Page Text: We are about to encounter a meteorological roller coaster in the form of a heatwave spike, a one-day warm spell in which temperature will zoom upward by over 15F. And then, cooling as quickly as it warmed.
In western Washington and Oregon, spring is the time for heatwave spikes.
The air aloft is still fairly cold, but the sun is getting MUCH stronger. Keep in mind that the sun this week is similar in strength to early September!
The key to all western /OregonWashington heatwaves is to have high pressure build to our east, producing easterly (from the east) winds. These winds warm by compression as they descend the western slopes of the Cascades. And easterly flow isolates the land from the cooling influence of the Pacific.
Below is the current European Center temperature forecast for Seattle Tacoma Airport. A predicted high of 56 today, but 73 tomorrow....roughly FIFTEEN degrees above normal. Then back to 55 on Friday and in the forties over the weekend.
The Seattle Times is even talking about snowflakes! (don't worry, that is not likely).
The latest surface air temperature forecast for 5 PM on Thursday will inspire you to dig out your tee shirts and fans (see below). 70s (light pink colors) from the Willamette Valley up into Puget Sound country. Warmer to the east of Puget Sound, where the downslope flow is strongest.
Note that this is a situation in which western Washington is WARMER than eastern Washington.
You must be asking yourself: what will cause such the spike heatwave tomorrow?
Let me show you, using some weather maps with sea level pressure, lower atmosphere temperatures (around 800 meters above sea level), and surface winds.
At 5 PM Tuesday, high pressure was just offshore, pushing cool air inland (white and blue colors are the coldest).
Today, the high pressure moves inland (the map at 5 PM today is shown below). An offshore pressure gradient develops that accelerates wind from the east. As the air sinks on the western slopes of the Cascades, it warms....and you can see a tongue of warmer air (red/oranges) moving northward west of the Cascades.
Warming causes air to become less dense, bringing pressure falls over western Oregon.
The warming continues on Thursday (see below), with orange colors (warmer air) extending into western Washington.
But the warmth won't last!
By Friday afternoon the high pressure has moved inland and a strong Pacific cold front is making landfall (note the cold air behind it...lots of light and dark blue colors).
So enjoy the warmth tomorrow..... the next week will be a cool, wet one.
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