The dreaded heat dome: What is it and why is it here?

Weather Blog

PORTLAND, Ore. (KOIN) — The heat dome is not a stadium, not a sauna, not a fad diet. It cannot be accessed by the Cloud, Uber, or purchased with Bitcoin. It’s a term used to describe unusually strong high pressure, and right now this invisible bubble is getting mighty strong over the Northeast Pacific. As it strengthens, so does the heat.

If this is the first time you’ve ever heard of a heat dome, you’re not alone. Typically heat domes set up shop right over the Four Corners in the very arid section of the southwest U.S.. What’s troublesome with this unwelcome visitor is the process of descending air. That downward motion on the atmosphere compresses air molecules which in turn get excited and warm rapidly at the surface. If there’s nothing to push the dawdling dome away, it will just hang like a nasty bathroom odor. Quickly we’ll be in a cycle of very hot days with warm air trapped overnight.

Forecast models are pointing to a series of extremely hot record-breaking days ranging from 103 to 113 over the weekend and into Monday for the Pacific Northwest. An excessive heat warning is in effect for the greater Portland metro area, as is most of Oregon and Washington, Saturday through Monday night.

What is a heat dome?

Three reasons why this is unprecedented for Portland

1) Number of consecutive days with temps 20 or more above normal, three of which are 25-30° above normal

2) The arrival of a heat wave at this point in June is the earliest on record for Portland

3) Records will likely be broken for daily temps, overall June temperature, and the entire history of record keeping for Portland.

Friday morning is our last breath of cool ocean air pushing onshore. Expecting clouds to linger at the coast after sunrise and partly cloudy skies prevail in the valley this morning. The morning temperatures are a tad warm to start. Mid 60’s PDX. The record highest minimum temperature aka warm low for this day is 64.

You’ll notice the heat today. Highs will range from the low to mid 90’s.

PDX Normal: 76 high / 55 low

Record high for this day June 25: 101° (2017)

Weekend temps graduate from 102/105 on Saturday to 106/110° on Sunday. Don’t be surprised if you run into some outliers for temperatures either on the high or low end of the scale. Offshore flow Sunday means the beach heats up to the mid-80s — possibly 90. Coastal records could break too.

Emphasizing warm nights, we could be breaking records night and day. Overnight lows could match our “normal” daytime high, which is 76. The extreme heat continues Monday, with a daytime high as hot as 107, or worse up to 110.

Danger behind the dome

If you’re conditioned to live in hot climates, chances are you’re familiar with your physical limitations in the heat. But if you live in a region where the normal June temperature is 76, then anything above 95 is going to be a difficult adjustment. Above 100 for more than a day? Now we have a big problem on our hands.

Heat takes the lead as the deadliest weather-related event in the United States.

*During 2004–2018, an average of 702 heat-related deaths (415 with heat as the underlying cause and 287 as a contributing cause) occurred in the United States annually.

http://dx.doi.org/10.15585/mmwr.mm6924a1

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