Hot weather in mid-July is hardly a surprise in Baker County, Jay Breidenbach points out.
This is, after all, statistically the county’s hottest month.
The daily record high temperature is 100 or above on 19 of July’s 31 days — the most of any month.
But Breidenbach, who is a meteorologist, concedes there’s nothing typical about the spell of hot weather that started with the summer solstice nearly a month ago.
“Normally it’s hot in the summertime, of course,” said Breidenbach, the warning coordination meteorologist at the National Weather Service’s Boise office, which handles forecasts for Baker County.
“What is not typical is the duration of this pattern.”
Here’s a few statistics to put into perspective Breidenbach’s point about the persistence of heat so far this summer.
• The last day the temperature at the Baker City Airport didn’t reach at least 83 degrees was June 16.
• Over the next 32 days — June 17 through July 18 — the temperature at the airport topped 90 on 22 days. That’s just below the average of about 24 such days — for the entire year — recorded between 1943 and 2012.
• The temperature surpassed 90 degrees on 19 of 20 days, June 26 through July 15. On the only exception, July 7, the high was 89 degrees. That snapped a streak of 11 straight 90-degree-plus days, the longest stretch in almost four years and the sixth-longest in at least the past half century.
That single degree prevented what would have been a record-setting stretch of 20 straight days with a high of 90 or hotter. The record at the airport is 16 days, set in 1994 and tied in 2017. Both of those hot spells spanned late July and early August.
The city enjoyed a respite over the first part of Miners Jubilee weekend, but it was of the modest variety — the high temperature was 88 degrees on both Friday, July 16 and Saturday, July 17.
The minor cooling trend was aided in part by smoke from the Bootleg fire in Klamath and Lake counties, which grew to more than 304,000 acres on Sunday, July 18. Smoke reflects sunlight and, if it’s thick enough, can reduce surface temperatures from what they would otherwise be.
The interlude was brief, though — Sunday’s high temperature was 94.
• The average high temperature for the first 18 days of July was 93.8 degrees. The month is on pace to be the hottest on record at the airport, and by a fair margin.
The month with the highest average high temperature is July 1985, when the average was 92.0.
The blame for this extended stretch of stifling days — or the credit, depending on your tolerance for heat — is what meteorologists call the “Four Corners High.”
This is an area of high pressure in the atmosphere, Breidenbach said.
A ridge of high pressure isn’t comparable, physically, to a mountain ridge, which is a spine of higher ground that typically separates two valleys.
Ridge, when used to describe high pressure, means an elongated area, sometimes extending for hundreds of miles, where the air pressure (measured by a barometer) is relatively high, which causes the air to sink.
When air descends it compresses and warms. Because warmer air can hold more moisture without the moisture condensing into clouds or precipitation, high pressure usually results in dry weather.
And in summer, when the sun angle is high, hot weather.
The Four Corners High, as its name suggests, frequently is centered during summer near where New Mexico, Arizona, Utah and Colorado meet.
But the ridge sometimes sprawls across much of the West, spreading far enough to the north and west to influence, and for periods to dominate, the weather in Eastern Oregon and Idaho, Breidenbach said.
High-pressure ridges do act something like their geologic namesakes in one sense — just as a mountain ridge can divert clouds, a high-pressure ridge has a similar effect on storms that sweep inland from the Pacific Ocean.
Although those storms rarely bring much rain, if any, to Eastern Oregon during summer, Breidenbach said it’s common for cold fronts to shove the Four Corners High back to the south every week or so.
Although these are technically cold fronts — the boundary between two air masses of distinctly different temperatures — meteorologists sometimes call the summer versions “cool” fronts to reflect that although they usher in cooler air, temperatures in the 80s rather than the 90s hardly qualify as “cold.”
But since the middle of June, the Four Corners High has shunted aside every front — cold or cool — that has initially threatened to move far inland.
“We really haven’t had any significant cold fronts move through to give us a break,” Breidenbach said.
Nonetheless, Baker County has fared better than much of the rest of the region, due in part to its relatively high elevation — Baker City is about 3,440 feet above sea level.
Breidenbach noted that in the last week of June, when the high-pressure ridge grew to possibly unprecedented proportions, extending as far as northern Canada, Salem posted a nearly unthinkable high of 117 degrees, while Portland reached 116. Both temperatures eclipsed the respective cities’ previous all-time records — set in August, not June — by nine degrees.
These stunning temperatures were due in part to air descending from the Cascade Mountains into the Willamette Valley, most of which is just a couple hundred feet above sea level, the descent causing already hot air to gain yet more degrees, Breidenbach said.
Pendleton, Hermiston and other cities in the Columbia Basin in both Oregon and Washington also had temperatures above 115 degrees in late June.
Baker City, by contrast, has so far topped out at 103 degrees, on June 29. That was the hottest temperature ever recorded during June at the airport.