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).
.png)
.gif)
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.
ReplyDeleteIndeed. It does seem to me that summers here are getting drier... might or might not be natural variability...
DeleteInteresting 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.
ReplyDeleteThese recent fire seasons, as far as acres burned, point to the importance mainly of the weather conditions that accompany thunderstorms. In most years, most of the fire loss is in Eastern Oregon and Washington and mainly due to ignition from dry lightning storms and warm dry weather following lightning started fires. In the past two summers this situation was been set up by prolonged warm, dry weather prior to the mid summer period. So the potential is there again for large fires this summer, especially in Eastern Washington, but it will be mainly the nature of any lightning storms (dry or wet), and the weather that follows the storms that will determine how many acres burn. We have had these situations in past summers and the area most affected usually varies from year to year; sometimes it is in Eastern Oregon, sometimes in southern Oregon, and some years here in North Central Washington. Because of this dependence on the nature of lightning storms, I doubt if Cliff or anyone else could make a consistent long range forecast of exactly where the largest fire loss will occur in any given year.
Delete"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.
ReplyDeleteSo which one is it higher elevation or this weather pattern from the desert southwest? We need a map with percentage ratios.
ReplyDeleteThere seems to be some high elevation smoke in the skies over portions of Whatcom County this morning.
ReplyDeleteSpeaking of lightning, I think it was Monday, Reed Timmer showed a video of strobe lightning in South Dakota not too far from Sioux Falls. it was interesting to see. I do catch storm chasers when they chase tornadoes and/or hurricanes, and the derecho from I think 2021 the midwest, and I believe began near Montana and hit urban areas like Cedar Rapids Iowa if I recall.
ReplyDeleteI spent much of spring 2024 watching a bunch of tornado videos, some current, many older ones, like the Super outbreak of 1974, Moor Oklahoma among them.
Cliff- in one of your recent blogs you mention that thunderstorms "like" the mountains and that seems to be true in Washington, with more lightning in the Cascades than in Seattle. But the lightning flash density map you provide here clearly shows less lightning over the Appalachian Mountains than on either side of them. I was a little surprised to see that that also seems to be true in the Rockies, with more lightning in Eastern Colorado than over the western part where the mountains are. Any idea why there is this difference?
ReplyDeleteSome maps show a marked thunderstorm frequency maximum in the southern Rockies, compared to the surrounding areas, but this map does not reflect that. Perhaps, there is less lighting in storms over the southern Rockies versus storms over the plains?