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FXUS65 KBYZ 202203
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
403 PM MDT Fri Oct 20 2017

.SHORT TERM...valid for Sat and Sun...

The weekend will be a very active period in the forecast. We have
two main concerns through the weekend. The first concern deals
with the potential for dangerous fire conditions and very strong
winds this afternoon and evening behind a very strong cold front.
The second concern is periods of strong winds expected through
the weekend (especially along the mountain foothills).

As of 3 pm, the cold front was about to move through Livingston.
Wind gusts behind the front were approaching 50 to 55 mph in
Bozeman and other locations to our west. We anticipate these wind
gusts to rapidly spread east behind the cold front as it across
the area. Folks should be prepared for northwest wind gusts
ranging from 45 to 60 mph thanks to very rapid pressure rises
behind the front. Some ascent will keep the strongest winds from
reaching the lower elevations, but isolated shower development
this evening (especially east of a Billings-Sheridan line) will
allow some of the stronger winds to reach the surface. The north-
south oriented cold front will move through Livingston around 4pm,
Reed Point 5pm, Billings 6pm, Miles City/Sheridan at 8 or 9pm and
then reach the ND/SD border around 9 or 10pm tonight. Relative
humidities have stayed mostly in the 20s in the region this
afternoon ahead of the front and higher than forecast which has
eased fire concerns slightly. Kept the Red Flag Warning in effect
however to account for the very strong post-frontal winds we
expect to move through. Any fires that are going on at the time of
the front's arrival will behave erratically behind the front. The
strong winds over the plains and the foothills will begin to
diminish after midnight as the front moves into the Dakotas, but
we still expect the foothill regions to remain breezy through the
night.

The second forecast concern deals with periods of strong winds
that will re-develop across the forecast area Saturday and Sunday.
Right now the strongest period of winds across the region will be
on Sunday, but windy conditions will remain prevalent through the
entire weekend, especially along the western foothills and in our
northwest zones near Harlowton and Judith Gap. Folks should be
prepared for 30 to 40 mph winds across the plains on Saturday with
40 to 50 mph winds possible in our foothills zones and western
zones near Harlowton, Livingston, Nye, and Big Timber.

Strong jet moves overhead Saturday night into Sunday morning which
will help tighten an already strong pressure gradient across the
Rocky Mountain front. Once the sun sets Saturday winds begin to
quickly ramp up across the gap wind regions such as
Livingston/Nye, and just off the foothills as the strong mountain
top level winds begin to be forced through some of these gaps.
Northwest zones such as Harlowton and Judith gap won't see the
strongest winds until Sunday afternoon as we mix these strong
winds to the surface with diurnal heating. With this strong jet
overhead, we expanded the high wind watch to include the rest of
Sweet Grass and Wheatland counties. As of this update, we're
expecting potential wind gusts along the mountain foothills to
reach 65 to 75 mph overnight Saturday and into Sunday morning.
Across the plains, we're expecting another windy day with wind
gusts potentially reaching 45 to 55 mph west of Billings-Roundup
line and 35 to 45 mph east of this line. We urge all folks
traveling this weekend to pay careful attention to the weather
forecast and try avoid traveling in high-profile vehicles if
possible.

Windy conditions could continue along the foothills into
Monday morning while the Plains will see the winds lessen around
sunset. Dobbs

.LONG TERM...valid for Mon...Tue...Wed...Thu...Fri...

Upper ridging should dominate our weather on Monday and Tuesday
with dry and mild conditions. Winds should slow from Sunday's
wind speeds...but they will remain gusty across the area as wind
aloft mixes down to the surface. High temperatures will generally
be in the 60s.

On Wednesday, we expect a cold front to move southward over the
Northern Rockies. This front will bring a period of showers and
wind (with enhanced wind possible near Livingston) followed by
sharply lower temperatures. Models differ on the details of the
front, with the GFS moving the front through the area faster and
the ECMWF slower. If the GFS solution were to verify, the plains
could experience a cooler day on Wednesday and a light rain
changing to light snow event Wednesday night. The ECMWF shows a
warmer Wednesday and more of a light rain to snow flurries event
Wednesday night. The models do agree on a cooldown with high
temperatures on Thursday in the 40s...possibly 30s. Accumulating
snow is possible in the mountains Wednesday afternoon or night
into Thursday morning. Some scattered rain and snow showers are
possible on Thursday as a disturbance moves through the upper
flow.

Upper ridging should return for Friday with generally dry weather
across the lower elevations. Some mid-level moisture could
produce a few mountain snow showers. High temperatures should rise
to the 50s. RMS

&&

.AVIATION...

A strong cold front will move from west to east across southern
MT/northern WY this afternoon and early evening with a shift to
gusty west/northwest winds and isolated showers and
thunderstorms. The gusty winds will continue through the early
morning. VFR will prevail tonight, though lower conditions are
possible in any showers or thunderstorms. Mountains will be
obscured tonight. RMS

&&

.PRELIMINARY POINT TEMP/POPS...

Sat Sun Mon Tue Wed Thu Fri
-----------------------------------------------------------
BIL 040/056 043/068 046/061 038/065 046/068 032/044 030/053
10/N 21/N 21/N 00/U 03/W 43/W 11/B
LVM 035/050 045/063 045/058 036/065 043/066 029/042 028/051
31/N 33/W 41/N 00/U 03/W 73/W 01/B
HDN 038/057 035/070 044/062 034/066 039/071 031/046 025/054
20/N 21/N 21/N 00/U 02/W 52/W 11/B
MLS 041/056 036/068 043/059 034/062 040/067 031/044 025/050
31/N 12/W 21/N 00/U 02/W 32/W 11/B
4BQ 040/055 034/070 043/058 033/061 039/070 031/044 026/049
21/N 11/N 21/B 00/U 00/U 42/W 01/B
BHK 040/054 034/066 041/056 032/059 038/065 031/042 025/047
11/N 01/N 21/N 00/U 01/N 32/W 00/B
SHR 035/054 032/069 041/058 033/063 036/072 029/042 023/050
10/N 11/B 21/N 00/U 01/U 63/W 01/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...High Wind Watch in effect from late Saturday night through
Sunday afternoon FOR ZONES 28-41-63-65-66.
Red Flag Warning in effect until midnight MDT tonight FOR
ZONES 125>133.
WY...Red Flag Warning in effect until midnight MDT tonight FOR
ZONE 274.

&&

$$
weather.gov/billings
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