533
FXUS65 KTFX 200648
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1248 AM MDT Fri Sep 20 2024

AVIATION SECTION UPDATED

.SYNOPSIS...

Breezy and gusty winds will continue through Friday in wake of a
fast moving disturbance, with a chance for showers over the plains
of Central and North Central Montana on Friday. Temperatures will
be below normal on Saturday, but warm back near to above normal
from Sunday through early next week.

&&

.UPDATE...

No major changes to the forecast were made. Just some slight
adjustments to the winds for tomorrow based on updated model
guidance.  -thor

&&

.AVIATION...
20/06Z TAF Period

VFR conditions are forecast to mostly continue across much of
Southwest (KWYS, KEKS, KBZN), Central (KHLN, KGTF, KLWT), and North
Central (KHVR, KCTB) Montana through at least 21/06Z, unless
otherwise mentioned, such as patchy fog development in the Southwest
Montana valleys potentially causing a period of MVFR/IFR conditions
at KWYS between 10Z and 18Z.

A disturbance moving through the area will continue moderate west to
northwest mid-level winds, which will cause periods of mountain wave
turbulence. Areas of low-level wind shear will also occur through
around 15Z and again after 03Z; in between, these gusty winds will
mix down to the surface.

A weak frontal boundary will also move south over the plains of
North Central Montana after 18Z, which may bring scattered showers
with periods of mountain obscuring MVFR/IFR ceilings to KCTB and
KHVR. Showers with lowering ceilings are less likely to reach the
KGTF and KLWT terminals. -Coulston

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

&&

.PREV DISCUSSION...
/ISSUED 535 PM MDT Thu Sep 19 2024/

Rest of today through tonight...primary forecast concern throughout
the period is the potential for fog, mainly in the valleys of
Southwest and Central Montana and in the Milk River Valley in North
Central Montana where the combination of light winds and clearing
skies will be favorable for the development of fog. Showers have
largely come to an end over the plains of Central and North Central
Montana; however, and isolated (rogue) shower can`t be ruled out
through the remainder of the afternoon over or downstream of the
Sweet Grass Hills and Bears Paw Mountains. Otherwise, breezy and
gusty west to southwest winds will gradually decrease through the
early evening hours, but remain "strong" enough (near 10-15 mph)
over the plains of Central and North Central Montana to keep the
boundary layer mixed and limit the development of fog tonight
despite recently saturated soils. With this being said, a few fog
prone valleys in Southwest and Central Montana and the Milk River
Valley in North Central Montana are expected to see favorable wind
speeds for the development of fog, with the latest HREF and/or NBM
guidance giving these areas a 10-20% chance for visibilities of 6
miles or lower. While dense fog is not currently anticipated, given
the abundance of low level moisture from recent precipitation it is
not out of the realm of possibility for a few low-lying spots within
these valley locations to see visibilities of 1 mile or less during
the overnight hours and into Friday morning. - Moldan

Friday through next Thursday...A progressive weather pattern
develops through Monday with a series of lower amplitude troughs
in the upper level flow moving east across western Canada. The
first trough and its associated low at the surface already move
east across southern AB tonight with a cooler airmass sliding
south in its wake across north-central MT on Friday, expanding
into southwest MT Saturday. Breezy west winds this afternoon and
overnight tonight on the plains will shift to the north and
northwest on Friday with a few showers possible near Glacier NP
and along the US/Canadian border but most areas will remain dry.
While afternoon temperatures are only slightly below seasonal
averages, the cooler airmass and clearing skies later Friday night
and again Saturday night will allow temperatures to fall to the
30s at many locations and bring the risk of frost to some areas.
Dry and warmer conditions develop Sunday as upper level ridging
transits the area before breezy conditions develop with the
arrival of the next upper level wave Sunday night and Monday.

There is some uncertainty still with precipitation associated
with the wave moving through the area Sunday night and Monday, but
this is a fast moving system with current probabilities around
20-30% for showers on Monday. Medium range model ensembles seem
to be in reasonable agreement in the depiction of upper level
ridging building across the western US by the middle of next week,
likely resulting in a return to near and above average temperatures.
- Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  50  69  38  62 /   0  10  20   0
CTB  46  61  34  61 /   0  60  70   0
HLN  48  71  39  64 /   0   0  10   0
BZN  42  72  32  63 /   0  10   0   0
WYS  27  63  25  62 /   0   0  10   0
DLN  42  69  31  62 /   0   0   0   0
HVR  49  66  37  61 /   0  30  30   0
LWT  47  66  36  58 /   0  10  20   0

&&

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

$$

http://www.weather.gov/greatfalls