PHOENIX - In the hottest big city in America, summer temperatures routinely top 100 degrees, and on rare occasions can creep beyond 120.
This week, the USA's 12th largest metro area is expected to flirt for at least three days with that top number. Not high enough to fry an egg on a sidewalk, but you might be able to sneak in the extra 40 degrees or so of heat if you set a dark-colored skillet in the sun first.
July has this area's hottest average high temperature, 106.1 degrees compared to 103.9 in June. But three of the four hottest days on record in Phoenix, including the all-time high of 122 degrees on June 26, 1990, have occurred in June.
Monday's high is expected to be 118 degrees. On Tuesday, it will be 120, and Wednesday it will be 119 before Thursday's "cool wave" brings it down to 114. At around 6 a.m. each day, we'll hit a low of 88 or 89.
Many factors contribute to the region's sweltering climate, but we’ll boil it down to five.
1. Location. Arizona is relatively close to the equator and as a result receives a lot of the sun’s energy, particularly at this time of year.
We're approaching the summer solstice at 9:24 p.m. MST Tuesday — 12:24 a.m. ET Wednesday for those of you used to daylight saving time — the longest day of the year in the Northern Hemisphere. That's when the sun is at its highest point in the sky.
Days are longer during the summer months in the Northern Hemisphere because of the tilt of the earth on its axis as it rotates around the sun. Those longer days offer more opportunity for things to heat up.
2. Elevation. The Phoenix area is about 1,000 feet above sea level.
Other parts of the state have the same desert landscape as Phoenix, and many of those places are farther south and closer to the equator.
Along Interstate 8 south of Phoenix are some of them: Yuma, about 140 feet above sea level; Wellton, 245; Tacna, 350; Dateland, 435; and Gila Bend, 735. They're all forecast to experience the same warm oven as Phoenix.
3. High pressure. That big H you see on a weather map represents high air pressure.
It's often behind Phoenix’s big June heat waves.
A pretty persistent area of high pressure generally hangs around the Southwest, which is a big factor in the sunny climate. Because high pressure often results in clear, dry conditions, it contributes to Phoenix’s extreme heat.
In simple terms, long, sunny days at this time of year mean more time for heating up and less time for overnight cooling.
4. The dry heat. June is the driest month of the year in Phoenix, with only 0.02 of an inch of rain on average.
The dry air contributes to the extreme temperatures often experienced late in the month before the onset of monsoon season. And the lack of humidity means it takes less energy for the sun to heat up the same volume of dry air than it does air with more moisture.
5. Urban heat island. The term describes the way concrete, asphalt and buildings in metro areas hold on to heat more than non-developed areas.
Development, particularly in the past 30 to 40 years, has caused temperatures, especially overnight lows, to increase.
The average overnight low for Phoenix in June 2016 was 82.1 degrees, which tied the record for that statistic set in 2015, according to the National Weather Service. That’s 4.4 degrees above normal.
Those warm nights also allowed June 2016 to tie June 2013 for the warmest average temperature, taking the average high and low and dividing by two, on record.
All five of the warmest Junes on record have occurred since 2006.
Why not later? Monsoon season starts June 15, but the storms peak from mid-July to mid-August, which can cool off a day quickly.
The monsoons won't deliver tolerable temperatures Expect readings to top 100 until at least September, sometimes October.
Follow Weldon Johnson on Twitter: @weldonjohnson
© 2017 USATODAY.COM