Woohoo!

November 15, 2009

6:01 P.M.

I've been having a lot of trouble getting homework accomplished today and focusing in general because I've had my eyes on two things. And they are both weather related (of course).

First of all, remember how I was talking about how if you brought that band of rain that was stalled over the Olympics just a little bit further south, we could get heavy rain in Seattle? Well that is what the forecast models are showing now. They still show prodigal amounts of rain in the mountains, especially the Olympics, with some areas receiving over 10 inches in a 24 hour period, but the rain there is actually looking to be lighter than what was previously forecasted. Seattle, on the other hand, which was looking like it would receive practically nothing as the "Pineapple Express" stalled over the Olympics, now looks like it may pick up as much as three inches before this series of storms is over.

But the biggest story is the wind. There are two storms that will bring very windy conditions to the area, and the second one could be a major windstorm.

I've been watching the models over the past few days, and I've had my eye on that second low pressure system that develops and slams into south Vancouver Island. There is still a bit of inconsistency regarding that system, but it definitely looks like a possibility. I'll talk about that later

Let's first start out with the first system. This system actually bears some resemblence to the December 2007 Great Coastal Gale. In that storm, a huge Pineapple Express developed and stalled over the area, bring copious amounts of rain to the mountains and causing the Chehalis River to crest at all time flood levels. Some places on the southern Washington coastal range saw in excess of 15 inches of rain in one day! That's about 40 % of Seattle's annual rainfall! As amazing as the rainfall totals with this storm were, the wind was more amazing. This storm prompted the National Weather Service to post their first ever "Hurricane Force Wind Warning," a warning used when sustained winds or frequent gusts of above 74 miles per hour are expected. And it held true - the Northwestern Oregon and Southeastern Washington coasts experienced amazing winds. There were numerous stations with gusts of 130 miles per hour. Waves on the ocean were as high as 70 feet. See the youtube video for some footage some guy took of the storm event on the Oregon coast. It is absolutely incredible.

This storm doesn't look to be that severe by any means, but, at least to my ameteur meteorological skills, there seem to be many parallels. The diagram above shows very strong sustained winds of 40 knots or more over the waters off the Washington coast (1 A.M. Monday). Notice the abrupt ending in the winds off of Cape Flattery. That is where the front passes through. However, Pineapple Expresses don't quite "pass through" like other fronts. The best way to compare them is to a huge firehose relentlessly spraying the northwest. And as long as the front and rain are over us, the winds will be too.

The front will gradually shift south through Washington before stalling on the north central Oregon coast. Here, it will re-energize as the surface low interacts with it. Look at how strong the winds become in a matter of hours! The above diagrams (at 4 P.M. Monday and 10 P.M. Monday) show just that. It's not very often you see those patches of white on the forecast models.

In the meantime, it will be raining hard here and in the mountains. The Olympics could get 10-20 inches of rain, and the Skokomish will have to be watched for major flooding. The North Cascades will also get hammered, though with somewhat lesser amounts. The Central Cascades look to escape the brunt of the storm as the "firehose" will be positioned to the north of them, and the Green River shouldn't have any problems.

Another interesting thing to note is the amount of lowland rain. As I previously stated, things are now looking a lot wetter for the lowlands. One model shows 24 hour amounts of 3-6 inches in the lowlands. Others, however, do not show that much precipitation. I will see if I can make an update later tonight as the new models come out on how much precipitation we will see and if we will get urban flooding here in Seattle.

And oh boy... here's the big one.

Current models show a 973 mb low tracking into south-central Vancouver Island. This guy has the potential to bring strong and damaging winds to the Puget Sound area. Often times, a good measurer of a storm's wind velocity in a given area is the pressure gradient between two parts of it. For example, the models are forecasting the pressure gradient between Portland and Bellingham to peak at around 16 millibars, which means that the pressure in Bellingham would be 16 millibars lower than the pressure in Portland. Wind flows from high pressure to low pressure, so we could see very strong southerly winds in the Puget Sound Lowlands. This storm would not be as strong as the Hanukkah Eve Storm of 2006 (that storm had a pressure gradient of 23.2 between Portland and Bellingham!) but it would be strong nonetheless. A HIGH WIND WATCH is currently in effect for our area for this storm, saying that sustained winds of 40 mph with gusts to 60 could occur. The coast and north interior have a HIGH WIND WARNING which means that the National Weather Service is fairly certain that they are going to get high winds. Gusts there could reach 70 miles per hour, with some 80s on the coast. I wouldn't be surprised to see a 90 or break the triple digits there either.

Stay warm, stock up on batteries and gas, and don't stand under any tall trees!

Charlie