Heat Dome Breaking Northwest Records Began With Rain in China

(Bloomberg) -- Heavy rain in China, an expanse of warm water stretching across the North Pacific and kinks in the jet stream are combining to drive an unusual heat wave that will set records in the Pacific Northwest.

Seattle and Portland may post their hottest June days in history, while heat warnings are posted in Canada as far north as the Arctic Circle. The dangerously hot temperatures raise wildfire risk, may worsen air pollution and pose public health threats in a region where many don’t have air conditioning.

The heat is building under a so-called heat dome that’s likely been exacerbated by climate change. It’s similar to the weather pattern earlier this month that led to a California heat wave, according to Jeff Masters, a meteorologists with Yale Climate Connections. Kinks in the jet stream have pinned summer weather in place leading to prolonged heat waves and drought, as well as storminess and flooding.

“The unusual waviness of the jet stream was associated with a pattern we have been seeing more often in summer, which has been connected to human-caused climate change,” Masters said.

The current heat wave over the Northwest started with flooding rains across China on June 23, said Masters. That fed energy into the jet stream across the North Pacific making it stronger than usual, setting off a chain reaction of weather patterns that led to the high pressure ridge building over western North America and driving temperatures up in the U.S. and Canada.

The heat, as well as the conditions that have caused widespread drought across the U.S. West, may have been made worse by warm water stretching across the North Pacific, as well as parts of the Bering and Chukchi seas near Alaska, said Jennifer Francis, a senior scientist at the Woodwell Climate Center. That pattern may have been exacerbated by less sea ice in the Arctic this year, a situation made worse in recent decades by climate change.

The worst heat will center on the Northwest and then seep east into Idaho by Monday, though California will also see oppressive conditions. The Golden State’s power grid manager said it’s closely watching the situation. Excessive heat watches cover areas east of Los Angeles, where temperatures could reach 110 degrees Fahrenheit (43 Celsius) Sunday and Monday, and other parts of the state.

Seattle on Sunday could reach 103 degrees, tying its all-time hottest reading and breaking the 96-degree mark for its warmest June day, said Bob Oravec, a senior branch forecaster at the U.S. Weather Prediction Center. Portland could also tie its record high of 107 on Saturday, with other parts of the region hitting unprecedented levels.

“For the whole Northwest through the entire week temperatures are running 25 to 30 degrees above average in some places,” Oravec said. “It’s pretty amazing.”

The extreme weather just days after the official start of summer signals threats may intensify through the season and challenge officials struggling to deal with growing heat, drought and wildfire risks. Electric grids across the West are forecast to be strained in coming months as hot weather sends power demand surging and drought leaves less water in hydropower reservoirs. California has already had its first threat of supply shortages, less than a year after the first rolling blackouts in two decades.

Read more: Drought Indicators Across Western U.S. Warn of the ‘Big One’

The drought across the West will make this weekend’s heat even hotter because the sun’s energy will go mainly into raising temperatures rather than evaporating moisture in the soil, said Bob Henson, a meteorologist and author of The Thinking Person’s Guide to Climate Change. Overnight lows are forecast to remain in the low 70s in Seattle, also a record.

“Heat is really going to accumulate in people’s houses,” Henson said.

Adding to Seattle’s discomfort, just 44% of homes there have air conditioning, the least among the top 15 U.S. metropolitan areas, according to data from the Census Bureau’s 2019 American Housing Survey.

The highs in the Northwest could stress California’s supplies as states often trade electricity across borders. Drought across the West is also taxing its reliance on hydro-electric power.

Portland General Electric Co., which provides power to Oregon’s largest city and surrounding areas, is encouraging customers to conserve even though it expects to have adequate supplies to meet higher demand, according to spokesperson Andrea Platt.

The Columbia nuclear power plant in Washington, which provides enough power for about 1 million homes, is back in service after shutting down for a scheduled refueling . And hydro facilities are at higher summer output levels after a spring spill operation to help fish migrate, according to the Bonneville Power Administration.

Meanwhile, U.S. natural gas futures on Friday headed for their biggest weekly advance since February as hot weather in northwestern states is expected to boost demand for cooling.

California power supplies will be strained most of the summer, said Barbara Clemenhagen, vice president of market intelligence at consulting firm Customized Energy Solutions and a former board member at the Electric Reliability Council of Texas, the grid manager in that state.

“If these temperatures persist through summer, conditions are going to be very tight,” she said.

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