I haven't even gotten to work yet but I can hear it already: "It's not supposed to get this hot here." People will say that to me very matter of factly. And it doesn't get this hot here very often. Portland breaks 100 about once a year, and it's not uncommon at all to stack a couple of sub-100-degree summers back to back.
So what's the deal?
First, let me get the global warming connection out of the way. You can't make one based on one regional heat wave. Keep in mind the word global. Got any friends back East? Drop them an email and ask about the cool rainy summer weather they're enduring, and try tying that into global warming using the same logic as our heat wave. You can't, because there isn't any. Logic, that is. Portland's had many heat waves before and we'll have more in the future, regardless of human climate impact. But climate change is a blog for another time, back to the heat.
One of the main premises of weather and climate is that an air mass will take on the characteristics of the surface beneath it. Arctic air mass? They originate over ice and snow in the heat-source free endless nights of the boreal winter. Marine air mass that we Northwest weather types yak on endlessly about? They originate over the nearby Pacific Ocean, which stays a pretty constant 50-55 degrees at our latitudes. That air mass is typically pretty thin, say from sea level up to a few thousand feet in summer. Those cooler marine air masses can usually find their way inland to the Cascades, keeping western Oregon and Washington reasonably comfortable. The marine air is modified, (i.e. warmed) as it moves over the warmer landmass, resulting in Portland's pleasant 75-80 degree summer days.
Which leads us to what's happening now, or, where in heck is the marine air?!
Big area of high pressure over the southwest expands northward. VERY warm air aloft, and no west winds to deliver the cooler coastal (marine) air. The temperature at about 2100 ft this morning was 82-degrees. At 5 am! Sunday morning it was 78. That'll help make today hotter than Sunday. Winds, both direction and speed are important parameters with Portland heat waves. There hasn't really been an east wind down here on the ground where we all live. But there is just above us. Sunday morning there were east winds from just above sea level to about 7,000 ft. That's a pretty thick layer of air coming from the hot inland areas instead of from off the cool ocean. This morning, those east winds extended all the way up to nearly 11,000 feet. That's a lot of warm air. And it sinks. And as it does, it gets even warmer as the air molecules are squeezed closer together by the weight of the air above.
So to re-cap:
No cool west winds, a thick layer of hot air and light east winds just above us, all conspiring to keep the cool air at bay. And out over the the bays and ocean. Until Wednesday, when the weather pattern shifts just enough to allow that cooler coastal air to seep inland once again, when you'll hear a giant collective "ahhhh" from western Oregon.
Thanks for watching KGW.
Keep Cool,
Matt Zaffino
KGW Chief Meteorologist
