Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 201038

Area Forecast Discussion
National Weather Service Missoula MT
338 AM MST Mon Nov 20 2017

...Snow-covered Mountain Passes This Morning...

.DISCUSSION...As expected snow is coming down pretty hard at both
Lookout and Lolo Passes. Other areas have been able to mix-out
into the 40s and even near 50 degrees like in the southern
Bitterroot Valley and southern Mission Valley. We made a call to
the Haugan, Montana area around 225 AM and discovered that
temperatures had already shot up to 40 degrees with rain and snow
being reported. Expect snow to continue at passes including Lost
Trail through much of the day today. An upper level wave will
bring rain showers to the northwest valleys this afternoon making
for a wet day. Showers will be moderate at times and couldn`t
rule out graupel in the most intense cells. Snow may mix with or
change over to rain at times at Lookout Pass, but the heavier
showers could provide wet snow to coat the roads for brief
periods. Showers are expected to diminish tonight.

The warm front that is supposed to move into the region on
Tuesday has been trending slower with recent model runs, so
Tuesday morning looks to be drier than previous forecasts. By
Tuesday afternoon moisture is expected to move into north-central
Idaho and northwest Montana. The amount of subtropical moisture
forecast to move into the region is a bit unusual for this time of
year, so those in north-central Idaho and northwest Montana are
likely to see quite the rain event through Wednesday.

Another break in precipitation is possible for the start of
Thanksgiving day, but the cold front is now trending faster so
precipitation and lowering snow levels may bring impacts during
the second half of Thursday. Drying is expected behind the cold
front but any showers that remain Thursday night and Friday should
fall as mountain snow and a mix of rain and snow in valleys.

The beginning of next weekend looks to be dry but another wet
weather system is possible by Sunday.


Cloud cover will continue to lower as the current weather system
moves into the region. Mountain snow and a mix of rain and snow
will initially fall at lower elevations before changing to all
rain later this morning due to a warm front passage. Increased
southerly winds have been common overnight so most of the lower
elevations are starting the day breezy and mild. A shortwave and
cold frontal feature will pass during this afternoon, and many of
the high resolution radar forecasts show a period of intense
shower activity between 20/2000Z and 21/0100Z. These showers will
have the potential to produce moderate to heavy snow at mountain
passes. Heavy showers could even introduce graupel to valley
locations and reduced visibility and low ceilings will be the
main impacts. Model guidance agree that showers will decrease
overnight with drier air moving into to the region.



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