August 19, 2020

A lightning barrage puts the western U.S. on fire

Note:  My weekly online weather discussion will come out at 9 AM Friday.  And I am working on starting a weekly weather podcast.  On this podcast I won't be as constrained as I was on KNKX, where certain topics (e.g., climate) were discouraged by the management.

During the last few days, hundreds of fires have been ignited by an extraordinarily unusual barrage of thousands of lightning strikes over the western U.S. Major fires are burning all over California and dense smoke has spread across the region (see below).  The city of Vacaville is being engulfed in flames and air quality is rapidly degrading.

Impressively, an amazingly dense plume of smoke extends from California hundreds of miles into the Pacific.

And several major fires have started here in the Northwest--most by lightning.  Here is a satellite image of northern Oregon, with smoke extending eastward from fires on the eastern slopes of the Cascades.

And more fires are found over north-central Washington.  This sudden wildfire blow up has its origin in two meteorological events.  First, a strong persistent ridge of high pressure that brought record-breaking temperatures and drying conditions over a vast area of the west.

And then there was the most unusual and extreme "lightning barrage" with over 10,000 lightning strokes  in 72 hr.   Keep in mind this is usually the dry season in California. Let me show you the lightning in 24 h chunks.

For the 24h ending 1 AM Saturday. there was lightning over the Sierra Nevada, but much more over New Mexico.

Lightning starting moving into southern CA during the  next 24h and extended up the Sierra Nevada into southern Oregon.

But the real barrage hit on Sunday, with over a thousand lightning strikes in CA and even lightning over western Washington, something described in my previous blog.

The onslaught over CA did not end on Monday, with thousands more lightning strikes in northern CA and southeastern Oregon.

And even more on Tuesday, mainly over the eastern side of CA and Oregon.

These lighting strikes hit fuels that have been dried by not only the normal drought of the western summer, but an extraordinarily warm, dry period the last few weeks.

A persistent ridge of high pressure over the West was the cause, illustrated by the upper level weather map at 5 AM Sunday. The orange/red area is where the heights (or pressures) were much higher than normal at this level (about 18, 000 ft).   The winds are also shown at that level.  Strong southerly (from the south) winds are on the western side of the ridge---this is very important.

Why?  Because it entrained lots of moisture from the tropics and pushed it northward, creating lots of thunderstorms (see moisture map at that time).  If you look carefully you will see tropical storms to the south, which helped supply even more moisture. And it was worst than that.  The thunderstorms were mainly high-based, with much of the rain evaporating before hitting the surface.  Lightning, without wetting the surface, on very dry surface fuels.  A recipe for disaster.


My blog on the KNKX firing is found here.


  1. To see video from a satellite’s perspective of actual fires and smoke intermingled with clouds, rampaging across the west, is unbelievable! The barreling, lightning filled thunderheads of August in the great basin often produced rain that never reached the ground (called virga, isn’t it). It was a cruel joke!

  2. Cliff, why don't you do a podcast? Then you wouldn't have to deal with these NPR distractions and you could still do the audio format.

  3. Thanks Cliff. I am glad you are no longer restrained by the Radio program's ideas of what can be talked about! Here in Nor. Cal. the smoke is intense. We are in El Dorado County and no fires YET and I hope it stays that way. Lots of friend though have been evacuated in the Santa Cruz area and Nevada Counties. What a mess.

  4. On August 2nd your blog was on benign wildfire year, it ended with: "The bottom line is that at this point there is no reason to expect an above-normal wildfire and wildfire smoke season. In fact, good reason to expect less wildfires and smoke than normal. One issue to take off your worry list.
    darn weather changes.

  5. wavelength.... I was talking about Washington State and that is turning out to be exactly right. At this point, we we are way below normal in acreage burned....and most of the fires have been grass/sage fires....with the cooling weather, my forecast is looking fine...cliff

  6. Thanks very much for explaining why lightning can happen without rain reaching the surface. Where I live in the SE U.S., that almost never happens. Lightning means lots of rain, which means little risk of fires.


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