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Aaaigh! It's Winter!
Author: TriSec    Date: 11/30/2019 11:02:17

Good Morning.

Hope you all had a great Thanksgiving out there. If travel was involved, I bet you're looking at tomorrow with some trepidation.

Here in New England - we're all mostly weather geeks. Our part of the country isn't like many other parts. Multiple storm tracks converge here; there's the Atlantic Ocean in play, and even sometimes the ol' "Montreal Express" - cold air rushing down from Canada to mess with us.

Sometimes all these things combine to form a rapidly developing and strengthening storm. This happens a few times every winter, and beyond that it's no doubt been occurring since long before anyone understood what was really going on. (quotes from Wiki and AccuWeather)

Explosive cyclogenesis is the rapid deepening of an extratropical cyclonic low-pressure area. The change in pressure needed to classify something as explosive cyclogenesis is latitude dependent. For example, at 60° latitude, explosive cyclogenesis occurs if the central pressure decreases by 24 mbar (hPa) or more in 24 hours.

This is a predominantly maritime, winter event, but also occurs in continental settings, even in the summer. This process is the extratropical equivalent of the tropical rapid deepening. Although their cyclogenesis is totally different from that of tropical cyclones, bomb cyclones can produce winds of 74–95 mph, the same order as the first categories of the Saffir-Simpson scale and give heavy precipitation. Even though only a minority of the bombs become so strong, some have caused significant damage.

For years, the term remained part of professional meteorology, and was rarely heard by ordinary citizens.

In the 1940s and 1950s, meteorologists at the Bergen School of Meteorology began informally calling some storms that grew over the sea "bombs" because they developed with a great ferocity rarely seen over land.

By the 1970s, the terms "explosive cyclogenesis" and even "meteorological bombs" were being used by MIT professor Fred Sanders (building on work from the 1950s by Tor Bergeron), who brought the term into common usage in a 1980 article in the Monthly Weather Review.

In 1980, Sanders and his colleague John Gyakum defined a "bomb" as an extratropical cyclone that deepens by at least (24 sin φ/ sin 60°)mb in 24 hours, where φ represents latitude in degrees. This is based on the definition, standardised by Bergeron, for explosive development of a cyclone at 60°N as deepening by 24 mb in 24 hours.

Sanders and Gyakum noted that an equivalent intensification is dependent on latitude: at the poles this would be a drop in pressure of 28 mb/24 hours, while at 25 degrees latitude it would be only 12 mb/24 hours. All these rates qualify for what Sanders and Gyakum called "1 bergeron".

All of this is deep weather geekery. it's not something anyone would normally think about, at least until just a year or two ago when somebody in the media discovered the terminology.

"Cylcogenesis" somewhow became "Bombogenesis", and now "Bomb Cyclones".

But there's nothing different going on. Since it's such a new term, I found it difficult to locate past storms that have undergone classic Cyclogenesis. But there's a few we might all remember that are potential candidates.

The Superstorm of 1993 (Storm of the Century) from March 12-13 is a prime example of a storm that underwent bombogenesis. The storm strengthened from 29.41 inches (996 mb) to 28.45 inches (963 mb), or nearly 1.00 inch (33 mb), in 24 hours. Much of this strengthening occurred over land.

Other examples of storms that underwent bombogenesis are Hurricane Charley in 2004 and Hurricane Wilma in 2005. The Blizzard of 2015 (Jan. 26-27), the Bering Sea storm of December 2015 and the northeastern United States storm of late-October 2017 experienced bombogenesis.

Except - nobody called it that at the time. It feels to me that at least around here, it's only been in the last 3 years or so that we've been breathlessly told that a "Bomb Cyclone" is headed our way. Naturally, this touches off the whole "Bread, Milk, PANIC!" effect.

It might snow for a day, so therefore I need enough supplies to last me for 3 weeks in case I get "snowed in".

Maybe it's just me, but such reporting can only lead to complacency and indifference. If every storm seems to be a "Bomb Cyclone" in recent winters, when the real one finally hits, will anyone pay attention?


2 comments (Latest Comment: 12/01/2019 21:22:44 by TriSec)
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