Phoenix weather: The city just got its first 100-degree day of 2018

Making note of the first 100-degree day in Phoenix is kind of like seeing the first car of a freight train. You know it’s only the beginning of a long line of such things to come.

Phoenix recorded its first 100-degree temperature of 2018 on Tuesday, when the thermometer at Sky Harbor Airport recorded triple digits at 2:48 p.m., according to the National Weather Service in Phoenix.

The reason for the unseasonably warm temperature is a strong area of high pressure over the region, according to the forecast discussion on the website for the National Weather Service office in Phoenix. The average high for April 10 is 84 degrees.

That 100-degree high also ties a record for April 10 set in 1989.

Is this too early for 100 degrees?

The milestone came a little early according to the historic averages for the city, but it didn't set a record.

The record for the earliest first 100-degree day is March 26, 1988. The record for the latest one is June 18, 1913.

On average, Phoenix sees its first triple-digit high on May 12 if you count the National Weather Service’s entire period of record, which dates to 1896. A more recent measure – the 30-year normal period, which is currently 1981-2010 – puts the average first 100-degree day at May 2.

Chances are that when the next 30-year normal statistics are compiled in 2020, that average might creep into April.

The urban heat-island effect, along with regional and global climate change are among the reasons most mentioned by meteorologists and climate scientists for Phoenix’s lengthening heat season.

How long will it last?

If you’re wondering how long we can expect this year’s temperature freight train to last, here are the numbers. The all-time average for the latest 100-degree day is Sept. 29. The 30-year date is Oct. 3.

The record for latest triple-digit high is still a vivid memory for those who follow such things. That date is Oct. 27, 2016.

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