Heat — Cascades of Pierce and Lewis Counties, Washington

2021-08-11 to 2021-08-14 · Cascades of Pierce and Lewis Counties, Washington

Event narrative

A stretch of unusually warm weather affected the valleys and lower elevations of the Cascades of Lewis and Pierce Counties. Temperature recordings at Longmire at Mount Rainier National Park showed temperatures ranging from the mid 80s to upper 90s through the event, with record high temperatures of 98 degrees set on August 13 and August 14. Low temperatures ranged from the mid to upper 50s.

Cedar Lake also recorded temperatures in the mid to upper 80s, with a record high of 87 on August 14.

Wider weather episode

A strong upper level ridge of high pressure began to build into the region around August 11, remaining in place through August 13 before pushing eastward. As the upper level ridge influence increased over the region, the lower level flow turned easterly, creating a downsloping effect across much of Western Washington. As a result of this setup, very warm temperatures were forecast for most of the area, with 850mb temperatures expected to peak near 25C during the heart of the event, with surface temperatures ranging from the mid 80s to near 100 and low temperatures during the overnight period ranging from the mid 60s to low 70s.

Excessive Heat Watch was issued on August 8, several days prior to the event, valid for all included zones beginning 12PM on Wednesday August 11 and continuing for some zones through Friday August 13 at 8PM and others Saturday August 14 at 7PM. The Watch was upgraded to a warning during the afternoon of August 10.

Fire weather was also a concern during the event, along with air quality impacts from smoke, however, no major impacts were noted during the period of unusually warm weather.

Source: NOAA Storm Events Database, event_id 982385. Narrative written by the NWS forecast office that issued the report.