Phoenix recorded a high of 106 degrees on March 21, breaking a record it had only just set the day before and stretching one of the most extreme early-season heat events in the city’s recorded history into its fourth consecutive day of unprecedented temperatures.
The reading came from Phoenix Sky Harbor International Airport, according to the National Weather Service. The overnight low that morning also broke records, dropping no lower than 70 degrees, which surpassed the previous warm-low mark of 67 degrees set in 2004 and marked the earliest 70-degree low Phoenix has ever recorded.
A week of records in Phoenix
The heat escalated through the week in steps that kept rewriting the same record. On March 18, Phoenix reached 102 degrees, marking the earliest triple-digit day the city had ever recorded. The previous earliest date for a 100-degree reading was March 26, 1988. On March 19, the high climbed to 105, surpassing a record of 97 set in 2017. Temperatures hit triple digits around 1 p.m. that day, hours earlier in the afternoon than the day before.
March 20 brought 106 degrees and the closure of hiking trails around the city due to heat illness risk. The splash pads at Phoenix parks opened weeks ahead of their normal schedule the same day.
An extreme heat warning remained in effect through 8 p.m. on Sunday, March 22. The National Weather Service forecast a slight easing to around 102 degrees by that date, though even that reduced figure would exceed the all-time March record Phoenix had held before this week began.
Records beyond Phoenix
The heat spread well beyond the city. In Martinez Lake, a small desert community roughly 145 miles west of Phoenix near the Arizona-California border, temperatures reached 110 degrees on March 19, breaking the previous national record for the hottest March temperature ever recorded in the United States. That record had stood since 1954, when Rio Grande City, Texas, hit 108 degrees.
By March 20, that mark had already been topped again. Four stations across Arizona and California, including locations in Yuma and the Southern California desert, each recorded 112 degrees, rewriting the national record for the fourth straight day.
Las Vegas hit 95 degrees, breaking its own all-time March high set just the day before. Death Valley reached 105 degrees, exceeding a record from 2022. San Francisco Airport hit 89 degrees, surpassing a record from 1953. Over 160 cities across the country had broken or tied their all-time March temperature records by the end of the week.
The heat extended into the central part of the country as well. Nebraska saw temperatures pushing into the 90s, with the National Weather Service in Omaha warning that the readings were likely to break long-standing records dating back more than a century. A red flag wildfire warning was posted across parts of the Plains. In Nebraska, the Cottonwood and Morrill fires burned more than 1,200 square miles before being largely contained.
What is behind the heat
The cause is a ridge of high pressure, known as a heat dome, parked over the western United States. The structure has been comparable in strength to systems typically seen in June, not March, blocking cloud formation and allowing surface temperatures to compound over consecutive days.
A team of scientists from World Weather Attribution, an international group that studies the causes of extreme weather events, released an analysis on March 20 concluding that the heat wave would have been virtually impossible without human-caused climate change. Climate Central, separately, determined that climate change has made a heat event of this magnitude at least four to five times more likely than it would have been in a pre-warming climate.
NOAA’s Spring Outlook, released the same day, forecasts above-normal temperatures across most of the United States through April, May, and June, with the highest probabilities concentrated in the interior West, Southwest, and southern Plains.
Health risks and what to do
Valley Health physicians and the National Weather Service both warned that early-season heat is particularly dangerous because bodies have not had time to adjust after winter. Risks are elevated for people with chronic health conditions, outdoor workers, visitors unaccustomed to the climate, and animals.
Health officials recommended drinking water and electrolytes consistently, avoiding outdoor activity during peak heat in the late morning and early afternoon, wearing lightweight light-colored clothing, and seeking shade or indoor cooling regularly. Signs of heat exhaustion, including dizziness, nausea, heavy sweating, and elevated body temperature, should be treated as reasons to seek medical attention immediately.
The extreme heat warning across the Southwest is expected to ease in the coming days. The records it leaves behind are not going anywhere.
