PORTLAND, Oregon — Portland is partway through a series of days with triple-digit temperatures, and the forecast prompted questions last week about whether Multnomah County planned to open cooling shelters. In the days leading up to the heat wave, county officials said that they were making plans to open cooling centers if thresholds were met, and they confirmed Sunday afternoon that they would do so.
But what are those thresholds? Heat wave conditions can vary, both in terms of the maximum daytime temperature and other factors like nighttime lows, humidity and overall duration of the wave.
The June 2021 heat dome shattered records for the highest temperatures Portland had ever seen, but it was relatively brief; temperatures only stayed above 90 degrees for a total of five days. Another heat wave in July 2022 only briefly topped 100 degrees, but it stuck around and became Portland's third-longest string of days above 90 degrees.
So how does the county weigh those factors and make a cooling shelter decision? Is there a unified measurement for opening shelters, or is it a judgement call based on looking at all the factors?
THE QUESTION
Is there a specific threshold that Multnomah County uses to open cooling shelters?
THE SOURCES
THE ANSWER
Yes, there is one specific measurement: If the Portland region hits the highest level on the National Weather Service's HeatRisk assessment, the county will always open shelters. The county will also consider opening cooling centers at the second-highest level, but it will depend on additional factors.
WHAT WE FOUND
First, an important clarification: Multnomah County defines "cooling center" and "cooling shelter" differently; they both feature air conditioning, water, food, support services and cooling resources, but centers are only open during the day. Shelters operate at all hours.
During milder heat events, the county might direct people to existing facilities like libraries where there's air conditioning. Bigger heat events will prompt the opening of official cooling centers, which are equipped to offer food and other resources, and severe events will require 24-hour shelters.
The National Weather Service's HeatRisk tool is an online map that color-codes the entire United States based on heat risk for each day of the coming week, using a scale that examines multiple factors such as the duration of the heat, the daytime and nighttime temperatures and how unusual the heat level is for the region at the current time of year.
The scale has five levels, each with its own number and color. Level 0 (Green) means little or no heat risk, Level 2 (Yellow) means minor heat risk and Level 3 (Orange) means moderate heat risk. At levels 1 and 2, the heat is most likely to impact people who are more sensitive to heat.
Level 3 (Red) means major heat risk, where anyone without adequate cooling and hydration will be impacted. Level 4 (Magenta) means extreme heat risk, which the National Weather Service defines as a rare or long-duration heat wave where there will be little or no overnight relief.
According to Multnomah County's webpage, the county will begin making plans and doing heat-related outreach operations at levels 1 and 2. At Level 3, county leaders will consider opening formal cooling centers or shelters. At Level 4, it's no longer a maybe — the county will open 24-hour shelters.
As of Friday, the forecast shows Portland and much of the Willamette Valley at Level 3 from Sunday through Wednesday next week, with pockets of Level 4 in the valley, particularly on Monday.