Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 220248

Area Forecast Discussion
National Weather Service Great Falls MT
848 PM MDT Thu Sep 21 2017


Satellite imagery this evening shows closed mid-upper level low
developing over the Great Basin within the SW extension of an
elongated trough that extends NE into central Canada.
Precipitation is increasing over SE ID and northern UT under
favorable dynamics ahead of the low and this should translate
north into SW MT over the next 3-6 hrs and continue to expand
north into central MT after 09-12z as the closed mid level
circulation drifts north into central ID. Just some minor updates
to timing of precipitation onset tonight from S to N based on
latest observed trends. Surface boundary also noted moving south
across N-central MT this evening, to supply some additional low
level cooling as N/NE flow in the low levels increases over the
forecast area. Snow levels still on track to lower tonight through
Friday morning, with significant snow accumulations in the mtns
of central and SW MT and mix or change to snow possible at
elevations from 3500-4500 ft Friday, particularly in the morning,
with accumulating snow likely remaining limited to elevations
above 4500 ft. Hoenisch



A developing weather system will bring widespread rain and snow to
Southwest and Central Montana tonight and Friday. North Central
Montana and the Hi-Line will see a chance for rain and snow as
well but accumulations will be much less than areas to the south.
High temperatures are expected to be only in the 40s but warmer
and drier conditions return for the weekend.


Updated 2345z.

Main concern for tonight through late Friday is a strengthening
weather system that will impact southwest and central Montana.
Surface winds are already shifting to the north/northeast across
North Central Montana in response to this developing system. Expect
developing widespread precipitation with significant mountain
obscurations and cigs lowering to IFR/MVFR overnight as rain mixes
with or completely changes to snow. Show will then change back to
rain by mid-day Friday, gradually tapering Friday evening. mpj/PN


/ISSUED 545 PM MDT Thu Sep 21 2017/

Tonight through Friday night...A developing storm system will
bring widespread rain and snow to Southwest and Central Montana
overnight. Latest model runs have trended this system about 100
miles further north than earlier runs were indicating. As a
result, snow levels (and temperatures) are expected to be lower
than originally indicated so have introduced a mention of snow
over the plains of Central Montana, including at Great Falls and
Lewistown, on Friday morning. However, temperatures over the
plains will likely remain just a touch too warm to allow much
snow accumulation (if any), and the best accumulations are still
expected to be in the mountains. Lower snow levels and heavier QPF
have also trended snow accumulations higher for the mountains of
Fergus County so have expanded the Winter Weather Advisory to
include the Big Snowy, Judith and Moccasin Mountains. Periods of
precipitation will continue for much of the day on Friday and even
into Friday evening before the system begins to pull away from
the region and precipitation tapers off to showers. mpj

Saturday through Thursday...Spotty shower chances will continue into
the weekend with periods of clouds and sun as the upper-level low
slowly moves to the east and away from our area. Upper ridging
begins to slowly move toward the area from the west through the
week. The main challenge during the week will be watching for
relatively fast-moving disturbances bringing a few showers to the
region, especially the mountains, during this time. However, the
overall trend will be a trend toward warmer (near normal or
slightly above) and drier conditions. CC


GTF  33  40  31  51 /  60  80  60  20
CTB  32  40  30  52 /  20  50  40  20
HLN  34  40  31  51 /  80  90  50  20
BZN  36  44  29  49 /  90  80  40  20
WEY  32  39  21  45 / 100  70  30  20
DLN  34  39  27  45 /  90  90  40  20
HVR  35  46  33  55 /  10  50  50  20
LWT  34  39  30  49 /  90 100  40  20


Winter Weather Advisory until midnight MDT Friday night above
5500 feet for Beaverhead...Gallatin...Madison...Meagher.

Winter Weather Advisory from midnight tonight to midnight MDT
Friday night above 4500 feet for Broadwater...Cascade...Central
and Southern Lewis and Clark...Fergus...Jefferson...Judith Basin.


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