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FXUS65 KMSO 150732 AAA
AFDMSO

Area Forecast Discussion...UPDATED
National Weather Service Missoula MT
132 AM MDT Sat Jun 15 2024

.UPDATE...No updates necessary to the previous discussion.

&&

.PREV DISCUSSION...

DISCUSSION...On Saturday, the low pressure system moves inland
and will push a cold front across the Northern Rockies. This
frontal passage will result in increasing westerly winds,
especially for Flathead Lake and the Mission Valley, as well as
Lemhi County. High resolution guidance has backed off on winds
slightly since the last forecast, showing about 10 to 20 percent
chance for gusts to exceed 40 mph in the valleys of western
Montana. Gusts are a little more impressive in Lemhi County and
along the Continental Divide. The front will also bring chances
for precipitation and cooling temperatures on Saturday. There will
be a chance for isolated thunderstorms (20-30 percent) for
western Montana and north- central Idaho on Saturday afternoon.
Thunderstorm outflow winds would further enhance wind speeds.

After a brief period of clearing on Sunday, a significant wet and
cold weather system is expected Monday into Tuesday, with a
general consensus (around 70-80 percent of model solutions)
supporting a closed low feature moving through the region.
Current model solutions show a roughly 30 to 40 percent chance
that liquid precipitation amounts will be 1.00 inch or more along
the Continental Divide into southwest Montana and extending
westward into eastern portions of Idaho and Clearwater County.
Snow levels are tricky with this particular system as forecast
models are notoriously biased too warm with late season closed
low systems such as this. Areas that receive the heavier
precipitation will likely see snow levels driven to 5000 feet or
lower. There is insufficient confidence in either low pressure
track or intensity currently, but you are encouraged to follow
future forecasts as 1 to 2 inches of heavy, wet snow on trees with
leaves could easily cause broken branches leading to localized
power outages with winter driving conditions over area mountain
passes.

For terrain above 6000 feet, a trace to 12 inches of snow is
possible. Snow amounts will vary with snow levels, where
uncertainty is still high. The message for backcountry travelers
at the current forecast lead time is to be prepared for winter
conditions on Monday afternoon through Tuesday morning and to
continue to monitor the forecast through the weekend. While snow
amounts may not be what we see in mid-winter, the snow will be
very wet and heavy. Wet snow falling on trees in full bloom will
result in plenty of downed trees and limbs, potentially blocking
Forest Service roads. Closer to towns, expect downed trees and
limbs to result in power outages. The higher terrain of the
Bitterroot, Anaconda, and Pintler Mountains, Bob Marshal
Wilderness, and Glacier National Park Region has the best chance
of receiving a foot of snow or more. We have extended the Winter
Storm Watch issued on Thursday to include the Sapphire and
Bitterroot ranges including Skalkaho Pass.

&&

.AVIATION...Westerly winds will gust to about 25-30 knots this
afternoon across all of western Montana and north central Idaho.
Increased cloud cover is also anticipated today. A few showers or
isolated thunderstorms are not out of the question, primarily
southeast of a line from KHLN to KHRF to KGIC. Showers or
thunderstorms will be capable of producing a few localized wind
gusts to 35 kts. Westerly winds will again gust in excess of 25
knots on Saturday with a frontal passage in the morning. Expect
increasing clouds and chances for rain showers to begin on
Saturday morning, also with the frontal passage.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Storm Watch from Monday afternoon through Tuesday evening
     for West Glacier Region.

     Lake Wind Advisory from 11 AM this morning to 10 PM MDT this
     evening for Flathead/Mission Valleys.

     Winter Storm Watch from Monday evening through Tuesday evening
     for Bitterroot/Sapphire Mountains...Butte/Blackfoot
     Region...Potomac/Seeley Lake Region.

ID...Wind Advisory from noon today to 8 PM MDT this evening for
     Eastern Lemhi County...Western Lemhi County.

&&

$$