Area Forecast Discussion
Issued by NWS Missoula, MT

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FXUS65 KMSO 232032

Area Forecast Discussion
National Weather Service Missoula MT
232 PM MDT TUE SEP 23 2014

...RECORD HIGHS EXPECTED WEDNESDAY and Thursday Western Montana...

.DISCUSSION...A weather disturbance and surge of moisture will
quickly move across north central Idaho and western Montana into
early tonight.

High pressure will build over the northern Rockies and produce
a much warmer air mass Wednesday. In addition, moderate southwest
winds aloft are expected to mix down to many of the valleys and
further warm the lower atmosphere. Record high temperatures seem
very possible, especially Missoula and Butte, but with slightly
less confidence in Kalispell. Very warm temperatures, on the order
of 15 degrees above normal are also expected in Grangeville and
Orofino areas Wednesday afternoon.

A cold front will probably stall over the western Clearwaters
Wednesday night into Thursday afternoon. This will leave much of
western Montana again within a very warm air mass and another day
with near record highs possible. The highest confidence areas for
record heat on Thursday is from Missoula to Butte.

Friday to Saturday will be a big cool down compared to Wednesday
and Thursday with temperatures about 20 degrees cooler. The big
cool down might sound chilly, but it will bring the region back
down to near normal temperatures for late September with many
valley locations in the upper 60s and 70s in western Montana,and
near 80 degrees in central Idaho.

The more significant impact this weekend will be the rain. While
confidence on the cool down is high, confidence on the timing and
location of rain is low. Currently, it looks very likely that some
areas will get wet, but exactly where and when is very dependent
on the track of an upper level low as it rejoins the main storm
track. These mergers are a very sensitive process, and so are hard
to forecast. Unfortunately for the Northern Rockies, this will
happen over central Idaho and Western Montana, hence the
difficulty in making a precise precipitation forecast for the
weekend. At this time it appears some valley locations may receive
around a quarter of an inch of rain this weekend, with the
mountains, especially in central Idaho, receiving half to three
quarters of an inch of rain.



.AVIATION...A weather disturbance will support a relatively moist
and unstable atmosphere into this evening over western Montana and
north central Idaho. A few showers and isolated thunderstorms are
expected. Gusty winds can be expected near showers. High pressure
should build over the region later tonight and support partial
clearing by morning.



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