605
FXUS65 KTFX 180505
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1105 PM MDT Mon Jun 17 2024

...Aviation Section Updated...

.SYNOPSIS...

Cool and wet conditions continue through tonight and early
tomorrow morning as a cold spring weather system moves through the
area. After widespread showers on Tuesday, we will continue to
have a few isolated to scattered afternoon showers and
thunderstorms during the afternoons each day through the end of
the week.

&&

.UPDATE...

Updated forecast is out. The main adjustment was to lower snow
levels to valley floors over portions of Southwest MT, especially
over Madison and Gallatin counties.

Overall, the snowfall has been light for most areas today. It has
been snowing, mostly above 7000 feet around Big Sky, Bridger,
Kings Hill per web cams. For areas lower than 7000 feet, snow fell
at times, but generally mostly melted out. Cooler air is working
into the system currently, this will change the rain to snow over
Southwest MT at all elevations a bit easier, as elevations in the
Southwest area mostly above 4000 feet. Snow accumulations at the
valley floors should be mostly limited to grassy areas, where an
inch or two is possible. In the mountains, up to 5 inches is
possible. Further north, the precipitation has become more
scattered over North Central MT. Snow amounts tonight should be
slightly lighter in the mountains, where up to 3 inches are
possible. Thus the winter weather advisory will continue for the
mountain areas overnight.

Otherwise, much of the rest of the current forecast is on track.
Temperatures will be a bit warmer on Tuesday, as the main area of
low pressure pulls away from MT. Even warmer temperatures are
expected by late in the work week. The air mass will still be
unstable by the end of the week, so scattered
showers/thunderstorms will be possible. Brusda

&&

.AVIATION...
18/06Z TAF Period

Widespread rain, a rain/snow mix, or snow will gradually exit
eastern portions of Southwest through North Central Montana through
12-18z Tuesday; however, another disturbance pivoting southeast
around the departing one will bring a return chance of showers and
scattered thunderstorms moving from northwest to southeast across
North Central and into portions of Southwest Montana beyond 12z
Tuesday. IFR/MVFR/low-VFR conditions will prevail across all
terminals regardless of falling precipitation, with the lowest and
most persistent CIGS occurring in THE northerly upslope favored
locations of Central and Southwest Montana. Mountain obscuration will
continue across the entirety of the Norther Rockies over the next 24
hours. - Moldan

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

&&

.PREV DISCUSSION...
/ISSUED 725 PM MDT Mon Jun 17 2024/

Key Points:

-Rain and mountain snow continue through Tuesday morning with
precipitation becoming showery during the day Tuesday

-Showers and thunderstorms will develop most afternoons
Wednesday through Friday as temperatures gradually warm

Through Thursday Ongoing widespread rain and mountain snowfall
continue across North Central and Southwestern Montana through the
evening and overnight tonight as an anomalously cold weather
system continues to work its way through the area. So far, most
areas have seen a general .1-.2 inches of rainfall, though areas
along a line from the Bears Paw Mountains to Great Falls to the
Bob Marshall Wilderness Complex have seen amounts come in a bit
higher, with up to .75 inches of precipitation in the past 24
hours, with some of that falling as snow above 6000 feet or so.
Where snow has fallen, it appears that accumulations have
generally been limited to grassy and elevated surfaces, and even
there accumulations have generally been around an inch or two
early this morning before daytime heating began to melt the snow
faster than it fell after sunrise. We will have to watch for some
accumulations after sunset again tonight, but this will come as
the main area of precipitation begins to move off to the
northeast, so any additional accumulations of snow will generally
be a coating of up to 6 inches on the highest peaks.

In the wake of this system tomorrow, upper level troughing and
cold air aloft will linger across North Central and Southwestern
Montana, which will help to spur the development of scattered to
widespread showers and maybe a thunderstorm or two across the
area. These showers and storms should bring a bit of additional
moisture to many of us, with most areas seeing up to 0.1 inches of
additional rainfall tomorrow. Temperatures will moderate a bit
Wednesday and Thursday as our upper level flow becomes
zonal/westerly, though we will have a few showers and
thunderstorms develop each afternoon. Ludwig

Thursday through Friday...ensemble clusters favor southwesterly flow
aloft over the Northern Rockies as shortwave troughing moves from
over the Eastern Pacific/Western Seaboard and towards the Northern
and Central Rockies. This southwesterly flow regime will help to
maintain scattered to numerous showers and storms, particularly over
Central and North Central Montana, each day. Additionally,
temperatures will moderate to near normal.

Saturday through next Monday...quasi southwest to zonal flow is
favored within the multi-model ensemble mean during the period,
which is expected to translate to well above normal temperatures and
isolated showers/storms each day across the Northern Rockies. -
Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  58  37  67 /  80  80  40  30
CTB  35  53  32  65 /  40  80  30  30
HLN  42  64  40  72 /  90  70  40  20
BZN  33  59  33  69 /  90  60  30  20
WYS  28  52  24  63 /  90  60  20  10
DLN  33  56  32  65 /  80  30  20  10
HVR  42  61  40  69 /  80  70  40  30
LWT  34  54  34  65 / 100  80  40  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until noon MDT Tuesday for East Glacier
Park Region-Southern Rocky Mountain Front.

Winter Weather Advisory until 6 AM MDT Tuesday 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-
Snowy and Judith Mountains.

&&

$$

http://www.weather.gov/greatfalls