Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus65 kmso 202206 

Area forecast discussion
National Weather Service Missoula Montana
306 PM MST Mon Nov 20 2017

Discussion...latest radar and satellite imagery is showing a
line of moderate to heavy showers extending from Lookout Pass to
Pendleton, Oregon. This line of showers will be the main concern
for travel impacts this afternoon and evening. Over the next 6
hours, this line is expected to move through central Idaho, then
into west-central Montana and then into southwest Montana. Snow
levels are around 4000-5000 feet, so most of the travel impacts
will be over mountain passes. Travelers over mountain passes
should expect sudden changes in Road conditions and visibility
across all mountain passes through this evening.

Precipitation will begin to taper off around midnight tonight and
partial clearing should lead to the development of fog or low
stratus clouds for Tuesday morning across western Montana and
central Idaho. Fog could become locally dense in areas,
especially across west-central Montana and central Idaho where the
most clearing is expected. For northwest Montana, lingering rain
showers might lead to pockets of light freezing drizzle overnight,
but confidence is low on freezing drizzle. Most of the rain
showers should exit the region by daylight on Tuesday and fog
development will be possible across northwest Montana as well.

Snow levels will begin to rise late Tuesday with an atmospheric
river impacting the region through Thanksgiving. Even mountain
passes will receive rain, with many high elevation locations
seeing over 1.5 inches of rain in a 48 hour period including
Wednesday and Thursday. Small streams will rise with increased
run off, and ponding of water on roads will be an issue due to
rain and melting snow in some areas. However, since the ground is
not frozen and current flows are low, the current rain forecast
is not enough to cause significant flooding concerns at this time.

Thursday night, a strong cold front will come through. Confidence
is moderate on the timing, however, when this front does come
through, the precipitation will drastically decrease as the rain
turns to snow. At this time, only a few inches of snow is
expected at the higher elevations, potentially affecting area
passes Friday morning. Strong winds are expected with this front,
with gusts in the 50 and 60 mph ranges possible in the mountains.
The strong winds are a result of good model agreement on a strong,
roughly 140 knot jet and 60 knot winds at 10,000 feet above sea
level supporting the front when it comes through.

The strong winds with the front are also causing some uncertainty
in the precipitation amount forecast for the valleys Thursday
evening into Friday morning. With such strong winds, it is
possible the valleys will be down-sloped and get very little
precipitation once the strong winds arrive.

Next weekend a ridge quickly rebuilds over the Continental Divide,
leaving central Idaho and northwest Montana under moist southwest
flow again. Mostly cloudy skies and light rain from time to time
are expected over the weekend and early next week. Snow levels are
expected to rise again quickly next week so most precipitation
would be rain again.


Aviation...moderate to heavy rain/graupel showers will be moving
across the region this afternoon and evening. Kmso and kbtm could
see locally heavy showers as a weak front moves through this
evening. Main impacts will be visibility reductions and low
ceilings through this evening. Precipitation will end around
midnight tonight and partial clearing will lead to fog development
across the area. Kmso and kgpi will see the best chance for fog
development at area terminals. With the recent rain, there is a
chance for dense fog development at kgpi and kmso for Tuesday


Mso watches/warnings/advisories...

National Weather Service Glossary of Abbreviations