High Wind in Montana, April 16, 2018

Area Forecast Discussion
National Weather Service Great Falls MT
1200 PM MDT Mon Apr 16 2018

.UPDATE...

Rain has changed to snow along the Rocky Mountain Front following
a brief transition through freezing rain. Winds have shifted to
the northwest with temperatures in the 30s to the north and west
of a line from around Havre to Great Falls. An elongated band of
precipitation extends roughly along and west of I15 from north-
central into southwest MT. This band is moving rather slowly to
the east, as rain/snow may persist for a few hours as showers move
through the band from south to north. Skies remain clear ahead of
this system, with much warmer temperatures to the south and east
of the Little Belt mountains. Adequate instability could still
develop for afternoon thunderstorms as the upper level jet and its
band of showers progresses to the east.

&&

.SYNOPSIS...

An upper level disturbance and its associated cold front will
spread rain and mountain snow showers across the region today. A
few areas across central portions may also see an isolated
thunderstorm this afternoon. High temperatures today will be
slightly cooler...with highs in the 40s and 50s. Rain showers and
thunderstorms will move to eastern Montana tonight into
Tuesday...leaving only some mountain snow showers possible.
Tuesday will see slightly cooler temperatures...breezy conditions
at times...and scattered rain and snow showers.

&&

.AVIATION...
Updated 1800z.

Shower activity will move eastward across Central Montana through
the day. Terrain obscuration is expected with temporary MVFR to IFR
possible around showers. Expect snow showers at KCTB with rain
likely elsewhere. Some isolated thunderstorms are also possible this
afternoon...mainly from Southwest Montana to KLWT. Gusty winds and
isolated small hail will be possible with any thunderstorms. Showers
move out of the area this evening with VFR returning.

&&

.PREV DISCUSSION...
/ISSUED 552 AM MDT Mon Apr 16 2018/

Today through Wednesday...Initial extension of an upper level
pacific low is starting to bring rain and mountain snow showers
across the western third of Montana...including northwestern
portions of the CWA. Expecting this first round of showers to be
mainly confined to the I-15 Corridor and west...along with some
areas along Highway 2. This afternoon a cold front will move across
the region...bringing a second round of widespread rain showers and
mountain snow above 4500 feet. Areas that remain out of abundant
cloud cover today may see just enough instability combine with amble
shear for an isolated thunderstorm this afternoon. Best chances
still look to be across central portions. Gusty winds and some small
hail will be the main threats. Snowfall today will be minimal at the
lower elevations...and generally light across the mountains...except
across western Glacier County where 2 to 6+ inches are possible
north of Highway 2 and along or west of Highway 89. Impacts will be
minimal and confined to mainly the morning hours. Will monitor...but
have decided against an Advisory for now. One other concern for
today will be moderate QPF values of up to a 0.5 inches or more for
some locations. This is still below today's flash flood
guidance...however...could add to localized flooding problems today.
Cold front exits the CWA this evening leaving generally diminishing
precipitation tonight. Brisk unstable northwest flow will be found
on Tuesday. Bringing breezy conditions and scattered rain or snow
showers. Little snow accumulation is expected for Tuesday. A weak
ridge then attempts to build in for Tuesday night into Wednesday.
This will diminish the breezy winds. Lingering moisture could bring
an isolated rain or snow shower...although generally dry conditons
are expected for Wednesday. Temperatures today will start to cool
and be in the 40s and 50s. These below normal temps then continue
for Tuesday and Wednesday...with highs in the 40s and 50s...and lows
in the 20s and 30s. Some areas in the southwest could even highs in
only the 30s with lows in the teens. Anglin

Wednesday Night through Monday...Forecast models continue to be in
very good agreement with the forecast solution through this period.
Lingering high pressure aloft will keep the area mostly dry
Wednesday night, as a low pressure system dives southeast from the
Pacific Northwest into the Great Basin. As this system moves into
the southwestern United States, the Pacific moisture wrapping around
the system will combine with a weak frontal boundary and easterly
upslope winds to bring scattered showers to most of the forecast
area, except for the Hi-Line. The system will then move east across
the southern Rockies Thursday night, allowing high pressure to build
back into the area and keep conditions dry with warmer than normal
temperatures through Friday night. A weak shortwave trough will then
approach Montana on Saturday, and its associated cold front will
bring a quick shot of light showers. In the wake of this cold front,
gusty westerly winds will move through the area Saturday night and
temperatures will cool back below normal. Yet another shortwave will
move through the area Sunday night into Monday, bringing another
chance of showers. Overall, each of these rounds of showers do not
appear to be very impactful at this time, but the Saturday afternoon
and evening winds have a chance of becoming strong. Coulston

&&

.HYDROLOGY...
Updated 1000 AM, 4/16/2018.

Flood advisories for lowland snowmelt flooding have been cancelled
for some portions of central Montana where snow analyses reveal
little remaining snow. However, 2 to 4 inches of snow-water
equivalent remains along along the Hiline east of Liberty County.
Although temperatures are quite cool today, a warming trend with
plenty of strong spring sun will continue to melt the snow through
the week. The flood advisory for Pondera county also continues,
where local DES reports persistent water flooding fields and still
crossing several roads.

As snowmelt water moves into primary drainages, areas of river
flooding will continue or even expand along the Hi- Line. Flood
Warnings will continue at least through today for the Big Sandy
Creek near Havre (Moderate to potentially Major flooding), Battle
Creek near Chinook (Moderate to potentially Major flooding), and
the Milk River near Harlem (Minor flooding, but slowly rising). A
Flood Watch is also in effect for the Clear Creek near Chinook;
the forecast currently stays below flood stage, but it may get
close on Tuesday.

River/creek levels will continue to be closely monitored in case any
additional river flood warnings are required.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  43  31  49  29 /  70  50  20  10
CTB  34  29  46  28 / 100  40  20  20
HLN  51  30  46  29 /  70  40  20  10
BZN  63  26  45  24 /  60  60  30  20
WEY  45  20  34  15 /  70  80  60  30
DLN  48  24  41  22 / 100  40  20  20
HVR  38  30  46  30 /  70  70  20  20
LWT  62  29  45  28 /  30  40  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

Flood Warning in effect until further notice for Big Sandy Creek
near Havre.

Flood Warning in effect until further notice for the Milk River
near Harlem.

Flood Warning in effect until further notice for the Battle Creek
near Chinook.

Flood Watch in effect until Tuesday morning for Clear Creek at
Chinook.

Areal Flood Advisory in effect until 945 PM MDT Tuesday for
Liberty...Hill...Blaine...Counties.

Areal Flood Advisory in effect until 1215 PM MDT Monday for
Pondera...Teton Counties.

Areal Flood Advisory in effect until 715 PM MDT Monday for
Fergus County.

&&

http://www.weather.gov/greatfalls