Wednesday, November 23, 2011

A Pacific Northwest Monster Storm

While the weather in the Delaware Valley certainly hasn't been exactly peaches of late, it could be far worse!

We talked a couple weeks ago about the monster storm in the Bering Sea in Alaska. Well, their neighbors to the southeast just had a pretty monsterous storm of their own the last few days.

Like in the entry linked to above, the Northern Pacific produces some major storms in the winter. Adding to their collection was the storm this week, responsible for flooding and heavy rain, hurricane force winds, and heavy mountain snow.

To the left is a map of 48 hour observed rainfall from Cliff Mass' Weather Blog (via their RainWatch site) for Metro Seattle (note, this is a solid blog to add to your queue if you have any interest in Pac-NW weather).

Also to the left and down just a bit, check out the observed precip image, from the University of Washington's experimental GFS model and what it was spitting out for approximately that same timeframe with its 5-day out forecast. Overall, this storm was not a surprise and behaved very well, which doesn't always happen with Pacific Northwest storm systems.

The weather in the Eastern US is challenging enough. But, given the data void that exists over vast expanses of the Pacific Ocean (there just are not many real-time observational data sites that exist over such a vast expanse of Earth), a lot of what is headed to the West Coast is handled exceptionally poorly by the models as the events approach. On the East Coast, you have 3,000 miles of pretty consistent surface observations, along with plentiful upper air observations to be able to at least get a better sense of how a storm system will behave as it moves closer. The West Coast does not have that luxury. Having worked in California and now forecasting Westwide, I can vouch for this. A simple rain event passing 200 miles offshore of California 2 days from now can turn into an all-day deluge without much warning sometimes.

That forecast to the left was from 5 days out, which showed excessive rainfall amounts. Was it perfect? Nope, but it was very passable for 5 days ahead of time. The highest rain total I saw came from June Lake, WA, at 10.10".

Dr. Mass has plenty of information in his blog linked to above about impacts from this storm. In addition to all the rainfall, wind gusts as high as 97 mph were recorded at Mt. Hebo, OR. Also impressive, 81 mph gusts in Astoria, OR, as well as Sea Lion Caves, OR.

Also, flooding is an issue. You can see the image at the left and below that shows rivers currently in flood stage in red and blue (moderate) dots. Orange and green indicate rivers close to flood action stage. There are quite a few, and with a substantial amount of more rain on the way over the next 3-4 days, this situation is not over with quite yet.

A lot of this can be linked to the Pineapple Express, a phrase coined to describe essentially what is a mostly continuous ribbon of moisture that often comes from the area of the Pacific Ocean near Hawaii. This can occasionally set up for days to even weeks at a time and batter parts of the Western US and Canada with heavy precipitation. A notable recent example of a similar phenomenon was the flooding rain that occurred in Southern California back in December of last year, where 2 feet of rain fell on parts of the mountains north of Los Angeles and the Sierra was punished with heavy snow. That was an extreme example of an atmospheric river (or a narrow corridor of enhanced moisture) at work.

All in all, a very impressive storm for the Pacific Northwest...probably one of the stronger ones they've had in a few years.