Death Valley heat in Kansas? How the end of June got so hot.
Norton Dam, Kan., hit 118 F. on Thursday, and 32 communities from Colorado to Indiana just posted their highest temperatures ever. Forecasters say back-to-back La Niñas are partly to blame.
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One reason for the seemingly relentless high temperatures is the presence of a broad ridge of high pressure inching its way across the continent, forecasters say. With skies generally clear, sunlight has a clear path to travel on its way to baking what in many places is an already parched surface.Skip to next paragraph
In Pictures Extreme weather 2012
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The vast majority of the region stretching from southern Texas north into Nebraska and across to eastern California is experiencing severe to extreme drought conditions that in some cases have lasted for more than a year. Similar conditions cover a patch of the country from Arkansas northeastward through parts of Missouri, Illinois, Kentucky, and Indiana. A similar patter is persisting in the Southeast from eastern Mississippi through Georgia and into South Carolina, with some areas there experiencing exceptional drought conditions.
Conditions seem to be mimicking last years, with a slight geographic shift, says Klaus Wolter, a researcher who specialized in regional climate forecasting at the National Oceanic and Atmospheric Administration's Earth System Research Laboratory in Boulder, Colo.
"Last year we had all that heat in Texas and Oklahoma. This year, things seem to be shifted a bit further west," he says.
Back-to-back years of La Niña conditions have set the stage, he says.
La Niña refers to one half of a see-saw pattern in ocean temperatures and atmospheric pressure along the tropical Pacific. During La Nina, tropical Pacific waters off the coasts of Central and South America become colder than normal, while waters in the western tropical Pacific become warmer than normal. During an El Niño event, the temperature patterns reverse.
Both La Niña and El Niño affect atmospheric circulation patterns in the tropics and beyond.