The western US faces opposite extremes of weather this week

Just about everything possible in the realm of weather will be happening in the West this week, except maybe snow.

The June gloom will keep the weather cool on the southern California coast as thunderstorms break out from inland California to the Rocky Mountains. Meanwhile, early-season heat will pick up in the Northwest, AccuWeather forecasters say.

A flow of moisture from the Pacific Ocean, known as a marine layer, will persist along the southern California coast, including the Los Angeles and San Diego metropolitan areas.

“This general pattern is common during June, but this one is a little stronger than average,” AccuWeather’s chief on-air meteorologist Bernie Rayno said. As the sun warms the interior of the southwestern US, the air rises, creating a vacuum effect. Air then flows in from the Pacific to replace the rising air over the southwest.

“The process creates a layer of low clouds, mist and drizzle along the coast, which can extend miles inland,” Rayno explained. “Hence the term ‘June blues’.” In some cases, people in coastal areas may not see the sun for days. In others, it can take until the afternoon hours for low clouds to erode enough to allow the sun to shine through.

The persistent breeze from the cold ocean will suppress the high temperatures along the coast. For example, the highs in downtown Los Angeles will range only from the upper 60s to the lower 70s this week. The all-time average high is in the low 70s in early June for the Los Angeles area.

Farther north, much of Washington, Oregon and even parts of Northern California will not have to deal with a flow of cool, humid air from the Pacific, quite the opposite in the middle of the week.

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In this area a breeze will blow in the opposite direction to that of Southern California. As air flows from the interior of the US toward the coast, air coming down from the Rocky Mountains will warm eastern Washington and Oregon. As the air descends from the Cascades, it will warm coastal areas from Washington to northern California.

For example, the highs will be in the 80s and upper 80s in Spokane, Washington, through Thursday, compared to the all-time average high in the lower 70s. Similarly, in Portland, Oregon, temperatures will climb into the upper 80s and lower 90s through at least Wednesday.

As a storm close to the level of the atmosphere’s jet stream moves north later this week, thunderstorms with little or no rain can spark lightning-induced wildfires in parts of the Northwest.

“Due to a lack of storms with heavy rain this spring, coastal areas of Washington and Oregon are trending abnormally dry, and it’s getting worse,” AccuWeather meteorologist Brandon Buckingham said. There is also a large area of ​​moderate to severe drought in inland Oregon.

“Conditions may tend to get wetter towards mid-June as some storms move in from the Pacific,” Buckingham said.

As long as the upper-level storm doesn’t break up by later this week, more general shower and thunderstorm activity may begin to moisten isolated parts of the Northwest.

As the upper level storm approaches from the Pacific and sits over the southwestern states for a while this week, it will bring a significant increase in thunderstorm activity to the region.

“With the center of the storm in Southern California through Tuesday, southeasterly winds will bring thunderstorms over the Sierra Nevada Mountains moving down the foothills into the San Joaquin Valley,” Buckingham said.

A combination of moisture pumped in from the Pacific and wind shear produced by the storm will unleash severe thunderstorms in parts of inland California Tuesday afternoon and evening. Wind shear is the change in wind speed or direction with altitude, and it can cause storms to turn and become severe.

“In addition to the Sierra Nevada facing a risk of hail, flash flooding and damaging winds, places like Redding, California could also experience similar conditions,” Buckingham said. “The potential for severe thunderstorms can also extend along much of the Interstate 80 corridor to Sacramento, California, and into Reno and Elko, Nevada.”

Rain during June tends to be fairly sparse over much of California, with winter storm impacts in the rear view, and impacts from the North American monsoon not usually in full swing.

With rain being a rarity in California during the month of June, there is a chance some cities could count a month’s worth of rainfall in a matter of hours early this week. The historic average June rainfall for Sacramento is 0.23 of an inch, while Lake Tahoe, California tends to pick up 0.55 of an inch this month.

Fresno, California, as well as Salt Lake City, are likely to experience one or more thunderstorms this week. A thunderstorm could even amble near Las Vegas or Phoenix as the pattern sets in. Meanwhile, rain showers can drench San Francisco on multiple occasions.

The same storm will help pump more moisture over the interior west with broader coverage of showers and thunderstorms in parts of the region compared to recent weeks.

With spring thaw in the western highlands underway, the additional potential for torrential downpours in the Rocky Mountains and intermountain region could further increase elevated stream levels this week. Experts recommend extra caution when venturing into canyons and along streams in the region, as downpours miles upriver can cause rapid rising water or flash flooding.

Any snowfall in the west this week will be confined to the region’s highest peaks, where few people venture.

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