Heat wave to bring dangerously high temperatures to western US
Excessive heat warnings have been issued across parts of the West as a prolonged and intense heat wave sets up across the region. AccuWeather forecasters warned that temperatures could soar to over 100 degrees Fahrenheit.
AccuWeather meteorologists say a dangerous late-summer heat wave is developing across the western U.S. this week, bringing higher temperatures more typical of July than late August or early September.
Forecasters say the heat will be notable not just for its intensity, but also for its duration. Above-normal temperatures and even record-challenging warmth are forecast for much of the West through the rest of this week and beyond the upcoming Labor Day weekend.
In recent days and weeks, many of the Western states have avoided prolonged periods of intense heat that have been common this summer as the frequent rainfall and humidity provided by the North American monsoon have helped keep temperatures in check across the region.
The frequent rainfall so far this month has made an impact on temperatures in the Desert Southwest. In Phoenix, for example, temperatures so far in August have been 1.2 degrees below average. While temperatures in the city generally peak at around 105 degrees Fahrenheit in August, the mercury has failed to reach the triple digits on many days. Albuquerque, New Mexico, and Las Vegas have also had below-normal temperatures so far this month.
In the Northwest, which has been drier as of late, it's been a slightly different story. In Portland, Oregon, temperatures have been about 4 degrees above average for August. Similar numbers are being reported in cities such as Seattle and Salt Lake City. The combination of high heat and little rain has led to the spread of wildfires as well, with several major blazes burning in the region. With this week's expected pattern, relief is unlikely to arrive soon.
An impressive ridge of high pressure will build across the West this week, allowing temperatures to steadily rise over time. With the jet stream pushed well to the north, the chances for meaningful, widespread rain will be close to zero with this pattern, according to AccuWeather Meteorologist Andrew Kienzle.
Heat advisories and excessive heat watches and warnings have been issued by the National Weather Service for parts of Arizona, Nevada and Southern California. Most of the warnings were scheduled to go into effect on Tuesday or Wednesday morning. In some cases, the warnings are not scheduled to expire until the day after Labor Day, a testament to just how long-lasting the heat is expected to be.
While rainfall associated with the North American monsoon has not been tough to come by recently, this ridge, also known as a heat dome, will largely prevent much more.
"With such a strong area of high pressure, the development of clouds and thunderstorms will be largely limited, keeping the West dry. Since dry air heats up more quickly than humid air, this will only help raise temperatures across the region," Kienzle said.
Which parts of the West will have the hottest weather?
Some of the most intense heat will be found in the Desert Southwest and California's Central Valley, where high temperatures well above the century mark will be common. In Fresno, California, high temperatures reached 103 F on Tuesday, and are likely to remain in the low 100s on Wednesday, potentially climbing even higher by the end of the week.
Palm Springs, California, is often one of the hottest cities in the country. Starting on Tuesday, high temperatures are likely to reach above 110 F each day for at least a week, including reaching a scorching 116 F at Palm Springs Regional Airport Tuesday and a forecasted 117 F on Wednesday. Even at night, relief may be tough to find, as lows may struggle to get below 90 degrees some nights. The record high for Aug. 31 in Palm Springs is 118 F.
The NWS in Phoenix said Tuesday would likely be the hottest day in over a month for many areas. The reading at Phoenix Sky Harbor International Airport on Tuesday reached 111 F after hitting 108 F on Monday, its hottest day since Aug. 6.
In Death Valley, California, which holds the record for the highest air temperature ever recorded on Earth, high temperatures are forecast to reach 122 F on Wednesday and 124 F on Thursday and Friday.
With a high of 100 F Tuesday afternoon in Portland, Oregon, the city endured the worst of the heat, breaking a daily record high of 98 was set in 1987, with Tuesday being more than 15 degrees above normal for the date. Farther north along the I-5 corridor, in Seattle, a similar Tuesday peak hit a high of 90, which broke the date's 1987 record and was around 10 degrees above average.
While these temperatures are not as extreme as those found farther south, the Pacific Northwest is much more vulnerable to this type of heat.
"Most buildings in these Northwest cities do not have air conditioning that can handle these waves of heat. As we've seen from recent events, this will make the risk for heat-related illnesses and deaths much greater," AccuWeather Senior Meteorologist Mike LeSeney said.
While these coastal cities in the Pacific Northwest may get a shorter surge of heat, a much more prolonged event may unfold elsewhere in the West.
"By Wednesday and Thursday, these high temperatures will begin to spill eastward into the northern Plains, all while continuing across the Southwest. After what may be a brief break on Friday, another strong push of hot conditions will overspread the western half of the United States," LeSeney explained.
Cities such as Billings, Montana, Bismarck, North Dakota, and Minneapolis will also run up to 15 degrees above normal late this week and into the weekend as the heat shifts eastward.
In addition to the heat, the bulge in the jet stream may also allow drought conditions to worsen across the West.
According to the U.S. Drought Monitor report released on Thursday, Aug. 25, nearly all of California, Nevada and Utah are under some stage of drought, with many places elsewhere in the West and much of the Plains also experiencing drought conditions.
Although there have been frequent rounds of flooding rainfall in the Southwest thanks to the ongoing North American monsoon, much more rain is needed to break the drought. With this change in the pattern, that relief is unlikely to arrive anytime soon, forecasters say.
That said, there will be a chance for some additional moisture during September. AccuWeather meteorologists will be watching for tropical development in the eastern Pacific during the Labor Day weekend.
"There is a chance a tropical storm or hurricane could swing northward and not only bring wind and rain to the Baja Peninsula of Mexico but [a tropical system] could inject more moisture into the southwestern U.S. sometime during the second week of September," AccuWeather Senior Meteorologist Alex Sosnowski said.
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