Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 192320
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
420 PM MST Mon Feb 19 2018

...Update to Aviation...

.SYNOPSIS...

A few flurries or brief light snow showers could linger across
northern and central portions through this evening...while the
remainder of the areas sees partly cloudy...cold...and dry
conditons. Bitterly cold temperatures and dangerous wind chills
are then expected for tonight for much of the area. See the Wind
Chill Advisories for the latest details. Southwest winds will
bring a slight warming trend for Tuesday...with below normal
temperatures overall still expected. Mainly dry conditions are
also expected...with some light snow possible across the southwest
and portions of the Hi- Line.

&&

.DISCUSSION...

Tonight through Tuesday....Large mid level low continues to
progress across the WY area while a broad tough remains over the
region. Stuck in this trough is a decent amount of moisture
bringing areas of clouds and flurries/light snow to the northern
half of the CWA...with cold and partly clear conditions elsewhere.
Expect these clouds and flurry chances to linger though the
evening hours until the trough moves out and a sfc high moves
south out of Canada. With this high will come very cold air. As
this high stall across the south...west to southwest flow will
increase just enough to cause dangerous wind chills for central
and northern areas. There remains some uncertainty on the strength
of the winds and tonight`s low temperatures. The lows tonight
will depend greatly on if this remnant moisture exits tonight and
can bring clear skies. Temperatures will plummet in this
scenario. Even if the skies don`t clear...temperatures will still
drop to below zero readings. Decided to issue a Wind Chill
Advisory for those areas with the best wind and cold potential.
Some of these areas are close to Wind Chill Warning
criteria...however...confidence was not high enough to issue.
Southwest MT will also be bitterly cold tonight...however...the
stalled high pressure will limit winds needed for any highlights.
Still can`t rule out very cold wind chills and it will need to be
monitored. Tuesday then sees a slight warming trend with the
mentioned southwest winds. Temperatures will still be below normal
with highs only in the single digits to teens above zero. Overall
dry conditions are expected for Tuesday...although some lingering
light snow is possible in the southwest...and some scattered
light snow showers are possible in the north from a weak clipper
system in northwest flow. Anglin

Tuesday Night through Sunday...A deep, positively-tilted low
pressure trough will remain over the western and central United
States through this period, keeping the forecast area generally
under a northwesterly flow aloft. A series of disturbances will
move through this flow, bringing a chance of snow mainly to the
western and southwest Montana mountains...with only slight chances
across the valleys and plains as the disturbances move through.
Some breezy winds may also accompany these disturbances...perhaps
bringing some areas of blowing snow. These winds should help
bring a gradual warming to the area, but temperatures will only
warm from around 20 degrees below normal for Tuesday
night/Wednesday to around 5 to 10 degrees below normal by Saturday
night/Sunday. The strongest disturbance of the long term is
forecast to move south along the Pacific coast, which will focus
the best precipitation there. However, the greatest chance for
(what is currently forecast to be) light snow over the entire
forecast area will be during the upcoming weekend, as a
broad disturbance and cold front moves northwest to southeast
over Montana. Widespread light to perhaps moderate snow is
possible from Saturday into Sunday. Accumulations and impacts are
hard to nail down at this point as a westerly component to the
disturbance could bring hindering downslope flow to some areas.
Stay tuned to future updates for the latest details on this
developing system. Coulston/Anglin


&&

.AVIATION...
Updated 2320Z.

Broad upper level low pressure trough and strong surface high
pressure system will remain over Montana tonight through late
Tuesday afternoon. Scattered to broken mid- and high-level clouds
will prevail over the region with areas of freezing fog possible
overnight. VFR conditions are expected to prevail through the
forecast period except for local IFR/MVFR conditions in fog. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF -17  13 -12  16 /  20  10  10  20
CTB -18  15 -15  14 /  10  20  20  10
HLN -14  13  -8  18 /  10  10  10  10
BZN -17  10  -9  16 /  20  10  10  20
WEY -26   8 -17  13 /  10  20  20  20
DLN -14  12  -8  13 /  10  10  20  20
HVR -19   8 -16   8 /  20  20  20  20
LWT -17  11 -11  16 /  20  10  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Wind Chill Advisory from 11 PM this evening to noon MST Tuesday
Blaine...Cascade...Chouteau...Eastern Glacier...Eastern
Pondera...Eastern Teton...Hill...Liberty...Toole.

Wind Chill Advisory from 11 PM this evening to noon MST Tuesday
Fergus...Judith Basin...Meagher.

Wind Chill Advisory from 11 PM this evening to noon MST Tuesday
Central and Southern Lewis and Clark...Northern Rocky Mountain
Front...Southern Rocky Mountain Front.

&&

$$

http://www.weather.gov/greatfalls



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