Area Forecast Discussion
Issued by NWS Missoula, MT

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

FXUS65 KMSO 162143

Area Forecast Discussion
National Weather Service Missoula MT
243 PM MST Mon Jan 16 2017

...Freezing Rain possible for the Wednesday morning commute...

.DISCUSSION...The ridge of high pressure persists over the
Northern Rockies for another 24 hours keeping the frigid air
trapped in the valleys across the Northern Rockies. Temperatures
tonight should be a few degrees warmer compared to previous nights
due to some high levels clouds streaming over the region.

The models continue to back off on the timing and intensity of the
upcoming system. The latest forecast appears to have light
precipitation moving into northwest Montana Tuesday afternoon and
evening. The precipitation type appears to be light snow at first.
Then late Tuesday night through Wednesday, most moisture begins
to impact portions of the Northern Rockies. The consensus is that
the bulk of the moisture will primarily impact Clearwater and
Idaho counties up into extreme northwest Montana. While the
remainder of the region will have light precipitation with
southwest Montana potentially being missed completely. The
precipitation will begin a snow then change over to freezing rain
then finally to all rain in the valleys. The timing of change over
is still uncertain, but many locations could have impacts from
the freezing rain during the Wednesday morning commute.

On Thursday a trough will amplify down the west coast into the
Great Basin. The change for the Northern Rockies will be a change
in air mass to cooler temperatures at or below normal thanks to a
weak cold front entering the region. This is not an exceptional
strong front so windy conditions are not anticipated. However
instability and some moisture with this front will bring scattered
snow showers, especially in central Idaho. Normal temps this time
of year are around 32 degrees for highs and mid to upper teens
for lows.

FRIDAY THROUGH SUNDAY...The trough and upper low pressure will
split to the south and move across the southwest U.S. into the
southern Plains states keeping the northern Rockies in a very
weak flow pattern through Sunday. This could be conducive for a
return of valley inversions and impact AIR QUALITY over the
region. There is bit of uncertainty with this now due to model

Another upper level low pressure system will move toward the west
coast next Monday. An increase in southwest flow pattern should
introduce moisture into the region. This combined with some
instability will bring snow showers to the region. Models are
consistent with this pattern change to a trough off the west coast
but differ a lot how much they want to amplify this trough which
will make a big difference for amount of precipitation falls over
the northern Rockies. Given the past few systems it wouldn`t be
surprising to see this system amplify and have a greater impact to
areas south of the Northern Rockies.


.AVIATION...High pressure will continue to cause a range of
impacts to aviation. Low stratus with light snow falling out of
the cloud layer will continue through the evening for KGPI. Other
TAF sites will likely see clear skies with some surface
visibility reductions due to haze in valley bottoms.


MT...ID...Air Stagnation Advisory until 5 PM PST this afternoon Lower
     Hells Canyon/Salmon River Region...Northern Clearwater
     Mountains...Orofino/Grangeville Region...Southern
     Clearwater Mountains.


$$ is the U.S. government's official web portal to all federal, state and local government web resources and services.