627
FXUS65 KMSO 160816
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
216 AM MDT Mon Sep 16 2024

.DISCUSSION...Southerly flow aloft will allow for increasing
moisture across western Montana and north central Idaho ahead of a
cut off area of low pressure currently located over central
California. This is a favorable pattern for the development of
showers and thunderstorms, particularly this afternoon and
evening. There is little in the way of shear, which means storms
will likely not be overly strong today. However, with moisture
amounts increasing to 150-200 percent of normal and storm motion
of only 10-20 mph, very heavy rain will be the main concern. In
particular, the latest high resolution models show a 20-40 percent
chance of hourly rainfall rates exceeding 0.50" in Idaho County.
Flood prone basins will need to be monitored this afternoon,
including the Williams Creek and Elk Horn burn scars from 2022 and
2023.

Forecast models are beginning to come into better agreement with
regards to the closed low track as it ejects northeastwards
through central Idaho into eastern Montana Tuesday into Wednesday.
This more southern track has caused precipitation amounts in the
forecast to trend lower, especially across northwest Montana near
the Idaho panhandle. While most all of western Montana and north
central Idaho can expect precipitation, the most likely area to
receive 0.50" of rain or more (70 to 80 percent chance) through
includes Idaho County in Idaho and locations generally along and
east of the Highway 93 corridor in western Montana.

Precipitation will largely come to an end for Thursday into the
early part of the weekend, with temperatures largely rebounding to
seasonal normals in the upper 60s to mid 70s. Then ensembles are showing a 10-15 percent
chance of a high impact, high elevation snow even late next
weekend in northwest Montana. There is a 10-15 percent chance for
a foot of snow above 7,000 ft in Glacier National Park. We`ll
continue to watch that potential very closely.

&&

.AVIATION...Southerly flow aloft ahead of a cut off low pressure
system over central California will provide conditions favorable
for showers and thunderstorms today. Showers and isolated
thunderstorms currently exist across Lemhi County in Idaho, with
wind gusts up to 35 mph being noted. This line will slowly shift
northwards into southwest Montana through 16/1500z before
generally fizzling out around KMSO. Thunderstorms will then become
more likely after roughly 16/2100z across all areas other than
far northwest Montana. Slow moving thunderstorms will be capable
of very heavy rainfall rates, generally along and south of the I90
corridor, including in the vicinity of KMSO, KHRF and KBTM. A few
gusts to 40 mph could also be a concern with storms.


&&

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

$$