It’s another steamy summer day across the eastern half of the United States. The only problem? It’s October.

Temperatures are peaking on Wednesday during an extended stretch of high heat and humidity east of the Mississippi River. The mercury is soaring well into the 90s from the nation’s capital to Florida to Texas, and just about everywhere in between. Wednesday looks to be the hottest day before the heat settles south of I-20 by Friday into the weekend.

As of 1 p.m., Washington, D.C., had already shattered its daily temperature record and tied its all-time October temperature by reaching 96 degrees, a benchmark last seen on Oct. 5, 1941. Newark, New Jersey, was forecast to climb to 91 – 21 degrees above normal – while New York’s Central Park may come close to hitting 90 for the first time in October since 1941.

It’s no different elsewhere up and down the Mid-Atlantic. Baltimore may reach 96 Wednesday, which would easily become its hottest October day on record. At noon, they had already reached 95. Philadelphia, meanwhile, could break into the 90s as well. By Thursday, however, the city will see temperatures fall dramatically, with highs stuck in the lower to mid 60s as a cold front sweeps in with northeasterly winds and occasional rain.

In all, about 209 million people, or about 71% of the population of the Lower 48 states, should see high temperatures of at least 80 degrees on Wednesday, with 131 million seeing temperatures at or above 90. These are remarkably high numbers for Oct. 2.

The heat on Wednesday follows a historically hot Tuesday, when more than two-dozen high temperature records were broken for the date in the Eastern U.S., along with 16 locations that set their highest temperature for any October day, according to the National Weather Service.

Farther south, that heat’s not in such a hurry to leave.

Take Atlanta, for instance. Hartsfield-Jackson International Airport has never recorded a temperature above 95 degrees this late in the year, but the National Weather Service is predicting a 96-degree high on Wednesday, Thursday, and Friday. They’ll finally “cool” into the 80s for the weekend, yet temperatures will still run several degrees above average through next week.

It’s been a remarkable summer and early fall for extreme heat in Atlanta and the rest of the Southeast. The city hit 90 degrees an astonishing 23 times in September – impressive when you consider the average September high is between 78 and 86 degrees. September as a whole wound up a hair under nine degrees above normal.

Atlanta has not seen a high below average since Aug. 26.

Birmingham, Alabama, meanwhile could hit the century mark – 100 degrees – on Wednesday, something that has never happened there after Sept. 22.

On Tuesday, Birmingham logged a 99 degree reading – beating the previous October all-time high record by five degrees, which is an extreme margin.

The cause of the heat wave is a large area of high pressure anchored over the Southeast, which is pumping warm and relatively humid air northward, while squelching rainfall and keeping relief-providing cold fronts at bay.

The heat dome even stretches back into Texas, where the 90s will stick around into the weekend. Temperatures will finally temper some by early next week as a cold front over the Plains and Upper Midwest sags south. The sharp front may drop temperatures ten or fifteen degrees in only a few hours west of I-35 late Saturday.

The heat during the past month has been notable as well. In Evansville, Indiana, for example, temperatures reached or exceeded 80 degrees every day of the month, which had never happened since records began in 1897, according to the Weather Service forecast office in Paducah, Kentucky.

While the heat wave peaks across much of the central and eastern states, in the Northern Rockies, winter has arrived early, with several feet of snow having fallen in Montana over the weekend, and with a small number of locations experiencing record lows in the wake of that storm. The temperature fell to a mere 9 degrees in Great Falls, Montana, on Oct. 1, obliterating the previous low of 22 degrees from 1959.

However, nationwide, the high temperature records overwhelmingly outnumber the cold records during the past week as well as longer periods as well. This is consistent with trends that have been tied to human-caused global warming, which is favoring warm temperature records, particularly above average overnight low temperatures.

Overall, increasing global temperatures are upping the odds and severity of heat waves around the world.

Along the boundary between the hot conditions in the East and cooler weather in the West, heavy rain and severe weather was firing up across the Great Plains.

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