When Is the Hottest Day of the Year?

The Exact Date Each Major City Peaks

Ordered from the earliest peak to the latest. The “average high” is the smoothed day-of-year mean high at each city's primary long-record station, 1970–present. Find your city and you'll see the pattern immediately: heat marches from the desert Southwest in late June out to the coasts by September.

Dates are the peak of a centered 7-day smoothed average, not a single record day, so they're stable rather than driven by one freak heat wave. Values reflect 1970–present, so a warming trend nudges the averages up slightly versus older normals. Dig into any city's full record on its page — Phoenix, Los Angeles and Dallas tell three completely different stories.

Why the Hottest Day Isn't the Longest Day

The longest day of the year is the summer solstice, around June 21. You'd think that's when it should be hottest — that's when the sun is highest and the days are longest. But the hottest day trails it by about four to six weeks nearly everywhere. Meteorologists call this seasonal lag.

Here's the mechanism. Even after the solstice, the ground, the air and especially the oceans are still soaking up more energy each day than they radiate back to space. Temperatures keep climbing as long as that surplus lasts. Only when incoming sunlight has weakened enough to match the heat being lost does the balance flip and the average finally starts falling. For most of the inland US that crossover happens in mid-to-late July. The bigger and slower the heat reservoir next door, the longer the lag — which is exactly why the coasts peak last.

The Three Americas of Peak Heat

Sort the cities by date and the country splits cleanly into three timing zones, each with a physical reason behind it.

The Two Cities Everyone Gets Wrong

If this piece has two headline surprises, they're Phoenix and Los Angeles — and they fail in opposite directions. Phoenix, the hottest big city in the country, peaks earlier than almost anywhere (June 29), because the monsoon acts as a natural thermostat. Los Angeles, one of the mildest big-city summers in the country, peaks latest of all the marquee cities (September 4), because the Pacific keeps June, July and August unusually cool and only loosens its grip in the fall. Same physics — the seasonal storage and release of heat by the land and sea — producing two answers ten weeks apart. If you want to know how hot each can actually get, our hottest temperatures ever recorded breakdown covers the all-time extremes, and the hottest states and cities in America ranks who's hottest overall.

So What's the Hottest Month?

If you zoom out from the single hottest day to the hottest month, the answer is simpler: July, for nearly all of the continental United States. In our station data July is the warmest calendar month in the great majority of the 41 cities here. The exceptions are the same edge cases as before — the desert Southwest, where June can edge out July (Tucson's warmest month is June), and the coasts and Gulf, where the ocean lag pushes the warmest month into August (Houston, Dallas, San Antonio, Miami, New Orleans) or September (Los Angeles, San Francisco). So “the hottest month of the year” is July almost everywhere, but the exceptions are precisely the places whose day also breaks the mid-July rule.

Right Now Is the Peak for Much of the Country

Publishing this in the third week of July isn't an accident. For 23 of these 41 cities — more than half — the single hottest day of the year falls between July 15 and July 25. If you're reading this in the eastern two-thirds of the US, you are, on average, living through the hottest stretch of your entire year this week. That has borne out in 2026: our July 2026 heat recap tracked more than a thousand daily heat records broken in the first half of the month alone. You can watch the records fall in near-real time on our records broken tracker, or look up what the weather did on this exact date in your own city over the past century.

Is the Hottest Day Getting Hotter?

Yes — and in some places a little later, too. Because our climatology uses 1970–present data, the average highs above already run a touch warmer than the older 20th-century normals for most cities. The peak isn't just rising in temperature; a warming ocean can also stretch the seasonal lag, nudging some coastal peaks slightly deeper into late summer. We dug into how much summer heat has climbed, city by city, in the US cities where summer has warmed most since 1990 — and you can see where 2026 fits in the long record in every state's hottest July on record.

How We Computed This

For each city we selected the densest long-record NOAA GHCN-Daily station within about 0.6° of the city center — the primary airport in nearly every case. Daily high temperatures (stored in tenths of a degree Fahrenheit) were averaged by calendar date across all years from 1970 to the present, February 29 excluded. Because a single date only has about 55 years behind it, the raw day-to-day curve is noisy, so we applied a centered 7-day smoothing before taking the peak — the reported “hottest date” is the top of that smoothed curve. This is a 1970-present normal, not a full-century climatology, and it reflects the warming of recent decades. The hottest-month figures come from the same stations, averaging daily highs by calendar month.

Frequently Asked Questions

Sources & Method

City day-of-year climatology: NOAA GHCN-Daily via our database (1970–present), computed as described above. The seasonal-lag explanation follows NOAA NCEI, “When to Expect the Warmest Day of the Year” and NOAA Climate.gov. Explore records and extremes across the country on our US weather records hub.