He defines a high pressure ridge as:

Strength wise, this has a chance to be the strongest heat ridge ever measured in the Pacific Northwest region. We can measure its strength by finding how high in the atmosphere the 500 millibar pressure level is -- it's usually around 17,000-18,000 feet or so in summer. But warmer air is less dense than colder air, which means a hot air mass will push the 500 millibar level higher into the atmosphere.   Hot ridges will get into the 580 decameters range (we use metric system and decameters -- or "dm" for its measurement). Super hot ridges will push 590.

He does mean dekameters, 580 dam, based on normal being 17000 - 18000 feet.

Article link: https://www.q13fox.com/weather/what-makes-this-heat-wave-so-unusual

Note: In the US/ICAO/ISO Standard Atmospheres, the 500 mbar pressure altitude is 5574 m (geopotential), but the real atmosphere is mostly "off-standard." No clue why the weather folk use dekameters instead of meters; until this, I didn't know they did.