Significant Heat Wave Ahead

FastCast—Tuesday, July 26 to Friday, July 29:

The_Weatherman2 Weather Blog is up and running again, as I have returned from 2 weeks of travel around the Western US! A significant heat wave (not like June 2021) lies ahead for the Pacific Northwest. It is likely that there will be 4 consecutive days above 90 degrees for most of Western Washington (except the coast, mountains, and areas very close to Puget Sound). Expect Western Washington highs to be in the mid to upper 90s on Tuesday and Wednesday and in the low to mid 90s on Thursday and Friday. Temperatures will be enhanced by high dewpoints, bringing feels like temperatures in the mid to upper 90s and possibly into the low 100s for isolated areas closer to the mountains. Nighttime lows will drop into the low to mid 60s, bringing some relief, but not much. Eastern Washington will be scorching, with record-breaking temperatures possible on Thursday and Friday. Expect highs there to be in the mid 90s to low 110s, with peak heat in the Lower Columbia Basin later in the week, where highs may reach dangerously hot levels of 110-115 degrees. Heat Advisories and Excessive Heat Warnings have been issued for most of the Pacific Northwest as of Monday evening. Stay tuned for updates as this heat wave continues, and call 2-1-1 for information about local cooling shelters.

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Continue reading the full blog below!

I am back to blogging after 2 weeks traveling around the Western US, and it appears that the hot weather I experienced outside of Washington will be returning with me. 

A significant heat wave (not like June 2021) will impact most of the Pacific Northwest through the rest of the week. While temperatures will be 5-10 degrees cooler than June 2021, the main impact of this heat wave will be its duration. Most locations (except away from the water and in the mountains) in Western Washington will have highs above 85 degrees through Sunday.

Let’s begin with Tuesday’s highs from the high resolution NAM model.

Expect lowland highs in the low to mid 90s, and in the mid to upper 90s away from the water. The coast will reach the mid 70s to low 80s, except in the upper 60s to low 70s at the ocean beaches. SW WA, the Willamette Valley, and Eastern Washington will reach the mid 90s to mid 100s. 

However, despite the temperatures shown on the map above, it will actually feel hotter. This is due to higher than normal dewpoints and in turn, higher humidity. Take a look at dewpoints on Tuesday afternoon (below).

For Western Washington, normal dewpoints are in the 50s at this time of year. As you can see, Tuesday will be much different, with dewpoints reaching the mid 60s to mid 70s. These high dewpoints will cause an increased heat index value. The heat index is basically the summer equivalent of the wind chill measurement used in winter. It measures the actual “feels-like” temperature outside, factoring in humidity and dewpoints.

Tuesday afternoon’s heat index is quite hot for the entire state. Expect heat index values in the lowlands to reach the upper 80s to low 90s near the water and the mid to upper 90s away from the water. Areas in the Cascade Foothills, SW WA, the Willamette Valley, and Eastern Washington will have heat indices in the upper 90s to low 100s.

The NWS has combined all of these factors into the NWS HeatRisk forecast. I will be including this forecast during the heat wave. The Tuesday forecast is seen below.

To understand what these colors mean, see below.

The key takeaway from this is that Tuesday will be dangerous for most of the lowlands’ population to be outside. (Note that colors on the map are different than colors in the description above due to a change to help the colorblind read the HeatRisk better)

The overall situation is nearly identical on Wednesday, as seen in the highs below from the NAM model.

Temperatures are nearly identical in the Lowlands, but cooler on the coast and hotter in Eastern Washington.

Dewpoints will again be abnormally high, as seen below.

Expect dewpoints to be slightly higher on Wednesday than Tuesday, bringing higher heat indices for the region, seen below.

Expect feels-like values on Wednesday to reach the low to mid 90s around the lowlands, and the mid to upper 90s in the foothills and away from the water. SW WA, the Willamette Valley, and Eastern Washington will have heat indices in the upper 90s to mid 100s.

This is reflected in the HeatRisk. Notice the addition of the highest category (purple) in parts of the area. Anywhere in purple has a “very high” heat risk to all people.

Remember that heat wave conditions don’t end during the night, and that nighttime relief will not be very good, with lows only dropping into the 60s for Western Washington, as seen below.

Nighttime lows are even hotter in urban areas, due to the infrastructure’s inability to release heat. These nighttime lows will be problematic for the many people around the Pacific Northwest without air conditioning.

Stay tuned for an update tomorrow…and stay cool!