Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 222051

Area Forecast Discussion
National Weather Service Missoula MT
251 PM MDT Sun Apr 22 2018

.DISCUSSION...A short wave will quickly develop late this
afternoon and produce scattered showers, and even a few lightning
strikes, across Lemhi county, ID into the Butte/Pintler region of
southwest MT through the evening hours.

The mid level low that develops with this wave will move toward
Yellowstone NP. Moisture will wrap around adjacent regions, with snow
levels expected to lower to 4500-5500 feet overnight into Monday.
Snowfall is expected during the overnight hours through Monday
morning, with a couple of inches possibly impacting travel over Homestake
and Macdonald passes, and Gilmore summit. HOWEVER, the impacts
will depend greatly on location of the low and timing of wrap
around moisture. Models have their differences on when wrap around
moisture will impact these areas, thus the uncertainty. If
snowfall starts overnight, then a few inches of snow could
produce some slick roads. If the best wrap around moisture
doesn`t occur until Monday morning, then impacts will be limited
as road temperatures increase to well above freezing. Stay tuned
to our social media feeds for further forecast updates.

This system will move well into central/eastern Montana Monday
afternoon as a ridge of high pressure begins to nose its way into
the Northern Rockies.

From here, the story remains the same: high pressure the rest of
the week will lead to a prolonged period of dry weather, warming
temperatures, and sunny skies Tuesday through Saturday. We have
high confidence that valley temperatures across north central
Idaho and western Montana will be comfortably in the 70-degree
range during this time, however Friday could be warm enough that
some locations could reach the 80 degree mark! We`ll continue to
watch this for any subtle variances, but all in all: this week is
shaping up to be a spectacular one.

One thing to note: with warmer weather comes the likelihood of
rising rivers and streams due to increased snowmelt runoff.
Typically, when the days are warm and nights are around or below
freezing (particularly in the higher terrain), snowmelt comes off
the mountains in an orderly fashion. That will be the case this
week, but we could see some smaller streams and creeks have more
substantial rises by Friday and Saturday. We`ll be watching this
now, and all spring, and update you as the snowmelt process


.AVIATION...All terminals can expect an increase in clouds this
evening, especially KBTM and KSMN. A weather system will develop
across southwest Montana this evening, bringing periods of
precipitation to KBTM and KSMN through 23/1800z. KBTM may receive
some snowfall overnight and Monday morning as snow levels lower to
around 4500-5500 feet. Light accumulations on grassy surfaces may
occur. KGPI and KMSO will experience mainly an increase in clouds
through Monday. All terminals can expect winds to shift from the
northeast but remain light; generally less than 10 mph.



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