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Area forecast discussion
National Weather Service Great Falls Montana
440 am MST Fri Jan 17 2020

Aviation section updated.

Synopsis...

Periods of light snow will spread across central and southwest
Montana this morning. Snow will begin to clear this afternoon. It
remains cold over the north. Temperatures trend warmer on Sunday,
possibly moving above average.

&&

Discussion...

An upper level shortwave trough will move quickly across the
region today, producing areas of light snow starting this morning,
and ending later this afternoon. Snowfall amounts should be less
than an inch for north-central Montana, but with 3 to 6 inches
expected for the Southwest Mountains where periods of moderate to
briefly heavy snowfall rates are possible. Snow is expected to
develop in time to generate some impacts to the morning commute,
including Helena and Bozeman areas. Winter weather advisories
remain in effect to address this light snowfall.

A shallow, Arctic airmass remains entrenched over the north-
Central Plains. Surface pressures are gradually rising for areas
generally north and west of Great Falls. The strengthening
pressure gradient has produced some increasing north winds. Many
reporting stations across north-central Montana have wind-chill
temperatures near or below -20f, and a few locations in eastern
Glacier and Toole counties are near or just below -40f. Thus, the
Wind Chill Advisory remains in effect, and may need to be
extended.

Pressure rises associated with the passing shortwave will maintain
cold temperatures for north-central Montana today and likely into
tomorrow. The coldest temperatures shift further east with the
passing wave, dropping most locations in Liberty, Hill and Blaine
counties back into the teens below zero later tonight. The
temperatures forecast along edges of the Arctic airmass remains
highly uncertain where it intersects higher terrain. Temperatures
could swing 30 degrees or more over just a few hundred feet of
elevation, particularly with veering mid-level winds present at
and above the temperature inversion.

After another chilly day on Saturday, forecast models indicate a
strengthening ridge aloft and a concurrent Lee-side surface
trough. This will initiate a weak downslope flow, but adequate to
mix out the Arctic airmass and produce rapid warming across most
of the region. Dry and seasonally mild conditions persist under
this ridge through Tuesday. A more active zonal flow returns for
the middle of next week, introducing chances for rain and snow.
Forecast confidence declines by the end of the period as model
solutions diverge, but overall maintain a rather mild pattern with
little significant precipitation.

&&

Aviation...
updated 440 am MST Fri Jan 17 2020 (12z Jan 17 taf period)

Clouds continue to increase over the region early this morning as an
upper level disturbance moves across the northern rockies. VFR/MVFR
conditions prevail, but temporary IFR cigs have developed at a few
of the terminals. Conditions decline to MVFR/IFR later this
morning as periods of light snow develop at most terminals with
the passing shortwave system. Expect improving conditions Friday
afternoon as the system moves off to the east.

&&

Hydrology...

The Flood Warning will continue for the city of Choteau. Flooding
from Spring Creek continues to impact portions of the city.

Ice jams are developing on portions of the Missouri River, from
the city of Great Falls, to the James Kipp campground in Fergus
County. No flooding has developed from the ice jams, but with
temperatures below freezing, the ice jam potential will continue
for the next several days.

&&

Preliminary point temps/pops...
gtf 8 -2 15 10 / 60 0 0 0
ctb -1 -12 8 2 / 40 0 0 0
hln 32 13 31 20 / 50 0 0 0
bzn 35 14 33 18 / 80 0 0 0
wys 19 4 22 6 / 100 20 20 10
dln 33 11 28 15 / 40 0 0 0
hvr 0 -14 3 -3 / 50 0 0 30
lwt 29 -1 22 10 / 60 0 0 10

&&

Tfx watches/warnings/advisories...
Winter Weather Advisory until noon MST today Beaverhead...
Broadwater...Jefferson...Meagher.

Wind Chill Advisory until 5 PM MST this afternoon Blaine...
Cascade...Chouteau...eastern Glacier...eastern Pondera...eastern
Teton...Fergus...hill...Judith Basin...Liberty...northern Rocky
Mountain front...southern Rocky Mountain front...Toole.

Winter Weather Advisory until 5 PM MST this afternoon Gallatin...
Madison.

Winter Weather Advisory until noon MST today central and
southern Lewis And Clark.

Flood Warning for Spring Creek in the city of Choteau until
further notice.

&&

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