Saturday, July 27, 2013

The Coolest Place in the Pacific Northwest

While much of the west side of the Pacific Northwest warmed into the 80s and east of the Cascades into the 90s and higher, one area has gotten cooler and cooler.  Ground zero for chilling out?  Portions of the Oregon coast.

And strangely, they have cooled while the rest of us have warmed and will warm as the weather cools over the interior this week.  Weird weather here in the Northwest!

Consider the temperatures at Newport, Oregon, on the central Oregon coast (station NWP03, see map below).   Temperatures had fallen there over the past 10 days to highs of 50-52F, but started warming a bit (to a torrid 55F) yesterday.  I might note that while the 50s were observed along the coast, 90s were only a short drive away to the east in the Willamette Valley!
 

During that period it was not only cold, but windy at Newport and other coastal locations, with winds increasing to over 24 kts!  The wind chill temperature is down in the mid 40s.  Feels like winter in summer!


 A hint of what is going on is found from the latest sea surface temperature chart (see below, in °C, purple is very cold, blue is cold, then warming with green, yellow to red).  The coastal Pacific is really cold--at 11 C (about 51F) and cooler.  At some locations the coastal Pacific has dropped to around 47F!
 In fact, looking at the measurements at some coastal buoys along the Oregon Coast (46050, 46015, see map and plots below) the water temperature has gotten cooler and cooler? Why?




Strangely enough the cooling is directly associated with our nice weather in the interior.  The warming interior caused pressure to fall relative to the high pressure over the ocean (the East Pacific High).  The resulting pressure differences produced day after day of strong northerlies along the coast (thus the origin of the powerful winds).  The following forecast of sea level pressure and winds from the UW WRF model for a few days ago illustrates this.


Strong northerly winds cause upwelling of cool water from below...but this only happens near the coast....thus the area of cold, coastal water. (see explanation of upwelling here)

But as the interior cools and an upper trough moves in during the next few days, the winds should relax along the coast and the upwelling should weaken.  So strangely, it will warm at Newport and other coastal locations.

3 comments:

Lance said...

Whoa, sea temperatures near 20c east of Vancouver Island, how does that happen?

Cora Reuter said...

Is this the same effect that happens along our coast? I've been meaning to ask you: Why is the weather at Ocean Shores always seem the opposite of what's going on in town? For the last 4 years, we have spent the first week of June in Ocean Shores. 3 of those years, it was raining and gloomy in Seattle most of the week, but sunny and clear at Ocean Shores. This year, the first week of June in Seattle was hot and sunny, mid-80's, but it was cloudy and cold at the coast. A local even told us that what ever it is doing there, it is always the opposite here. What gives?

Gary said...

Lance: I am no meteorologist, but I couldn't help notice the extreme variation in sea temp around the SE tip of Vancouver island. The shape of the cold surface temp in the Strait of Juan de Fuca compels me to conclude that the tide was rising there, bringing the 11C cold coastal water into Puget Sound.

As you note, the temps in the Salish Sea (east of Vancouver Island) some 60 miles to the north are some 9C warmer. I'm guessing the water there is warmer because it's nearly surrounded by land (and its higher temps), is shallower (and therefore heats up faster), and is fairly isolated from the cold coastal currents.

Cora, I would guess that what you've observed regarding the weather at Ocean Shores vs that in Seattle has something to do with the pressure difference. When it's clear inland, the high summer sun has a chance to heat up the land; surface heat conducts to the air, which becomes less dense and rises when warmed.

The air at Ocean Shores is not warmed nearly so much, because the ocean water does not warm nearly as fast as does the land. Being colder and more dense, it doesn't rise as much as the warm inland air. This creates a lower pressure inland, which draws the cooler marine air onshore to replace it. Onshore flows usually produce clouds because the air is forced to rise, cool, and cause condensation. The warmer it is inland, the greater the onshore flow; and, because the coastal water is especially cold in the summer, the winds can be very unsummerlike!

Cliff has written about the "June gloom" typical in a Seattle summer (but not 2013!), where there is a thick layer of low clouds that never seems to burn off. As a result, the air temps inland and on the coast are nearly the same, as are the pressures, so the onshore flow is largely absent, creating the likelihood of a sunny day at Ocean Shores.

One summer we vacationed along the Oregon coast. After a few days of nonstop SW wind (with blowing sand), clouds, and temps in the low 60's, we headed inland to warm up. In the Willamette valley (where we should have stopped) temps were in the 80's; but we continued eastward across the Cascades to Bend, where it was 105F!

I've spent many weeks over the years commuting between San Francisco and Walnut Creek to the east. The road between them crosses the Berkeley Hills via the Caldecott Tunnel. During the summer, it's typically foggy at the west entrance, but brilliant sun greets you when you emerge at the east portal; during the winter it's just the opposite. I believe that's a result of the same pattern--inland heating causing onshore flow along the coast in the summer, giving rise to the oft-quoted "The coldest winter I ever spent was a summer in San Francisco".