“Bombogenesis” is a term that’s been thrown around a lot in recent years when you listen to the weather on television, much like “polar vortex.” But, in fact, it’s been part of the meteorological vocabulary for decades. The word is used to describe a storm that intensifies rapidly over a relatively short period of time, which is what is predicted to happen to the storm in the Great Plains today and tonight (March 13). Pressure has already dropped to record levels in at least one location, according to a tweet today from the National Weather Service (NWS), and the NWS expects the storm to evolve into a blizzard of historic proportions.
National Weather Service (NWS) tweet on March 13, 2019.
Technically speaking, bombogenesis is what happens when the central atmospheric pressure of a mid-latitude North Atlantic cyclone drops 24 millibars or more in a 24-hour span. A cyclone, generally speaking, is just another name for a low pressure system that rotates counterclockwise in the northern hemisphere. Mid-latitude means between 30 and 60 degrees north of the equator. The lower the atmospheric pressure within a cyclone, the more intense the storm. This rapid intensification led to meteorologists often saying that a storm “bombed out,” as if it exploded like a bomb.
This kind of dramatic drop and rapid intensification can happen when a cold air mass collides with a warm air mass. Meanwhile, rapid upward acceleration of air can occur, kind of like inside the tube at the drive-up teller in which you place your check and deposit slip. This upward movement is caused by the jet stream high in the atmosphere removing air from the upper part of the column, allowing air from below to quickly replace it. This reduces the weight of the air below, causing pressure to fall at sea level, and turning an ordinary storm into a blizzard or a Nor’easter. Bombogenesis is common in storms over warm ocean waters, but happens less frequently in storms that develop over land.
Bombogenesis is a popular term for what meteorologists call “explosive cyclogenesis,” and it became more widely used after the 1980 publication of a paper on the subject by MIT professor Frederick Sanders, and his Ph.D. student at the time, John R. Gyakum.
It’s a Little Known Fact
The average sea level pressure of a winter storm in the U.S. is around 1,000 millibars. While the lowest pressure measured in a storm doesn’t define it as a “bomb” – it’s how fast the pressure decreases that makes it a bomb – here are some low pressure records for the U.S. that you may find interesting:
• Lowest sea level pressure: 892 millibars at Matecumbe Key, Florida on September 2,1935 during the “Labor Day Hurricane”
• Lowest sea level pressure (non-tropical): 927 millibars at Dutch Harbor, Alaska on October 25, 1977
• Lowest sea level pressure in the lower 48 states: 955 millibars at Canton, New York on March 3, 1913; again at Block Island, Rhode Island on March 7, 1932
Impending Great Plains Blizzard
The latest computer models indicate pressure getting as low as 970 millibars near the center of the developing blizzard in the Great Plains, resulting in wind gusts reaching 70 mph. This pressure level pales in comparison to those often measured in tropical systems at sea, but for a storm developing on land it’s a big deal. It results in heavy precipitation and powerful winds that can destroy homes, businesses and power grids across a large region. Travel may be impossible because of blowing snow or flooded roads, and loss of electricity may last for days or weeks.
Blizzard Warnings have been posted by the NWS from Colorado and Wyoming all the way to northwestern Minnesota. Updates can be found here. The storm will last through Thursday, but the effects of the storm have the potential to last much longer.