Summertime heat is set to build across the West as a gradual shift in the weather pattern occurs the week of Aug. 15. Forecasters say temperatures will climb steadily between 10 and 18 degrees Fahrenheit above average in the upcoming days in Portland, as well as Medford and Seattle.
"Much like recent hot stretches, this will be caused by a large bulge in the jet stream, acting to keep the storm track lifted north and allowing temperatures to surge in the coming days," said Andrew Johnson-Levine, AccuWeather meteorologist.
Temperatures are expected to peak around midweek across many locations in Oregon, north-central California and Nevada, before gradually sinking closer to average. Farther north into Washington state, the heat likely will persist into the weekend.
Meteorologists say the upper-level pattern across the country's eastern half will play a prominent role in how many days the heat lingers over the West.
"The dip in the jet stream and cooler temperatures in the eastern (United States) will act as a roadblock in the atmosphere, which should keep the hot conditions around the West for much of the week," Johnson-Levine said.
The hottest regions outside Central California are likely to be the Willamette Valley, Southern Oregon and areas east of the Washington Cascades. By Wednesday, Aug. 17, temperatures are forecast to climb to near or over 100 Fahrenheit across most of these locations. Hot conditions will retreat slowly from the Willamette Valley on Thursday, Aug. 18, but will continue to grip areas such as Medford and Kennewick, Washington, through late week.
The influx of hot weather will expand across Northwest states Oregon, Washington, Idaho and Montana. The heat also will grip portions of Central California and Nevada throughout the week.
An expansive swath of excessive heat watches have been issued from north-central California through the San Joaquin Valley. The watches cover numerous counties through the latter half of the week and span from Redding to Bakersfield, California.
Outdoor plans and activities may need to be altered as the hot conditions set in across the West to limit the risk of heat-induced illnesses. Residents are urged to drink plenty of water and utilize air conditioning if it is available. For those without access to air conditioning, experts recommend wearing breathable, light-colored fabrics and cold washrags on the neck and wrists.
Although the peak of the heat is expected around midweek, conditions likely will remain hot through at least the weekend. An uptick in rainfall chances may provide some relief to the Northwest by the start of the week of Aug. 22.
Wildfires have peppered the dry Northwest landscape over the last couple of weeks. The most expansive fire still ongoing is the Moose Fire in central Idaho. As of early Monday, Aug. 15, the Moose Fire had burned more than 78,000 acres and was at 34% containment.
The Significant Wildland Fire Potential Outlook for August, projected by the National Interagency Fire Center, depicts that portions of Oregon, central and eastern Washington, Idaho, Montana and California will face a higher-than-average wildfire risk.
Alyssa Smithmyer is a meteorologist with AccuWeather.
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