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We talked yesterday about the shortening days and how that's causing average temperatures to begin the ascent that leads to winter. I'm also wondering based on the latest MJO (Madden Julien Oscillation) if we have felt the worst of this summer's heat?

I want to show you what I'm seeing and thinking in that regard. Let's begin with the MJO and its definition.


The Madden-Julian Oscillation (MJO) is a tropical disturbance that propagates eastward around the global tropics with a cycle on the order of 30-60 days. The MJO has wide ranging impacts on the patterns of tropical and extratropical precipitation, atmospheric circulation, and surface temperature around the global tropics and subtropics. There is also evidence that the MJO influences the ENSO cycle. It does not cause El Niño or La Niña, but can contribute to the speed of development and intensity of El Niño and La Niña episodes.


As you will see below, the EURO (our best physics supported and reliable model) shows the MJO to begin a movement that takes it out of phase 2 towards the end of the July and into phases 3 and maybe even 4 the first week of August. You can see that by following the dotted green lines on the phase diagram below. Each dot represents a day in the progression. Notice there are 8 different phases.

Phases 2 in July along with 3 and 4 in August are all decidedly cool in the phase temperature analogs in my area. Take a look.

This cool-down won't happen right away. We are currently coming out of a pleasant pattern and will have to endure a mean day of heat Sunday before the cooler pattern gets firmly established next week. The models are showing it though with the 5-10 day temperature departures on the GFS and EURO showing this.

THE GFS 5-10 day departures

The EURO 5-10 day departures

The GFS keeps the cool going into early August with these 10-15 day departures.

You will also notice that the Climate Prediction Center is hedging that way too with its 6-10 and 8-14 day temperature departures looking this way.

6-10 day temperatures

8-14 day temperatures

Additionally for the first time in over a month CPC does not show any excessive heat risk anywhere in the central US. July 31st through August 6th. That is a big deal.

So what I'm seeing is that after Sunday's wicked heat and humidity, it could be at least a couple weeks before any chance of significantly above normal temperatures threaten the central Midwest. By then, we've lost even more solar heating power and the same air mass that would have gotten you 95 in early July gets you only 90 in early August. It get's progressively tougher from here on out to get temperatures that would beat any we've seen so far this year. In other words, there's a good chance we have seen the hottest temperatures of the summer despite Sunday's steam.

Speaking of Sunday, it still seems that heat index values of 103-108 are in the works along with a heat advisory.

The GFS heat index Sunday

The EURO heat index Sunday

Storms are a good bet late Sunday or Sunday night as a cold front makes its way south bringing the cooler pattern with it for next week. Some of the storms will likely be on the strong side with some decent downpours in some spots. It's still a bit early to get precise on where and how much but the EURO shows this for rain totals.

Well, there you have it. I'm on the record for saying we've likely seen our hottest temperature of the summer. Don't confuse that with me saying we won't get hot again because we will, and on more than one occasion. I'm just saying nothing as hot as what we've already seen. TGIF and roll weather...TS

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