It's time to discuss, for everyone who's new here, why this thunderstorm we're having today is a really rare occurrence. The geography of our part of the West Coast, you see, tends to get much of our weather via cold fronts coming in off the Pacific, while thunderstorms tend to ride along warm fronts and require heat and humidity, which are most common to southeast of the U.S., but obviously happen elsewhere in the summer, especially. Just rarely here, and rarely in Portland either.
Some of you will probably recall the awesome nighttime thunderstorm we got in April 2012 that produced a bunch of pretty photos.
Per this guy:
Thunderstorms work best with hot, humid air.
At the latitude of San Francisco, the Pacific Ocean is not very warm.
There is also a cold current that comes from the Gulf of Alaska down the coast of California. This produces offshore fog, and will cause moisture to condense out of the air (rain, fog).
As this air (cold, slightly dryer after rain) moves onshore, it heats up slightly, becoming cool, and often dry air.
So no real fuel (hot humid air) for thunderstorms, thus, few thunderstorms.
So, today is special! And we're expected to get a good drenching of an inch or three, which we still desperately need, tapering off by this evening but still potentially affecting the A's home opening tonight.
More rain is heading in by Thursday, washing our sidewalks and dusty buildings once more, with warmth and sun returning in time for the weekend.