Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 270002

Area Forecast Discussion
National Weather Service Great Falls MT
555 PM MDT Sun Mar 26 2017



Tonight through Tuesday...Mainly clear skies over the state this
afternoon will give way to increasing cloudiness this evening as an
initial surge of moisture but little in the way of lift move in from
the west associated with an incoming Pacific upper trough. Upstream
radar observations show light precipitation just beginning to move
into western ID this afternoon. With this feature weakening as it
moves into he upper ridge in place, much of this precip will fizzle
as it move into MT but a few light showers are possible, mainly
across western zones during the evening period. Main upper trough to
the west moves onshore Monday morning and splits with much of the
energy diving SE into the Great Basin, though recent model runs have
trended a bit stronger with energy moving across the northern
Rockies late Monday and Monday night. Inverted surface trough looks
to shift east across the region this period with mid level winds
becoming somewhat variable and eventually shifting to the NW Monday
night, resulting in band of frontogenically forced precipitation
from SW MT NE into the central MT Mtns Monday night. Bulk of this
precipitation looks to fall east of Dillon to three Forks to Neihart
line including the Gallatin Valley. Snow levels Monday night should
begin above pass levels but fall to near the valley floors by Monday
morning, resulting in several inches of snow across the higher
terrain and potentially in the Bozeman area as well depending on the
timing of changeover to snow. This is a fairly drastic shift from
previous model runs for the Bozeman area and will be monitored for
potential winter highlights as snow could particularly impact the
Tuesday morning commute in the Bozeman area. Upper ridge builds back
in on Tuesday for drying conditions. Hoenisch

Tuesday Night through Sunday...The main focus during this period is
the storm system that is forecast to impact parts of the northern
Rockies / northern High Plains on THU/FRI. Model guidance is in
decent agreement bringing a strong shortwave SE through the Pac NW,
then closing the low off/deepening it over the central Rockies as it
slows down. It still looks like it will be a split system, but the
models continue to differ on the exact track of the upper low and
how strong the system will be. Of note, though, the model guidance
has trended a bit further north/east with the low track which could
allow the precip shield to be a bit further north as well. But,
again, given the model differences, I didn`t make too many changes
to the previous forecast. The main change was to up pops just a bit
across central Montana where confidence has increased a bit given
the more northern/eastern track. In addition, I lowered temperatures
just a bit as clouds/precip and a cold front dropping south out of
Canada may tend to keep temps lower, especially by Thursday night.
Right now, thinking the main window for precip will be late
Wednesday night through early Friday morning. Overall, it does look
like it will be cold enough for a transition to all snow, even at
lower elevations, but for now, given the warm antecedent
conditions and lower snowfall totals, I do not expect significant
impacts at lower elevations.

In the wake of this system, drier/breezy conditions develop by next
weekend. Temperatures may tend to moderate quite a bit as well with
above to well above normal temps possible. Martin


Updated 2355Z.

VFR conditions are generally expected over the next 24 hours, unless
otherwise mentioned. A moist southwest flow aloft ahead of a
shortwave trough will spread mid and high clouds with scattered rain
and mountain snow showers over the area through the period, which
will mainly obscure mountain tops. At lower elevations, showers will
be more hit-and-miss as a disturbance moves over the area through
12Z, especially over the plains. A few showers moving over the
southwest valley terminals may lower ceilings to high MVFR levels,
but any lowering will likely be brief. The shortwave trough
mentioned above will likely bring another round of scattered showers
to the area after 18Z, with brief MVFR ceilings possible mainly over
the southwest.


GTF  36  59  34  56 /  10  30  30   0
CTB  32  54  32  52 /  20  30  20   0
HLN  36  54  34  55 /  20  40  40   0
BZN  35  55  31  51 /  30  50  90  20
WEY  26  40  23  41 /  70  60  50  20
DLN  32  49  28  50 /  20  60  60   0
HVR  32  61  35  59 /  20  10  30  10
LWT  34  57  33  52 /  10  20  50  20



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