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fxus65 ktfx 150011 

Area forecast discussion
National Weather Service Great Falls Montana
511 PM MST Thu Dec 14 2017


A quick update was made to extend the freezing fog advisory across
southwestern portions through the night. Satellite imagery showing
fog remains from the Gallatin valley northward along Highway
287/12 to the Helena valley. With ridging over head...and light
winds expected all night...will keep the freezing fog advisory
through the night. There is the possibility winds may increase
just enough later tonight...possibly ending the fog early. This
will have to be monitored through the night. Anglin/coulston



Stubborn freezing fog is expected to persist in the valleys of
southwest Montana through Friday morning. Accumulating snow will
then overspread the region from northwest to southeast late Friday
morning through early Saturday morning. Precipitation will fall
as rain or a rain/snow mix at lower elevations on Friday before
changing to snow that evening. The snow will then end gradually
later Saturday morning through early Sunday morning.


updated 0000z.

Persistent fog will bring continued LIFR conditions to the
Bozeman valley (including kbzn) this evening...and likely through
much of the overnight hours. IFR fog may also develop across a few
other southwestern valleys later tonight...including khln and
possibly keks. Any fog that does develop is expected to linger
until around 15z...although may end earlier if winds can increase.
The remainder of the sites will see VFR conditons with some high
clouds for tonight.

For the rest of Friday...VFR and breezy conditions will generally
be found with some brief MVFR to IFR conditions as fog lifts
across the southwest. A cold front is expected to bring snow...and
possibly brief sleet...from north to south late Friday afternoon
through the evening hours. Mainly only affecting kctb to khvr for
this forecast forecast period...moving southward across most
other sites after 00z_saturday. MVFR to IFR conditions will be
possible with any snow or sleet shower. Anglin


Previous discussion...
/issued 258 PM MST Thu Dec 14 2017/

Rest of today through Saturday night...high pressure ridging aloft
will break-down on Friday as a disturbance continues approaching
from the Gulf of Alaska region. This disturbance will then cross
our area on Saturday and be followed by high pressure aloft
building-in from the west by early Sunday morning. At the surface,
a Canadian cold front will cross the border and enter the hi-line
Friday afternoon. This front is then expected to stall along the
Rocky Mountain front and central Montana Mountains by Friday
evening. It will then remain there through Saturday before
dissipating thereafter. Above-normal temperatures will prevail
over north-central Montana ahead of the cold front, then cool
somewhat behind the front for Friday night through Saturday night.
With recent cold air entrapment in the valleys of southwest
Montana, overall cooler readings are expected there throughout the

Predominantly fair weather is expected to continue through Friday
morning. However, patchy freezing fog should persist in the
southwest Montana valleys before dissipating toward noontime on
Friday. In addition, gusty downslope winds are expected to develop
over north-central Montana overnight tonight into Friday, but
model guidance indicates peak gusts should remain below high wind
criteria. The aforementioned disturbance will allow snow to
overspread our region from northwest to southeast late Friday
morning through early Saturday morning. Thereafter, the snow will
taper-off gradually and end area-wide by early Sunday morning. At
lower elevations, precipitation will fall as rain or a rain/snow
mix for a time on Friday before changing to snow that evening.
Snow totals are still expected to reach a trace to 3 inches for
the plains/valleys, with totals of up to a foot in the mountains.
Issued winter weather advisories for Marias Pass and Kings Hill
Pass, where confidence is high accumulating snow will impact
travel. Will let future shifts decide if advisories need to be
expanded in areal coverage.

Sunday through unsettled weather pattern will reside
over the region, with a gradual shift towards colder temperatures
over north central Montana by late in the period. Breezy west winds
develop on Sunday allowing the I-15 corridor to warm up a bit from
Great Falls to Cut Bank, otherwise expect another round of light
snow to move through the region late Sunday night through Monday. A
few snow showers linger into Tuesday, otherwise the next major
weather system will be the cold front pushing southward from Canada
into Montana Wednesday into Thursday. A much colder air mass will
follow on the heels of this system under northerly upper level flow
late Wednesday through the end of next week.


Preliminary point temps/pops...
gtf 34 45 27 33 / 0 10 70 50
ctb 33 42 24 33 / 0 40 70 40
hln 22 37 24 30 / 0 0 60 40
bzn 16 36 21 29 / 0 0 70 50
wey 10 25 16 24 / 0 0 80 50
dln 20 37 22 30 / 0 0 40 30
hvr 30 42 25 36 / 0 40 60 20
lwt 31 47 25 30 / 0 0 70 40


Tfx watches/warnings/advisories...
Winter Weather Advisory from 5 PM Friday to 11 PM MST Saturday
Cascade...Judith Basin...Meagher.

Freezing fog advisory until 8 am MST Friday Broadwater...central
and southern Lewis And Clark...Gallatin.

Winter Weather Advisory from 11 am Friday to 11 am MST Saturday
northern Rocky Mountain front.


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