Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 190245

Area Forecast Discussion
National Weather Service Billings MT
745 PM MST Thu Jan 18 2018

Winds continue to gust from 50-60 mph at Livingston and near Nye,
and will make no change to the wind advisory for these locations.
Winds will decrease gradually thru the night as cold front works
in from the west and the airmass becomes increasingly unstable.
Other foothill locations such as Red Lodge, Fort Smith and
Sheridan could see a period of enhanced SW gusts later tonight,
but do not see a significant mountain wave potential in the
forecast temp/wind profiles. Something to watch though. Also, will
be interesting to watch Sheridan in terms of temperatures. 850mb
plume to +14C exists in the lee of the Bighorns, and even a modest
SW wind could easily push their temps to the 50s. Best time for
this would be in the pre-frontal hours from 06-10z.

Complicated system moves into the area later tonight and
Saturday. There are a couple weak impulses in the Pacific flow as
the ridge breaks down, each of which will be associated with some
mid level frontogenesis and upper divergence associated with 140
kt H3 jet. That being said, models remain different in their
details. Greatest chance of precip appears to be W/NW of Billings
between 06-12z, shifting S/SE to include the Billings area after
12z. Current forecast has these trends covered. There could also
be a risk of light freezing rain in the colder sheltered valleys
east of the foothills. Even with surface temps above freezing, the
existing frozen ground could result in some slight icing on some
roads/walkways. Have added a mention of ZR- late tonight and early
Friday. Something for early morning travelers to watch for.



.SHORT TERM...valid for Fri and Sat...

Deep upper trough was moving onshore this afternoon and this will
be the main weather player for the next 24-36 hours.

First, the mountains and existing Winter Storm Warning. A deep
slug of tropical moisture was advancing toward our southwest
mountains this afternoon. Moisture was 2-3 standard deviations
above normal. Snow will start to pick up tonight, and with
powerful jet (140kt) moving into western Montana, orographic lift
will be impressive. Strong lift with deep moisture should provide
periods of heavy snow tonight through Friday night. Models were
advertising 700mb wind speeds of 60kts moving in, and this will
provide abundant blowing snow with near whiteout conditions in the
high country. Winter Storm Warning in good shape. Now to winds.

Winds have hit wind criteria at Livingston and Nye several times
today. Surface pressure gradient is progged to relax this
afternoon and tonight, taking the gap aspect away from this event.
That being said, 700mb winds of 55-60kts move in there tonight
with the atmosphere becoming more unstable for potential mixing
winds. The 700mb front works in overnight, and believe the strong
wind potential will decrease dramatically then. Will keep the Wind
Advisory in place as strong wind potential is still there for the
evening hours. Mountain wave potential is certainly there for Red
Lodge and Sheridan tonight. Strongest winds stay off the surface
with no real push to drive these down the slopes. The entire
atmoshpere becomes more unstable tonight and this limits a
critical layer from developing at mountain top level, so not sure
how far down the slopes the 60kt winds at 700mb will work. Will
bump winds up a bit and have the evening crew watch closely. Now
to precipitation chances for lower elevations.

As the shortwave trough moves inland, it splits. The Models take
the vast majority of the energy southward toward Colorado and this
leaves Montana in a splitting flow regime. Split flow patterns
are not great for precipitation chances, but there is a great deal
of moisture with this system, with an atmosphere becoming more
unstable. Strong downslope flow will limit PoP chances most of the
night for the plains, but chances increase late tonight and early
Friday as downslope decreases. Models want to spread
precipitation onto the plains late tonight and Friday, with the
ECMWF being the most aggressive. Low levels are progged warm with
850mb temperatures staying above zero, so precipitation will
likely start out as rain, or a rain and snow mixture. Quick
hitting nature of this event, and warm low levels, should keep
snow accumulations down. Models bleed some higher QPF into the
foothills, due to an increasingly unstable atmosphere. Will have
to watch this, as strong upslope flow never really develops, with
mid level wind remaining out of the west/northwest. Will keep Red
Lodge out of Advisory criteria for the time being, but will need
to monitor the situation closely as banding might set up there.
Billings looks to warm for much in the way of snow accumulation.
Roads could become slick though as even wet snow might make things
slippery as the roads have been cooling down quickly at night
with a frozen ground.

A cooler day is expected Friday behind a cold frontal passage
tonight. Highs Friday will be kept to around 40 degrees. Will keep
the higher PoPs on Friday mainly south of Billings as the
strongest part of the splitting trough dives south. Weakly
cyclonic flow will take over for Friday night through Saturday,
but drier air will work in from the west/northwest. This will
decrease PoP chances from northwest to southeast. TWH

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

Overall, the weather pattern looks mainly quiet through most of
the extended period with no big precip events nor arctic fronts.
Sunday will see ridging over the forecast area give way to a fast
zonal flow aloft by Monday as a system moves across southern
Canada. High pressure ridging builds once again Tuesday and
Wednesday with the axis situated over Montana. A large trough and
upper low move onto the Pacific northwest coast late Wednesday
then southeast into the four corners area by Thursday night into
Friday. Models are in very good agreement through the entire
period including the positioning of the upper low and trough. As a
result, the bulk of the energy and precipitation at this time
looks to remain south of our forecast area until possibly Friday.
However, this is still a ways out so model fluctuation is
possible. Temperatures will generally be slightly below normal
with readings in the upper 20s to middle 30s. Hooley



Clouds will begin to lower from west to east this evening into
the overnight hours as a Pacific front approaches the area. The
front will bring a wind shift to the north after 06z. Snow will be
likely for the Beartooth/Absaroka Mountains and foothills with
scattered rain and snow showers across the lower elevations. VFR
conditions will prevail through this evening but areas of MVFR to
IFR conditions will be likely for KLVM and the adjacent
Beartooth/Absaroka Foothills mainly after 09z. Mainly scattered
MVFR conditions can be expected with rain and snow shower activity
across the lower elevations. Mountain obscurations will be likely
late this evening through the overnight hours. Hooley/STP



    Fri     Sat     Sun     Mon     Tue     Wed     Thu
BIL 032/040 022/035 017/030 015/035 017/029 013/029 012/033
    36/O    21/B    11/B    12/S    11/N    11/B    23/S
LVM 034/039 018/033 014/033 017/037 019/036 019/033 016/035
    78/O    32/S    21/N    23/S    21/N    22/S    34/S
HDN 028/038 020/034 013/029 010/031 014/028 007/030 009/030
    26/O    31/B    11/B    12/S    11/B    11/B    22/S
MLS 028/037 020/032 013/026 011/030 014/027 009/026 011/026
    23/O    11/B    11/B    12/J    12/S    11/B    12/S
4BQ 029/041 023/035 017/031 013/033 016/029 008/027 012/032
    12/O    22/S    21/B    01/B    12/S    10/B    11/B
BHK 029/040 021/035 014/030 010/032 013/027 009/025 012/026
    11/E    11/E    11/B    02/J    12/S    10/B    12/S
SHR 030/040 022/033 016/029 011/033 014/030 010/031 010/032
    13/O    44/S    31/B    12/J    21/B    11/B    22/S


MT...Wind Advisory in effect until 6 AM MST Friday FOR ZONES
     Winter Storm Warning in effect until midnight MST Friday
      night FOR ZONE 67.


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