High Wind in Montana, November 19 to 20, 2017

Area Forecast Discussion
National Weather Service Great Falls MT
1005 AM MST Sun Nov 19 2017

...Updated Aviation Discussion...

.UPDATE...

Made minor tweaks downward to high temperatures for today, but
still remaining above guidance, given expected mid- to high-level
cloud cover associated with a pronounced chinook arch cloud that
should persist through the day today. Upped wind speeds and gusts
a bit across much of the area east of the current wind warnings.
There is concern for plains locations east of the current warning
area to see low-end warning criteria. We will keep an eye on this
closely, especially toward late this afternoon and into the
overnight, and issue any additional warnings as necessary. CC

&&

.SYNOPSIS...

Low pressure moving from British Columbia into Alberta tonight and
strong westerly flow aloft will bring increasing winds to the region
today with strong winds likely across western portions of north
central Montana. A Canadian cold front will move southeast across
the area Monday, bringing cooler temperatures and a shift to
northerly winds along with a chance for rain and snow showers. High
pressure then rebuilds through the middle of the this week for
warming temperatures and the redevelopment of windy conditions.

&&

.AVIATION...
Updated 1705Z.

VFR conditions will prevail though tonight under varying amounts of
high cloudiness streaming through strong westerly flow aloft.
Mountain wave turbulence is likely to persist and/or worsen on later
today as flow aloft increases from the west, bringing increasingly
stronger winds to western portions of north central MT. Gusts
increase to 35-50 kts at the KCTB and KGTF terminals with similar
gusts expanding east late Sunday afternoon and evening. Strongest
winds with gusts in excess of 60 kts are likely along the immediate
east slopes of the Rocky Mtn Front late this afternoon and evening
with gusts to 50 kts further east late tonight. A cold front crosses
the Canadian border and begins moving south across the Hi-Line
toward the end of the TAF period, resulting in winds decreasing and
switching to northerly. CC/Hoenisch

&&

.PREV DISCUSSION...
/ISSUED 420 AM MST Sun Nov 19 2017/

Today through Tuesday...Already strong mid level westerly flow will
increase today as the broad upper level ridge over the region
flattens in response to shortwave energy dropping south through BC.
Strong pressure gradient across the Rockies will deepen further
today supporting strong winds along the Rocky Mtn Front and adjacent
plains with strong winds spreading east into adjacent portions of
north central and central MT this evening as a mid level level wind
maximum spreads southeast across north central MT while shortwave
energy splitting off of the BC upper trough moves east across
southern AB. Combination of upper level forcing and the passage of
the mid level wind maximum should support of period of winds with
gusts near 50kts as far east as the I-15 corridor of N-central MT
tonight extending east along the north slopes of the Little Belts.
Period of strongest winds along the Rocky Mtn front appears to be
late this afternoon and evening with areas to the east seeing
strongest winds overnight tonight into early Monday morning.
Canadian cold front sweeps SE across the forecast area Monday with a
shallow push of cold air. This in addition to a plume of Pacific
moisture streaming into the Northern Rockies will bring snow to
areas along the Continental Divide Monday with scattered rain/snow
showers for areas to the east, becoming mostly snow showers by
Monday night as snow levels lower. Additional shortwave energy
quickly moves east across the region Monday night in response to a
rapidly building upper ridge along the west coast. This could
provide a period of light overrunning precipitation with forecast
temperature/moisture profiles suggesting some potential for freezing
drizzle as well over portions of north central MT due to the
shallowness of the moisture. Drier and warmer conditions
move in Tuesday with building upper level ridge. Hoenisch

Tuesday night through Sunday...An unusually-strong high pressure
ridge aloft will reside over our area Tuesday night as a warm front
advances northeastward over the eastern half of North-Central MT.
This strong ridge will then prevail through Wednesday before being
broken-down by a shortwave trough Thanksgiving into Friday morning.
In addition, a Canadian cold front still looks to pass through our
region late Thanksgiving into Friday morning. Model guidance depicts
another high pressure ridge aloft becoming established over our CWA
later Friday through next weekend. However, the GFS suggests a
Pacific weather disturbance will traverse this ridge late Friday
into Saturday. Atmospheric profiles remain favorable for periods of
strong, gusty downslope winds along the Rocky Mountain Front,
especially Tuesday night through Thanksgiving.

The above pattern will yield periods of upslope precipitation along
the Continental Divide and Southwest MT mountains. At lower
elevations, the best potential for isolated to scattered snow and/or
rain showers looks to be Tuesday night into Wednesday morning and
again on Friday into Saturday. As for temperatures, readings will
tend to be about 10-20 degrees above-normal Tuesday night through
Thanksgiving night. In fact, many plains and valley locations should
have afternoon highs reach well into the 50's or 60's on Wednesday
and Thanksgiving. Thus, a few places may flirt with their record
highs on those days. A cooling trend will then begin on Friday due
to the aforementioned cold frontal passage. While lows should still
be above-normal, highs should be close to normal by Sunday of next
week.
Jaszka

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  51  40  46  23 /   0   0  30  30
CTB  48  31  36  15 /   0   0  30  50
HLN  45  30  45  28 /   0   0  30  30
BZN  41  27  43  28 /   0   0  30  30
WEY  30  17  33  24 /   0   0  60  60
DLN  41  29  44  31 /   0   0  30  30
HVR  50  31  38  12 /   0   0  20  30
LWT  49  36  44  21 /   0   0  30  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning from noon today to 8 AM MST Monday Cascade...
Central and Southern Lewis and Clark...Eastern Pondera...Eastern
Teton...Judith Basin...Toole.

High Wind Warning until 5 AM MST Monday Eastern Glacier...
Northern Rocky Mountain Front...Southern Rocky Mountain Front.

&&

http://www.weather.gov/greatfalls