Previsão do tempo, weather forecast: A lightning barrage puts the western U.S. on fire

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.