WeatherWatcher: Excessive Heat Warning in effect until 11pm PDT Wednesday night

Tuesday, August 15, 2023

Sunny day at Richmond Beach, Shoreline.
Photo by Carl Dinse
The National Weather Service in Seattle has issued a Excessive Heat Warning for the greater Seattle area including the cities of Shoreline and Lake Forest Park. 

From the National Weather Service:
  • What: Dangerously hot conditions with daytime temperatures in the low to mid 90s and lows in the 60s and 70s expected. This will pose a major risk of heat-related illness.
  • Where: Bellevue and Vicinity and Seattle and Vicinity. 
  • When: Until 11 PM PDT Wednesday. 
  • Impacts: Major Heat Risk level poses a major risk for heat- related illnesses for anyone without effective cooling or adequate hydration.  

Forecast: We will be in a heatwave through the end of the week, the worst of it though is expected Tuesday and Wednesday. High temperatures could get into the low to mid 90's both days. What is going to make us uncomfortable are the nighttime lows, in the 70's and upper 60's.

Once we get through Wednesday, things will start a slow trend into a cooler pattern. Thursday and Friday highs are expected to come down into the low to mid 80's. 

Then, Saturday and Sunday we cool down enough to keep high temperatures in the 70's. By the weekend our overnight low temperatures will come back down into the upper 50's.

Currently there is no significant rainmaker in sight, however there are some models indicating that we might see some dry thunderstorm activity over the mountains this coming weekend. Most of the activity stays down in Oregon but the Cascade Mountain range right now is under a red flag warning. 

A red flag warning means that conditions are causing extreme fire danger. The criteria for a red flag warning is a relative humidity 15% or below, in combination with sustained or frequently gusting winds above 25mph. Both conditions have to be occurring for at least 3 hours out of a 12-hour period to issue a red flag warning.

I've been asked why the Puget Sound lowlands area, including Shoreline and Lake Forest Park, are not under a red flag warning. We don't have the consistently strong enough winds or a low enough relative humidity right now. This does not mean that fire danger isn't high, as we still have a lot of dry fuels around which is typical of late July and August in our region.

Relative humidity has been in the 40-50% area so far during this heatwave, which is a little more humid than normal, and winds have been calm, with the biggest gusts averaging around 15-18mph.

For current weather conditions visit


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