Get ready for a roller coaster! Afternoon high temperatures in Phoenix on Tuesday are forecast to be in the low to mid-70s before skyrocketing into the 100-102º range Saturday.

If you are wondering how rare it is to go from the 70s to the first 100-degree day of the year, you have come to the right place.

Looking back over the past 125 years (1896 - 2020), there have only been 16 years when the high temperature in Phoenix was in the 70s, four days or less before the first triple-digit high of the year. Drilling down a bit further, since the high this coming Tuesday is right around 74º, there have only been four years where the high has been 74º or less, just four days before the first 100º reading of the year.

The coolest high temperatures preceding the first triple-digit day of the year are as follow:
Four days before: 70º in 1919
Three days before: 70º in 2001
Two days before: 80º in 1961
One day before: 88º in 2003

As for the biggest temperature change four days before the first 100º of the year, the current record stands at 31º in 1919, going from a high of 70º to 101º. This year, the forecast high on Tuesday is 74º, and on Saturday, it is 101º, making it a change of 27º, which would tie as the 4th largest temperature swing on record (when comparing the high on the first 100º+ day with the days preceding it).

Record temperature swings preceding first 100º day:
31º: 1919 (70º to 101º four days before)
30º: 2001 (70º to 100º three days before)
28º: 2001 (72º to 100º four days before)
27º: 1910 (73º to 100º four days before) and this year may tie that!

As you can see, the event that is forecast to happen this year in Phoenix is a rare one!