Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 240953

Area Forecast Discussion
National Weather Service Missoula MT
353 AM MDT Mon Apr 24 2017

.DISCUSSION...Early morning showers are bringing light snow
accumulations to Lost Trail Pass, and chances for accumulations
will exist down to around 5000 feet from Lost Trail Pass through
Butte and Homestake Pass. Short-lived road impacts will be
confined to Lost Trail Pass as temperatures are warm enough
elsewhere to keep most of the snow off roadways. Showers will
arrive in multiple waves today with the early afternoon being the
time period for widespread shower activity. There will also be a
threat for lightning out of stronger showers mainly south of
Highway 12 in Idaho and Montana. Much of north-central Idaho is in
the path of each wave of showers so there may be little time
between showers today through tonight. Late this evening and into
tonight, the northern extent of a developing low is forecast to
clip southwest Montana so light snow accumulations are again
possible down to around 5500-6000 feet.

Shower chances decrease overnight but will again increase through
Tuesday afternoon with the passage of a shortwave disturbance.
The next wet weather system begins to move into the region Tuesday

A shortwave trough will bring rain & snow (above 6000 feet) to
most on Wednesday morning through early Thursday morning. This is
another high confidence wet period. Thursday morning will be cold
enough for showers to bring light snow down to valleys as low as 2500
to 3000 feet. Widespread accumulating snow is not expected below
5000 ft as ground temperatures are fairly warm, but a quick
dusting is not out of the question. The flow remains moist on
Friday morning as a secondary low moves southeast, so more snow
showers are possible Friday morning for similar elevations.

Saturday is forecast to be drier than most other days in the week.
However, the lack of a distinct ridge, as well as lingering
moisture in northwest flow keeps some chance of showers in the
forecast. Another wet weather system looks poised to bring
precipitation Sunday.


.AVIATION...Low ceilings and a mix of rain and snow have overtaken
southwest Montana early this morning. The circulation responsible
for the precipitation is forecast to move off to the east around
sunrise so conditions will improve through mid-morning. Multiple
disturbances will pass through north-central Idaho and western
Montana today as a trough positions over the region. Instability
this afternoon will aid in shower coverage, so obscured terrain,
periods of lowered ceilings, and isolated thunderstorms are likely.
While showers begin to decrease in northwest and west-central
Montana, north-central Idaho and southwest Montana maintain high
chances for rain and snow with lowered ceilings into tonight as
the low pressure system passes.



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