155
FXUS65 KTFX 142350 CCA
AFDTFX

Area Forecast Discussion...CORRECTED
National Weather Service Great Falls MT
550 PM MDT Fri Jun 14 2024

UPDATED AVIATION SECTION

.SYNOPSIS...

After a few warm days, cooler temperatures will return to the
Treasure State over the weekend and into next week, along with
some gusty winds Saturday afternoon and evening. Monday and
Tuesday will bring widespread precipitation, with rain at lower
elevations and snow in some of the higher terrain above 6000 feet.

&&

.DISCUSSION...

Key Points:

-A few thunderstorms are expected across far SW MT this
afternoon, with a few more thunderstorms across North Central and
Southwestern Montana on Saturday

-Strong wind gusts to 60 mph are expected Saturday evening and
early Sunday morning along the Rocky Mountain Front to Cut Bank

-Widespread rainfall still expected early next week, though
widespread heavy rainfall is looking less likely

-Mountain snowfall is also expected with this system, mainly
above 6000 feet

-Unsettled weather with showers and thunderstorms late next week
as temperatures gradually rebound

Short term (through Sunday)... Upper level ridging centered over
Eastern Montana this afternoon is resulting in southwesterly flow
aloft across the western portion of the Treasure State. This
southwesterly flow aloft is promoting warm temperatures area wide,
with a few thunderstorms also developing along the Montana/Idaho
border. While these storms should exit the area by sunset, we will
have to watch for a few instances of gusty winds and small hail
with these storms as they remain south of a Bozeman to Dillon
line.

The upper level ridge that was mentioned above will push further
east tomorrow as an upper level trough begins to work its way into
the area. This trough will lead to increasing clouds through the
morning, with a cold front beginning to push through the area
during the afternoon, which will be accompanied by a few showers
and even a few thunderstorms. Temperatures will fall sharply
behind this front, going from the low 70s to mid 50s within an
hour or two of the fronts passage. Gusty winds will be
responsible for the spreading of these cooler temperatures, and
winds should remain gusty across North Central Montana through the
evening. Winds may linger along the Rocky Mountain Front and the
adjacent plains, where a few wind gusts to 50-60 mph remain
possible. Looking at the state of the atmosphere tomorrow evening,
there will be the potential for a wind gust or two to around 60
mph in and around Cut Bank, though this will be highly dependent
on the exact timing of the arrival of a mountain wave and if it
arrives before the lowest 500-1000 feet of the atmosphere decouple
from the days mixed layer, these wind speeds will be attainable.
With that said, the NBM does support the idea of a 60 mph wind
gust, though a lot of the higher resolution guidance suggests that
the higher winds will remain along the immediate Rocky Mountain
Front. Given the way these types of events play out, I think it is
more likely than not that these winds do remain primarily along
the Front, but I have elected to leave the High Wind Warning for
now to see if the next 12-24 hours bring some more certainty one
way or the other. Sunday will start out breezy across the area,
though winds should gradually weaken through the day as this first
low pressure system moves further east.

Extended (Monday through next Friday)... The first half of next
week will be cool and wet as a shortwave trough works its way
through the Northwestern CONUS. Rain and mountain snow will begin
to work in from the Southwest on Monday as a surface low pressure
system begins to develop over Southern WY and Northeastern UT in
response to the arrival of this upper level trough. For the most
part, most areas will see at least .2 inches (generally the 25th
percentile) of liquid precipitation between Monday and Tuesday
night, with many areas seeing at least a half inch at the 50th
percentile. Where things get interesting is at the high end of the
distribution at any particular location, with many areas seeing
the potential for 1.5-2 of rain at the 90th percentile. Why the
large range? From what I have been able to gather through a few of
the operational forecast models (such as the GFS), it appears
that there will be some mesoscale features embedded within this
system, which will be capable of producing a sustained period of
moderate to heavy rainfall for the areas that wind up seeing these
features. Given that most areas will not see these features, I
have begun the process of nudging precipitation down across the
area, as the inherited forecast was generally above the 75th
percentile (or higher) with the more recent runs of the NBM. Even
though a lot of areas will likely see less precipitation than the
current forecast suggests, I still want to be cognizant of the
potential for higher amounts of precipitation where the small
scale features develop.

Beyond midweek, zonal flow aloft will allow our temperatures to
gradually increase through the second half of the week, while also
allowing us to see the development of afternoon showers and
thunderstorms each afternoon. Ludwig

&&

.AVIATION...
15/00Z TAF Period

VFR conditions are mostly expected to continue through at least
16/00Z across North Central (KCTB, KHVR), Central (KLWT, KGTF,
KHLN), and Southwest (KBZN, KEKS, KWYS) Montana, unless otherwise
noted.

A low pressure trough just off the Pacific Northwest coast will keep
the area under a southwesterly flow aloft, which will bring some
mountain wave turbulence. Initially, a weak disturbance in the flow
will bring scattered showers and thunderstorms to Southwest Montana
through around 02Z, with the primary threats being erratic wind
gusts and lots of lightning, but brief periods of mountain-obscuring
MVFR conditions are possible in heavier rain. Another disturbance
will then bring a chance for scattered showers to portions of
Southwest and Central Montana between 09Z and 15Z. As the trough
approaches Montana after 12Z, the flow aloft, along with the
mountain wave turbulence, will increase. Also, as the airmass
becomes unstable once again, scattered showers and thunderstorms
will move east across the area after 17Z. An associated frontal
boundary will also spread gusty westerly winds across the area, with
portions of the Rocky Mountain Front receiving gusts in excess of 50
kt at times. -Coulston

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  51  72  42  64 /  10  60   0  10
CTB  46  64  41  58 /   0  40   0  30
HLN  54  71  42  67 /  20  50   0   0
BZN  50  74  36  65 /  40  50   0   0
WYS  43  68  35  60 /  10  10   0   0
DLN  50  74  34  65 /  20  10   0   0
HVR  51  72  44  62 /  10  60  20  20
LWT  49  75  37  63 /  40  90  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Saturday afternoon through late Saturday
night for Eastern Glacier, Western Toole, and Central Pondera-
Northern High Plains.

Winter Storm Watch from Monday morning through Tuesday evening
for East Glacier Park Region-Southern Rocky Mountain Front.

Winter Storm Watch from Monday evening through Tuesday evening
for Big Belt, Bridger and Castle Mountains-Elkhorn and Boulder
Mountains-Gallatin and Madison County Mountains and Centennial
Mountains-Little Belt and Highwood Mountains-Northwest
Beaverhead County.

&&

$$

http://www.weather.gov/greatfalls