Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 072006

Area Forecast Discussion
National Weather Service Missoula MT
206 PM MDT Fri May 7 2021

.DISCUSSION...A deep trough of low pressure over western British
Columbia is pushing a cold front over the Northern Rockies this
afternoon. The front is quite clear on satellite imagery, as are
rain showers extending from north-central Idaho into central
Montana. Enough instability exists with the cold front to spawn
some thunderstorms across north-central Idaho and southwest
Montana this afternoon. These storms will not reach severe
criteria, but will still be able to produce lightning and erratic
outflow winds. The trough over western Canada will migrate south
and east over the course of the weekend, keeping unsettled weather
in the forecast through at least Monday. It becomes a closed low
by later Saturday morning, centered over western Montana.

While rain will be the primary precipitation type today, snow
levels will become low enough by Saturday morning to produce
snowflakes in all but the lowest valleys of the lower Salmon River
in Idaho. Surface temperatures will be warm enough to prevent any
valley accumulations, though, so area roadways will remain clear
of snow except for a dusting on area passes such as Lost Trail,
Lolo, and Marias Passes. Mountain ranges such as the Missions,
Swans, and the Glacier Park will see three to six inches on
Saturday. By late Saturday afternoon, the closed low migrates east
of the Continental Divide. This position of the low will be
conducive to continued precipitation along the Divide. As a
result, Homestake, Rogers, and Marias Passes could see another
dusting of snow on Sunday.

Unsettled weather will linger on Monday. By Tuesday, a broad ridge
begins to build over the Northern Rockies. Some lingering moisture
could still fuel some scattered showers in western Montana on
Tuesday, while the rest of the work week will see a return to fair
weather with seasonable (or a a little above normal) temperatures.
Confidence in model guidance deteriorates by Friday.


.AVIATION...Scattered showers will lower ceilings and obscure
terrain today through Saturday across the Northern Rockies
airspace. All terminals should expect gusty winds, primarily out
of the west, through Saturday as well. This afternoon, there will
be a chance for thunderstorms, especially at KBTM. Any storm that
does approach a terminal will be capable of erratic, gusty
outflow winds.



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