SEATTLE — Much of western Washington has been under a Heat Advisory since last week and will remain so until Tuesday night when higher-than-average temperatures are expected to begin leveling off.
But what is a Heat Advisory, exactly? And when would the National Weather Service (NWS) issue one?
A Heat Advisory is issued when high temperatures create a moderate to major risk of heat-related illness in the impacted area. The threshold for a Heat Advisory is different for each region, dependent on what the average temperatures are and how long temperatures are expected to remain elevated.
"How unusual is it for this time of year to see temperatures as high as they can be?" said Jeff Michalski with the NWS. "It's also using the overnight low - will we see any cooling?"
Western Washington's current heat wave presents a period of higher-than-normal temperatures for this time of year over a prolonged period, which people in this region are likely unprepared for, Michalski said. The normal temperature for this time of year is a high of 75 degrees and a low of 56. More recently temperatures have been in the 90s, with lows in the 60s, leaving little opportunity for people to cool off at night.
Michalski said the NWS uses that average temperature data, then cross-references it with data from the Centers for Disease Control to see what conditions present elevated risks of heat-related impacts for a given population.
Heat-related impacts can be especially felt in urban areas where there is more concrete and less green space. Researchers have found that paved roads, parking lots and buildings absorb and retain heat, radiating it back into the air. In some cases, neighborhoods in a highly developed city can experience temperatures 15-20 degrees hotter than a less developed neighborhood.
"If we're just living in the cities with a lot of concrete, you're not seeing that cooling at night as you would in those country areas, or areas outside the city," Michalski said.
An area with more trees and vegetation would get the added benefit of shade and cooling, as they absorb water through their roots and cool their surroundings by releasing water vapor into the air through their leaves, according to the Environmental Protection Agency.
During a Heat Advisory, people are encouraged to take extra precautions to avoid heat-related illness, especially if they work outside, are particularly sensitive to heat or do not have access to adequate cooling or hydration. Drink plenty of fluids, stay in air-conditioned rooms, stay out of the sun, and check on relatives and neighbors. Young children and pets should never be left unattended in vehicles.
KING 5's Drew Andre contributed to this report.