Winter Storm Warning 10, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
1137 PM MDT Sun Oct 6 2019

...AVIATION SECTION UPDATED...

.SYNOPSIS...
Fair but breezy conditions continue tonight through Monday.
Monday will be warmer, with strong and gusty west winds expected
across north central Montana. On Tuesday, a strong cold front
moves south from Canada, bringing much colder temperatures and
accumulating snowfall that persists overnight and through the day
on Wednesday.

&&

.UPDATE...
No Changes to the current forecast for tonight. All looks on
track. No precipitation is expected tonight. Clouds are
increasing over the Rocky Mountain Front as a Chinook arch
develops. Strong winds could develop by morning over the Rocky
Mountain Front and then continue into Monday along the adjacent
Plains. Thus the High Wind Watch will continue.

Looking ahead, the cold front for Tuesday looks on track. Expect
falling temperatures during the day on Tuesday, along with
rain/snow developing. In most areas, the rain will change to snow
fairly quickly. Because temperatures are likely to fall well below
freezing fairly quick, roadways could become a bit icy quicker
then the previous snow event. The snow could be heavy at times,
especially in the mountains. Thus the winter storm watch will
continue. Brusda

&&

.AVIATION...
Updated 1136 PM MDT Sun Oct 6 2019 (06Z TAF Issuance)

Upper level ridging will exert an influence on the region for 1 more
day, resulting in passing high clouds and strong surface winds.
Overall, VFR conditions will prevail over the region until late
Monday, when ceilings begin to lower over the Rocky Mountain Front.
Breezy winds tonight will give way to strong surface winds on Monday
over North Central MT. Expect a strong cold front to move southward
through the region on Tuesday, with widespread rain/snow and low
ceilings. Mountains/passes will start to become obscured on Monday
afternoon over the Rocky Mountain Front. Brusda/RCG

&&

.PREV DISCUSSION...
/ISSUED 550 PM MDT Sun Oct 6 2019/
Skies are clear over the region today, under the influence of a dry
northwest flow aloft. Breezy conditions continue due to a persistent
and moderately strong surface pressure gradient.
Upstream, a strong upper level trough currently over southeast
Alaska intensifies and dives southeastward over the next 24 hours,
allowing surface low pressure to develop in Alberta. As a result,
downslope pressure gradients strengthen further along the Rocky
Mountain Front and combine with strong mid- to upper-level winds,
producing an increasing potential for high winds across portions
of north central Montana Monday and Monday night. A high wind
watch remains in effect for this region. The latest model guidance
suggests that the highest wind gusts will be confined to ridgetops
and wind-prone gaps close to the Rocky Mountain Front. This
commonly-windy area has higher warning criteria, so uncertainty
remains in determining if winds will become strong enough to
produce widespread damage or impacts. This high wind watch will
continue to be evaluated through the evening and overnight,
anticipating a late decision to either upgrade or cancel the
watch.

The upper level trough and an associated surface cold front sweep
southward from Canada on Tuesday, bringing sharply colder
temperatures and widespread precipitation. The precipitation will
start off as rain but rapidly changes over to snow as temperatures
drop behind the cold front. Am expecting accumulating snowfall to
develop on Tuesday. Heavy snow will develop first in the westerly
flow up to and just over the Continental Divide on Tuesday. The
forecast has been updated to move the heaviest snow closer over
the mountains, with a tight snowfall gradient along the Rocky
Mountain Front. The snow then spreads south with the advancing
cold front as temperatures fall through the day across North-
central Montana. Snow continuing overnight and through the day on
Wednesday before gradually tapering off from northwest to
southeast Wednesday night. Snowfall amounts have also been
increased slightly over Southwest Montana. Deterministic forecast
models, ensembles, and the National Blend of Models (NBM) are all
in very good agreement that moderate to heavy snowfall is likely
during this period and temperatures will be 20 to 30 degrees below
seasonal averages. Winter storm watches have been posted for much
of the forecast area anticipating the arrival of this strong
early season storm.

The storm system finally moves east of the forecast area Thursday
and Thursday night, leaving western and central Montana beneath a
building short wave ridge for Friday and the weekend. Note that
low temperatures are forecast to drop near 10 degrees or colder on
Thursday morning. Mostly dry conditions can be anticipated
Thursday through Sunday with temperatures slowly rebounding back
toward seasonal averages.

mpj/PN

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  64  41  51 /   0   0  10  80
CTB  35  57  30  40 /   0   0  60  90
HLN  34  66  42  56 /   0   0  10  80
BZN  28  65  37  61 /   0   0   0  80
WEY  17  53  26  54 /   0   0   0  30
DLN  29  60  37  57 /   0   0   0  50
HVR  35  66  40  53 /   0   0  10  50
LWT  35  63  45  55 /   0   0   0  80

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from 6 AM MDT Monday through late Monday night
Eastern Glacier...Eastern Pondera...Eastern Teton...Liberty...
Toole.

Winter Storm Watch from Tuesday afternoon through Wednesday
evening Broadwater...Cascade...Central and Southern Lewis and
Clark...Fergus...Jefferson...Judith Basin...Meagher.

Winter Storm Watch from Tuesday evening through Wednesday
evening Gallatin...Madison.

Winter Storm Watch from Tuesday morning through Wednesday
morning Eastern Glacier...Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

High Wind Watch from 6 AM MDT Monday through late Monday night
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

http://www.weather.gov/greatfalls