Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 191751
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1050 AM MST Tue Feb 19 2019

...Updated Aviation Section.

.UPDATE...

Updates this morning focused on capturing the observed cold
temperatures around the region and adjusting some of the high
temperatures for today. The Flood Watch in Madison County for the
Jefferson River from Twin Bridges to north of Silver Star was
extended through Friday morning after speaking with the River
Forecast Center. Based on decent model agreement, we ended up
bringing light snow into Northcentral and Southwest Montana a few
hours earlier than previously expected, for tonight into Wednesday
morning. -TP

&&

.SYNOPSIS...

Breezy, Klondike, southwest winds are expected today over the
plains of North Central Montana and into portions of Central
Montana. These winds are expected to cause areas of blowing snow,
primarily in open areas, which could lead to hazardous travel due
to reduced visibilities. By Wednesday morning, a cold front will
begin to push south across the region. This cold front will bring
another shot for accumulating snow and falling temperatures.

&&

.AVIATION...
Updated 1040 AM MST Tue Feb 19 2019

VFR conditions are primarily expected through late tonight, with
some areas of blowing snow potentially reducing visibilities to near
MVFR conditions around the KGTF & KCTB terminals during the
remainder of the day. A weak disturbance moving across Central and
Southwest Montana tonight will bring increasing chances for light
snow to most of the terminals into Wednesday morning, with ceilings
and visibilities falling to MVFR levels. Mountain obscuration is
expected tonight and into Wednesday morning across Southwest and
Central Montana. Cold and snowy conditions are expected to persist
through Thursday morning as another cold front drops south across
the region. -TP

&&

.PREV DISCUSSION...
/ISSUED 430 AM MST Tue Feb 19 2019/

Today through tonight...primary forecast concern will be blowing and
drifting snow along the Rocky Mountain Front and Eastern Glacier,
Eastern Teton, Cascade, Judith Basin, Meagher, and Central and
Southern Lewis and Clark Counties where a Winter Weather Advisory
remains in effect until 9pm Tuesday.

H500 trough axis over the Gulf of Alaska this morning will dig south
towards the Pacific Northwest by Wednesday morning, with impressive
height falls of 100-150m overspreading the Pacific Northwest and
slightly weaker height falls of ~50-100m occurring across the
Northern Rockies over this timeframe. At the surface, lee-side
surface trough will begin to sharpen during the day today as an
~1004mb surface low moves southeast from Southeast Alaska to East
Central Alberta/West Central Saskatchewan by Wednesday morning and
gradually weakens. This will cause the pressure gradient to
strengthen quickly along the Rocky Mountain Front and foothills of
the Central Montana mountains this morning, before gradually
weakening this evening. Thankfully, the H700 flow during the
strongest pressure gradient period will be 15kts or less, which will
help to lessen the risk of strong winds at the surface. None-the-
less, breezy, Klondike southwest winds of 15-25 mph with gusts to 35
mph (higher wind gusts to 50 mph are possible at ridgetops and in
wind favored locations) are expected today and early this evening
across the aforementioned regions. With a non-compacted/crusted
snowpack residing over the region, expect patchy to areas of blowing
snow to occur through early this evening, which could reduce
visibilities to around 1/2 mile in open areas. For this reason, will
continue a Winter Weather Advisory for blowing snow. In addition,
significant drifting could block driving lanes and cause some issues
within city limits. Finally with respect to high temperatures for
today, kept values within the Milk River Valley of Hill and Blaine
Counties below 10 degrees given the valleys stubbornness to mix out
on days like this, even when guidance suggests it should happen.

Wednesday through Thursday night...primary forecast concern is
accumulating snow across most of the region.

H500 trough axis will continue to dig south towards Southern
California/the Desert Southwest through Thursday afternoon, before
lifting northeast towards the Four Corners region by Friday morning.
At the surface, a cold front extending west/southwest from the
surface low over East Central Alberta/West Central Saskatchewan
Wednesday morning, will push south into North Central Montana by the
mid/late morning hours Wednesday and into Southwest Montana by
Wednesday evening/Thursday morning. Weak divergence aloft will aide
ascent and combine with frontogenetical forcing to help support
light snow across the region during the day Wednesday and into the
morning hours on Thursday. Conditions appear favorable for the snow
to back-up off of the Little Belts into the surrounding foothills
and possibly as far north as Great Falls Wednesday evening/Thursday
morning. This could aide in locally enhanced snowfall amounts for
the United States Highway 87/89 corridor from near Armington
Junction to Great Falls. At this time, widespread 2-4" snowfall
totals are expected across a large portion of North Central Montana,
with generally 1-2" for the valleys of Southwest Montana.
Mountainous regions of the Divide and Central Montana could see 6-
10", with 4-6" possible in the northern foothills of the Little
Belt/Highwood mountains. Future winter weather headlines may be
needed for this event. Snow will gradually end Thursday
afternoon/evening from north to south, with overnight temperatures
falling into the single digits below zero to teens below zero.

Friday through Tuesday...temperatures will remain well below normal
over this timeframe, with another shot of Arctic air potentially
arriving by early-to-mid week next week. In addition, another period
of breezy to strong winds will be possible Friday into Saturday
along the Rocky Mountain Front, which could lead to another blowing
snow event. - Moldan

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  16   7  19   3 /   0  20  40  80
CTB  16   6  20  -1 /   0  20  70  60
HLN  11   4  23   3 /   0  30  40  60
BZN  10   0  21   2 /  10  40  40  40
WEY  14  -4  18  -8 /  10  60  70  40
DLN   9   1  16  -2 /  10  40  30  50
HVR   5 -10  15   3 /   0  20  40  60
LWT  20   1  21   4 /   0  20  40  60

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 PM MST this evening Cascade...
Central and Southern Lewis and Clark...Eastern Glacier...Eastern
Teton...Judith Basin...Meagher...Northern Rocky Mountain Front...
Southern Rocky Mountain Front.

Flood Watch through Friday afternoon Madison.

&&

$$

http://www.weather.gov/greatfalls


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