Dennis’ Tidbits


April 3, 2020

No thunderstorms for us! 

Dennis 5Here on the immediate Pacific West Coast, we average only around a half dozen thunderstorms per year, but once you get about 75-100 miles to the east, that number goes up. We usually don’t have the atmospheric dynamics that produce violent storms as we’re generally under the influence of what is called Pacific maritime air, which is very stable. 

Once you get into the interior areas of places like Washington, Oregon, and California, that number goes up to at least 10, up to 20 a year. Our local mountains and deserts can get a couple of dozen such storms in a busy year during the summer months depending on how much summer monsoonal air flows into that region from the southeast – air that flows all the way from subtropical climates. The more often that a high pressure is camped over the Four Corners region, the more thunderstorms will occur in our mountains and deserts. The air circulating clockwise around that high pulls loads of warm, moist, unstable air out of the tropical regions.

Continuing eastward, we cross the Colorado River into Arizona where thunderstorm activity really ramps up with as many as 50 such storms occurring in places like Sedona, the Grand Canyon, Flagstaff, Prescott, and Tucson. All this happens during a ten or eleven-week span, encompassing the short period from early July until around mid-September, then it quickly tails off. Over 90 percent of Arizona’s thunderstorm activity happens during the summer.

Once you cross the Continental Divide, it’s a whole different ballgame as the Gulf of Mexico air pretty much runs the show, working in conjunction with pulses of cold air from the north in the Plains and Midwest where most places average from 30-60 storms a year. It’s the real epicenter of intense storms and that involves the Deep South, Southeast, and especially Florida, the lightning capital of the U.S. In this area, up to 80-100 thunderstorms occur annually thanks to their proximity to the ever-present influence of that warm, humid, unstable atmosphere. In this region, thunderstorm activity peaks during the summer as well, but thunderstorms can happen at any time of year there.

More from McWeather’s Glossary:

Sounding: In meteorology, an upper-air observation; a radiosonde observation.

Standard Atmosphere: A hypothetical atmosphere based on climatological averages comprised of numerous physical constants of which the most important are: (1) a surface temperature of 59 degrees Fahrenheit and a surface pressure of 29.92 inches of mercury (1,014 millibars) at sea level; (2) a lapse rate in the troposphere 6.5 degrees Centigrade per km, a tropopause of 11 km.

Station Pressure: The actual atmospheric pressure at the observing station.

Supercell Thunderstorm: A large and intense severe thunderstorm with strong updrafts and downdrafts that may last for several hours. Can produce large damaging hail and tornadoes. Most common in the Great Plains, the South, and the Midwest where cloud tops can extend as high as 60,000 ft. in the atmosphere.

Surface Inversion: An inversion with its base at the surface, often caused by the cooling of the air near the surface as a result of terrestrial radiation, especially at night. 

Stay safe, ALOHA!