Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 191017

Area Forecast Discussion
National Weather Service Great Falls MT
317 AM MST Sat Jan 19 2019


A decaying Pacific storm system will sweep east across the region
today bringing gusty winds and mild temperatures. Winds relax
tonight as weak high pressure builds into the region before the next
storm system impacts the region Sunday into Monday. Snow, possibly
mixed with rain across the valleys of central and southwest Montana
Sunday will transition to all snow Sunday night. Accumulating snow
and falling temperatures late Sunday and Sunday night could create
difficult driving conditions through Monday morning.



Today and Tonight...Upper level ridge over the Northern Rockies this
morning is rapidly flattened today as a deep upper low off the BC
coast moves inland with trailing shortwave energy tracking east
along and N of the Canadian border this evening. Plume of Pacific
moisture associated with the system will shift east across the
region this morning with some light precipitation possible over the
mountains, but overall moisture with this system is decreasing as it
moves across the region with only an inch or two of snowfall
anticipated today across areas near the continental divide.
Increasing westerly flow aloft and a deepening lee-side trough of
low pressure will produce gusty winds today, especially across north-
central MT, where winds will also scour out the lingering cold
airmass at the surface. 700 MB flow increasing to 50-60kts this
afternoon should translate to 40-50 mph wind gusts across western
portions of north-central MT this afternoon with 60-70 mph wind
gusts along the immediate east slopes of the Rockies. Still some
marginal concern that high wind thresholds could be reached,
particularly in the Cut Bank area this afternoon, but snow-cover
across most of the area should limit mixing some, however this will
need to be monitored closely today. Still some potential for
localized blowing/drifting snow today in areas along the east
slopes, primarily this morning before temps rise well above freezing
this afternoon. Winds slowly diminish tonight as the lee-side trough
weakens and winds aloft decrease. Hoenisch

Sunday through Saturday...

The week begins with a somewhat complex system affecting the region.
As a low pressure system approaches from the west on Sun, a warm
front may lift north at least through part of the CWA. Highs in the
upper 30s to mid 40s are expected for much of the lower elevations,
especially for the SW Valleys. As a result, whatever snow may fall
at lower elevations Sun morning may mix with or change to rain
during the afternoon hours. However, as the low passes through the
CWA Sun evening, winds will shift and draw cooler air back south
from Canada, allowing for a quick change back to snow for most
places. The heaviest snow for north-central Montana is likely to be
later Sun eve into Sun night, with the heavier (but likely moderate
at most) snowfall shifting southward late Sun night into early Mon
afternoon. At lower elevations, snow totals generally between 1 and
4 inches are expected. Mountain snow totals are currently forecast
to be mostly in the 5 to 10 inch range, and advisories may be
necessary for many of our passes. After discussing with neighbors,
will hold that decision to the day shift, or next night shift.

Drier air will work into the state Mon night into Tue, allowing for
a period of drying and clearing skies as the eastern edge of a ridge
builds in from the Pacific. However, the axis of this ridge will
remain offshore, which will keep us in northwestern flow aloft, with
the potential for an active pattern from Wed into the weekend. The
next decent shot for precip appears to be Wed into Wed night. Beyond
that, more systems are certainly possible, but model agreement is
low, so POPs and QPF amounts were kept on the lower side for now.

After the aforementioned warmth Sun, temps will drop back toward
normal Mon, with highs upper 20s to mid 30s. A warming trend then
commences Tue as the ridging builds in from the west. Highs Tue are
currently forecast to be in the 30s for the north-central plains,
but mid 20s to lower 30s for the SW valleys. However, temps over the
Plains may need to be raised a bit depending on the amount of
sunshine and strength of downsloping winds we expect. Through the
latter half of the week, general W-SW`ly flow is expected much of
the time, allowing for highs to remain near to a bit above normal
for much of the CWA.


Updated 0600Z.

VFR conditions prevail tonight under a strengthening westerly flow
aloft, bringing increasing high level cloudiness to the region. A
weakening upper level disturbance passes across the region Saturday
morning for a period of broken mid level clouds and possibly some
light snow showers and mountain obscuration in the KBZN and KEKS
vicinity. Otherwise, main impact to aviation through Saturday will
be increasing winds and associated Mtn wave turbulence/low level
winds shear in areas east of the Rockies. Strongest winds initially
along the east slopes tonight will spread east across the plains by
Saturday afternoon. Hoenisch


GTF  49  30  41  24 /  10   0  60  60
CTB  43  24  39  18 /  30  10  30  40
HLN  46  26  40  22 /  10  10  60  60
BZN  43  26  42  22 /  30  30  60  60
WEY  29  18  34  17 /  70  80  80  80
DLN  42  28  42  24 /  20  20  20  50
HVR  37  20  40  18 /   0   0  10  60
LWT  47  26  41  23 /   0   0  50  50



Flood Advisory through 1015 PM MST Saturday evening for a portion
of the Missouri River in Cascade County.


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