Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 192128

Area Forecast Discussion
National Weather Service Missoula MT
228 PM MST Sun Feb 19 2017

.DISCUSSION...Precipitation has slowed its progression into Idaho
and western Montana this afternoon. As a result, the heavier
precipitation expected tonight has been delayed, and is now
expected to begin in earnest on Monday. That being said,
convective showers may drop light valley rain and mountain snow
through this evening, but with little impact. A rumble of thunder
could even be heard in central Idaho.

When the more impressive moisture begins tomorrow, conditions
will be cold enough to produce a rain/snow mix for most valleys,
with snow falling at 3500 feet and higher. As warmer air
infiltrates during the day, snow levels will rise, causing any
rain/snow mix in valleys to transition over to all rain by Tuesday.
Mountains could pick up a quick 3-6 inches of snow Monday, with
an additional 5 to 12 inches by the end of the day Tuesday.
Mountain passes (namely Lolo and Lookout) will be most impacted by
periods of moderate snowfall that could create difficult driving.

Temperatures on Tuesday will moderate some as well, helping to
add melting snow to the equation for valley locations. Snowmelt
will combine with light to moderate rainfall, bringing runoff
issues back into the picture. NW Montana could be most impacted,
given the hefty snow amounts that remain on the ground there.
Snowmelt and rainfall will make for very sloppy conditions Tuesday
and perhaps Wednesday as well, with standing water becoming a
common feature.

The Northern Rockies will remain in an active pattern, with the
looming possibility for much colder air to dominate the region
late in the week into the weekend. There are still significant
differences in forecast models on just how cold the airmass will
be during this time, and has resulted in low forecaster
confidence. So, if you are making plans for late in the week into
next weekend, at the very least plan for high temperatures in the
20s to 30s and the likelihood of snow.


.AVIATION...Intermittent, light showers will be possible across
the Northern Rockies tonight ahead of the slowly-advancing
weather system. Impacts will be minimal. The next system is
expected to bring widespread high terrain snow and valley rain on
Monday. Impacts from rain/snow will vary from slightly lowered
visibility and lowered ceilings throughout the day Monday into
Tuesday, with impacts spread evenly between all terminals. KGPI
and KMSO will see the most prolonged impacts from rain, snow, or a
rain/snow mix during this time.



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