211
FXUS65 KMSO 230146 AAA
AFDMSO

Area Forecast Discussion...UPDATED
National Weather Service Missoula MT
746 PM MDT Wed May 22 2024

.UPDATE...A winter weather advisory has been added for above 4000
feet in the southern Clearwater Mountains of north-central Idaho.
Snow levels have also been lowered for tonight across portions of
north-central Idaho and west-central Montana.


&&

.DISCUSSION...At 7 pm, the temperature at Hamilton dropped to 37
degrees, and observations below 5000 feet show a general cooling
trend. This trend suggest lower overnight temperatures and
decreasing snow levels throughout the night. The forecast now
predicts around half an inch of snow in the southern Bitterroot
Valley, including Hamilton. The development of this low-pressure
system needs to be closely monitored for potential snow impacts
in the valleys.


&&

.AVIATION...A cutoff low moving into the northern Rockies region
is causing widespread rain showers and mountain obscurations.
Snow levels will lower tonight causing lower ceilings overnight
tonight. Timing is very uncertain, but snow levels are expected to
reach the surface overnight at terminal KBTM, and will be near
the surface there by 23/13Z. Heavy precipitation, rain at first
then snow, is expected at KBTM between 23/02Z and 23/13Z.


&&

.PREV DISCUSSION... /ISSUED 1237 PM MDT Wed May 22 2024/

..HEAVY SNOW IN THE HIGHER TERRAIN ACROSS LEMHI COUNTY INTO
SOUTHWEST MONTANA TONIGHT...

DISCUSSION...The winter storm for the higher elevations remains
on track from previous forecasts. Confidence has increased in the
details of the impacts enough that we upgraded to winter storm
warnings above 5,000 ft in west central and southwest Montana.
Snow amounts will vary considerably with elevation, but elevations
above 5,000 ft will see significant impacts due to high snow rates
over 1 inch per hour for several hours. Also, where the leaves
have come out on the trees, the heavy, wet snow can cause
significant damage due to snow loading breaking branches, which
may also lead to some power outages.

There will be a break between systems to end the week, though the
region will remain under a cool, showery pattern.

Memorial Day weekend will start off on Saturday with another
cutoff low moving into the region and causing high elevation snow.
All guidance so far is pointing to an overall warmer system with a
little less precipitation. So fewer snow impacts, but an overall
cool and wet start to Memorial Day weekend. Conditions will
generally improve through the weekend with above average
temperatures expected by Monday.

Overall, the pattern remains active next week, but ensembles agree
well on a 2 to 4 day period dominated by a ridge at some point.
There is, however, considerable differences in the timing other
than it will be too late for Memorial Day.

AVIATION...A cutoff low moving into the northern Rockies region
today is causing widespread rain showers and mountain
obscurations. Snow levels will drop down tonight causing lower
ceilings overnight tonight. Timing is very uncertain, but snow
levels are expected to reach the surface sometime tonight at
terminal KBTM, and will be near the surface there by 23/13Z. Heavy
precipitation, rain at first then snow, is expected at KBTM
between 23/01Z and 23/13Z.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...     Winter Storm Warning until noon MDT Thursday for
     Bitterroot/Sapphire Mountains...Butte/Blackfoot Region.

ID...Winter Weather Advisory until noon MDT /11 AM PDT/ Thursday for
     Eastern Lemhi County...Southern Clearwater Mountains...
     Western Lemhi County.

&&

$$