The term of the Northwest Summer 2023 is now clear: Modestly warmer and drier than usual but without the “excitement”.
By excitement, I mean record heat waves or heat/wind combinations that can create massive wildfires.
The atmosphere can be “stuck” into certain configurations due to areas of persistent sea surface temperatures and tropical thunderstorm patterns, among other reasons.
This year, the atmosphere has been “stuck” in a condition that has brought excessive rainfall and cooler weather for California and warmer/drier weather for the Northwest.
A measure of the “stickiness” of atmospheric currents can be seen at sea surface temperatures along the West Coast, where there are many memories. As shown below, the waters off California and Oregon are significantly cooler than normal (the figure shows the difference from normal in degrees Celsius, almost twice that for degrees Fahrenheit). Swimming on the Oregon coast won’t be pleasant.
What exactly is this “stuck” atmospheric pattern that we are in?
I can graphically illustrate the difference from normal over the past 30 days in elevation of a pressure surface of 500 hPa (or equivalent to pressure at about 18,000 ft) over the past 30 days (below) .
A low pressure trough forms over the southwestern United States and extends into the eastern United States (in blue). In contrast, a higher pressure band (yellow/orange) was located west of BC and extended into southern Canada. The high pressure on Canada over the past months has been linked to the boreal bushfires.
This pattern tends to make Washington State warmer and drier than usual but is not associated with major heatwaves for us. A cool/wet model for California.
Interestingly, the whole paradigm is now changing and this shift will dominate our summer.
Here is Central Europe’s extended forecast through August 10 for an altitude of 500 hPa (again, think about a pressure of about 18,000 ft) and the difference from normal for that time period (color). Averaged over this period, the forecast is for a high pressure peak centered in the Rockies and a trench in the eastern Pacific.
The UW model system’s forecast for next Sunday at the same level shows this pattern clearly: tough upper levels offshore and ridges inland.
I can tell you what this means for us.
We’ll be dry next month, moving between periods in the 70s and lower 80s.
This is the latest forecast for Seattle lasting for 10 days. You see what I mean?
What about Tri-Cities? This pattern is warmer for them, with multi-day highs above 100F (see below)
For those thinking about wildfires, the grass and fuel in the area is dry enough to burn, but we won’t see high winds. So there will be grass fires, especially if people are not careful. But they won’t be big.
The only place with some modest winds would be the eastern slopes of the Cascades. This is the normal climate of the area and why the wind turbines are there.
