Heat index values at 1:45 p.m., July 25 (Weather.com)

(This story has been updated).

It happens almost every single summer: The nation’s most sultry air takes an opportunity to smother the capital. Today’s the day.

Early Monday afternoon, the heat index, what the temperature feels like factoring in the humidity, was higher in Washington, D.C., than any city in the nation. It hovered within a few degrees of 110 degrees.

It was higher  here than Miami, Charleston, Atlanta, Raleigh, Dallas, Houston and Little Rock.

Even if you’re a purist and consider just the air temperature, the only hotter weather in the U.S. could be found in the desert Southwest, where it wasn’t as humid.


Temperatures at 1:15 p.m. July 25. (Weather.com)

The air temperature in D.C. today is forecast to approach the century mark this afternoon, challenging the record set in 1930 of 100. If we hit 100, it will be the first instance since July 26, 2012.

Dual areas of high pressure are to blame for the excessive heat and humidity.

One area of high pressure is centered at high altitudes directly over the mid-Atlantic — a “heat dome.” This is directly responsible for the hot air.


GFS model simulation of weather pattern at around 18,500 feet (500 mb) July 25. High pressure (or high geopotential heights) was centered over the mid-Atlantic. (WeatherBell.com)

At the surface, a second area of high pressure is centered just off the Southeast coast. Its clockwise circulation is steering extremely humid air from both the Atlantic and Gulf of Mexico into the D.C. region.


GFS model shows high pressure centered off the Southeast coast of the U.S. on July 25. (WeatherBell.com)

This configuration of pressure systems is characteristic of our most brutal heat waves and seems to occur annually for at least a day or two.

Going back to 2011, we have identified at least one day each year in which D.C. has boasted the nation’s most oppressive heat. Here are past examples documented:

June 11, 2015

May 18, 2015

June 18, 2014

July 16, 2013

July 17, 2012

June 20, 2012

July 22, 2011