Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 200331
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
831 PM MST Sun Nov 19 2017

.UPDATE...

No significant changes to going forecast through tonight.

Winds have varied quite a bit over the plains of north central
Montana, as they have decreased and increased significantly
throughout the late afternoon and early evening. This trend will
continue throughout the evening, but winds should generally be
fairly strong after midnight and into the early morning hours
prior to the cold frontal passage tomorrow morning. The bottom
line is that it will be quite a windy night over the plains, where
gusts to at least 40 mph will be common throughout the night.
Gusts to 65 mph are expected along and west of Interstate 15 over
the plains and into Judith Basin County. The strongest winds will
remain close to the Rocky Mountain Front, where gusts to 90 mph
continue to be a possibility.
Coulston

&&

.SYNOPSIS...

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

&&

.AVIATION...
Updated 0055Z.

VFR conditions will continue through tonight for the terminals with
strong westerly downslope winds over the plains. Gusts in excess of
60 kt are likely close to the Rocky Mountain Front, with occasional
gusts between 35 and 50 kt over the rest of the plains areas. Ridge
top winds of 30 to 50 kt will also be possible over the mountains of
southwest Montana. Overall, widespread mountain wave turbulence and
areas of low level wind shear are expected overnight. As a
disturbance approaches the area from the northwest, snow will move
into the mountains along the Continental Divide after 06Z, causing
some mountain obscuration there. This disturbance will move a
Canadian cold front south over north central and central Montana
after 12Z, which will shift winds over the plains more northerly and
decrease them. The more upslope flow will bring areas of rain and
mainly mountain snow to the area for the remainder of the day, but
the rain-snow mix will become all snow after 18Z over the plains, as
low VFR/high MVFR conditions deteriorate to MVFR/IFR.
Coulston

&&

.PREV DISCUSSION...
/ISSUED 555 PM MST Sun Nov 19 2017/

Today through Tuesday...High wind event in progress is working
out close to expected, with a few isolated wind gusts to warning
criteria possible east of the Rocky Mountain Front in the warning
area through this evening. Combination of upper level forcing and
the passage of the mid level jet streak should support a 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 mainly late this afternoon and early this evening
with areas to the east seeing strongest winds overnight tonight
into early Monday morning. A cold front sweeps south and southeast
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. Will keep mention of freezing drizzle out of the grids
for now until a bit higher confidence, especially considering
negligible impacts currently, but will need to keep a close eye on
this. Drier and warmer conditions move in Tuesday with building
upper level ridge. CC/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  41  46  25  46 /  10  50  60  30
CTB  35  40  15  37 /  10  50  40  20
HLN  29  46  28  46 /  10  50  40  30
BZN  28  44  27  46 /  10  50  50  30
WEY  21  34  25  40 /  10  80  80  50
DLN  30  46  31  50 /  10  30  30  30
HVR  39  42  14  30 /  10  20  20  10
LWT  40  47  23  43 /  10  70  70  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Warning until 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



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