Thursday, January 7, 2010
Hurricane in the Columbia Gorge
For the last few days, strong easterly winds have hit the Columbia Gorge, the Bellingham area, the eastern Strait of Juan de Fuca, and some western Cascade foothills towns (such as North Bend and Enumclaw). And in fact, there is some amusing footage of a TV reporter being blown away today by "100 mile per hour" winds on Crown Point overlooking the Gorge (check it out at http://www.kgw.com/news/local/Freezing-rain-possible-in-Gorge-Thursday-night-80931217.html)
Here is another version: http://www.youtube.com/watch?v=PVeB6jFU3s4
The wind action of the past few days has been caused by a large pressure difference across the Cascades, a difference that has some connection with the frigid, cold air in the eastern half of the U.S.
In my last blog I talked about mild conditions the past week, but the warmth has been mainly expressed west of the Cascades. Take a look at the pressure and temperatures over the NW U.S. at 10 AM this morning (graphic). Very, very cold air is found east of the crest of the Rockies in Montana and the high plains. The Rockies blocks the the coldest air and any air that gets over is warmed as it sinks into eastern Washington. Eastern Washington has intermediate cold air and the Cascades blocks most of that from getting over into western Washington and Oregon. So the west has a very effective "double defense" against the cold of the interior of the continent. If only the Seahawks had as good a defense!
Cold air is relatively dense, so the coldest areas tend to have the highest pressure...and that is apparent on the chart. And the crest of mountains, which separate regions of very different temperatures, are also re locations of big pressure changes. And pressure changes drive winds (my book has a lot more on all of this if you are interested in learning more). But to get strong winds you need one more ingredient...gaps in the terrain to let the air through!
I have also included a higher-resolution version of the pressure/temperature chart for your amusement (see graphic). Today the pressure difference across the Cascades grew very, very large and the winds responded where there were gaps or weakeness for the air to move through.
The most profound gap is the Columbia Gorge...the only near-sea-level gap across the Cascades. Winds accelerated in the Gorge, with the strongest winds on the west side (NOT IN THE NARROWEST PORTION AS INCORRECTLY NOTED IN MANY TEXTBOOKS!!). Steady winds of 20-35 mph, with gusts to 50-60 mph were observed and in a few favored locations on bluffs and buildings (like Crown Point) the winds were even stronger (thus the buffeted reporter).
Strong winds also pushed through the Fraser River gap into Bellingham and through the Stampede Gap of the central Cascades, bringing strong downslope/gap winds into North Bend, Issaquah, Enumclaw and the like.
Want to see some amazing winds in the gorge? Here are some examples at Corbett, Oregon and Prindle, WA. Wow.
However, this is all going to end. The cold air is moving out of eastern Washington, the pressure differences are relaxing, and warm air is spreading over the entire NW. This change is associated with the eastward movement of the large-scale ridge of high pressure that has dominated our weather for over a week. But with this warm air will come something else...rain. Wet will return. And there is no end in sight to above normal temperatures for us.
PS: For those of you who are interested in math education, I have updated the math blog of two days ago with a link to a similar math assessment given by a professor in the department of Earth and Space Studies at the UW (another 200 students). Nearly identical results unfortunately.
Posted by Cliff Mass at 8:52 PM