Dew Points and Heat Advisories
Temperatures will be hot the next few days. Humidity will have to be watched to see the heat index will ever rise to the levels of an advisory.
The humidity hasn’t been too bad so far this summer during the hottest periods. Dew points are an easy way of tracking humidity. During ninety-degree heat, dew points in the lower sixties and lower are a no show, meaning they don’t cause the heat index to rise above the actual temperatures.
On the other hand, dew points in the seventies do make a difference. Dew points which start to climb into the middle seventies or higher will start to add danger to heat waves.
The 7 am dew point map (inserted) shows higher values over the Mississippi Valley. I also put the current heat advisory area on the map. The correlation is not by accident! It is the intersection of hottest daytime forecast temperatures with the highest dew point values.
A backdoor cool front will be in the area later this week. One of the most uncomfortable days might be Friday as fronts tend to “pool” humidity out ahead of them. If the front doesn’t quite make it through your area, the dew points will rise with no change in the temperature pattern.
The front may produce a few showers but once again, widespread decent rain totals seem out of reach.
The hot temperatures will continue through the weekend and into early next week. By hot, I mean upper nineties to around one hundred.
By the middle of next week, there are still hints of a stronger fronts making it to the Ozarks. I’ll keep my fingers crossed on that one!
Here’s a chart for calculating the heat index for a given temperature and dew point. You might see charts like this which use relative humidity as the humidity variable. While this works, you have to make sure you use the relative humidity during the late afternoon for the calculation which isn’t known in advance because it drops as temperatures rise (the whole relative thing). Dew points on the other hand are much more consistent from day to night and back again.
Heat Index Chart