Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 170322
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
822 PM MST Fri Feb 16 2018

...Snow and blowing snow with a frontal passage tonight followed
by a larger scale and longer duration winter storm to impact the
region this weekend...


.SYNOPSIS...

A series of storm systems will move across the northern Rockies and
Montana this weekend beginning with windy conditions and blowing
snow this afternoon before a cold front drops south brining a period
of snow and wind shift to the north tonight. A brief break between
storms is expected Saturday morning before a larger and longer
duration storm impacts the region from Saturday afternoon through
Sunday night. Significant snow accumulations are likely for much of
the region this weekend along with much colder temperatures and
dangerously low wind chill values by Sunday.

&&

.UPDATE...

So far there is only scattered precipitation across the forecast
area. However, latest short term model runs continue to indicate
that snow will fill in across northern portions of central
Montana over the next few hours. Areas of snow will then continue
to move from northwest to southeast with precipitation diminishing
towards morning. The next storm system is then expected to begin
affecting the region during the late morning and early afternoon
hours on Saturday. Have made minor updates to tweak PoPs to be
more in keeping with observed and anticipated precipitation
development through the remainder of tonight. Have also made
updates to overnight low temperatures as well as winds based on
latest National blend of models and bias corrected short term
model solutions. Not feeling extremely confident in tonights
winter weather highlights but will keep them in place for now as a
few spotters have reported 2 to 3 inches snowfall under a couple
of the heavier bands. mpj

&&

.AVIATION...
Updated 0003Z.

Quick round of snow to cause reduced VIS/CIGs this evening, then
widespread aviation impacts from snow this weekend.

Latest surface observations show a cold front is just about to cross
the International Border into Montana. Along and ahead of this
front, a band or two of snow will impact much of our forecast area.
IFR conditions are expected with this band, but there is the
potential of TEMPO VLIFR conditions in SN/+SN and this will be
closely monitored through this evening. Attention then turns to the
next system which will bring a longer-duration period of snow and
aviation impacts later Saturday through the weekend. MARTIN

&&

.PREV DISCUSSION...
/ISSUED 503 PM MST Fri Feb 16 2018/

Today through Sunday Night...Initial shortwave embedded within NW
flow now dropping through BC will continue to dig SE through the
Northern Rockies tonight along with an associated upper level jet
max. This will result in the rapid development of a cold front
late this afternoon along the Canadian border which drops south
through the forecast area this evening. In addition to snow
showers already developing in the somewhat unstable environment
this afternoon, a band of snow is likely to develop along the
front and push south this evening with potential for a quick
period of moderate snow rates and gusty north winds. A winter
weather advisory for snow and blowing snow covers ongoing blowing
snow impacts this afternoon as well as the period of snow and
gusty winds associated with the frontal passage this evening.
After a brief lull Saturday morning, attention then turns to a
strong lobe of shortwave energy that descends south into the
Pacific NW this weekend carving out a larger scale upper trough
over the NW US. Shortwave and upper jet energy along with a fairly
deep push of moisture will eject out of the Pacific NW low late
Saturday and Saturday night followed by additional disturbances
moving over the deepening cold airmass through Sunday night.
Models advertise a fairly robust surge of moisture into the region
late Saturday and Saturday night resulting in widespread moderate
to locally heavy snow accumulation Saturday night. Snowfall rates
decrease Sunday as the airmass cools and moisture decreases but
winter weather impacts continue with additional light snowfall
through Monday morning as well as temperatures falling through the
single digits below zero with likely wind chill impacts as well.
A winter storm watch covers this second larger scale and longer
duration event with confidence fairly high in central and
Northwest portions of the forecast area seeing 6- 12 inches of
snow accumulations with 1-2 feet of snow in the mountains.
Hoenisch

Medium range period begins with a broad positive-tilt trough over
western North America and surface high pressure over Montana. Snow
from the weekend storm will dissipate from northwest to southeast
through the day with a frigid Arctic airmass remaining in place over
the region through Tuesday morning. Latest model guidance is showing
that much of Montana will see overnight lows in the teens and 20s
below zero with brisk winds across north central Montana fueling
bitterly cold wind chills of 40 to 50 below. Models gradually push
the upper level trough eastward Tuesday into Wednesday with model
solutions diverging significantly through the remainder of the week.
While overall confidence remains relatively low, it does appear that
temperatures will gradually warm each day but will remain well below
seasonal averages. Additionally, there is some chance for another
round of light snow Thursday or Friday. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  10  25  -1   1 /  70 100 100  80
CTB   4  17  -5  -2 /  70 100 100  70
HLN  15  34   6  10 /  60  90  80  60
BZN  16  36  13  17 /  80  50  60  70
WEY  13  29  15  25 /  90  90  90  70
DLN  17  37  19  24 /  60  40  60  60
HVR   3  16  -2   2 /  40  50 100  40
LWT   7  26  -1   5 / 100  90 100  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 AM MST Saturday Broadwater...
Gallatin...Jefferson...Madison.

Winter Storm Watch from 5 AM MST Saturday through late Sunday
night Beaverhead...Blaine...Broadwater...Cascade...Central and
Southern Lewis and Clark...Chouteau...Eastern Glacier...Eastern
Pondera...Eastern Teton...Fergus...Gallatin...Hill...Jefferson...
Judith Basin...Liberty...Madison...Meagher...Northern Rocky
Mountain Front...Southern Rocky Mountain Front...Toole.

Winter Weather Advisory until 5 AM MST Saturday Blaine...
Chouteau...Fergus...Hill...Liberty.

Winter Weather Advisory until 5 AM MST Saturday Cascade...Judith
Basin...Meagher.

Winter Weather Advisory until 5 AM MST Saturday Central and
Southern Lewis and Clark...Eastern Glacier...Eastern Pondera...
Eastern Teton...Southern Rocky Mountain Front...Toole.

Winter Weather Advisory until 5 AM MST Saturday Northern Rocky
Mountain Front.

Flood Warning for an ice jam on the Missouri River near Townsend
until further notice.

&&

$$

http://www.weather.gov/greatfalls


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