A ‘bomb cyclone’ is about to slam Ireland, the United Kingdom

An explosively intensifying low pressure system, commonly called a “bomb cyclone,” is about to hit Ireland, Scotland and England. Heavy snow, strong winds and a sudden thaw are expected, with the United Kingdom Met Office expecting a disruption to commerce and travel.

Amber warnings are in effect for central Scotland, with yellow warnings for snow, ice and wind across the area and in northern England. Western England and Wales, meanwhile, have yellow warnings for rainfall, which could lead to localized flooding.

The swiftly strengthening storm will slip northwest of the United Kingdom by Sunday afternoon before potentially wobbling southeast and weakening over Scotland into Monday.

The U.K. Met Office has named the system Storm Bert in accordance with local conventions. In the United States, federal agencies only recognize names for hurricanes, not nontropical storms. Europe faces one to two dozen powerful nontropical storms, akin to nor’easters in the United States, per year.

Names are compiled by Met Éireann, Ireland’s government weather forecasting entity, the U.K. Met Office and KNMI (the Dutch national weather forecasting service).

An exceptional bomb cyclone

It’s the time of year when “bomb cyclones,” or low-pressure systems that rapidly intensify, are forming over the oceans. One just blasted the Pacific Northwest with strong winds and is dumping more than a foot of rain in the mountains of Northern California. Another is taking shape in the northeast Pacific.

For a storm to technically undergo “bombogenesis,” its air pressure has to drop by a certain threshold within 24 hours. In the case of Storm Bert, which is emerging at the same latitude as Dublin, that threshold is 22.1 millibars in 24 hours. (Typical sea-level air pressure tends to be around 1,015 millibars).

Bert is expected to see a pressure drop from 988 to 948 millibars in 24 hours, strengthening at nearly twice the rate needed to qualify as a “bomb.” By Saturday morning, Bert will be missing 4 percent of the air from its middle. That creates the vacuum effect that drives strong inward winds.

Strong winds this weekend

Winds will arrive abruptly during the predawn hours Saturday in Ireland. They’ll be out of the south-southeast with gusts to 60 mph. That will be associated with the low-level jet stream, which will be pumping warm air into the region. That’s why any snow that initially falls across the United Kingdom early Saturday will flip to rain as mild southerly winds raise the temperature.

Across England and Wales, gusts of 45 to 55 mph are possible Saturday. That includes in London, meaning flight disruptions are possible. Any disruptions at London’s Heathrow Airport, one of the busiest in the world, could have a ripple effect on air travel throughout Europe.

A strengthening low-level jet stream might then bring a brief period of winds gusting 60 to 65 mph across southern England, including London, on Sunday morning.

Gusts of 45 mph are probable across northern England and Scotland, except along Scotland’s west coast and in the Hebrides Islands. That’s where exposed shoreside locations will see gusts over 60 mph.

Heavy rain and snow

A few flakes will fly Friday night in Liverpool, Manchester and Leeds, but the steadier snow will happen farther to the north. The high terrain of the North Pennines National Landscape will see 3 or 4 inches of snow, but totals up to 6 or 8 inches could be found in Scotland. Northwest Ireland might see 2 or 3 inches of slushy accumulation.