We have actually experienced “dirty” thunderstorms, here in the Pacific Northwest but most people have never heard them called by that name. One form of this type of thunderstorm occurred each time Mt. St. Helens erupted.
The hot gasses and particulates expelled by the eruptions spewed large amounts of debris including ash and other particulates produced thunderstorms that then dropped the debris over a wide area of Oregon. The ash cloud rose to over 60,000 ft. and actually circled the earth multiple times by means of the jet stream.
The particular type of “dirty” thunderstorm that brought this topic to my attention occurred in Canada. In an article from Livescience.com published April 20, 2018 and written by Megan Gannon it was explained that these thunderstorms were generated by wildfires in Canada. “Wildfires can fuel “dirty” thunderstorms that fill the stratosphere with as much smoke as a volcanic eruption.” “That revelation comes from a study on the biggest fire-fueled thunderstorm event on record, which occurred on the night of August 12, 2017, in British Columbia, Canada.”
Four thunderstorms were generated in the short span of 5 hours. There is a meteorological term for this particular type of storm which is pyrocumulonimbus storms. They are the same as a typical thunderstorm except that they contain a large amount of smoke.
The article quotes David Peterson, a meteorologist with the U.S. Naval Research Laboratory, who reported the results of his research to the annual meeting of the European Geosciences Union in Vienna, Austria saying “Essentially this is a giant chimney taking smoke from the surface to high altitudes, at least to aircraft-crusing altitudes.”
Peterson compared the amount of aerosols sent into the atmosphere by the Alaskan volcano Mount Kasatochi (nearly 1 million tons) to the amount (200,000 tons) that was sent up by the British Columbia pyrocumulonimbus storms. The wildfire-caused storms proved to produce the amount of aerosols comparable to a moderate volcanic eruption. He explained that scientists haven’t studied these storms long enough to understand their climatic ramifications.
I’m sure you remember how severe our fire season was in 2017. In this column I documented the 7 major wildfires that were raging in September in this column with the title “Just When You Think It Can’t Get Any Worse, It Does.” They spewed tons of smoke into the air and it’s certain that at least some of the thunderstorms that were produced over the state were “dirty” thunderstorms. One of the worst fires was the “Chetco Bar” wildfire. Here is the summary I published back then: “The Chetco Bar fire: Located Kalmiopsis Wilderness, Oregon. The number of acres involved is 31,000. The fuel is timber, brush, Closed timber litter. It started on 7/12/17 and the cause is listed as lightning/natural. Residences threatened- 750 single residences (2 destroyed), 50 minor structures (1 destroyed). Resources being used: 280 people, 6 crews, 3 helicopters, and 12 engines. The fire is 14% contained.” The fire started in July and was only 14% contained two months later in September. The big question arises as to what will this year’s fire season be like.
One of the indicators of what kind of fire season we will have is the measurements of the snowpack taken in the mountains. They make an estimate of the water equivalent of that melted snow and report it out as a percentage of normal for each of the basins. The areas in red indicate less than 50% of normal water equivalent in the snowpack. Rogue and Umpqua 49%, Klamath 40%, Harney 33%, Owyhee 18%, and John Day 11% of normal. Those numbers show a large area of the state that is much dryer than normal. The tan color in the middle of the state indicates 50-69% of normal with 57% of normal for Upper Deschutes and Crooked while 53% Lake County and Goose Lake. Next comes yellow 70-89% of normal for the Willamette. Shaded in green with 90-109 % of normal is 90% for Grande Ronde, Powder, Burnt, and Imnaha. Finally the one area that is actually above normal for Hood, Sandy, and Deschuttes at 103 % of normal water equivalent. These numbers indicate that most of the state is well below normal for this time of the year.
Here’s a look at the actual snowpack report. The blue circles indicate normal or above normal snowpack. I don’t know about you, but I see only one circle that is filled in with blue. There are only 10 green circles that range from 56.25 inches of snow to 93.75 inches of snow at this time. It is quite easy to see that the snowpack is desperately low and so is the water equivalent of that snow.
Our Spring rainy season doesn’t have much time left, so it looks like we could be in for another dry Summer and that could mean another serious wildfire season. Only time will tell.
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