Just in time for spring, and Daylight Savings Time, our first thunderstorm of the year passed through the mid-Valley last week. There was heavy rain, gusty winds, and ice pellets (small hail). But no thunder. So how could it have been a thunderstorm?
First, let’s see how a “thunderstorm” is defined. Wikipedia.org gives a very good definition:
“A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth’s atmosphere known as thunder. Thunderstorms are usually accompanied by strong winds, heavy rain and sometimes snow, sleet, hail, or no precipitation at all. Thunderstorms may line up in a series or line, known as a squall line. Strong or severe thunderstorms may rotate, known as supercells.”
Thunderstorms occur because of rising of relatively warm, humid air or the descent of cold, dry air. Vertical movement of air, known as “convection,” is the key to storm formation.
Thunderstorms can develop in nearly any geographic location, but the most significant ones are found in mid-latitude regions, where warm moist air interacts with cooler air. Thunderstorms are responsible for many severe weather phenomena, including downburst winds, large hailstones, and flash flooding caused by heavy precipitation.
Stronger thunderstorms are capable of producing tornadoes and waterspouts.
The eastern half of the US, particularly the Great Plains, is the “severe thunderstorm capital of the world.” The combination of warm, moist air (from the Gulf of Mexico), hot, dry air (from Mexico and the desert Southwest) and cool, dry air (from Canada) produces a volatile combination of temperature and moisture which frequently leads to severe events. Typically, the annual pattern sees most storms developing in the south (Texas and the Gulf Coast, for example) in early spring – right about now!! As spring and summer develop, the action moves farther and farther north, with the “storm track” (paths that storms follow as they move) reaching the northern US by summer.
In contrast, Oregon lacks the “volatile combination” that causes such big storms on the Great Plains. We lack warm, moist air (our ocean is too darned cold), and that alone reduces the intensity of storms. While Oregon does see tornadoes and other severe storms every year, they are quite weak compared to those in, say, Oklahoma. While true thunderstorms are relatively common in Oregon, they occur mostly over the Cascades and eastward. In the Willamette Valley, thunder is not heard often.
Which brings me to last week’s “thunderstorm without thunder.” In the Valley, most storms which have some of the characteristics of severe storms (high winds, heavy rain, hail) are labeled “thunderstorms” by the National Weather Service. Why? Because they resemble thunderstorms in many ways. Because they MIGHT produce thunder. And because there just isn’t a good name for such a storm.
I would love to hear from you if you have an idea for a name for such a storm. Or if you have a story about a Valley severe weather event. Please send me an email or post a comment here if you have.
And the next time you hear the local weather forecast calling for “possible thunderstorms,” realize that you may not hear thunder – but it’s unlikely that your neighborhood will be destroyed by a mammoth storm.
Yes, our storms are wimpy – and that’s okay with me!