7:55 PM Wed, Jan 10, 2007 | Permalink
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I love a good snow storm, but I usually don't get too excited about a widespread valley snowfall when we're still dealing with onshore flow. That means the winds are coming in from the ocean, which has a warming influence on cold air masses from the north. That influence may only reach 500 feet or so above sea level, but almost every time, with onshore winds, it's enough to keep the valley from seeing a widespread snowfall. This time, after the initial front passed by, the air wasn't cold enough and the moisture wasn't solid enough to deliver a big snow in Portland. Sure, there were areas that received and inch or two, more above 500 ft, but these accumulations were from showers. The difference being that showers are smaller in areal coverage, and while they can produce intense precipitation: rain or snow with hail, they tend to be short-lived and don't impact the whole area.
One of the best set ups for snow in Portland is offshore flow with cold dry Arctic coming down the Gorge and spreading across the entire Willamette Valley. Then, a storm comes in from the west bringing the necessary moisture, but the center of the storm stays south of Portland so that the cold offshore wind field is maintained. We can get several inches very quickly over a broad area under that scenario. It can also degenerate into a freezing rain situation as the cold air layer at the surface is eroded from above by the warmer Pacific winds.
And speaking of freezing rain, my co-anchor Tracy Barry brought up a great point tonight when she asked about what happens when we transition out of the cold air mass that is moving in tonight. That can also be a freezing rain set up, but this time, it looks like temperatures will moderate before rain returns.
Winter 2006-2007 continues!
Thanks for watching and surfing KGW.
Matt Zaffino
KGW Chief Meteorologist
I live in Hockinson at approx. 850ft we have 3.5 inches on the ground!
Matt:
All this talk about snow is great, but the rest of us were wondering when we might get some more of that warm weather... perfect for say... playing golf. And speaking of golf... have you ever had a hole in one?
i love snow :)
Today on the noon weater news there was a nice posting that due to the equinox the sun rite now rises due west and sets due east. BOY that is a big change. How long will this last? Will it be long enough that I need to get my compases fixed? carl