ACCUWEATHER GLOBAL WEATHER CENTER – AccuWeather reports  after a week of relentless heat across the West, a much-needed cooldown is on the horizon.

A trough of low pressure is expected to dive into the western half of the United States this week sending a much-cooler air mass into the region, one that will drop high temperatures 5 to 10 degrees Fahrenheit in most places when compared to this past week.

While temperatures will end the weekend on a warm note, the majority of the West will experience some form of cooldown by the middle of this week.

“Cooler weather will spread south across the West through Tuesday,” AccuWeather Meteorologist Alyson Hoegg said.

Folks in Seattle; Sacramento; Los Angeles; San Diego; Boise, Idaho; Missoula, Montana; Salt Lake City; and areas in between will all see a temperature drop through Wednesday.

“Cities along the I-5 corridor, such as Seattle, Portland, and Medford, Oregon, will see daytime highs similar to those of mid-October,” Hoegg said.

California, devastated with wildfires, will get some relief. Thermometers that read in the 100s across the Central Valley are expected to read in the lower 80s, certainly a noticeable and welcome change.

Last week and this week will have quite the contrast in the West, with temperatures dipping below average for the first time since the beginning of September in some locations.

Exceptional drought and the recent stretch of scorching heat has caused problems, including turning California into a tinder box. 

Many fires are currently raging across the state, including the Butte fire, which exploded in growth early on Friday, and the Valley fire, which began on Saturday afternoon.

The Valley Fire began on Saturday afternoon and had burned 62,000 acres and 10-percent contained by Monday night. Mandatory evacuations were in place for parts of Napa and Lake counties.

Four firefighters were sent to the hospital Saturday with second-degree burns, according to Cal Fire.

According to the USDA Forest Service, 40 large fires are currently burning across the West. Five states are dealing with these dangerous blazes and they include California, Washington, Oregon, Idaho, and Montana.

The Rough fire east of Fresno is threatening to sweep through an ancient grove of Giant Sequoia trees, according to the Associated Press. This lightning-caused fire is only at 36 percent containment as of late Sunday as firefighters rush to get it under control.

While the weekend will end warm, the drop in temperature this week will help firefighters battling the blaze in some ways, but also could hurt efforts in other ways. 

The unsettled weather may bring some rain to parts of the West, although thunderstorms could cause more wildfire problems due to lightning.

“Anytime a cold front pushes through the west during the fire season, problems ensue,” AccuWeather Meteorologist and firefighter Evan Duffey said.

Duffey noted that cold fronts usually bring stronger and sometimes unpredictable winds that could rapidly spread fire, making it hard for incident managers to position teams.

Jordan Root is a meteorologist for www.AccuWeather.com .