WeatherArchive / Hottest day of the year
When is the hottest day of the year where you live?
On average, the warmest day comes weeks after the longest day. Find the climatologically hottest and coldest days for any place, plus the record highs and lows of the last 30 years.
Why the hottest day lags the longest day
The sun’s input peaks at the June solstice in the northern hemisphere (December in the south). But land and especially the sea keep absorbing more heat than they lose for several weeks after that, so temperatures keep climbing. This “seasonal lag” puts the average hottest day in mid-to-late July across much of the US and Europe, and into August on coasts, where the ocean’s heat capacity slows everything down. The same lag shifts the coldest days into January or even February.
Records behave differently from averages: a single heatwave can set a record weeks before or after the average peak.
Questions people ask
When is the hottest day of the year in the US?
For most of the contiguous US the average hottest day falls in July, commonly in the second half of the month; coastal California and the Pacific Northwest peak later, in August or even September.
Is the hottest day the same as the summer solstice?
No. The solstice is the day of most sunlight, but temperatures lag behind by roughly three to six weeks.
How is the average hottest day found?
We average the daily maximum for every calendar day across 30 years, smooth it with a 15-day window, and take the peak.