Weather Service Report


796 
FXUS65 KMSO 221014
AFDMSO

Area Forecast Discussion
National Weather Service Missoula MT
414 AM MDT Fri Aug 22 2014

...HIGH ELEVATION SNOW AND PROLONGED MODERATE TO HEAVY VALLEY RAIN
TODAY THROUGH SATURDAY...

.DISCUSSION...Scattered showers and embedded thunderstorms ahead
of an approaching strong low pressure system will occur this
morning across much of north central Idaho and western Montana. The
approaching low pressure system is very well defined on water
vapor imagery and is pretty consistent with what models have been
showing for the last few days. This upper low will close off and
linger over the Northern Rockies this afternoon through much of
Saturday. Widespread significant precipitation of over 1 inch,
locally up to 2 inches, is expected in many areas of the region as
abundant moisture wraps around this low. This scenario of
widespread, steady (and heavy at times) rain has been advertised
the past few days. About the only change to this scenario is the
increasing confidence for potential 24 to 36 hour rainfall
amounts. 

The following are the biggest potential impacts today and
Saturday:

1. Significant rain is possible in much of central Idaho,
Southwest, West Central, portions of Northwest Montana, and along
the Continental Divide through noon Saturday. Flood watches have
been issued for potential impacts from excessive rainfall.

2. Valley rainfall amounts of 0.50 to 1.00 inch are likely with some
very local amounts of 1-1.5 inches are possible, especially in the
Seeley/Swan, Missoula/Bitterroot, and along I-90 from Missoula to
Deerlodge. Mountain rainfall amounts over an inch are likely with
locally heavier amounts of two inches are possible along the
Continental Divide and Bitterroot/Sapphire Mountains.

3. Snow is expected above 6500 feet, however any potential
accumulations will be limited to the higher elevation trails and
peaks above 7000 feet. Those with camping or backcountry plans
should take heed for rapidly changing, raw, unseasonably cold
conditions.

4. In addition to the above, temperatures will be some 20 degrees
below normal for this time of year. Overnight lows below freezing
are possible in the West Glacier region and Seeley Swan valleys.
This will also be a potential impact to those with
outdoor/backcountry plans.

Monday should see the last upper level wave in the northern tier
trough produce another round of light precipitation before the
transition to a high pressure pattern through midweek. Main
concern for building high pressure and clearing skies is cold
mornings and patchy frost on Tuesday and Wednesday. Otherwise,
expect nice weather in the afternoons next week. Focus could then
shift to another developing fall-like weather system toward the
end of the week. 

&&

.AVIATION...Showers and thunderstorms are likely today at all
terminals. Convective precipitation will become stratiform this
evening and persist through Saturday morning. Mountain
obscurations will occur with limited visibilities at times during
heavier rains. Expect widespread lowering of ceilings during the
afternoon hours through Saturday morning from persistent rainfall.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

$$

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Western Regional Climate Center, wrcc@dri.edu