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Hello, this is Chris Gibson with the National Weather Service in Missoula, Montana. Today
I’d like to show you some examples of a weather phenomena we observe frequently in
this area – Heavy snow squalls organized in bands as seen on Doppler Weather Radar.
This slide provides an example of what these snow bands look like on weather radar. In
this case, from November of 2003, a series of bands have formed in east to west lines,
parallel to the flow of winds near mountain-top level. At this time Missoula would be in the
clear, in between snow squalls, but a commuter headed south towards Stevensville or Florence
would run into a wall of intense snow just south of Lolo. This illustrates the localized
nature of the snow bands. Later that same night, the snow squalls are
much weaker but still oriented from West-Northwest to East-Southeast. At the time pictured, a
band of snow showers was impacting the I-90 corridor from Alberton to Missoula, and east
along I-90. Another weaker band if present over the Northern Bitterroot Valley, in the
vicinity of Stevensville. Here is a heavy snow band situation from January
29, 2013. In this case, a large band impacted much of the population of Western Montana
for many hours though the morning. This band is unusual in that it is oriented from north-northwest
to south-southeast. Snow squalls were moving from north to south parallel to the band while
the entire band was also slowly shifting east. At this time, about 900 AM, I-90 near the
Nine Mile exit was directly under the band and impacted by heavy snow (upper left). Meanwhile,
in the Rattlesnake Valley, just northeast of Missoula, the snow band had yet to arrive
(upper right). Two hours later, at 1100 AM the band had shifted
directly over Missoula and was beginning to impact I-90 east of the city. To the southwest,
at Lolo Pass, the showers had decreased with some sunshine developing at times. Meanwhile,
the heavy snow had arrived over the Rattlesnake Valley near Missoula (upper right). By this
time the streets of downtown Missoula where also being severely impacted by this narrow,
but intense band of snow. Hopefully these images give you some background into why it
can be so difficult to forecast accurate snowfall amounts in these type of situations. Hopefully,
this also illustrates how is it possible to have heavy snow change to bright sunshine
in just a few minutes near one of these bands.