High Wind in Montana, December 10 to 11, 2017

Area Forecast Discussion...UPDATED
National Weather Service Glasgow MT
652 PM MST Sun Dec 10 2017

.DISCUSSION...

6:00 PM UPDATE:
Sent an update tonight simply to include the latest hourly model
updates for temperatures and winds and chances for precipitation
over our eastern zones overnight. Won't amount to much if anything
at all.
BMickelson

AFTERNOON UPDATE:
Synoptic Setup: Currently a trough lies over Nunavut, the Hudson
and the Great Lakes. A ridge lies over the California the Pacific
Northwest Coast and the Gulf of Alaska. In between northwest to
northern flow has established from Alberta through northeast
Montana and into Colorado. A shortwave is dropping down in the
flow over southeastern Saskatchewan.

This afternoon through Tonight: Shortwave will move into North
Dakota tonight clipping the far northeastern corner of the CWA.
Winds aloft are expected in increase. However, with inadequate
mixing these winds are not expected to make it to the surface
except for the occasional gust. No precip is expected with this
wave.

Monday through Tuesday: Ridge to the west will move inland and
spill over the front range into a large chinook over Alberta
Monday night. The movement of the ridge should kick out the
shortwave by Monday late morning. The Chinook should be in full
force over Montana by Tuesday morning leading to a very warm day.

Tuesday night into Wednesday night: As the ridge rides down the
front range another shortwave similar to tonight will follow it
through the area bringing a cold front and strong winds for the
whole CWA.

Thursday and Thursday night: Another brief warm chinook is
anticipated in the NW flow.

Friday onward: A pattern change sets up. The large ridge in
control of the western half of the CONUS and Canada dissolves.
This gives room at a minimum for a large Pacific trough to move
through cooling things off from here onward. Friday, Friday night,
and Saturday Night all look to have higher PoPs with a significant
chance at rain/snow used NPoP here to help substitute for FB's
inadequacy. Unfortunately, beyond these generalities model
uncertainty takes over and change can be expected to details and
timings. GAH

830AM UPDATE:
Changes to the forecast were minor. Hourly temps across Phillips
and Petroleum continue with the chinook eating their inversions
early. RH across the board was about 10 percent too high. This is
a warning sign for fire weather and if wind ends up busting
expectations significantly would not be surprised to throw a red
flag later. Currently, winds still look to be weak to
marginal/breezy today. GAH

OVERNIGHT DISCUSSION:
The short term will again be dominated by high pressure under a
large ridge of high pressure over the mountain west. The main
concern for the period will be the degree of cloud cover over the
region and at what times. IR imagery shows some high-level cloud
cover over the region, which should somewhat inhibit radiational
cooling, thus keeping morning lows higher than consensus. The
blended solution keeps partly cloudy skies over much of the
region, with mostly cloudy skies building into the northeast. This
should inhibit insolation as well later today, keeping highs a bit
lowered in the northeast. If large breaks in any cloud cover can
occur during the day, with little snow on the ground and good
mixing expected to occur in the afternoon, daytime highs may end
up even higher than forecast.

Mechanical mixing, and some hints at a tightening pressure
gradient over the region will lead to some blustery conditions
during the overnight hours tonight into tomorrow, and while
conditions generally remain below wind headline criteria, should
the NBM be believed, the Little Rockies may be a place to keep an
eye on through the later afternoon hours into late tomorrow night.

Generally the long term remains dominated by ridging in the west
and high pressure at the surface across the region. A small
amplitude wave looks to push through eastern Montana around
midweek, but as it is expected to be more shortwave in nature,
should just move through the large-scale flow without influencing
the shape or strength of the overall ridge. Precipitation chances
due to this wave will be minor, and the only real effect should be
to knock down the temperatures behind it for a day or two, and
some local wind enhancement will certainly be possible.

The next significant wave is still being resolved late in the
week and early into the weekend. This trough does look to be
strong enough to modify the overall ridge, to a certain extent,
and will work to flatten the ridge some. This is where some
precipitation chances really begin to push into the region. There
is enough discrepancy in the model solutions still that the PoPs
are generally going to be slight chance, with a few scattered
areas of chance PoPs in there as well. Bigelbach

&&

.AVIATION...

LLWS: Low level wind shear is expected to set up rapidly tonight
as a strong mid-level wind off the ground moves in from southern
Saskatchewan. Timing appears to be 02 to 07Z for the TAF sites.

FLIGHT CAT: VFR-MVFR.

SYNOPSIS: VFR through tonight. The western edge of a disturbance
will bring lowering clouds to northeast Montana tomorrow.
Ceilings will lower for all sites, but KSDY and KGDV will
experience MVFR levels from the late morning through the afternoon
hours.

WIND: West-northwest winds of 10-20 kts this afternoon.
Increasing to 15-25 kts with gusts 25-30 kts tonight. Decreasing
to 10 to 20 kts Monday.

GAH/BLM

&&

.GLASGOW WATCHES/WARNINGS/ADVISORIES...NONE.

&&

weather.gov/glasgow