Heat — San Juan, Washington

2021-06-26 to 2021-06-29 · San Juan, Washington

Event narrative

An extended period of hot weather affected the San Juan Islands at the end of June. The ASOS at Friday Harbor recorded high temperatures in the mid 90s from 6/26-6/28 before temperatures finally began to cool on 6/29.

Wider weather episode

A 600dm ridge of high pressure centered over the Desert Southwest in mid-June retrograded over to the West Coast/East-Central Pacific Ocean by the start of the 3rd week of June. The pattern began to amplify on June 20th, with the ridge axis building along the West Coast, coinciding with a large area of low pressure deepening over Hudson Bay to the east. This feature, along with deepening low pressure over the Gulf of Alaska were the primary factors in the omega block setting up off the Pacific Northwest Coast by the end of the week. The strength of the Hudson Bay vortex kept the 600dm ridge high centered over the Pacific Northwest for nearly a week, yielding record breaking temperatures (multiple days of over 100 degree temperatures in a row with low temperatures resembling the average high temperatures for the time of year).

The record-breaking heat from this anomalous pattern led to multiple heat-related fatalities (heat stroke and heat stress) across Western Washington is also expected to be related to numerous drownings across the area, largely in part due to hypothermia as people sought reprieve from the heat in local area lakes and large bodies of water. In addition, several brush fires were also ignited due to dry fuels present amidst hot temperatures. All fires were contained without major impacts.

Source: NOAA Storm Events Database, event_id 969670. Narrative written by the NWS forecast office that issued the report.