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!

It was a toasty Easter Sunday in the Valley of the Sun, with Phoenix Sky Harbor hitting 98º. This tied the record high for the day, last set in 1961.

This high also ties as the third warmest Easter on record. The warmest was 1990, coming in with a high of 100º. Second place is 1936 with a high of 99º. And this year is tied with 1930.

Record-setting temperatures were spread across the northern portion of Arizona as well. Cottonwood reached a high of 84º, which broke the record for the day of 82º set back in 1961. Phantom Ranch hit 97º and Seligman reached 92º, which tied the records for the day both set in 1961.

The clouds that moved in later in the afternoon on Sunday were in response to a storm system that will brush the state to the north tomorrow. This system will help to weaken the high allowing temperatures to lower slightly to start the week.

A very strong ridge of high pressure has been anchored over the Southwest US the past few days, resulting in record temperatures across the region.

Phoenix Sky Harbor recorded a high of 97º on Saturday (April 3rd), which tied the record for the day, last set in 1943.

Another interesting fact is the average high temperature so far this month (April 1st-3rd) has been 95.3º, which will go down as the 2nd warmest start to April since records began. The record warmest first three days of April goes to the year 1943, with an average high of 95.7º.

The heat was not confined just to the Valley of the Sun, with Flagstaff coming in with a high of 71º, which also tied the record for the day last set in 1961.

Stay cool!

We all know summer is fast approaching, and the closer it gets, a question always comes up: will this be the coolest day until next Fall? After all, the high temperature today (March 26th) in Phoenix was a nice 66º!

The good news, high temperatures have been 66º or cooler past March 26th before. In 1922, the high temperature on May 10th came in at 65º, which is the record for the latest 66º or cooler high temperature (going from Spring into Summer). Also, just last year, the Valley of the Sun recorded a high of 66º on March 27th.

Ok, now to the bad news, so you may want to stop reading if heat makes you uncomfortable. In the past twenty years (2001-2020), the high has only dropped to 66º or below, seven out of those twenty years. That means there is about a 35% chance Phoenix could see the high drop to 66º or lower before summer. If you are more of a glass-half-empty kind of person, there is a 65% chance that March 26th was indeed the coolest temperature the Valley will see until Fall. Even if it is, it is nowhere near the record earliest last 66º or cooler day, that trophy goes to the year 1972 when the last day was Feb 2nd! So remember, it can always be worse!

The graph at the top of this post shows the twenty and thirty-year rolling averages of the percent of years with a high of 66º or lower along with the number of days with a high of 66º or lower per year.

Phoenix officially hit 80º for the first time this year on Feb 2nd, which is only one day earlier than the 30-year average of Feb 3rd (based on 1981-2010 data). But the comment alway comes up: it feels like it is getting earlier every year.

So... is it? Let's go to the data!

Before we get started, it should be noted that weather observations go back to 1896 in Phoenix. The weather station moved around to a few locations in Central Phoenix from 1896 to 1953. From 1953 onward, it was located at Phoenix Sky Harbor but has moved locations there three times (1953-1994, 1994-2000, and 2000 to present).

Ok, now that we have that out of the way, the graph above depicts the 30-year rolling average, from 1925 to 2021, for the first day Phoenix has recorded 80º+. It also displays the 10-year rolling average to show a bit more detail.

It is quite apparent that yes indeed, based on the 30-year rolling average, the first 80º+ days is getting earlier. In 1925, the average first 80º+ day was Feb 21st, and in 2015 the 30-year rolling average came in at Feb 1st. The 30-year rolling average with this year plugged in comes out to Feb 3rd. (Note: these dates were converted from truncated Julian day)

These data also show that the overall trend is beginning to flatten out, especially compared to the late 1980's into the 1990's.

Will this trend continue? We shall see in the coming years as data comes in.

It felt a bit like early April in Phoenix today (Feb 2nd) as Sky Harbor's high temperature came in at 82º! That's 13º above average for the day and ties the record high set back in 1925!

This also marks the first 80º+ day of the year, which is only a day early compared to the 30-year average first day of Feb 3rd.

The earliest first 80º day of the year occurred on Jan 1st and has happened three times (1918, 1981, and 2012). The latest first 80º day was in 1973, when we held off until April 6th.

We all know the heat is coming sooner or later in Phoenix, but hopefully, we are not talking about the first 100º day for another couple of months!

Yuma is not known for being a rainy city, especially since the average rainfall for the year stands at just 3.56". But this week, there was an exception to that rule.

A cut-off area of low pressure sat just off the coast of Northern Baja for several days allowing moisture to increase across the region. By Wednesday, the atmosphere was primed, and with just a little energy from the low, several rounds of rain moved through the southwest corner of Arizona. By the end of the day on January 20th, Yuma measured 1.12" of rain, which broke the rainfall record for the day. The old record was 0.56" set back in 1933.

To put this into perspective, that's 31% of the city's average rainfall typically measured in a year. There have also been 16 years, since records began in 1876, that Yuma has not even recorded more than 1.12" in an entire year!

Certainly not complaining about the rain, as in the desert, we will take every drop we can get!

On Tuesday, January 19th, at around 6:17 am, Phoenix Sky Harbor recorded its first measurable rain of 2021! The average first measurable rain for a year, using the 30-year average (1980-2010), is January 12th.

There have been 11 years since 1896 when measurable rain was recorded on January 1st, with the latest-ever first measurable rain in a year being June 7th set back in 1973. The second latest is May 29th set in 1937, and the third latest jumps to March 18th, recorded in 2012.

So has the first day of measurable rain in a year changed over time?

Of course, after all, you are dealing with the weather, which feeds directly into the climate. The graph below shows the first day of measurable rain (in Julian days) and the 30-year rolling average. As can be seen, the latest 30-year average was January 21st in the late 1930s, which was mainly influenced by 1937. The earliest average came in on January 10th in the early 2000s, and since that time, we have been on a slow increase, with the average (including this year) sitting at January 17th.

Something of note, there is no correlation between the first day of measurable rain in a year and the yearly rain total.