August Was Portland’s Hottest Month Ever

The key factor: warm nights.

This August was the hottest month in Portland history, says the National Weather Service.

The NWS announced this morning that the average temperature over those 30 days was 75.1 degrees, breaking the previous record: 74.1 in July 1985.

Jon Bumgardner, a meteorologist in the NWS’s Portland office, says the finding is inexact: It doesn’t include the temperature at any given hour over the full month. Instead, it’s “basically the high plus the low divided by two,” Bumgardner says. “And that’s computed for each day.”

The record follows a July that saw highs of 95 or above for a full week—the first time that’s ever happened in Portland. The city saw two more heat waves in August, both of them elevating overnight lows above 60 degrees for several consecutive nights. It’s those sultry nights that secured the record, Bumgardner tells WW.

“To have 75 as the actual average temperature is pretty amazing because usually we cool off into the 50s at night,” he says. “It makes me wonder if whether a small factor in that could be the growth of the urban heat island as Portland’s population continues to increase.”

He’s referring to the “arc of heat” that runs across the east side of the city—swaths of concrete slab that at night release heat baked in during the day. Such heat islands can be deadly—and are the part of the built environment where Portland City Hall can most effectively cut into the local impacts of climate change.

As Portland continues to suffer from extraordinary homicide and traffic death rates, it’s worth considering this, too: Academics have long tried to draw a link between heat and violence, though the causation has never been conclusively established.

Be thankful for one mercy: Portland and the rest of the Willamette Valley are spared from the brutal heat dome that has settled over California this week.