Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Missoula Montana
430 am MST Mon Dec 9 2013
..sub zero temperatures concerns shifting to snow impacts...
Fairly weak northerly flow aloft will be present over the northern
rockies during the next couple of days. Disturbances embedded
within the flow will bring periodic light snow to the region
during this time, with the primary impact being hazardous driving
conditions. This pattern will not discriminate between low and
high elevations, especially since Arctic cold air is still in-
place across much of the area. Ironically, the thick cloud cover
developing overhead at the moment will warm temperatures
throughout the day, with most locations warming well above zero
for the first time in several days.
Pattern still showing evidence of a significant shift midweek...
Northerly flow aloft will slowly shift to a more westerly flow by
midweek. This shift in flow will dramatically increase
temperatures across the northern rockies, eroding away much of the
remaining Arctic air mass. Storm systems are likely to be lined up
one right after another in this flow regime, however there is
still a question mark as to how strong these storms will be once
they come onshore from the Pacific Ocean and move through a
persistent coastal ridge. Mountain snowfall appears highly
certain, however amounts are much less certain. If storms can
maintain strength while moving through the coastal ridge, travel
impacts over mountain passes will be the main focus during the
latter half of this week through the weekend. On the other hand,
most low elevations will likely warm above freezing by the end of
Aviation...a weather disturbance will bring another round of snow
showers today across western Montana and north central Idaho
obscuring the area terrain and reducing visibility at times. Snow
showers will be on the increase throughout the morning today and
are expected to slowly taper off in the afternoon as drier air moves
in aloft. This break is expected to be short-lived as another
system moves in overnight tonight bringing more snow showers on
Tuesday. Similar flying impacts this morning are anticipated
tonight as well.
Montana... Winter Weather Advisory until noon MST today Bitterroot/Sapphire
Winter Weather Advisory until noon MST today Kootenai/Cabinet
region...Lower Clark Fork region.
Winter Weather Advisory until noon MST today Flathead/mission
Winter Weather Advisory until noon MST today Potomac/Seeley Lake
region...West Glacier region.
Idaho...Winter Weather Advisory until 11 am PST this morning northern
Clearwater Mountains...Orofino/Grangeville region...
southern Clearwater Mountains.
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