Scientific Forecaster Discussion
fxus65 kbyz 180239
Area forecast discussion
National Weather Service Billings Montana
739 PM MST Wed Jan 17 2018
water vapor imagery shows ridging over the northern rockies with a
deep Pacific low off the British Columbia coast. Plenty of high
cloud is spilling over the ridge and across our cwa, but otherwise
it will be a dry night. Main issue is of course the wind. Lee side
trof is in place and will deepen later tonight as area of pressure
falls over the Columbia Basin shifts east. We have already seen a
wind gust of 59 mph near Nye, and 50 mph at east Livingston dot. A
Wind Advisory is in place and will make no changes. Strongest
winds should occur late tonight and Thursday morning, when gusts
could reach 65 mph.
Have adjusted winds up a bit this evening to account for current
observations at Livingston and Nye. Have also raised sky cover per
the increased high cloudiness. Also, we are near some forecast
lows in eastern valleys so have dropped temps a bit in spots. Have
raised temps along our western foothills as it will be a mild and
windy night, with warm advection ongoing.
Short term...valid for Thu and Fri...
Short wave moving across southern Canada today will help push out
Arctic air in our eastern river valleys. Ridge will then build
over the region leading to some warm temps for Thursday.
Dynamic system is then poised to hit area tomorrow night into
Friday. Ahead of the weather system the pressure gradient is
progged to strengthen tonight through Thursday. Wind Advisory
currently in effect should cover this event well. There is a
slight chance some stronger wind gusts of 65-75 mph duct down into
these areas as well Thursday afternoon as jet stream lines up in
a favorable position over the region for a brief time ahead of
In addition, ahead of the associated front, we are a little
concerned about mountain wave activity late Thursday/Thursday
evening along and near the foothills, including the Red Lodge mtn
vicinity. Proggs currently do not show much momentum Transfer
downward, but this will still need to be monitored with high-
resolution proggs as we get closer to this time frame, 65-70 kts
are quite possible at mountain top level and could affect
recreation activities Thursday afternoon.
Large upper trough will move inland as 130 kt jet stream
slides into our western mountains and zones Thursday night and
brings a stream of moisture into the mountains. This should result
in a good period of orographics on west facing slopes through
Friday. Low to mid level winds of 30-45 kts are then possible in
the mountains as well during this time.
At the lower elevations, the primary push of cold air is late
Thursday night, after 2 am. Decent frontogenesis forms and hangs
over the mountains and foothills through Friday. Initially, lower
elevation snow ratios should be on the low side due to relatively
mild low level temps, but increase Friday morning. A few inches
of snow accumulation look possible in the foothills from
Livingston to Red Lodge. Billings and surroundings areas may see
around an inch or so of wet snow. This may occur during the Friday
morning commute, so something we also need to monitor for any
travel condition impacts. At this time we believe impacts will be
marginal due to relatively mild temps and limited snowfall.
Snow gradually ends from north to south Friday, lingering in the
mountains Friday evening. This system is not associated with
Arctic air, so temps in the 20s and 30s are still expected for
Long term...valid for Sat...sun...Mon...Tue...Wed...
Overall inherited forecast appears in good shape, with a
progressive, but mainly dry pattern. The be periodic snow
potential from several waves, but no significant accumulation is
expected outside of mountain areas.
Precip appears to linger in mountains and southern most zones
Saturday and Saturday night, as trof splits as it crosses the
region and drags energy south. Shortwave upper level ridging
develops overnight, and prevails Sunday.
Another Pacific wave and moisture moving toward the region Sunday
night, meanwhile the sfc gradient tightens over preferred gap
wind areas, so expect to see winds around Livingston ramping up
by Sunday afternoon, and continuing into Monday. Gusts around
60mph are possible. The Pacific wave crosses the region Monday,
cutting off the strongest of the winds in gap areas, and bringing
a slight chance of snow through much of Tuesday.
Upper level ridging approaches the area Tuesday night, but moves
quickly eastward through the area Wednesday afternoon, bringing
zonal to southwesterly flow to the region by Wednesday
afternoon/evening. This looks like it will again result in mainly
mountain snow, but some energy does slide east through the area,
and may bring some limited snow potential. Have increased
coverage of slight pops through the end of the period.
Temps will generally be below seasonal average through the
extended period, with mainly 30s and a few 20s through the period.
VFR conditions will prevail over the area into Thursday with
passing high clouds. Gusty winds will continue over western areas,
strongest vc klvm, where SW surface winds are expected to increase
overnight with gusts of 40 to 50 kt possible. Expect low level wind shear over
kmls and kbhk through tonight. Stp
Preliminary point temp/pops...
Thu Fri Sat sun Mon Tue Wed
bil 031/048 030/036 020/033 015/031 015/035 017/024 013/030
00/north 46/o 21/b 11/u 02/S 22/S 12/j
lvm 035/051 031/033 017/032 014/034 017/038 020/034 020/032
00/north 88/S 32/S 21/north 22/S 32/S 23/S
hdn 019/043 025/035 019/033 012/030 010/031 016/024 008/031
00/east 26/S 21/b 11/u 02/S 22/S 12/j
mls 015/038 025/035 021/031 012/027 012/030 014/022 004/024
00/b 23/S 11/b 11/b 02/S 22/S 11/b
4bq 021/045 027/037 023/034 015/032 013/034 015/024 005/027
00/b 12/o 21/east 11/b 02/S 22/S 11/b
bhk 020/045 025/040 021/035 012/032 011/032 013/023 003/025
00/b 12/o 11/b 11/b 03/S 22/S 11/b
shr 021/050 028/036 019/031 014/030 012/034 015/027 012/031
00/b 13/S 22/S 21/b 01/b 22/S 11/b
Montana...Wind Advisory in effect until 6 am MST Friday for zones