Storm to bring needed rain to part of western US while elevating fire danger in others

Renee Duff

A Pacific storm will bring both good and bad news to the western United States, depending on where you're located.

A deep dip in the jet stream in the West will lead to a cooler stretch of weather along with the threat for rain this week, according to AccuWeather Senior Meteorologist and western U.S. blogger Brian Thompson.

Pockets of rain from Northern California to Washington and western Montana from a storm on Sunday was a signal of this cooler, wetter pattern beginning to take shape.

A plethora of clouds are seen on satellite across the West on Sunday, May 17, 2020, indicative of the unsettled pattern moving into the area. (CIRA/RAMMB)

"The heaviest area of rain through Tuesday is forecast to be in southwest Oregon and far Northern California, which is where the rain is needed the most," Thompson said.

These areas are suffering amid severe to extreme drought conditions, according to the latest outlook released on Thursday, May 14, by the United States Drought Monitor. Elsewhere in the West, drought conditions ranging from moderate to extreme stretch from southern Colorado and northern New Mexico to California's Central Valley and the eastern slopes of the Cascades.

Through the first half the week, a general 1-2 inches of rainfall is forecast across the Northwest and Northern California, with lesser amounts in the valley regions and higher amounts up to 3-4 inches in the mountains.

Several inches of snow and slippery travel will be possible across the highest peaks into Tuesday, including Interstate 80's Donner Pass in California.

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On Tuesday, the threat for showers and thunderstorms will shift eastward into western Montana, Idaho and Nevada. Some thunderstorms in western Montana can be severe, bringing strong wind gusts and large hail.

Even west and south, from Idaho into northern Nevada, some storms can contain small hail.

The storm will essentially run into a roadblock in the atmosphere, causing it to slow down and pivot north and westward from Tuesday through Wednesday. A non-tropical storm in the East and a large high pressure area from the northern Plains to the Northeast are contributing to this traffic jam in the atmosphere, known as a Rex block.

Typically, storms systems move along from west-to-east across the U.S. at fairly decent pace when the jet stream is not in a convoluted pattern such as its current state.

The slowed movement of the storm could lead to an extended period of soaking rainfall and perhaps a localized flooding risk across part of the interior Northwest from Tuesday through Wednesday.

The jammed up pattern will lead to unsettled weather lasting through the end of the week across the Northwest with rounds of rain and high-elevation snow showers.

"South of where the rain is, the wind will kick up across the Southwest early this week, elevating the fire danger in some areas through Tuesday," Thompson said.

Fire and wind advisories were already in effect from California to Colorado at the end of the weekend.

Fire and wind advisories in effect in the Four Corners region as of Tuesday, May 17, 2020. (AccuWeather)

The combination of strong winds, low humidity and dry weather will contribute to an enhanced risk of rapid ignition, growth and spread of fires. Use of campfires and agricultural burning is discouraged in the pattern. Cigarettes should also be properly discarded.

Wind gusts are likely to frequent 30-40 mph across the Southwest into Tuesday, with locally higher gusts possible.

"We are now firmly in fire season across the Desert Southwest, so we'll have to keep an eye on this area over the next couple of months until the monsoon season starts to kick in," Thompson added.

While there was an uptick in warmth with the gusty winds through Monday, as temperatures in Phoenix returned to the triple digits, the warmup will be brief, with temperatures expected to be trimmed on Tuesday.

"After a pretty toasty first half of May, temperatures will largely hover closer to, and even below average heading into Memorial Day weekend," Thompson said.

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