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fxus65 kbyz 201023 
afdbyz

Area forecast discussion
National Weather Service Billings Montana
323 am MST Mon Feb 20 2017

Short term...valid for tdy and Tue...

Water vapor imagery shows a shortwave moving into eastern Mt, with
local radars showing an area of showers in Fallon/Carter counties.
There is also a trailing band of showers along pv axis in Rosebud
County. Precipitation is light, scattered and will exit our east
around sunrise.

Moist SW flow aloft will bring periods of snow to the beartooth
absarokas today and Tuesday. Given up to 3 g/kg of moisture on the
300k surface, and 700-500mb lapse rates near 7c/km, the snow will
accumulate to several inches. That being said, deeper moisture
plume and strongest orographic ascent appears to nose into the
higher terrain of northwest WY, I.E. To our south. Will not issue a
highlight and will keep snow accums to 8-12 inches for SW favored
aspects.

Biggest issue in the short term period is wind. Shortwave moving
thru the Pacific northwest today will induce strong pressure falls in
central Montana this afternoon, allowing gradients to become
increasingly supportive of gap flow. Mid level winds expected to
increase to 50-60 kts by early evening, so feel we will see gusts
reach advisory level at Livingston and Nye even with a
destabilizing airmass. Will also need to keep an eye on Big Timber
here, and have pushed gusts up in all of these areas. Also, we
could see a period of mountain wave potential at Red Lodge and
along the east slopes of the bighorns in the pre-frontal late
afternoon and evening. Mountain top winds not quite strong enough
for a significant risk of high wind, and models do not currently
show strong downward motion, but have raised gusts at Red Lodge
and Sheridan. Something to keep an eye on today.

Winds will decrease in all of these areas late tonight and early
tomorrow, then ramp up again from midday thru the evening on
Tuesday. 00z GFS has trended toward the other models, showing a
later and weaker Pacific shortwave with a bit less mid level
wind. That being said, 700mb winds of 50-55 kts will spread across
the area in the afternoon as surface low tracks west to east thru
our cwa. Upstream shortwave suggests ascent, but mixed winds will
be on the increase across our west and central parts during the
peak heating hours. Gusts should reach 60 mph at lvm/Nye, and
approach or exceed 50 mph at Big Timber and Harlowton.

For highlights, have issued a Wind Advisory for Livingston and
the beartooth foothills from this afternoon thru Tuesday evening
to cover both periods of wind. Based on the latest model trends,
will hold off on any additional highlights for now, but this will
need to be watched. Will continue messaging thru wx story and severe weather potential statement
for these next two days of wind.

Temps will continue to be well above normal the next two days.
Tuesday will be the warmest day of week, if not the year so far,
with deep mixing in a rather mild airmass. Should see highs into
the 60s many areas on Tuesday. Could also see some showers spread
over the lower elevations on Tuesday per the Pacific shortwave
and instability.

Jkl

Long term...valid for Wed...Thu...Fri...Sat...sun...

The long term forecast beginning on Wednesday, and lasting through
next weekend, is fairly difficult given the messy nature of the
expected atmospheric pattern. While precipitation chances will be
difficult to forecast in the long term, the consensus in the
deterministic, and ensemble, model runs is for a change to below
normal temperatures beginning on Thursday and lasting through the
weekend.

Broad trough along the US West Coast trough will begin moving
inland, and slowly amplifying on Wednesday as it approaches
Wyoming. To our north a broad surface high in Canada will begin
pushing south and sometime in the afternoon or evening a cold
front is expected to drop in from the northeast. As the incoming
trough is quite broad, with limited upper level support for any
organized precipitation, most of the precipitation will be a
rain/snow mix and driven by small scale convergent bands, upslope
flow along the terrain, and along the front as it pushes southwest
through the day. On Thursday, the trough will continue to push
east into Wyoming. The best period of diffluence, and lower level
upslope flow, will be overhead the region on Thursday. As the
colder temperatures will be well established, all snow is expected
in any precipitation. The best chances for accumulating snow will
be in extreme southeast Montana and Wyoming near Broadus,
Ekalaka, Lame Deer, and Sheridan. Further north, and west of these
locations, snow is still expected, but accumulations will be
lighter as the upper level support will be limited.

Residual snow showers will remain over the region for Friday, but
with limited upper level support, accumulations will be light and
limited to the mountains, and in any heavier snow showers. Lower
heights and cooler weather will remain over the area through the
weekend. A weak disturbance or two could yield another chance for
isolated snow showers over next week so left a mention of snow
through the weekend. Dobbs

&&

Aviation...

Mountain obscurations will remain through the taf period as
mountain snow showers persist. A few of these showers could affect
klvm through the period as a rain/snow mix, briefly reducing
conditions to MVFR/IFR. Otherwise, VFR conditions will prevail at
all terminals. Winds will begin to elevate this afternoon at klvm,
with 40 kt gusts possible by tonight. At kbil, kshr, and kmls,
winds will light in the morning though expect afternoon increases
in southwest winds with occasional gusts reaching 20 or 30 kts.
Dobbs
&&

Preliminary point temp/pops...

Tdy Tue Wed Thu Fri Sat sun
-------------------------------------------------------
bil 056 040/062 035/047 027/034 016/029 011/027 014/032
0/b 02/west 13/west 56/S 53/S 22/j 11/b
lvm 054 039/058 031/040 020/029 011/027 009/027 013/032
2/west 24/west 23/west 45/S 43/S 22/j 11/north
hdn 054 035/062 033/046 025/034 016/031 012/028 014/032
0/b 02/west 13/west 46/S 53/S 22/j 11/b
mls 053 035/061 034/044 027/034 017/030 015/031 018/034
0/u 12/west 23/west 44/S 42/S 12/j 10/b
4bq 057 036/064 034/046 027/033 014/029 008/029 014/032
0/u 02/west 22/west 47/S 83/S 12/j 00/b
bhk 052 034/061 034/040 025/032 013/027 011/028 015/034
2/west 02/west 13/west 44/S 42/S 12/j 10/b
shr 055 036/063 032/044 023/032 014/027 009/027 008/030
0/b 02/west 23/west 67/S 73/S 23/j 11/b

&&

Byz watches/warnings/advisories...
Montana...Wind Advisory in effect from 1 PM this afternoon to midnight
MST Tuesday night for zones 65-66.
Wyoming...none.

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