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Upcoming heat to enter "extreme caution" and "danger" categories

Hopefully you're a fan of big heat and tropical humidity. Mother Nature is getting ready to send us a lengthy stretch of Key West-like weather. In other words, daily highs of 87-94° and dew points staying near or above 70°.

Forecast highs thru July 18th. Dew points will be near or above 70° each day, making it feel very hot.
We have seen stretches of upper 80s and lower 90s over the last several years. It's not that uncommon to see a 3-5 day stretch of such temperatures. This particular heatwave, though, will be accompanied by very high humidity values, which will make it feel uncomfortable to simply disgusting outside.

Potential for hazardous heat from July 20-26. Climate Prediction Center
While it will certainly be very warm to hot this weekend, the true "big-time" heat and humidity don't arrive until next week. The entire week is setting up to be very hot and sticky. It doesn't end there, though. Most forecast models maintain highs around or above 90° and dew points in the 70s through at least the 22nd. 

That's why all of the Great Lakes region is under a "moderate" risk of hazardous heat for the period July 20-26th. That essentially means we should expect heat that can be dangerous to humans, pets and possibly infrastructure for at least 1-2 days during that period.

Probability of heat index temperatures rising above 100° for the period July 18-22. Climate Prediction Center
So how hot is that? As of now, all of Indiana and Southwest Michigan falls under a 70-90% chance of seeing at least one day with a heat index above 100° during the period July 18-26th. In all likelihood, there will be multiple days with "feels like" temperatures soaring above the century mark.

Possible heat index temperatures on July 19th according to one model.
The absolute worst of the heat looks to be from Thursday the 18th to Sunday the 21st. That's when heat index temps could easily rise above 100° area-wide. Most long-range forecast models are spitting out values higher than that. 

Potential heat index temperatures on July 20th according to one forecast model.
We're talking values like 105° to as high as 113° being suggested by models. Of course, it's important to remember that we are several days out, and these values could certainly change. And sometimes models overdo heat index temperatures just a bit. 

However, this forecast isn't one that just popped up overnight. Models have continued advertising a dangerous heatwave day after day across the Great Lakes and Midwest. That's why confidence in hazardous heat over the next 1-2 weeks is rather high.

Heat index chart showing how dangerous particular temperature-humidity combinations are. NOAA/NWS
And it'll be heat that falls in the "extreme caution" to "danger" categories. Heat exhaustion, heat cramps, heat stroke and other illnesses will all be possible no matter how healthy someone is. And they can develop and become extremely dangerous or even deadly in short period of time. 

If you're curious, we have only seen heat index temperatures at or above 105° a total of 9 times over the last decade. And we haven't seen them that high since July 25th of 2012!

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