Glenn Zimmerman’s long-range St. Louis summer 2021 forecast

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ST. LOUIS, Mo. – Do you remember when temperatures last hit 100 degrees? Well, July 14th, 2018 was the only 100-degree temperature reading during that summer.

For our forecasts for this summer, we are using the year 2011 analog. The setup for that year is similar to this year. A neutral phase El Nino pattern for a second summer in a row can mean a hotter summer. Model projections show a large area of above-normal temperatures centered on the central and southern plains and we will be on the edge of that. So with that in mind, let’s dive into summer.


June is normally one of the wettest months of the year. And I think the way the patterns are shifting, we are still in a wet mode. Let’s watch how the jet stream pattern set up this year because I think there will be some swings and with those swings, some rain, and storms. We have yet to see a real true severe season so far this spring. I think we will have our fair shot of strong storms in June with heavy rain. Temperatures will swing with the jet stream too. So, a few days in the 90-degree temperatures, especially to begin the month. Then back to the 80s or even 70s are not out of the question.

June 2020 temperatures ran a little above normal, but not overly so with 15 days over 90. I think this coming June will average out to be a little cooler than normal. In June 2020 we were dry, with a rain deficit of 1.50 inches. I think we will see a couple of bigger rain events that will bring us to normal or a little above in 2021.


July is when summer starts to crank. You know what that means: heat, humidity, and lots of dry time. With a global pattern shifting and evolving, the average temperatures in July will ride along with a bigger heat pattern for the plains and into Texas. While our soil currently is away from any drought alerts, I think that in July it will start to dry. So a lack of rainfall due to big heat centered in the middle US, we are going to get the heat going. Summers have been trending warmer for the last several years, but mostly that has been because of warmer overnight temperatures and not the highs. This July, I think the highs will ride above normal.

July of 2020 was hot with 22 days above 90. And it was wet with almost 5 inches above normal. 2021 will be at least as hot, and I think we will hit the elusive 100-degree mark this July. I think it will be drier than last year with below normal rainfall and that will make it feel hotter.


August has more heat normally. When we talk about the “dog days of summer,” we are talking about August, especially the first couple of weeks. When we get into that type of hot pattern we look to the tropics for relief. Any tropical storm or hurricane will affect the pattern and bring down the heat. This year, the Gulf will once again be a target for active tropical systems. So we will watch to see how those affect our heat and drought. Once again, I think we have a strong chance to hit 100 during August, and maybe a couple of times. So hotter than normal and drier than normal. A similar scenario carrying over from July.

August 2020 was cooler than normal and just a bit wet. But, August of 2021 will be warmer than normal and drier than normal. One tropical storm may change that with an inland trajectory, but that will be a slim chance.

I think this summer will be remembered for some pretty hot days but also a couple of pretty strong storms.

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