It’s Not the HEAT, It’s the HUMIDITY

Southern Californians are finally getting a break from what has seemed like an endless siege of record-breaking hot, muggy weather. And while it’s true that August has been characterized by triple-digit temperatures, no records were broken. However, the humidity has been extraordinarily high, brought on by a succession of unusual weather patterns. Here is a look at our long, hot summer.

June and July: The muggy days began in earnest in June, when the El Nino, a warm water pattern, pushed unusually warm waters up the California coast. In July, El Nino was responsible for pulling a series of tropical storms--Darby, Estelle, Frank, and Georgette--off their usual track into the Pacific and toward the California coast. The steamy air settled into the Los Angeles Basin and stayed.

AUGUST: As El Nino waned, a subtropical high took over. This high-pressure air mass is situated farther west than usual, and as a result, moist air from the Gulf of California is sweeping into Southern California--literally transporting Arizona’s summer weather Southern California.

* While the Southwest swelters, the Great Lakes states have experienced record cool temperatures because of the dipping course of the jet stream around the dome of high-pressure air.

* Meanwhile, El Nino’s warmer waters persist--exerting local influence in the form of a weaker-than-normal sea breeze.

Down in the basin: In a typical summer weather pattern, the sea breeze pushes onshore and cools the basin, pushing warm air and pollutants east. Instead, this year an unusually persistent offshore flow becomes heated as the air descends into the basin because, as air descends, its molecules circulate faster, generating heat.

* In the mountains and deserts, smaller systems build massive thunderheads as hot air escaping from the basin encounters patches of cooler air at higher elevations, causing the rains that led to flash flooding in Big Bear a week ago.

Welcome relief, but . . . The Southland’s cooler temperatures are the result of the return of a stronger sea breeze. In a typical summer weather pattern, the sea breeze pushes on shore and cools the Basin, pushing warm air and pollutants east. In the mountains and deserts, massive thunderheads build as the heated desert air encounters cooler air at higher elevations. Another August feature is the inversion layer

How Hot Is It? Temperatures have been within normal range during the summer, but the muggy conditions have made the usual heat feel especially uncomfortable. The heat-humidity index measures that discomfort by combining both elements.

Source: WeatherDate, Inc., National Weather Service