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Tuesday, March 31, 2020  Spokane, Washington  Est. May 19, 1883
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News >  Idaho Voices

Volcano produced rare ‘dirty thunderstorm’

By Michelle Boss

April is such a volatile month in terms of weather.

Looking at solely Spokane numbers, the difference between the coldest high temperature (40 degrees) and the warmest high temperature (75 degrees) was 35 degrees.

Differences in overnight lows were similarly extreme. The coldest minimum temperature was 26 degrees on April 10, and the warmest minimum was the record of 50 degrees on April 20. I doubt anyone complained about it being “too” warm last weekend when area temperatures soared into the mid-70s and even low 80s. No afternoon high temperature records were broken in Spokane or Coeur d’Alene, but highs in the low 80s on the April 19 in Ephrata and Moses Lake did set records for those cities.

While we have not seen much in the way of thunderstorm activity this spring – our peak month for thunderstorms is not until June – one part of the globe has seen some rare lightning this month. Most of us have read about the eruption of the Icelandic volcano Eyjafjallajokull. While all the focus has been on the ash plume and its disruption of air travel, scientists have also been taking a closer look at the phenomenon called a “dirty thunderstorm.”

A rare form of lightning was seen during the eruption that scientists still don’t fully understand. In a typical thunderstorm, lightning occurs when an electrical charge separation occurs (between negative and positive charges) which is great enough to overcome the poor conductivity of the air.

Scientists have many theories on how this occurs. One popular theory is that a storm becomes electrified due to the collisions of ice particles and hail stones within the storm. Using that same logic, scientists think that the collision of ash particles (or of ash particles, water droplets and ice) during a volcanic eruption could produce a similar charge separation, which would result in the electrical discharge we see as lightning.

Volcanologists at the Alaska Volcano Observatory were able to collect some exceptional data on “dirty thunderstorms” back in January 2006. After volcanic lightning was observed during the eruption of Mount Augustine in Alaska, two electromagnetic lightning detectors were installed about 60 miles away. Just two days later, Augustine exploded with another four big eruptions. Though lightning was not observed visually, the lightning detectors recorded continuous radiation and bursts of lightning within the rock and ash as it rushed upward from the vent. About 3 minutes after the main explosion, another 300 lightning discharges were recorded.

I plan to write more about lightning in an upcoming column, but next week I’ll take a look at a bit of Bloomsday weather history, and recap how the first full month of spring measured up.

Michelle Boss can be reached at weatherboss@

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