For the majority of July, we’ve been nice and seasonably cool here in the Pacific Northwest. We’ve been warming up over the past couple days, and by next week, we may have our first day of the month above 80 degrees! So the end of our “normal” summer weather is in sight.
However, while we’ve been nice and seasonable, the remainder of the country has been sweltering under a massive ridge of high pressure. In fact, if this heat wave lasts long enough, this July could be the all-time warmest month on record for the country. The current warmest month? July 1936, at the peak of the Dust Bowl. For what it’s worth, last June was the hottest June on record, beating out June 1934, another Dust Bowl month.
First off, so you can get an idea of the enormity of this heat wave, let’s take a look at the current weather alerts map from the NWS over the United States.
Everywhere from North Dakota to Michigan in the north to Louisiana in the south is under some sort of heat advisory or warning. This is because there is an absolutely massive ridge of high pressure over the central U.S., bringing sunny skies and warm, southerly flow into the region. As a result, temperatures have skyrocketed over a large swath of the country, with many areas soaring into the triple digits.
To make matters even worse, this air is very humid. You see, there’s this giant pool of 80+ degree water called the Gulf of Mexico, and when you combine those water temperatures with southerly flow and sunny skies, areas further north can get absolutely pounded. And that is exactly what is happening right now.
Take a look at the current weather alerts from the Des Moines, Iowa NWS forecast office. The entire state has an “Excessive Heat Warning.” The ENTIRE STATE!
Here’s a picture of the latest GFS model. Notice how there is a HUGE ridge of high pressure over the central U.S., with 500mb heights WELL above their climatological averages. Generally speaking, the higher the heights, the warmer the temperatures, as the temperature of the atmosphere is directly related to its thickness. When 500 mb heights are approaching 600 dam (decameters, or 10s of meters), you know that it the atmosphere is REALLY warm!
Combine those high heights with blazing July sunshine, and extremely high humidities, and you’ve got a recipe for extreme heat. Amazingly, what makes this heat wave particularly noteworthy is not simply the maximum temperatures associated with it but how long it is forecast to last. The heat will last through the weekend, and that may be just enough to make this July the hottest month in United States history.
