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Summerlike heat bakes central states, breaks records

Records have fallen in the Lone Star State, where readings spiked as high as 112 degrees. The Weather Service predicts scores of records will fall throughout the central U.S. through Thursday.

Predicted temperature difference from normal Wednesday in the central United States. (WeatherBell)
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The calendar says May, but the atmosphere has fast-forwarded at least a month. A sprawling dome of summerlike heat is parked over the central United States, bringing temperatures 20 degrees or more above normal, with scant rainfall. Tornado chances have flatlined across the southern Plains, but the risks of wildfire and heat-related illness are surging instead. And many more hot days are ahead.

Temperatures spiked to 99 degrees in Kansas on Monday and a staggering 107 degrees in Oklahoma, setting a record in the Sooner State for early May, according to Maximiliano Herrera, a climate historian.

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San Angelo and Abilene, Tex., hit record highs of 107 degrees Monday, their hottest weather so early in the year. Abilene did it on Sunday, too.

The heat in Texas has pushed electricity demand to midsummer levels, according to reports from local news outlets and Bloomberg News, but the entity that operates the state’s electrical grid has projected sufficient supply, the Dallas Morning News reported.

Farther south, Rio Grande Village in the Big Bend of Texas hit 112 degrees Saturday, and the heat’s been blistering across the border, too — Herrera reported a 112.3-degree reading at an elevation of 615 meters (2,018 feet) in Monclova in Mexico’s Coahuila state.

Through Thursday, scores of population centers from Texas to Wisconsin could well see record highs near or above 90 degrees, including Kansas City, St. Louis, Little Rock, Madison, Wis., and Nashville. Thursday could be the hottest day, with a zone from Texas to central Wisconsin enduring temperatures near or above 90 degrees.

The setup

Dominating the nation’s weather is an “omega block,” or a stubborn weather pattern that results in an atmospheric bottleneck of sorts. Clockwise-spinning high pressure parked over the center of the country is flanked by a pair of counterclockwise-rotating lows, which fit together like meshed gears. That means none of the systems are in a hurry to move, and while inclement weather has gripped the Pacific and Atlantic coastlines, a heat dome is reigning over the Plains.

High-pressure systems bring sinking air, which compresses and warms by the time it reaches the surface. In the warm months of the year, they’re often called “heat domes.” They also deflect weather systems and storminess to the north, allowing sunlight to pour in uninterrupted. May is ordinarily a time punctuated by repeated rounds of violent severe weather, but save for the High Plains, most of the south-central United States, including central and eastern Texas and Oklahoma, will remain largely storm-free.

The high-pressure zone is most intense where it’s centered in Quebec and Ontario, where the greatest temperature differences from normal reside — readings near the Hudson Bay are up to 30 degrees warmer than typical. In the coming days, the heat dome will ebb westward a bit, anchoring over the Great Lakes and St. Lawrence River.

How hot it will get

Amarillo, Tex., will probably hit 100 degrees Tuesday. Zapata, in southern Texas, should jump to 101, while Dallas soars into the mid-90s. Dallas’s average mid-May high is about 82 degrees. Dallas will probably stay in the 90s into next week, with the unrelenting heat dome refusing to budge from its post.

In Oklahoma City, highs in mid-May are typically in the upper 70s but will probably be exceeded by about 10 degrees each day through the remainder of the week.

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By Thursday, widespread 90-degree highs will reach all the way into southeast Minnesota and western Wisconsin, some 25 degrees above normal. Chicago should reach the mid- to upper 80s, missing 90 only because of the cooling influence of Lake Michigan.

Moderately high humidity will make air temperatures feel several degrees warmer.

In St. Louis, temperatures could surpass records Tuesday through Thursday, with highs in the low 90s.

The 90s will collapse back south somewhat toward Texas, Oklahoma, Arkansas and Louisiana into Friday, but mid- to upper 80s should still fan as far north as the Upper Peninsula of Michigan.

How long the heat will last

Indications are that for the mid-Mississippi Valley and northern Plains, the heat will take a breather this weekend and relent some. But for Texas, southern Oklahoma, southern New Mexico and Arizona? It gets even worse next week.

Tucson could climb into the lower 100s on Sunday, and Houston into the upper 90s. Heat indexes could reach the triple digits, with actual air temperatures hitting the century mark for more than 6 million Americans.

Beyond the start of next week, the overarching pattern looks to support anomalous warmth for quite some time, particularly in the southern Plains and Southwest.

How unusual is this?

The weather across the central Lower 48 is more commensurate with what might be expected in mid- to late June than mid-May. Amarillo, for example, hit 101 degrees Saturday, earlier than it has since such record-keeping began. Its average first 100-degree day is June 20. It beat the record by eight days.

Human-induced climate change is playing a role in making early-season heat waves more frequent, more intense and longer in duration. The same hot, dry pattern is also contributing to preseason wildfire incidence in the desert Southwest, including in New Mexico, where the state’s second-largest wildfire on record has already torched 203,920 acres.

In the coming three months, the National Oceanic and Atmospheric Administration’s Climate Prediction Center is forecasting continued above-average heat to dominate the western United States.

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