Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 160539
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1040 PM MST Mon Dec 15 2014

Aviation Section Updated

.UPDATE...
Current infrared satellite imagery, surface observations, and
spotter reports indicate extensive low-level clouds and areas of
fog mainly north and east of a Great Falls-to-Lewistown line, all
the way to the US/Can border. Given that the observation at the
Cut Bank airport has carried 1/4 mile visibility for several hours
and have reports of dense fog in central/eastern Teton County,
have decided to issue a freezing fog advisory to cover portions of
Teton, eastern Pondera, eastern Glacier and Toole counties for
tonight through 11 am tomorrow. Travelers in those areas should be
prepared for very low visibilities and areas of black ice on local
roadways. Patchy areas of fog are also likely over eastern portions
of the Hiline counties and in the valleys of southwest MT tonight.
Only other adjustment this evening was to tweak low temperatures
down a degree or two from Great Falls south to Bozeman/Dillon as
clearing skies have allowed current temps to reach forecast lows by
9pm. High clouds lifting north from central Idaho should slow the
falling temps during the overnight period. Waranauskas

&&

.AVIATION...
UPDATED 0540Z.
Low clouds and dense fog will continue to affect portions of the
region over the next 24 hours. Cut Bank will see the greatest
impacts with widespread VLIFR conditions continuing through much of
the night. Patchy dense fog will be possible elsewhere...with
Bozeman and Great Falls being the 2nd best areas to see areas of
dense fog. Isolated snow showers will develop over far Southwest MT
mainly after 21z Tue...and spread northward into Central MT after
00z Wed. Brusda

&&

.PREV DISCUSSION...
/ISSUED 445 PM MST Mon Dec 15 2014/

Tonight through Wednesday...A weather system approaching the west
coast Monday afternoon will move into western Montana by late
Tuesday night and then into eastern Montana by late Wednesday. This
weather system will bring a threat of snow to the area. Models do
not indicate much in the way of snowfall with the system so have
generally so have not gone real high with the chances of measurable
snowfall. In fact areas towards the Canadian border should not see
any snow. At the current time what little snow falls should be
mainly over southwest Montana where mountains could see from 1 to 3
inches and valleys could possibly see up to a half-inch. The main
weather problem in the short term will be freezing fog. Freezing fog
should redevelop over most of the east slopes this evening and
expect at least local dense freezing fog. Later tonight expect
patchy freezing fog to develop in the southwest valleys and also
over north-central Montana. This freezing fog will continue through
Tuesday morning. Blank

Wednesday Night through Monday...Forecast models continue to
indicate that the region will be under the influence of a
splitting westerly flow aloft through the period. Overall, there
will be a chance of snow in the mountains of western and southwest
Montana, but the plains will generally stay dry due to breezy
westerly downsloping winds. Two upper level low pressure troughs
will move through the western CONUS. The first one will move
through Wednesday night into Thursday, while the second one
effects the area Saturday into Sunday. However, the flow aloft
will move only some of the energy over Montana and send the bulk
of the energy over the southwestern CONUS. As a result, there will
be a slightly better chance of snow in the mountains during these
times, but am not anticipating enough snow to warrant winter
weather highlights at this time. After the second trough passage,
the flow aloft becomes quite strong (700 mb winds of 60 to 70 kt)
for Sunday night into Monday, which may cause winds to approach
High Wind criteria, especially along the Rocky Mountain Front.
Have therefore increased winds during this period and will
continue to monitor the situation for potential High Wind
highlights. Temperatures are expected to remain near normal
through most of the period. However, as the winds increase Sunday
into Monday, temperatures should warm to about 10 degrees above
normal across most of the area. Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  16  27  25  36 /   0   0  10  20
CTB  15  25  19  34 /   0   0  10  10
HLN  14  33  23  33 /   0  10  20  20
BZN   7  31  23  33 /   0  10  30  30
WEY   9  31  24  31 /   0  20  40  40
DLN  15  34  24  36 /   0  20  30  20
HVR  15  30  17  30 /   0   0   0   0
LWT  18  32  24  36 /   0   0  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

FREEZING FOG ADVISORY until 11 AM MST Tuesday Eastern Glacier...
Eastern Pondera...Eastern Teton...Southern Rocky Mountain
Front...Toole.

&&

$$

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