California Wildfires and the Lightning Siege: How Unusual Is It?

Charles Rotter / 20 mins ago August 26, 2020

Reposted from the Cliff Mass Weather Blog

California is burning and smoke has covered the northern half of the state and is spreading across the U.S.  Most of the fires were started by a huge “lightning siege” that started on August 15th.  How unusual was this massive lightning event?  That question will be answered below.

Smoke situation this morningThe situation this morning was extraordinary.  According to CALFire, more than 14,000 firefighters are dealing with 650 fires (two dozen major ones) that have burned over 1.25 million acres.  There have been 7 fire-related deaths and 1400 structures lost.The “lightning siege” over the past ten days has resulted in over 13,000 lightning strikes, many of which were from high-based thunderstorms that did not provide much rain to the surface (rain evaporated on the way down!).How unusual was this large number of lightning strikes in mid-August?The answer:  very unusual.When I want to get information about lightning statistics, I know where to go: Professor Robert Holzworth of UW ESS and Dr. Katrina Virts, a past associate of Dr. Holzworth who is now a NASA scientist.  Dr. Holzworth runs a major lightning network (WWLLN) and a lightning expert, and Dr. Virts is the Mozart of lightning statistics.Anyway, within of hours of inquiring about the situation, Dr. Virts sent me a graph showing 3-day lightning totals going back to late 2009 (below, click to enlarge).

The event that occurred last week was the sixth highest for that period, which is impressive by itself.  But there is more.  It was the greatest 3-day lightning total in the entire period during the midsummer (June-August) period.   So this was quite an extreme event to occur in the warm/dry California summer.  One that followed an extreme warm period with a record-breaking upper-level ridge of high pressure centered over southern Nevada.An important aspect of the unusual event was the ability to tap the moisture of tropical storm and move it into central California (producing the thunderstorms).  This is illustrated by the map below, which shows moisture around 10,000 ft (700 hPa pressure level) for 5 AM on August 17th.  The moisture levels getting into California were as much as 4-5 standard deviations from the normal.  Trust me…this is very, very unusual.  Like never happening before on that date.

Sometimes the atmosphere rolls the meteorological dice and gets two sixes.  And, of course, the slow warming of the atmosphere from increasing greenhouse gases, the spread of invasive, flammable grasses, and the huge influx of people into rural areas make things that much worse.On the other hand, there is very little smoke over Washington State and things look favorable over the next week.  I am becoming increasingly confident that Washington is going to dodge the wildfire bullet this summer.

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