Warmest Temperatures of the Year To Arrive This Weekend

We’ve had quite a few heat waves so far this spring. This past April was the by far the warmest April on record at Sea-Tac and many other places across the Pacific Northwest. May started out hot and then cooled to more seasonable levels, but with an average temperature of 59.8 degrees, Sea-Tac was still 4.2 degrees above its average monthly temperature of 55.6 degrees, good enough for their third warmest May on record. Now, June is here, and it doesn’t look like the heat will be going away any time soon.

Let’s take a look at the 1000-500mb thicknesses over our area right now. Thicknesses of the atmosphere are directly proportional to temperature, so the higher the thickness, the higher the average temperature in that region. The diagram below is taken from Robert Houze’s introduction to atmospheric sciences for majors class I took during autumn quarter my junior year; hopefully it will help you understand the concept of thicknesses. Geopotential height is essentially the height above ground (I’ll explain it more in a future post or page) and p1 and p2 are different pressure surfaces.

Now, here are our thicknesses.

Right now, we have high pressure in the eastern Pacific and low pressure in the Gulf of Alaska. We also have very high heights over the desert southwest indicating very warm air over there. As the week continues, expect these heights to increase and expand northward as a ridge builds over the Western United States.

While I’m at it, let define what a ridge is. Although many weathermen like to use the phrase “a ridge of high pressure,” this can be a little misleading, as a ridge refers to an area of relatively high atmospheric pressure in the upper atmosphere. Often times, our highest pressures (and coldest temperatures) of the year occur when we are under the influence of a large trough of low pressure in the upper atmosphere with much higher pressure at the surface. When temperatures are cold, the air is denser, and pressure decreases more rapidly with height. This means you can simultaneously have high pressure at the surface while having low pressure aloft, and vise versa. In fact, some of the highest pressures aloft in the world are found in the eyes of hurricanes because the air temperatures there are so warm.

By the weekend, a massive ridge will reside over the Western U.S. and British Columbia, with a large trough offshore near 150 degrees W. This ridge will help guide all weather coming off the Pacific into the Alaskan Panhandle, and we will stay dry and HOT on the process.

A map of the thickness at the same time shows that thicknesses are quite high over our neck of the woods, and they are really high in the Desert Southwest. In fact, much of the Desert Southwest has an excessive heat warning from Friday to Sunday. I have a feeling that aptly-named Furnace Creek at Death Valley will break 120 this weekend.

Seattle has not gotten to 90 yet this year. We just might break 90 on either Saturday or Sunday. The deciding factor will be if we see enough offshore flow off the Cascades to warm us up just a couple extra degrees. When air sinks, it warms, so if we get a really solid offshore flow, we could heat up quite a bit. The foothills of the Cascades are slightly cooler on average than the lowlands, but they are usually hotter during these heatwaves because they get more of a temperature boost from offshore flow.

I’ll have more details as the heat wave approaches. One thing is for sure – the beaches are going to be PACKED this weekend!

Thanks for reading,
Charlie