WeatherWatcher: Friday the 13th windstorm that isn't, wet weekend ahead

Friday, November 13, 2020

Wind driven waves on Puget Sound waters from Richmond Beach
Photo by Carl Dinse

Earlier this week many forecast models were showing a very strong low pressure system develop and making landfall anywhere between Astoria, Oregon, and northern Vancouver Island on Friday. 

If this storm arrived anywhere in the northern 2/3rds of its uncertainty we would have had a pretty major windstorm coming in. Given the history our area seems to have with storms on Friday the 13th during storm season I was convinced it had to happen.

I didn't want to write a report on it just yet, given how extremely uncertain the computer forecast models were being. Even tonight, less than 24 hours away from this storm, forecasts have not been consistent.

Generally, it's much weaker than originally forecasted. In addition to the weaker low pressure system, it is looking more and more like it'll be tracking right over the top of us, instead of to our north. This means we are not looking at a lot of damaging wind, but it will be breezy. The storm is now expected to pass over us between the hours of 10am and 2pm on Friday.

This decreases the chance of strong winds, but increases the chance of a strong convergence zone in the afternoon and evening hours. In the morning I'm expecting breezy winds, most likely in the range of gusts 25-30mph. There could be a stray 35-40mph gust but it's not very likely. Once the convergence zone gets going, winds will likely calm down unless we end up north or south of the convergence line.

Temperatures are on the cool side, especially in the upper atmosphere. If the convergence zone gets going and strong, we could see some thunderstorms, hail, wintery mixes in with the moderate-heavy rain. 

Nothing shows any snow, but I think it's possible that we could see some wet snow mixed in, especially after the sun goes down Friday evening. I'm not expecting any accumulating snow. If we do see some accumulations it'll probably be in the form of hail or sleet, and it'll be short lived.

The Puget Sound Convergence zone that I'm talking about here is a wild card. It is probably the most challenging weather phenomena to forecast on the planet. This setup has a history in our area of bringing surprise hailstorms, thunderstorms and snow, even when temperatures start the day in the 50's.

Though not likely that we will see hail, snow, or thunder on Friday, I didn't want to have it completely ruled out. I'm not trying to scare everyone, I just want to make sure we're not surprised if we see any of the above mentioned wintery or stormy precipitation tomorrow evening.
In general though for Friday, plan to start the day with breezy conditions and steady rain. It'll shift over to showers or a convergence zone in the afternoon and evening hours before tapering off overnight. That convergence zone, if it forms over Shoreline and Lake Forest Park, could give us many kinds of weather depending on strength.

Saturday another round of rain is expected before breaking up into showers Saturday night. Sunday and Monday rain is likely. Temperatures are ranging between the low 40's and low 50's between the storms. 

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