The first 100º day of the year signals the unofficial start to summer, and this year, it happened right around 2:15 pm on May 5th.

Using the new 1991-2020 thirty-year averages, the average first 100º+ day occurs on May 2nd. The earliest 100º+ day occurred on March 26th back in 1988, and the latest was in 1913 when it held off until June 18th!

And if you thought this was a little late compared to recent years, you would be right. This is the latest first 100º day since May 21, 2010.

The Valley of the Sun averages 111 days a year with a high of 100º+, so looking at the positive side, only about 110 more days to go!

The high temperature on December 9th hit 80º at Phoenix Sky Harbor. This temperature is 14º above average for this time of year, and just 4º away from the record of 84º set back in 1981.

This also marks the second December day this year with a high temperature of 80º+. Since 1896, there have only been 15 years (now including this year) that have seen two or more 80º+ days in December.

• 7 days with 80º+: 1980
• 5 days with 80º+: 1939, 1940, 1950
• 4 days with 80º+: 1965
• 3 days with 80º+: 1938
• 2 days with 80º+: 1917, 1946, 1949, 1977, 1981, 2003, 2010, 2017, 2020

Looking at the total number of days in the weather record for December, there have only been 63 days out of 3,853 days with a high of 80º+. In other words, these temperatures are reasonably rare.

If you don't like this December "heat", temperatures will drop back into the 60s tomorrow into the weekend as a storm system moves through the state.

The average high temperature for December 7th is 67º, but this year, Phoenix Sky Harbor hit 80º. The record for the day is 83º, which was set back in 1938.

So how rare are 80º days in December? The last time Phoenix had an 80º+ temperature in December was back in 2017, and before that it was in 2013. Since 1896, when records began in Phoenix, there have been 31 years with a high of 80º+ in December.

Another way to examine how rare this is, look at the total number of days. Out of 3,851 December days on record, only 62 of them have seen a high of 80º+. That's only 1.6% of December days!

The most number of days in December with a high of 80º+ was 7, set back in 1980.

High temperatures are forecast to be right around 80º tomorrow as well, which would make it the 2nd day this year with a high of 80º+ in December. Only 14 years have had 2 or more days with high temperatures of 80º+ in December (see list below).

• 7 days: 1980
• 5 days: 1939, 1940, 1950
• 4 days: 1965
• 3 days: 1938
• 2 days: 1917,1946,1949,1977,1981,2003,2010,2017