Every spring someone at the coffee shop asks whether it has hit 100 yet, and every fall someone asks whether we are done with it. The answers live in a National Weather Service table that almost nobody reads. This is that table, translated, with the records, the 2026 season so far, and one correction most people never hear: the official “Phoenix” number is not Scottsdale’s.
Whose thermometer counts
When the news says Phoenix hit 100, it means the official station at Sky Harbor International Airport. The official Phoenix record runs back to 1896, kept at Sky Harbor since the 1930s and at earlier Phoenix sites before that, and the NWS Phoenix office keeps its milestone tables on it. Every date below comes from that record unless we say otherwise. Scottsdale has its own official thermometer at Scottsdale Airport, but its daily record only starts in 2000, too short for most of these comparisons. We come back to what it shows near the end.
The NWS publishes two kinds of average for each milestone. One covers the whole period of record, 1896 to 2025. The other covers the current climate normals, 1991 to 2020. The gap between them is the most useful thing in the table.
The milestones, on average
- First 100°F day: May 10 across the whole record; May 2 in the 1991–2020 normals.
- Last 100°F day: September 29 across the record; October 5 in the normals.
- Days of 100°F or more per year: 94 across the record; 111 in the normals.
- First 110°F day: June 18 across the record; June 11 in the normals.
- Last 110°F day: August 13 across the record; August 26 in the normals.
- Days of 110°F or more per year: 13 across the record; 21 in the normals.
- Days at or below freezing per year: 8 across the record; 1 in the normals.
Read the two columns together and the story is plain. The triple-digit season now starts about a week earlier and ends about a week later than the long-run average, the 110° stretch runs nearly two weeks longer at its back end, and a hard freeze at Sky Harbor has become a once-a-year event at most. The May and September guides are written to the normals, which is the right call: those are the numbers you will actually live with.
The records
For 100°F:
- Earliest first 100: March 26, 1988, until 2026 broke it (below).
- Latest first 100: June 18, 1913.
- Earliest last 100: September 2, 1904. Latest last 100: October 27, 2016.
- Most 100° days in a year: 145, in 2020. Fewest: 48, in 1913.
- Longest unbroken run: 113 days, May 27 to September 16, 2024.
For 110°F:
- Earliest first 110: May 8, 1989.
- Latest first 110: never. In 1911 Sky Harbor’s station did not reach 110 at all.
- Earliest last 110: June 5, 1912. Latest last 110: October 7, 2024.
- Most 110° days in a year: 70, in 2024.
- Longest unbroken run: 31 days, June 30 to July 30, 2023.
The extremes: the all-time high is 122°F on June 26, 1990, the day before’s 120°F is third, and 121°F on July 28, 1995 is second. July 2023 put 119°F on the board more than once. The all-time low is 16°F on January 7, 1913, and the most freezing days in one year was 35, in 1964. Those old cold numbers are not coming back.
Look at where the hot records cluster. The longest 100° run, the most 110° days, the latest 110° day and the longest 110° run all belong to 2023 or 2024. Most of the “fewest” and “earliest last” records belong to the 1900s and 1910s.
March 18, 2026
At 2:57 p.m. on Wednesday, March 18, 2026, Sky Harbor reached 100°F, the earliest triple-digit reading in the record, eight days ahead of the 1988 mark. It reached 102°F by 5 p.m., which also made it the warmest March day on record at that point, and it smashed the date’s old daily high of 95°F, set in 2017.
It did not stop there. The NWS March 2026 summary lists record highs of 105°F on March 19, 20 and 21. Since no 100° day had ever been recorded before March 26, those were by definition the earliest 105s in the record as well. The same list shows nine record-setting days at 100°F or hotter between March 18 and 27. March 2026 averaged a high of 92.9°F, 14.8° above normal, and the previous warmest March had averaged 86.7°F. It rained six hundredths of an inch all month. April followed with a trace of rain and its third-warmest mean temperature on record.
