Area Forecast Discussion
Issued by NWS Great Falls, MT

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058
FXUS65 KTFX 141750
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1045 AM MST Tue Nov 14 2017

Aviation Section Updated.

.UPDATE...

Surface pressure is rising approximately along and west of I15.
The overnight high wind warning was allowed to expire as observed
wind speeds are declining as forecast. Light snow will continue
through mid-day over the Northern Rockies, but with little
continuing impacts the winter weather advisory was allowed to
expire for this area as well. Isolated light snow showers may be
possible over western portions of the N-central plains as higher
pressure builds in from the north. The greater weather challenge
this morning has been a band of moderate to heavy snow that moved
across southwest Montana. Observations indicate the primary band
and its associated surface front are moving away through West
Yellowstone, having almost completely exited our forecast area.
Snow showers will continue today, but impacts to travel will
decline through the afternoon with a mix of sun and clouds. The
forecast for today was updated to better match these observed
trends. PN

&&

.SYNOPSIS...

Gusty winds and near to above normal temperatures will be the theme
across Central Montana over the next couple of days, although areas
from Havre to Chinook may stay cooler than areas further south.
Across Southwest Montana, snow showers will impact the morning
commute today, followed by drier conditions tonight through
Wednesday.

&&


.AVIATION...
Updated 1745Z.

VFR conditions prevail, with the exception of possible IFR/LIFR in
FZFG at KHVR late tonight through Wednesday morning. Areas of mid-
level cigs around 070AGL will continue thinning this afternoon
across N-central MT. Lingering clouds associated with an early
morning snow band over SW Mt will exit to the east. Mountain
obscuration in orographic clouds remains likely through at least
this evening. PN

&&

.PREV DISCUSSION...
/ISSUED 438 AM MST Tue Nov 14 2017/

Today through Thursday...Surface analysis this morning shows a
Pacific front arcing from central Alberta south through central
Montana, before stalling in the vicinity of SW MT. Downsloping in
the wake of the front will lead to a much lower chance of precip
across Central MT today. However, a moist/convergent flow and
low-level instability along the stalled front across SW MT will
likely allow for multiple bands of light to moderate snow to
impact that area through early this afternoon. For our main
population centers of SW MT (Dillon, Bozeman, Ennis), a quick 1-3
inches of snow is expected which will cause at least minor impacts
for the morning commute. For now, the plan is to highlight this
potential with an SPS, as impacts do not appear to be
widespread/significant enough to warrant a Winter Wx Advisory. Up
along the Rocky Mtn Front, the potential of strong wind gusts
will continue through early this morning, but will then quickly
decrease below High Wind Criteria as the low/mid level jet
weakens. Right along the Front, snow and blowing snow will
continue to cause impacts over Marias Pass and the Winter Wx
Advisory will continue there this morning. Over the plains, a
surface trough will swing through with gusty winds this afternoon
and maybe a brief rain/snow shower. In its wake, a moist/easterly
flow should allow areas of dense, freezing fog to develop along
the Milk River Valley late tonight.

After a dry day Wednesday, another front swings through WED night/THU
in very similar fashion as today`s. The main difference may be a
lack of better forcing/moisture, so precip amounts may end up
lighter. Although, once again Marias Pass will likely see some
travel impacts. MARTIN

Thursday night through Tuesday...Progressive pattern aloft will
continue through the end of the work week. Models bring another
upper level trough and associated surface cold front through the
region Thursday evening. This system is expected to be quite similar
to that of yesterday with the main impacts expected to be mountain
snows in Western/Southwest Montana with strong and gusty winds east
of the divide. High temperatures behind the front on Friday are
expected to be mainly in the 30s with temperatures slowly rebounding
to near or slightly above seasonal averages by Sunday.
Unfortunately, model solutions diverge significantly over the
weekend to such an extent that, by early next week, the upper
level trough/ridge pattern between the two models is shifted
nearly 180 degrees. Have trended the forecast closer to the wetter
GFS pattern but confidence beyond Saturday is quite low at this
time. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  25  45  34 /  10   0   0  10
CTB  40  19  41  25 /  10  10   0  20
HLN  40  22  42  29 /  10   0   0  20
BZN  36  17  42  30 /  60   0   0  30
WEY  34  16  36  27 /  70  10  10  70
DLN  38  19  43  31 /  50   0   0  50
HVR  40  17  37  24 /  10   0   0  10
LWT  38  22  45  31 /  10   0   0  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None

&&

$$

http://www.weather.gov/greatfalls



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