Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 210954

Area Forecast Discussion
National Weather Service Missoula MT
354 AM MDT TUE APR 21 2015

.DISCUSSION...Today will be the warmest day of the week as the
high pressure ridge shifts directly over the Northern Rockies.
There will be a bit more afternoon cloudiness as mid level
moisture gradually increases across the area and interacts with
fairly impressive daytime heating for this time of year. In fact,
a few isolated thunderstorms may form as temperature reach some 10
to 15 degrees above normal. But these will largely remain locked
over the terrain, given the extremely weak steering winds.

However this all appears to change on Wednesday as a rather
strong and significantly colder cut of low pressure system drifts
into Washington and towards Montana. The passage of a very slow
moving cold front ahead of this upper low will team with peak
heating to produce widespread showers and thunderstorms across
much of the Northern Rockies. The focus of storms will start
along the Bitterroot Mountains and unhurriedly shift east across
the rest of western and southwest Montana Wednesday evening.
Although severe weather is not expected, those with outdoor plans
should prepare to encounter lightning, wind gusts to 45 mph, and
pea sized hail with some storms. Farther north, boaters on
Flathead Lake are likely to contend with early afternoon winds
gusting 20 to 25 mph before showers and thunderstorms ultimately
impact the lake later in the day.

Models continue to struggle with the path and strength of the
cut-off low as it exits into Canada. General logic with these
types of features would support a slower passage and thus, have
lingered precipitation chances well into Thursday, especially
across northwest Montana. However, this forecast may ultimately
prove too pessimistic if the low moves faster into Canada,
resulting in a much nicer day. Either way, models agree that a
more showery regime will be in place across the area on Friday
through Sunday, with chances generally increasing each day.

Beyond the weekend, models are struggling to depict the overall
pattern, so have maintained the consensus of most likely
solutions which supports unsettled conditions continuing into next


.AVIATION...A warm and pleasant day is expected yet again today as
the apex of the high pressure ridge moves directly over the
Northern Rockies. Light and variable (and most likely terrain-
driven, overall) winds should once again be anticipated after
21/2100Z. Otherwise, stable and dry conditions will persist once



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