If you were in town for spring training that week, you saw something no previous generation of Cactus League fans had: a 105° March afternoon.
The rest of 2026, so far
These figures are our own tally of the preliminary daily data NOAA’s regional climate center publishes for Sky Harbor, through October 1, 2026. The NWS will publish official season totals in its year-end review, and those govern if they differ.
- First 110°F: June 13, two days behind the 1991–2020 average.
- Days of 100°F or more: 128 through October 1, well past the 111-day normal but short of 2020’s 145.
- Days of 110°F or more: 39.
- Hottest: 117°F, reached on July 24, July 25 and August 26.
- Longest 100° run: 46 days, June 1 to July 16.
- Last 100° so far: September 26. October can still produce one.
August 2026 averaged a high of 109.4°F, the third-warmest August on record. For a sense of the year before: 2025’s first 100 came on April 10 and its first 110 on June 14.
Scottsdale is not Sky Harbor
Scottsdale Airport sits at about 1,431 feet, roughly 300 feet above Sky Harbor’s 1,113, and about 13 miles north-northeast of it. Its daily record starts in mid-2000. We tallied both stations over the same 24 summers, 2002 through 2025, from the same NOAA daily data:
- Days of 100°F or more: about 94 a year at Scottsdale Airport, against about 116 at Sky Harbor.
- Days of 110°F or more: about 12 a year in Scottsdale, against about 29.
- Typical first 100: about May 14 in Scottsdale, against about April 30.
- Typical first 110: about June 21 in Scottsdale, against about June 8.
- Typical hottest day of the year: 114°F in Scottsdale, against about 116.5°F.
The gap is biggest in the worst years. In 2024, when Sky Harbor logged its record 70 days at 110°F or more, Scottsdale Airport logged 24. In 2026 the two stations hit their first 100 on the same day, March 18, though Scottsdale only touched it. As of October 1, Scottsdale Airport’s 2026 count stands at 105 days of 100°F or more and 24 days of 110°F or more, its first 110 came on July 6, and its high for the year is 115°F on August 26.
Two cautions. Twenty-four years is a short record, and an airport thermometer describes an airport. Old Town sits between the two stations, and the far north of the city sits higher than either, but there is no long official record for those places, so we will not put numbers on them. What the comparison does settle is that “Phoenix hit 115 today” usually means a few degrees less at the north end of Scottsdale, not more.
What the dates mean on the ground
The first 100 moves the hike. Once triple digits arrive, trail time belongs to the hour after sunrise. The summer sunrise rules have the start-time table. The city’s own Preserve page says that if it is over 90 degrees at any point in your hike, it is too hot for your dog, which rules out afternoon dog hikes for much of the year.
The first 110 changes the economy. By the time 110 shows up in June, the resorts are already pricing for summer and for locals. The summer resort playbook covers how to use it.
The last 110 is the one to watch in late summer. The normal is now August 26, and in 2024 it was October 7. A monsoon storm can cool one evening and the next afternoon can be 110 again; the monsoon field manual covers the storms.
The last 100 is the real start of the season. The normal is October 5. The October guide is built on it: the patios fill when the 100s stop, and in a stubborn year that is not until the second week.
How to keep score yourself
- NWS Phoenix, “Historical Extreme Temperatures” (weather.gov/psr/ExtremeTemps): the milestone tables above for Phoenix, Yuma and El Centro, updated each year.
- NWS Phoenix monthly climate summaries: one-page PDFs with the month’s averages, rank and every daily record set. The March 2026 sheet is the one to frame.
- NOAA’s NOWData (through weather.gov/wrh/climate, office PSR): daily highs for Sky Harbor and for Scottsdale Airport, the station to check if you want Scottsdale’s own number.
The table will need updating again. Of the records above, the ones most likely to fall next are the late ones: the latest last 100 (October 27, 2016) and the latest last 110 (October 7, 2024).