It might be only April, but summer weather is already baking the desert Southwest and bringing triple-digit heat. Phoenix could hit 100 degrees this weekend as a record-breaking air mass brings dangerous heat and fire weather concerns to the region. The heat is in sharp contrast to the unusually cold weather dominating the eastern United States yesterday and today.
The National Weather Service is warning of “critical fire weather conditions,” the exceptional early-season heat combining with single-digit humidity to transform the already-parched landscape into a tinder box.
Most of the Southwest is already in the midst of an “exceptional” drought, the highest tier on a six-step scale. Signs point to the drought continuing to worsen with time with an anomalously hot and dry summer expected.
It's important to emphasize that fires occurring right now are generally not dangerous ones; in fact, conditions across much of CA are currently optimal for beneficial & risk-reducing prescribed fire. But this does not bode well for peak fire season to come... #CAwx #CAfire https://t.co/9UfQKvTGGF— Daniel Swain (@Weather_West) April 1, 2021
The desert Southwest is still running dry from a virtually nonexistent monsoon last summer — a pronounced reduction and, in some cases, a total absence of the warm-season showers and thunderstorms that make up most of the region’s annual rainfall.
Phoenix typically starts April with temperatures in the lower 80s, but Thursday hit 95 degrees. Friday is expected to climb into the lower 90s, with upper 90s expected both weekend days and Monday.
A return to upper 80s — less harsh but still above average — is expected Tuesday and beyond.
In New Mexico, Albuquerque is expected to see highs in the mid-80s Monday. That should be more tepid than farther west, but would still break the daily record of 81 degrees set in 1972.
Las Vegas, meanwhile, is anticipating lower 90s over the weekend, with a return to breezy weather and 80s by the workweek. A record could be tied Saturday.
Even in California’s Bay Area, record heat brought temperatures well into the 80s. A number of spot fires are burning across the inland mountains. And while fires earlier in the season are typically more localized and subsequently less dangerous, they paint an ominous picture for what might lurk ahead.
Another day of record breaking heat in the #BayArea, where three high temperature records were tied and two broken. #CAwx pic.twitter.com/fXMzPpJnn3— NWS Bay Area (@NWSBayArea) April 2, 2021
“You would think most people … are acclimated, but there is still a community vulnerable that can be impacted by temperatures even in the upper 80s,” said Sean Benedict, a meteorologist at the Weather Service in Phoenix. “We have a product called heat risk here, [that points to] low-end heat risk around 86 here. Certainly this early in the season it might catch people off guard, and we might have a lot of folks from out of town too.”
His office is forecasting Phoenix to tie a daily temperature record Saturday and break a new one Sunday.
Benedict also said that, if Phoenix can hit the century mark Sunday, it will be the fourth-earliest triple-digit heat on record at Sky Harbor Airport.
Since World War II, the average date of Phoenix’s first 100-degree reading has shifted earlier by about three weeks, backing up from May 17 to April 28. On the tail end of the season, 100-degree days are sticking around about 10 days later. All told, that’s nearly a month more triple-digit heat than was typical just 70 years ago, largely due to climate change and the urban heat island effect (the tendency for cities paved with heat-absorbing materials to warm more rapidly than surrounding communities).
Last year, Phoenix hit 100 degrees on a record-breaking 145 days.
The anomalous heat is courtesy of an area of high pressure building north of the Four Corners region over the Palmer Divide and High Plains. That “heat dome” brings clear skies and sinking air, along with dry air and above-average temperatures.
Highs some 10 to 25 degrees above average will dominate the central and western Lower 48 in the coming days, the core of the heat shifting from the Southwest to the Plains and parking by Tuesday or Wednesday. It will probably diminish in intensity by late next week, though above-average temperatures appear favored in Phoenix for the forecastable future.
The high temperatures and low humidity are brewing fire weather concerns, the landscape a potential breeding ground for flames. The Weather Service offices in Flagstaff and Tucson have issued several red flag warnings for fire danger this year, and the Phoenix office warned that isolated “dry thunderstorms” could initiate fires with rain-free lightning strikes Friday, along with “erratic winds to 50 mph” that could also bring blowing dust.
Roughly 40 percent of the Southwest is experiencing an exceptional drought, with more than 50 million people experiencing abnormally dry conditions. The most severe drought category includes 55 percent of Arizona. The U.S. Drought Monitor writes that, in exceptional drought, “fire restrictions increase, large fires occur year-round, lakes, ponds, and streams are dry … [and] native plants are dying.”
Peak fire season is still months away in Arizona, but the parched landscape is particularly concerning, since this is the time of year when the stage is being set for just how bad the fires will eventually get.
“The fuels are prepared now,” Benedict said.
So far this year, Phoenix has picked up about 1.05 inches of rainfall, around a third of what would typically be expected. Most of the region’s annual rainfall comes down in the summertime, but last year’s paltry monsoon dug the state deeper into a deficit; Phoenix recorded a 103-day rain-free streak last year.
With just over an inch of rain, last year was the driest recorded at Sky Harbor Airport dating back to at least 1950. And with abnormally hot and dry weather looking increasingly likely into this summer, the potential for a lengthy and dangerous fire season continues to loom.