Bomb cyclones, atmospheric rivers, and what it all means for the Saints game Monday night
SEATTLE (WAFB) - It was hard to watch a newscast or log onto a news site or social media this weekend without coming across the phrases ‘bomb cyclone’ and ‘atmospheric river’ and how those features were impacting the West Coast. But what in the world do they mean and are they new?
Bomb Cyclone Origins
Aided by the explosion of social media in recent years and the tendency for some sites to seek clicks, the phrase ‘bomb cyclone’ has started to make its way into the general lexicon. But the use of the word ‘bomb’ in a meteorological context is nothing new to forecasters. Meteorologists Fred Sanders and John Gyakum are credited with popularizing its meteorological use in a 1980 paper titled, “Synoptic–dynamic climatology of the bomb.” The American Meteorological Society (AMS) defines a ‘bomb’ as:
An extratropical surface cyclone with a central pressure that falls on the average at least 1 mb h-1 for 24 hours.
In other words, a meteorological ‘bomb’ is a non-tropical area of low pressure that intensifies rapidly. Specifically, the central pressure of the low pressure must drop at least 24 millibars (mb) within 24 hours to receive the classification.
Much like ‘bomb’ or ‘bomb cyclone’, the phrase ‘atmospheric river’ is not a new one for meteorologists, although its usage in news coverage has become much more common in recent years. The phrase was first used by MIT researchers Reginald Newell and Yong Zhu in the 1990s. The AMS defines an atmospheric river, in part, as:
A long, narrow, and transient corridor of strong horizontal water vapor transport that is typically associated with a low-level jet stream ahead of the cold front of an extratropical cyclone.
Simply put, atmospheric rivers are relatively narrow plumes of moisture-rich air that are often associated with heavy precipitation. They can be associated both with non-tropical weather systems like the one currently impacting the West Coast, or with systems that are tropical in origin, such as a hurricane.
Putting it all together
The storm system impacting the West Coast in recent days both qualifies as a ‘bomb cyclone’ due to a dramatic drop in pressure near its center and also has an associated ‘atmospheric river’ that has been hitting parts of California especially hard. A buoy located in the northern Pacific off the coast of Washington recorded a pressure drop of greater than 50 mb over the course of 18 hours. The storm system also helped produce a record low pressure for the region.
The atmospheric river has been the source of record and near-record setting rains for parts of northern California. Sacramento picked up more than 5 inches of rain on Sunday, setting a new 24-hour rain record for the city. San Francisco wasn’t far behind, with more than 4 inches of rain marking its wettest October day on record and its 4th wettest day on record for any in the calendar year.
Impacts on Saints-Seahawks game
The ‘bomb cyclone’ will continue to spin just offshore of Seattle today and tonight, although the low pressure center is not as intense as it was on Sunday. The Saints-Seahawks game is set to kickoff at 7:15 p.m. CDT (5:15 p.m. in Seattle) Monday night and to be certain, weather will be less than ideal. A steady light to moderate rain is in the forecast, with temperatures likely hovering in the low 50s for most of the game. Toss in some breezy to windy conditions with winds running 15-20 mph and gusting higher at times, and both the passing and kicking games might be rather dicey. But we all know the Saints are now a running team, right?
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