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Severe Weather Northwest Style

by Matt Zaffino

Bio | Email | Follow: @Zaffino

Posted on December 1, 2007 at 6:51 PM

Updated Wednesday, Nov 4 at 2:47 PM

Wow. I can't remember the last time we had such an incredible array of weather issues around the Northwest. Let's start with the snow. Portland didn't see much because as the storm developed off the Washington Coast, it induced too much of a south wind. This warms the lowest elevations enough to turn the precipitation to liquid. This is always a concern when forecasting a storm that develops to the north of Portland. We had enough cold air in place for sea level snow, in fact there was snow at the beach early Saturday morning. But the transition to a south wind happened fast enough to squelch our opportunity for accumulating snow in the city. Not the case at my house, at 1200 ft:

Matt's House Saturday 430 pm. 1200 ft. 33º, Winds SW 23 G 39 mph

The Cascades are another matter of course when it comes to snow. A dangerous matter, in fact. Our early season snowpack is becomging increasingly unsafe. We have light, low density snow that is being loaded with increasingly heavy wet snow. This is a classic recipe for avalanches. But it's not just heavy snow on top of light snow. Three to eight inches of RAIN is expected to fall Sunday night and Monday on top of two to three FEET of new snow that falls before the snow level climbs to 7,000 ft Sunday night. Avalanche Watches and Warnings blanket the Cascades.

But the main event coming up will be the wind. A strong Pacific storm will develop and move into the Coast. Below is a computer forecast map valid for 1 pm Sunday.


The map shows a strong low making landfall on the south Washington coast. Potentially damaging south winds will follow the storm up the coast. If the storm continues to strengthen as it makes landfall, winds could be damaging even in the valleys. A second storm will follow this one Monday afternoon. It will be a stronger storm but make landfall farther north. The two storms will generate huge swells that may reach 45 feet off the Oregon coast!

The second storm has prompted the National Weather Service in Portland to issue the first Hurricane Force Wind Warning for the Northwest. It's not that we've never seen winds like this before, this is just a new class of wind warning for a non-tropical storm that has hurricane force winds. Sustained winds will reach 70 to 80 mph with gusts of 100 mph expected late Sunday and Monday.

This storm may take a track similar to a damaging wind storm that moved up the Coast in October 1967. Weather fanatic Steve Pierce of Vancouver sent me these archived weather maps from that storm:


There are some major differences between the 1967 event and what is likely to happen Monday, including the upper air pattern:


But between Hurricane Force Wind Warnings, Winter Storm Warnings, Avalanche Warnings and High Surf Advisories, the next two storms are likely to become case studies we look back on to judge future storms.

Matt Zaffino
Chief Meteorologist