427
FXUS65 KMSO 121854
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
1254 PM MDT Wed Jun 12 2024

.DISCUSSION...
The Northern Rockies will remain under the influence of a ridge
of high pressure through Friday, leading to a period of warm and
dry weather. Generally light winds are expected Thursday, before
westerly winds kick in Friday as an upper level jet begins to move
overhead associated with a Pacific trough approaching the OR/WA
coast. Valley areas will experience gusts of 15-25 mph. Higher
gusts will focus across the Mission Valley and Lemhi County, where
NBM probabilities for gusts of 30 mph or greater reach 50-60%.

A significant change will impact the Northern Rockies this
weekend into early next week. The aforementioned Pacific trough
and surface cold front will move across eastern Washington into
western Montana Saturday. Westerly winds will increase along and
behind the cold front Saturday afternoon and evening, especially
across the US-93 and I-90 corridors, where NBM probabilities for
gusts of 40 mph or greater hit 40-60%, with higher probabilities
of >75% across Lemhi County and the I-90 corridor from Deer Lodge
through Butte. Furthermore, in addition to modest pressure rises
associated with the front, the threat of gusty winds is bolstered
by the potential for convective mix winds with showers and
thunderstorm activity.

The forecast becomes challenging and complex late Sunday into
Tuesday. Model guidance continues to display a wide range of
potential outcomes as a secondary trough moves across the region.
Roughly ~50% of ensemble members show a closed low scenario, with
widespread precipitation and lowering snow levels, potentially as
low as 4,500-5,000 feet. The other half of ensemble members show a
progressive trough scenario, with higher snow levels of 6,000+
feet, showers, and cooler temperatures. Impacts under this case
would mainly target the higher peaks and backcountry areas.
Nonetheless, even under the progressive trough scenario,
recreation will be impacted and those heading into the backcountry
should be prepared for cold, windy, and generally unpleasant
conditions for June.

Circling back to the closed low scenario, theres concern for
utility infrastructure and significant impacts to higher elevation
areas (>5,000 feet elevation). Snow loading from heavy wet snow
will be capable of damaging vegetation and causing difficult
travel across backcountry roads. Higher end snow totals within the
NBM (10% chance to exceed or hit amounts) reach 1-2 feet above
6,000 feet across the Sapphire Mountains, Anaconda-Pintler and
Flint Creek Ranges. /Lukinbeal

&&

.AVIATION...Wind gusts of 15-25 knots will be common until around
sunset. Mostly clear skies are projected to continue through
Thursday with high pressure building into the Northern Rockies.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$