I asked a while ago what was the hottest day of the year. But I only got a lot of smart aleck remarks 
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Okay, I got a globe pencil sharpener a while ago. And it charts the apparent course of the Sun. So now I have a better way to parse the question: what is ‘the limit of the heat’?
It actually occurs right around this time of year. So what is it? And what causes it to come around this time of year?
Helpful and serious replies only . Thank you.
I want to say I read the hottest recorded temperature was in Death Valley, like 130 degrees Fahrenheit or something…
(That’s not a theoretical limit but it’s a start.)
~Max
As an upper maximum you could take the temperature of the Sun and apply the inverse square law over the distance to the Earth’s highest point, when the earth is closest to the sun in its orbit.
~Max
First of all, in the Northern hemisphere, maximum temperatures occur when the Earth is farthest from the Sun, due to the inclination of the Earth’s axis. Also, the maximum temperatures usually occur sometime after the maximum insolation, because of thermal lag.
The earth is tilted with respect to it’s orientation to the sun. This is the reason we have seasons; in the summer in the Northern Hemisphere, the sun appears to be higher overhead. The sun gives more energy to the earth in the form of heat when it is higher overhead. This causes higher temperatures in the summer. Also, the longest day occurs on June 21, summer in the northern hemisphere. The hottest part of the year actually occurs a bit after the summer equinox on June 21. This is because it takes some time for the earth and oceans to warm up. This is known as the lag of the seasons.
Here are some links:
https://www.weather.gov/lmk/seasons
This is a little confusing. The earth is actually farthest from the sun (aphelion point) In early July.
You are correct in that it is the inclination of the earth’s axis that is the cause of the seasons, and for the summer to be warmer.
According to my local chart, the hottest day was July 20 (while the warmest night was July 26-27). But bear in mind that it’s a LOCAL chart. Your location may vary.
If this year’s weather is statistically “normal,” most locations in the contiguous United States will experience their hottest day of the year between July 15-31…
For most of the country, the warmest day occurs sometime between mid-July and mid-August. The amount of solar radiation reaching Earth (in the northern Hemisphere) peaks at the summer solstice on June 21, but temperatures tend to keep increasing into July. The continued warming occurs because the rate of heat input from the sun during the day continues to be greater than the cooling at night for several weeks past the solstice, until temperatures start to descend in late July and early August.
That’s based on the 1991-2020 U.S. Climate Normals. It’s surprisingly difficult to find global data or historical data, although a deep dive into earlier 30-year climate normals might help.
The OP is vague about the details of the question. Particular locations may fall at the early or late side of “normal” or outside it entirely. As an average, there is no way of telling when the hottest day will occur in any given year. The U.S. as a whole will be affected by wind patterns, cloud patterns, rain patterns, even volcanic output. Normals in other northern hemispehere countries will vary by latitude and geography as well as patterns. Southern hemisphere coolness during its winter will affect the average of the Earth globally.
So there is no one answer to a question this vague. “Sometime mid-summer” would likely be closest.
Decades ago, when the Internet was young, I was able to find 100-year daily weather data for a particular location in Arizona I was interested in buying. I downloaded the data and made a nifty spreadsheet which graphed the average, maximum, and minimum temperature for every day. Having that much data to average made the graphs really smooth. Sadly, I went looking for the data a few years ago, and I couldn’t find it. I swore it was on the NOAA website, but it must have gotten shunted off somewhere inaccessible. It’s probably still available by request.
Huh.
I still have the data.
Here is the graph, showing average high, average low, max high, min low for 100 years of data, every day of the year:
@Exapno_Mapcase I live in SE Michigan. I am looking for the weather patterns for that.
BTW I feel obligated to mention. Tomorrow is Lammas Day. In England it was the blessing of the first fruits of the harvest. That is irrelevant. The day is mentioned in Old Farmer’s Almanac. And it is obviously mentioned for a reason.
What is the significance of that day weather wise?
EDIT: @beowulff Your graph only gives the number of the days. I don’t have time to figure it out. So which day then is the hottest?
Ask your local newspaper. I bet they know.
It looks like the highest part of the blue line (average daily high) is from around day 180 to 195, before beginning to slowly decline. That’d make it June 30th (on a non-leap year) to July 14th, which would be, for Beowulff’s location in Arizona, the hottest part of the year for that set of data.
But, as he notes, he did that analysis decades ago, and it may be a little different now.
Well, it looks like day 194-196 are the hottest, which would be July 14-16.
Also, here’s a page with various data for Detroit, in SE Michigan, which the OP seems to be interested in.
In their data, the average daily high in Detroit peaks on July 19th.
In addition, a couple of things to note on reported “average” high and low temperature readings, at least in the U.S.:
The National Weather Service calculates averages high and low temperatures for each location, based on thirty years of data, and revising their averages every ten years. So, from 2011 through 2020, the averages were based on the thirty years of observations from 1981-2010; beginning this year (2021), the NWS is using averages calculated from the years 1991-2020.
And, when they make these calculations, they smooth the data, so you get a smoothed, gradual curve, as the Detroit chart in my link above showed.
By comparison the surface temperature of the MOON varies from 284 degrees Fahrenheit(140 degrees Celsius) to --275.8 degrees Fahrenheit (-171 degrees Celsius).
Weather-wise, there’s almost undoubtedly no significance whatsoever. The timing of it seems to set to being late enough in the growing season in England that farmers would have been able to start harvesting wheat (and making flour from it) by then, but that’s not “weather,” it’s climate.
In England the quarter days (Lady Day, Midsummer Day, Michaelmas and Christmas) were significant for both religious and secular purposes. For a farmer, they would probably have been rent days.
Halfway between, were the cross-quarter days, like Lammas day, which were often holidays and also had a religious significance, sometimes related to earlier pagan festivals,
Also the Arizona monsoon season runs through July and August, so the increased moisture and rain limits the temperatures at what would otherwise be the peak. I’ve always understood the warmest (and coldest) time of year to be a month after the solstice. So roughly the 21st of July and January. That generally tracks, but hottest or coldest day is too granular. It may be best to say the third week of those months is generally the maximum/minimum, excepting microclimates and such of course.