Basin Counties)
have not dried out as much.

Similarly hot and dry conditions are forecast for Sunday, but
winds are not forecast to be quite as strong. After a brief and
minor cooldown on Monday, hot and dry conditions are forecast to
return for at least the next week after that.
-Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  58  95  57  89 /   0   0   0   0
CTB  55  90  52  87 /   0   0   0   0
HLN  62  98  60  95 /   0   0   0   0
BZN  57  96  56  91 /  10  10  10  10
WYS  47  83  46  82 /  10  10  20  30
DLN  56  92  55  88 /  10  10   0  10
HVR  58  93  56  86 /  10   0  10   0
LWT  57  89  54  84 /  10   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until midnight MDT tonight for Central and
Eastern Lewis and Clark National Forest Areas.

Red Flag Warning until midnight MDT tonight for Helena and
Townsend Ranger Districts of the Helena National Forest.

&&

$$

http://www.weather.gov/greatfalls