Winter Storm in Idaho, February 23 to 25, 2018

Area Forecast Discussion
National Weather Service Missoula MT
218 PM MST Fri Feb 23 2018

.DISCUSSION...Cloud cover remains over much over north-central
Idaho and western Montana today, and about the time it starts to
breakup, cloud cover associated with the next weather system will
arrive. The next weather system will spread snow into the region
beginning this evening in northwest Montana and north-central
Idaho and these areas will also see the majority of the snowfall
with this first system. One of our main concerns for tonight and
Saturday is the addition of gusty south winds in the Camas Prairie
of Idaho near Grangeville. New snow of 6-10 inches fell in
Grangeville which has primed them for blowing and drifting snow
with the addition of wind. Travel conditions along Highway 95
between Grangeville and Cottonwood may become impassible with
drifting snow and near whiteout conditions during Saturday
morning. A Winter Storm Warning has been issued for the Camas
Prairie for snow and blowing snow. The northern Clearwater
Mountains are still likely to see 6-10 inches as well as Lookout,
Lolo, and Lost Trail passes with lower elevations of north central
Idaho to see 2-4 inches. Western Montana will generally see 1-3
inches with higher amounts along the ID/MT border of northwest
Montana by Saturday evening.

Our next weather system, which has been trending a little faster
for its arrival, will bring another round of snow to north-central
Idaho and western Montana on Sunday. Mountain snow totals for the
second storm will generally range from 8-12 inches while valleys
will generally see 2-5 inches by Sunday night. This weather system
will have more wind so the high terrain is likely to have gusty
westerly winds and Grangeville and the Camas Prairie may see even
stronger winds than the Saturday event, so blowing snow is again
of concern. Most of the region will see gusty winds by Sunday
afternoon with the passage of the cold front. Snow bands are
likely to form behind the cold front so periods of intense
snowfall during Sunday evening will make for low visibility,
quickly changing road conditions, and locations with higher snow
amounts. The Bitterroot Valley remains one of the focuses for the
snow bands so higher snow totals remain possible. Snow will linger
through Monday morning.

Snow showers will continue on Monday, especially across the
terrain but even valley showers will be possible. With enough
clearing, Tuesday morning will be quite cold with temperatures
dropping below zero in many places. The remainder of the week
features a general trough overhead leading to colder than normal
temperatures and unsettled, showery weather. There are hints at
enhanced periods of snowfall but forecast models are struggling to
resolve the details that far out. Regardless, more snow is on the
way with no significant warm up in sight.

&&

.AVIATION...Latest GOES East RGB loops show a broad area of
stratus in much of north-central Idaho and western Montana.
Surface observations show this cloud cover lifting some but
terrain remains obscured. Any improvement to ceilings will be
shortlived as the next weather system is quickly moving into the
region. Snow is expected to redevelop and intensify across the
Northern Rockies after 24/0300Z and continue to be present for the
rest of the next 24 hours. While widespread snow is likely, the
heaviest snow rates will be occurring along the Montana- Idaho
border. Conditions near Grangeville, ID and vicinity are expected
to deteriorate overnight with gusty south winds and blowing snow.
Lowered ceilings and decreased visibility will be common during
Saturday.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...     Winter Weather Advisory from 8 PM this evening to 5 PM MST
     Saturday Kootenai/Cabinet Region.

     Winter Weather Advisory from 8 PM this evening to 5 PM MST
     Saturday Lower Clark Fork Region.

ID...Winter Weather Advisory from 7 PM this evening to 4 PM PST
     Saturday Northern Clearwater Mountains...Southern
     Clearwater Mountains.

     Winter Storm Warning from 7 PM this evening to 4 PM PST Saturday
     Orofino/Grangeville Region.

     Winter Weather Advisory from 7 PM this evening to 4 PM PST
     Saturday Lower Hells Canyon/Salmon River Region.

&&