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Hot Times Ahead
A Guest Dispatch: March 7, 1998
by Peter R. Chaston, meteorologist
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.
(previous dispatch)
(table of contents)
Photo: © John D. Cunningham/Visuals Unlimited.
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