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Hot Times Ahead
A Guest Dispatch: March 7, 1998
by Peter R. Chaston, meteorologist

Drought-dried, cracked mud The winter storms fueled by El Niño will wind down soon - but what can we expect from the coming summer? Fortunately, we can do better than guesswork; we have weather records of El Niños going back several decades from which to make some inferences. When meteorologists compare summers following past strong El Niño episodes, it's clear that El Niño profoundly changes upper air flow patterns, including the paths of the two jetstreams—and that these changes can continue to affect weather into the summer. In particular, the summer that followed the last major El Niño, in 1982-83, was excessively—even repressively—hot in the United States, especially in the region between the Rocky Mountains and the Appalachian Mountains.

The scorching was widespread and prolonged, the worst in many people's memory. The summer of 1988 was also very hot, although its heat was not quite as pronounced as in 1983. It was, however, an excessively dry summer, which contributed to people's impression of its heat, and to widespread crop failures.

From late May into September of 1983, much of the nation's heartland regularly experienced daytime high temperatures in the upper 90s and 100s. It was so hot for so long in the Dallas—Ft. Worth, Texas area, for example, that residents were buying blocks of ice to put into their backyard swimming pools, to cool the water temperature down to 90 degrees so that they could use their pools! (This was, of course, before the hot tub craze.)

Day after day after day in the summer of 1983, places such as Kansas City, Wichita, Oklahoma City, Dallas, Omaha and Little Rock sizzled in temperatures from 100 degrees to 110 degrees in the shade, not that there was much shade to measure temperatures from, as trees drooped and plants wilted. It was so hot and dry for months that the ground actually cracked in many places. The oppressive heat led not only to cattle deaths in the Great Plains, and damaged crops in the breadbasket states, but also to heat stroke and death among people as well, including weak or elderly people who had no air conditioning.

Will it happen again this summer—perhaps even worse than in 1983—given that the 1997-98 El Niño is the strongest and most persistent ever recorded? My prediction is a cautious yes: we are likely to see a long, hot summer, with many areas experiencing daytime highs in the high 90s and 100's, especially from the Rockies to the Appalachians, and at times in the east coast states.

Moreover, with the scorching heat, will we also endure a severe drought? My prediction: not necessarily, at least initially, as heat and drought are not absolutely coupled in an El Niño aftermath. Quite the contrary, much of the nation is likely to receive frequent thunderstorms this spring, significantly more than usual. In fact, many clusters of storms are likely to merge, forming large heat transporting blobs known as "Mesoscale Convective Systems" or "MCSes," which are as big as the state of Iowa and can persist for over 12 hours. (These are similar to the merging El Niño storm cells observed by correspondent Mark Hoover in the equatorial Pacific near the Galapagos.)

MCSes typically form when a tropical connection of moisture (a moisture plume) occurs, similar to the so-called "pineapple express tail" seen on many recent storms that hit California. Developing storms east of the Rockies feed on airborne water vapor transported from the Pacific via the same conveyor-belt type mechanism. Once established by El Niño, the persistent tropical moisture feed enhances thunderstorm development and overall storm energy, making the storms efficient and copious rain producers. The southern branch of the jetstream is the principle engine of this moisture transport. And recently, it has occasionally been strengthened by El Niño to over 200 miles per hour.

Lately we've also seen how, through most of our fall and winter, El Niño pushed the northern branch of the jetstream (also known as the polar jetstream) well up into Canada, establishing an early warm pattern. The polar jetstream separates cold air to the north from warm air to the south, acting almost like a fence separating regions with mild temperatures from regions with frigid temperatures. This winter, most of the cold polar air has stayed locked away in Canada, and the midwest and east have enjoyed remarkably warm temperatures as a result.

The pattern will continue, and so will the heat build-up, in the form of a huge, persistent high-pressure system that prevails through the summer, as it did in 1983. The result: a corralled hot air mass that stretches from the Rockies to the Appalachians, and at times expands east to the Atlantic and west throughout the great Basin and Range region. Since the southwest U.S. is already typically very hot in the summer, we end up with everything but the far west in the grips of a mammoth, persistent high-pressure system of oppressive heat. The heat eventually affects the ability of tropical moisture to create rain; by mid-summer, most of the thunderstorms and MCSes will have fizzled because the atmosphere will be too warm aloft to permit them to form. It's so hot aloft that water vapor simply can't condense.

In a nutshell, then, this El Niño—the strongest and most persistent in recorded history—is likely to produce a wet and stormy spring for most of the country (residents of Tornado Alley, take note). And then, much of the country can expect a long, very hot summer. This El Niño will not let us forget it anytime soon.

Peter Chaston is a professional meteorologist, weather consultant, and author of "Terror from the Skies," "Hurricanes!" and co-author with Joseph Balsama of "Weather Basics." In 1995, Chaston predicted that the next El Niño would be abnormally strong.

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Photo: © John D. Cunningham/Visuals Unlimited.

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