Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 250935

Area Forecast Discussion
National Weather Service Missoula MT
335 AM MDT Wed Apr 25 2018


Highlights through Friday:

1) 10 to 20 degrees above normal high temperatures.
2) 20s to 30s low temperatures possible each morning many valley
3) Rivers rising 1 to 2 feet

A weather disturbance will bring some clouds over the region through
this afternoon, but skies should clear by tonight. With a high
pressure system building east of the Continental Divide, a north
to east breeze will develop this afternoon into tonight.

Only minor changes to the forecast for next weekend. Saturday
continues to look like a good day for thunderstorms due to a deep
trough and low pressure system arriving on the west coast. Moist
southwest flow into central Idaho and western Montana will cause
some thunderstorms, but areas north of St. Ignatius and Seeley
Lake have much less of a chance for thunder the way the models
currently look. Models of course disagree on the exact timing and
location of the low, but generally models agree very well on the
big picture of a low pressure system moving into the region.

Saturday night, Sunday, and most of Monday this slow moving system
moves east of the Continental Divide and taps into Gulf of Mexico
moisture from the plains. It then wraps that moisture around over
the Divide and into western Montana. There is considerable
differences among models where the heaviest precipitation will be,
but most models currently place 12-24 hours of moderate rain over
some portion of western Montana. There is a significant chance
that somewhere in western Montana will receive 1 to 2 inches of
new rain this weekend. For those who may be affected by this
please read the hydrology section below for more details.


.AVIATION...A 1025 millibar high pressure system will build east
of the Continental Divide later today causing a north to east
breeze to develop after 25/18Z at GPI and along the Continental
Divide by or after 26/00Z. Winds could gust as high as 20 knots
this evening at all the terminals except for SMN. Other than the
middle to high clouds and a few showers along the Divide, expect
VFR conditions today. Continued warm and dry Thursday with VFR


.HYDROLOGY...The week got off to a warm start, and as we head into
the middle and end of the week we are seeing some warm
temperatures in the mountains with many locations staying in the
upper 30s and 40s overnight. This combined with warm daytime
temperatures is causing rivers to rise as is typical this time of
year. A few rivers currently have forecasts near flood stage early
next week, mainly in northwest Montana. However, the very wet
system that is forecast late next weekend is very concerning. One
to two days of moderate rain would add significantly to run-off
and contribute to small stream and river flooding. This is far
enough out in the forecast that uncertainty in timing and
intensity makes it imprudent to issue a watch or warning, however
we will be watching this system very closely.



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