The Weather Notebook: No Lightning Out West

No Lightning Out West
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Dave Thurlow, Host

The western states Washington and Oregon are renowned for rain and most of California, of course, for just the opposite -- but one meteorological feature common to all three West Coast states is a scarcity of lightning. Hi, I'm Dave Thurlow from the Mount Washington Observatory and this is The Weather Notebook.

Lightning striking in a forest in the Pacific Northwest. William G. Morris, 1934. NOAA Photo Collection

Now, let's just compare the amount of thunderstorms and lightning in the three West Coast states to the state with the most thunderstorms, Florida. In Florida, on the average, 200 days a year there's a thunderstorm somewhere in the state. And on the West Coast, in Washington, Oregon and California, it's only about 5 or 10 days there's a thunderstorm with lightning that's actually reported. Why is this? Well, to brew a decent thunderstorm you need three key ingredients -- a source of moisture, cold air way up high so that warm air near the surface can rise, and a mechanism that forces that air to rise rapidly -- and seldom do these conditions coincide on the West Coast. Blame it on the Pacific Ocean.

Pacific water temperatures are too cool, even at the height of summer, to allow air masses passing over to pick up much moisture -- so that kills the first ingredient. The Pacific also puts a damper on the ability for air to rise by breeding a shallow layer of cool, stable air that hovers near the surface with no hope of rising quickly. Even when thunderstorms do hit the West Coast -- most commonly in the fall and spring -- they tend to be wimpy, one-clap affairs with cloud tops maxing out at 15 to 20 thousand feet, whereas a classic Midwestern thunderhead can tower to 60 thousand feet.

Thanks to today's contributing writer David Laskin, from Seattle, Washington. The Weather Notebook is underwritten by Subaru with major support provided by the National Science Foundation.