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What sort of build up is coming closer to Christmas?

'Weather bomb': Why the explosive name?

Dayna Vettese

Friday, December 19, 2014, 5:52 PM - #SantaBomb. You may have seen it circulating social media, or heard it on the radio or on television. But what is it? Why are people saying it to refer to this potential Christmas storm?

First we need to explain what a "weather bomb" is. 

It's a meteorological term used to explain the rapid intensification of a low pressure system. 

What does that mean? 

Our weather (or lack of weather) happens due to high and low pressure systems that move through our atmosphere. Low pressure systems are what tend to bring us our precipitation, clouds and strong winds (or weather associated with those low pressure systems). Meteorologists gauge how strong a storm system is by how low the pressure is at its centre.

The lower the pressure, the stronger or "deeper" the storm. 

For example, a central pressure of 980 millibars (mb) could be associated with a low pressure system. That's not too bad a storm -- a regular low pressure system. Once we get values in the 970s or 960s mb, we're talking about deep/strong low pressure systems. When a low pressure system is strengthening (or "deepening") that means its central pressure is decreasing (going down).

The term weather bomb is a meteorological term used when a low pressure system "deepens" at least 24 mb in 24 hours. This is the definition/criteria of a "weather bomb."

UPDATED FORECAST: Attention turns to 'significant' weather system arriving December 24

With weather bombs, it's all about the wind. Some weather bombs can be associated with heavy rain or snow. 

However, not all weather bombs bring heavy precipitation. The wind associated with these strong low pressure systems is what makes it an intense storm system. Tropical storm to hurricane force wind gusts can be associated with weather bombs. 

The takeaway is that you can't always expect heavy precipitation with storms that meet weather-bomb criteria.

"Bomb" is a scary and destructive word. So why is it associated with this type of weather phenomenon? 

When we refer to some intensifying rapidly, we think of it as explosive. 

For example, in business, if a stock is growing quickly it’s said to have "explosive growth." That's what weather bombs are: Explosive deepening/strengthening low pressure systems. 

Weather bombs are more common along the east coast of North America than they are over land but they can occur over land with the proper conditions. But that's another story for another day. 

Now, why is the term #SantaBomb being thrown around? These are some of the reasons.

  • 1. The storm system we anticipate will impact eastern Canada in the coming week will strike sometime between Dec. 24 and Dec. 26, hence the "Santa." 
  • 2. The forecast models on Wednesday showed this storm to rapidly intensify, with its central pressure potentially meeting weather-bomb criteria. 
  • 3. People are witty. Someone combined the fact that it could meet weather-bomb status and the fact that its impact will be felt around Christmas and coined "#SantaBomb."

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