April 11, 2019

What the Heck is a Bomb Cyclone?

This term has been used a lot lately, but if you’re like me, you didn’t have a clue exactly what it meant… other than it wasn’t good. I thought it was a term meteorologists (remember when they used to be weather men or weather women?) made up to make their reporting on a storm sound more dramatic than the next meteorologist… kind of like the names they use to describe their “Super Duper, Almighty, My-Doppler-Is-Bigger-Than-Your-Doppler” weather radars!?!

Actually, bomb cyclone is a real term used to describe a real weather event! It occurs when the barometric pressure drops 24 millibars or more in 24 hours or less. (No I’m not going to explain a millibar!) It is caused when a region of warm air and a region of cold air collide, creating a counterclockwise movement (or cyclone) in the air resulting in high wind speeds, often exceeding 80 miles per hour which is comparable to the winds in a category 1 hurricane. They may or may not be accompanied with major precipitation events.

Bomb cyclones do have more official sounding names, explosive cyclogenesis, meteorological bomb, and bombogenesis are just a few. While bomb cyclones are a relatively rare even in this part of the country, there are other severe weather events that are more common and we are just entering the season when we are more likely to experience them. Severe Weather Awareness week was March 25-29, but let’s take a few minutes today to review these events and the precautions we should take.

In general, watches indicate conditions are favorable for the development of certain weather conditions. Usually these cover a large area and don’t require immediate action, but let you know you should keep advised of developing weather conditions. On the other hand, warnings indicate that the weather condition is occurring, is imminent, or has been indicated by radar or confirmed by a trained weather spotter. In the case of a warning, you should take immediate action to protect yourself, your property, and others.

A severe thunderstorm watch means that the potential exists for the development of thunderstorms which may produce large hail or damaging winds. When a watch is issued, you can go about your normal activities, but keep an eye to the sky and an ear to a weather radio or your local radio and television stations for further updates and possible warnings.

A severe thunderstorm warning, on the other hand, means that a severe thunderstorm is occurring or is imminent, based on doppler radar or weather spotter information. You should move indoors to a place of safety. The term severe refers to hail that is quarter size, 1.0 inch in diameter, or larger and/or wind gusts of 58 mph or more. If golf ball size hail, about 1.6 inches in diameter, or larger is falling, it indicates that a storm is very well organized and likely has a rotating updraft. Any storm producing hail this large should be closely monitored for the potential of a tornado developing.

Although lightning can be deadly, it is not a criterion the National Weather Service uses to define a storm as severe since any ordinary thunderstorm can produce lots of lightning. Also, excessive rainfall may lead to flash flooding, but heavy rain is not a criterion for classifying a storm as severe. Severe strictly refers to hail at least one inch in diameter and/or wind gusts of at least 58 mph.

A tornado watch, like a severe thunderstorm watch, means that conditions are favorable for a tornado to form. A tornado warning is the ultimate in severe warnings, it means that a tornado is either occurring or imminent based on radar or a weather observer. You should take cover immediately.

A flash flood watch is issued when conditions are favorable for flash flooding in flood-prone areas, usually when the soil is already saturated from recent rains or snow melt, or when upcoming heavy rains will have the potential to cause a flash flood.

A flash flood warning is issued when a flash flood is imminent or occurring in the warned area. A flash flood is a sudden, violent flood after a heavy rain, especially when runoff is channeled through narrow valleys or ditches. Rainfall intensity and duration, topography, soil conditions, and ground cover all contribute to flash flooding.

For more information on weather watches and warnings, visit the National Weather Service website at www.weather.gov or the National Oceanic and Atmospheric Administration, or NOAA, website at www.noaa.gov.