NWS Missoula, MT wrote its last area forecast discussion before the first event at Apr 5, 1:58 PM MST, 3 hours 2 minutes earlier.
Area forecast discussion, Apr 5, 1:58 PM MST, 3 hours 2 minutes before
Area Forecast Discussion
National Weather Service Missoula MT
258 PM MDT Thu Apr 5 2018
...Snow, Blowing Snow and Icy Roads in Western Montana Tonight
Through Friday Morning...
.DISCUSSION...A very abnormal weather system (more typical of
January or February) is still poised to affect primarily western
Montana beginning this evening and continuing into Friday morning.
A punch of moist air associated with a front coming off the
Pacific Ocean will collide with an arctic airmass sagging south
out of Canada, resulting in concerns for widespread snow, gusty
northeast to east winds and a dramatic drop in temperatures. Wet
or slushy road this evening will likely transition to black ice as
wind and cold temperatures allow rapid freezing on paved
surfaces, especially over bridges/overpasses and other elevated
surfaces. Travel across western Montana is expected to become
difficult to dangerous at times tonight into the Friday morning
commute. Numerous winter highlights are in place. A summary of
some of the potential impacts follows.
Snow: Widespread snow across western Montana is expected, with
general snow amounts in the 1 to 4 inch range. An area of
moderate to heavy snow is expected to develop from roughly
Lookout Pass through the I-90 corridor to roughly MacDonald Pass
and north through the Mission valley. These areas could see snow
amounts closer to 3 to 6 inches, with higher values over mountain
passes.
Ice: Roadways which remain wet or slushy into this evening stand
to see the greatest potential for rapid ice formation tonight as
the arctic front passes. Temperatures will drop into the low 20s
to upper teens be tomorrow morning for areas along and east of a
line from roughly Yaak to Plains to Lolo to Butte. These
locations are most likely to see issues from black ice on
roadways.
Winds: Gusty northeast to east winds will develop, with gusts to
30 to 35 mph common across exposed areas of western Montana.
Stronger winds will be funneled through Badrock Canyon, Hellgate
Canyon, and along portions of Highway 2, Highway 12, Highway 200,
and the I90 corridor. Of particular concern is Highway 35 along
the east sides of Flathead Lake and Swan Lake, where wind gusts
to near 50 mph are possible. In addition to blowing snow and
lowered visibility, some tree damage and power outages are
possible.
For those across central Idaho, the brunt of this system hangs up
along the Idaho and Montana border. While rain and higher
elevation snow is expected, a rapid drop in temperatures is not
likely. Therefore, any winter impacts to roadways should be fairly
minimal.
The arctic front quickly recedes mid-day Friday, and thus
roadways should begin to warm and see improvement by afternoon. A
brief drier period is expected before the next weather system on
Saturday.
As the arctic airmass retreats into eastern Montana, a very moist
atmospheric river will move into the Northern Rockies Saturday.
This weather system will bring moderate to heavy rain to areas
below 5000 feet in north-central Idaho, and along the MT/ID
border. For locations along and east of the Clearwater River in
north-central Idaho, could receive 2 or more inches of rain in a
36 hour period, starting Saturday morning. Due to the already
saturated ground, combined with the expected rainfall over the
weekend. There will be the potential for an increase in standing
water, rock and landslides, as well as sharp rises on area streams
that feed the Clearwater River. Higher elevated towns such as
Pierce and Elk City that have several inches of snow on the
ground, should expect large areas of standing water. Highways 12
and 14, could have the potential for rockslides and increased
ponding due to runoff along the road.
Mountain passes, such as Lookout, Lolo, and Lost Trail Passes,
will have periods of slick driving conditions due to snowcovered
roads. During the afternoon, on Saturday, snow could briefly
change to rain, that will create pockets of standing water and
slushy roads.
The rest of western Montana will see a wet and snowy weekend as
well. However, we do not expect the amount of precipitation as
locations in Idaho. The main impacts will be to outdoor
activities, so plan on a wet and cool weekend if spending anytime
outdoors. We even expect a slight chance for a few thunderstorms
along the Sapphire Range and the rest of southwestern Montana.
Winds gusting up to 40 to 45 mph under these showers, will be a
possibility.
Much of the the Northern Rockies will be dominated by a building
high pressure for the first part of next week, then becoming
active once again with valley rain and mountain snow by mid week.
&&
.AVIATION...A second push of arctic air will make it's way into western
Montana this evening causing strong wind gusts to 40 knots, snow
and limited visibility/low ceilings. Ahead of the front, expect
low clouds and fog over portions of northwest Montana. Downslope
winds will be hazardous for aircraft flying on the west side of
north to south oriented mountain ranges especially the Mission and
Swan Ranges. Snow will end by 06/1200Z across the area but expect
easterly winds generally between 10 and 20 knots through
06/1800Z. Lingering low clouds with some mountain obscuration is
possible on Friday especially along the Continental Divide. Timing
estimation of arctic front:
Eureka, Happy's Inn, Kalispell, Polson and Ovando, Drummond to
Avon between 06/00z-02z I-90 corridor between Lookout Pass, Lolo
Pass, Missoula and Stevensville between 06/03z-06z
&&
.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Warning from 6 PM this evening to noon MDT Friday
Butte/Blackfoot Region...Potomac/Seeley Lake Region.
Winter Storm Watch Friday afternoon Butte/Blackfoot Region...
Potomac/Seeley Lake Region...West Glacier Region.
Winter Weather Advisory from 9 PM this evening to noon MDT
Friday Bitterroot/Sapphire Mountains...Missoula/Bitterroot
Valleys.
Winter Storm Warning from 9 PM this evening to noon MDT Friday
Lower Clark Fork Region.
Winter Storm Warning from 6 PM this evening to noon MDT Friday
Flathead/Mission Valleys.
Winter Storm Watch Friday afternoon Flathead/Mission Valleys.
Winter Weather Advisory from 6 PM this evening to noon MDT
Friday West Glacier Region.
Winter Weather Advisory from 9 PM this evening to noon MDT
Friday Kootenai/Cabinet Region.
ID...None.
&&