The oddly muggy air and dark clouds on Wednesday night foreshadowed a weather phenomena rare to Juneau: thunderstorms.<\/p>\n
Thunderstorms only happen about once every other year in Juneau. The reason why, in two key words, is \u201cicefield\u201d and \u201clatitude.\u201d<\/p>\n
The massive Juneau Icefield \u2014 the fifth largest in the western hemisphere that separates the capital city from British Columbia \u2014 typically keeps thunder from our doorstep, as it did Wednesday, according to National Weather Service meteorologist Rick Fritsch.<\/p>\n
\u201cIn this particular pattern that we\u2019re set up for right now, about an hour before the storm got to us, coming from British Columbia, it was producing thunder and lightning,\u201d Fritsch said. \u201cYou take away the heat source \u2014 the warm earth surface \u2014 as the clouds move over the icefield. You take away the heat source, you take away the fuel for the thunderstorm.\u201d<\/p>\n
After passing over the icefield, the cumulonimbus, or thunderclouds, morphed back into their tamer, familiar cousins \u2014 the raincloud. As the clouds hit Juneau at about 9 p.m. Wednesday, the \u201cthunder part of that storm collapsed and it just became a garden-variety rain shower,\u201d Fritsch said.<\/p>\n
This is a common theme for would-be summer thunderstorms in Juneau. According to Fritsch, Juneau simply doesn\u2019t get hot enough to create the upward air drafts that build cumulonimbus clouds. When Juneau does get hot enough, it typically benefits from dry air currents pushed into the area from British Columbia, which pass over the icefield.<\/p>\n
Another factor making thunderstorms rare in Juneau is latitude.<\/p>\n
\u201cPhysically, our atmosphere at 58 degrees latitude is thinner than that of lower latitudes,\u201d Fritsch said. \u201cThunderstorms at or near the tropics can be near 50,000 feet above the surface of the earth. … Up here at 58 North latitude, a really big thunderstorm is something that goes up to maybe 15,000, 20,000 feet. There just isn\u2019t enough atmosphere to support a thunderstorm.\u201d<\/p>\n
Southeast saw an \u201cextraordinary\u201d number of thunderstorms three summers ago, Fritch said, an occurrence brought together by several natural factors, including wildfires in the Yukon. That storm front came from the North, bypassing the Juneau Icefield.<\/p>\n
[A crack, a shriek, a bolt of lightning: Juneau sees rare thunderstorm<\/a>]<\/p>\n \u201cWe had a very aggressive line of thunderstorms, almost like a squall front that came down from the Yukon across this skinny portion of British Columbia,\u201d Fritsch said. \u201cIt was an arc of thunderstorms that was really the width of the panhandle and it just came barrelling down like a ton of bricks over the northern panhandle. We had special marine warnings for thunderstorms, we had lightning that was captured on photograph, tree damage along the Haines Highway. It was a pretty dicey day.\u201d<\/p>\n Though thunderstorms are rare in Juneau, they are much more common on Southeast Alaska\u2019s outer coast.<\/p>\n \u201cIn the winter, the opposite of the offshore (winds) are the onshore. … When the land is cooler than the water, the water … represents the heat source instead of the land. So these cool, moist systems coming off the Gulf of Alaska, warm relative to the land, they blossom into thunderstorms and we see a lot of thunderstorm activity from Icy Bay all the way down to Cape Fairweather. … That\u2019s late autumn into early winter.\u201d<\/p>\n For now, Juneau\u2019s thunderstorm forecast is clear.<\/p>\n \u201cWe don\u2019t have any in the forecast right now, and the pattern is shifting so that it\u2019s less likely that we get some,\u201d NWS forecaster Brian Bezenek said. \u201cThrough the summer we\u2019re looking at above normal temperatures, but as we move out of May and June it will get more moist.\u201d<\/p>\n \u2022 Contact Outdoors reporter Kevin Gullufsen at 523-2228 or kevin.gullufsen@juneauempire.com.<\/p>\n Related stories:<\/p>\n Foam on the water a sign of life and death<\/a><\/p>\n