By AccuWeather Meteorologist
Updated Sep. 6, 2021 10:38 AM EDT
Record-challenging heat scorched the Southwest this past weekend, and temperatures are expected to reach their peak early this week. As residents turn on fans or air conditioners, air quality will continue to deteriorate and drought conditions will worsen, making firefighting immensely difficult.
On Monday, an area of high pressure will be anchored over the Great Basin, and temperatures will be 5 to as much as 15 degrees Fahrenheit above average from California to Washington, according to AccuWeather Senior Meteorologist Tyler Roys. Residents will likely be turning on their fans or air conditioners once again.
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Earlier in the year, the Northwest experienced a historic heat wave, which set all-time temperature records and contributed to hundreds of deaths. This week's heat wave, focused instead on the Southwest, won't be as extraordinary, as wildfire smoke can block some of the hot sun, but it can still be dangerous.
Extreme heat is the most deadly weather phenomenon over the past 30 years, according to data from the National Weather Service. On average, extreme heat events have killed more people in the United States from 1991 to 2020 than any other weather event.
This heat wave will be particularly hazardous considering Labor Day is usually celebrated via outdoor events, such as cookouts and backyard get-togethers.
"This building high pressure will help to bring record-breaking temperatures to some areas across the West over the holiday weekend and early this week," said AccuWeather Meteorologist Alex DaSilva.
Las Vegas, for example, is expected to have temperatures rise over 5 degrees above normal on Labor Day and Tuesday. Tuesday's high temperature could even approach the 1977 record of 108 F on Sept. 7.
While residents of the gambling capital of the world are typically accustomed to very high temperatures this time of year, there are many who are particularly vulnerable to heat, including young children and infants, older adults, people with chronic medical conditions and pregnant women, as well as tourists and visitors from cooler climates.
An excessive heat warning is in effect for Monday and Tuesday, spanning Las Vegas; Grand Canyon, Arizona; Death Valley, Nevada; and Barstow, California, alerting the public of the dangerously hot conditions and risk for heat-related illnesses.
Temperatures in Fresno, California, are also anticipated to toy with records early this week. Rising about 10 degrees above average on Tuesday, the temperature can approach the Sept. 7 record of 106 F, set in 1988.
A heat advisory has been issued for parts of California, including Bakersfield, Fresno, Coalinga, Atascadero, Sacramento, Redding and Temecula on Monday.
"High temperatures will also hover around 100 F or higher in Phoenix through much of this week," said AccuWeather Meteorologist Ryan Adamson. While temperatures aren't expected to reach any records, it'll be a toasty Labor Day in the Valley of the Sun.
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AccuWeather forecasters urge residents and visitors alike to minimize outdoor activity, check in on friends and relatives who are vulnerable to the heat and never leave a child or pet locked in a car. On average, 38 kids die each year by being left in a vehicle, according to the NWS.
Fortunately, there is some relief from the heat in the near term for the West, when temperatures could ease up.
"The dome of high pressure should begin to move east toward the end of next week allowing for some relief from the heat," said DaSilva.
Wildfire smoke to reduce air quality
"Another product of this high building in will be decreasing air quality as the high pressure creates stagnant air, preventing the wildfire smoke from moving out," said Roys.
Air Quality Alerts have already been issued for parts of the West, including in Phoenix; Medford and Salem, Oregon; northwestern Wyoming and Yakima, Washington.
While Phoenix's Air Quality Alert is primarily due to ozone, most of the other alerts list wildfire smoke as the main problem. An alert issued by NWS Eureka, California, on Sunday, stated that everyone should "avoid any outdoor activity given the hazardous air quality levels," and that residents should even consider leaving the area due to coughing, shortness of breath, difficulty breathing, chest tightness, palpitations or nausea.
In Jackson and Klamath counties of Oregon, NWS Medford warned that wildfire smoke has reduced air quality and that smoke can irritate the eyes and lungs, and can worsen some medical conditions. Officials recommend residents stay inside, keeping windows and doors closed, avoid strenuous outdoor activity and use air filters to ventilate the room.
Unfortunately, this smoke will likely hinder attempts to tame the active fires of the West, including the largest single fire in California history, the Dixie Fire and the particularly dangerous Caldor Fire.
As of Sunday, 12 large active fires burned in California alone, with two more in Nevada, according to the National Interagency Fire Center. The Caldor Fire, located east of Sacramento, California, has burned over 215,400 acres and is 44% contained. The Dixie Fire, which burns to the north near Chico, California, was larger than the state of Rhode Island at the end of August and is currently 56% contained.
With firefighters battling multiple fires, poor visibility and poor air quality, assistance from the weather is not looking likely. One silver lining is that calm winds associated with the current pattern won't help fires spread quickly.
Drought to worsen across the West
"Unfortunately, another byproduct of this dome of high pressure setting up will be that little to no rain will fall across the West," said DaSilva.
Though monsoon moisture helped with drought conditions in parts of the West, many areas did not receive enough or even any rain to ease the drought conditions. About 60% of the West is in an extreme drought, according to the United States Drought Monitor. In California, that number is approaching 90%.
Las Vegas and Los Angeles have only received a trace of rainfall since the beginning of August, and Fresno hasn't reported any precipitation since April, which means the ground and vegetation are very dry across these areas.
Red Flag Warnings have also been issued across Idaho, Montana, Wyoming and the Dakotas, warning residents of dangerous conditions that can allow wildfires to spark and spread easily.
Not only is this hazardous for wildfire fuel, but it can also allow the air to heat up even more, perpetuating the drought, fire and heat wave cycle and therefore contributing to the triple-digit temperatures expected this week in the Southwest.
An area of disturbed weather over the Pacific Ocean is forecast to travel northeastward and brush part of the Northwest spanning Tuesday and Wednesday. While moisture is limited with this feature, it could produce spotty showers in coastal areas of Washington and Oregon, and potentially trigger spotty thunderstorms over the Cascades. Any lightning, with little or no rain, could spawn new wildfires in the region.
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