Heat wave to bake West on Memorial Day and beyond

While temperatures so far this May have been near average for much of the western United States, a brutal warmup is on the way. AccuWeather forecasters say a heat wave is in the offing as a particular pattern in the upper levels of the atmosphere begins to take shape.

For many locations along the West coast, the average temperature for the month so far has been about 0.5 to 1.5 degrees Fahrenheit above average. While many locations had a handful of days with abnormal warmth, this low of a departure from normal is reflective of the fact that major heat waves were largely kept at bay.

Beginning Sunday, a shift in the weather pattern in the upper levels of the atmosphere will allow unseasonable heat to build across the West.

"A strong area of high pressure at the jet stream level of the atmosphere will begin to work its way over Northern California this weekend," AccuWeather meteorologist Thomas Geiger said.

"This feature will remain locked in place into midweek and will cause extreme heating," Geiger explained.

As this area of high pressure in the upper levels of the atmosphere strengthens, dry and summerlike air will expand northward and eastward from California.

While summerlike heat will largely be confined to the valleys of Northern and central California on Sunday, heat will quickly expand by Monday. By early week, summerlike heat will have a grip over the Pacific Northwest, much of Nevada and California.

AccuWeather forecasters say temperatures will trend 15 to 25 degrees above normal each day into at least midweek.

Excessive heat warnings have already been issued for parts of the area, namely California's Sacramento and San Joaquin valleys. As early as Sunday afternoon, temperatures can flirt with the triple-digit mark for the first time this year in cities like Redding and Sacramento, Calif.

The heat will increase for these valley cities come Monday, as both locations are forecast to top out in the low 100s and break daily high temperature records. The average first reading of 100 degrees or more in Redding occurs in the first week of June, while Sacramento usually hangs on until the second week of June.

On Monday, high temperatures in the Pacific Northwest will range from the 60s and 70s at the immediate coast, to 80s and 90s east of the Cascades. Similarly in California, the immediate coastline will remain around normal while temperatures soar inland. Much of inland California will be in the 80s and 90s with valleys reaching into the 100s.

Anyone participating in outdoor Memorial Day celebrations will need to account for the heat by staying hydrated, wearing light-colored clothing and applying plenty of sunscreen.

The heat will continue to build on Tuesday. Highs in the 90s will be widespread for inland areas of the Pacific Northwest and California, while 80s and 90s will be common across Nevada and Idaho. Another day of triple-digit heat is in store for the valleys of California.

On Tuesday, Medford, Ore., is forecast to climb into the low 100s and break the record high for the date of 100 degrees set back in 1986. Not only is Tuesday's forecast high in the city about 25 degrees above average, Medford does not typically experience its first triple-digit heat day until Independence Day.

With such a prolonged bout of summerlike heat, cooling demands will skyrocket as temperatures soar. An increased cooling demand can place a strain on the power grid and residents' wallets alike. Rolling blackouts are not out of the question as millions try to beat the heat.

In addition to increased cooling demands, the record-challenging temperatures, low humidity levels and persistent drought conditions across the West can lead to an increased risk for wildfire start and spread.

Drought conditions across the West as of Thursday, May, 27, 2021. (U.S. Drought Monitor)

A majority of California is still in the midst of extreme drought, so any fuels such as grass or brush are very dry. Any spark could lead to a wildfire, so those celebrating during Memorial Day weekend should take extra precautions to prevent any raging infernos.

AccuWeather forecasters say temperatures will begin to moderate later in the week as a storm tracks into the Northwest. However, not everyone will feel the full relief from heat, as temperatures are forecast to remain above average for portions of the Southwest into the start of June.