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by Chris Scragg
Puget Sound Weather Geek
Return of the Thunderstorms on Cinco de Mayo!
What to Expect May 5, 2015:
- It’s a sweater wearing day. Cooler temperatures in the mid 50s.
- Hold on to your hat! Gusty winds (15-25mph) continue through the day.
- Time your dog walks. Showers will intermittently interrupt the sunshine through the morning into early afternoon.
- Keep your eye on the sky. Showers will liven up with lightning, thunder, or small hail this afternoon.
- When thunder roars, head indoors. Beware of dangerous lightning, watch the weather from the safety of your home, or on my live stream!
Any fellow weather geeks should be excited by today’s forecast! Scattered thunderstorms are in the forecast for Puget Sound this afternoon and evening.
The cause is (unsurprisingly) an upper level low pressure system that has meandered it’s way onshore. As is typical with these systems, this one is carrying a large blob of really cold and fast moving air in the upper parts of the atmosphere at about 25,000 ft (near airline cruising altitude).
Upper Level Low Pressure Systems:
An upper level low pressure system can be described as rotating pocket of cold rising air in the upper atmosphere. These systems are responsible for most of our thunderstorm activity. They are typically harder to forecast because of the lack of frequent observations at those altitudes.
If you follow this blog with any regularity, you’ll find that a great deal of our lightning or hail excitement comes from upper level low pressure systems.
I spent some time to look at some of the most notable thunderstorm events in Washington that I remember during the last few years, and I found that nearly every one was associated with an upper level low pressure system.
March 31st 2015:
A multi-day thunderstorm outbreak took place as a deep upper level low pressure system traversed the Northwest. Some amazing images were captured around the Puget Sound.
August 9th-10th 2013 Extreme Lightning Producer:
On August 9th, an upper level low pressure system was spinning along the Oregon coast, causing numerous thunderstorms across central OR, that eventually moved north into western Washington, bringing with it the best lightning I’ve ever seen.
July 19th 2012:
A very similar situation was in place on July 19th, 2012 when a closed upper level low was situated over the northern CA coast and OR border.
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