Day after day, satellite and radar imagery show big cumulus clouds and thunderstorms over eastern Oregon, while most of the remainder of the region has none.
To illustrate, below is the visible satellite image from Monday afternoon, with lightning shown by the green dots.
This pattern is not a fluke this year.
Below is the average lightning density map for the U.S. (2015-2020). Not much lightning along the West Coast due to the cool Pacific, with eastern Oregon getting the most in our region.
MUCH more in the southeast U.S.
So why are thunderstorms favored in eastern Washington, you ask?
There are at least three reasons.
Thunderstorms are associated with vertical instability driven by rapidly decreasing temperature with height. Warm surface temperatures are thus good for business.
The Pacific Ocean is relatively cool, with surface temperatures around 50°F. This cool air spreads over western Oregon and Washington and works against the instability that produces cumulus convection.
The second reason is explained with a topographic map below. Much of eastern Oregon is an elevated plateau, which serves as an elevated heat source during the day. Elevation heating helps enhance the vertical temperature change (gradient) aloft, which helps produce convection and thunderstorms.
Finally, southeast Oregon is closer to the northward plume of moist, unstable air associated with the Southwest Monsoon, as illustrated by an example from a few years ago (below).
Interestingly, there has been a very, very weak Southwest Monsoon year so far. As a result, precipitation is WAY lower than normal this summer in Phoenix (see below, green is this summer, purple line is normal).
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Meanwhile here in the farthermost SW Puget sound area we have one of the bone driest summers I can recall in 35 years, that golden plum of moisture is no help.
ReplyDeleteInteresting explanation. Never realized much of Eastern Oregon is as elevated as it is. Thanks for educating us.
ReplyDeleteJust read a stat that this time last year Washington and Oregon had 1.3 million acres on fire, this year only 40,000. Also this time last year over 12 thousand personnel on fires this year 2500. May be drier but your predictions, Cliff, have been true thus far. Let us hope these new batches of TStorms that are going to affect Eastern Oregon and Eastern Washington stay wet enough to not have any new starts. Hold overs may be a problem though. Looking forward to some rain if a cell comes over us, but these events do tend to lead to some starts. Fingers crossed.
ReplyDelete"Energy," and lots of it.
ReplyDeleteYes: That elevation map (in some German!) is interesting and brings, with Cliff’s insight, a new understanding to our PNW geography and its weather impacts.
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