Lightning on Kitsap Peninsula
Image provided by Adam Sapek
During the 24 hours ending at 1 a.m. this morning (Friday), lightning spread across the area (each + or – sign is an individual lightning bolt)
During the previous day, eastern Oregon and Washington enjoyed thundering performances
Wednesday has a strong band across northern Idaho and more through southwestern Oregon
While Tuesday there was thunder that filled southwestern Washington and western Oregon.
So why did the Northwest get this flashy period?
Every Northwestern resident knows the answer instinctively: Blame California!
And they will be right.
Over the past few days, a low center has emerged along the California coast (see chart 500hPa–about 18,000 ft–from Tuesday afternoon). Winds are also shown, showing southerly winds over the southwestern United States and southeasterly winds (from the southeast) over the northwest.
This flow is favorable for instability and thunderstorms over the northwest.
First, easterly currents in the lower atmosphere push the cool marine influence out to sea.
Cool, dense air low near the surface is problematic for thunderstorms, which depend on rapid cooling with altitude.
Second, the circulating wind carries warm, humid air overhead in our region. This is evident from a moisture channel satellite image, which shows the distribution of water vapor in the west on Tuesday afternoon. You can see the humidity swinging around low.
Steam is great for thunderstorms, as it condenses into clouds and releases rain latent heat. And such heating helps to make the air more buoyant.
Circulation is also pulling warm lower-atmospheric air into our region, which is also good for thunderstorms (temperatures and winds at about 10,000 ft late Tuesday shown below).
So, for some reason, the lows along the California coast are favorable for northwesterly thunderstorms.
And some of these storms are quite dramatic and beautiful. Below is the image visible around 6pm on Thursday. Each oval cloud structure is the arc-shaped anvil of a thunderstorm.
The radar image at the moment (below) shows some significant echoes, indicating heavy rainfall (red and orange being the heaviest)
Some good news… expect dry conditions on Saturday as California lows have weakened.
