Bomb cyclone set to bring another round of snow to eastern US

As large parts of the United States continue to dig themselves out from the aftermath of a major winter storm, another system is expected to develop off the south-eastern coast.

Last weekend's storm dumped more than 20 inches of snow in some areas, disrupting thousands of flights, cutting power to hundreds of thousands, and causing multiple deaths.

Whilst this weekend's potential storm is not expected to be as widespread or as long-lived as the previous system, portions of the Mid-Atlantic and some places in the far north-east are forecast to see further disruptive wintry weather.

Extremely cold weather will grip much of the eastern states, as far south as southern Florida into early February.

The storm will start to develop close to the Gulf Coast on Friday, pushing a rain-snow mix across the southern Ohio and Tennessee Valleys.

By Saturday, the system will strengthen rapidly as it moves out into the Atlantic, with heavy snow and gales developing around the Mid-Atlantic states. It is expected to become a 'nor'easter'. This is the term given to a deep area of low pressure that brings strong north-easterly winds to the East Coast from the Atlantic, and can deliver heavy rain, snow and gales.

Winter storm watches, external have been issued for parts of northern Georgia, South Carolina, eastern Tennessee, North Carolina and southern Virginia. Snowfall in these regions could reach up to 15 inches (38cm). Coastal gales and a storm surge will be additional hazards, as high astronomical tides combine with powerful onshore winds from the North Carolina Outer Banks northwards. Blizzard conditions are likely, leading to potential power outages and difficult travel conditions in the region.

By Sunday, the snow and strong winds are expected to shift northwards, and may impact major cities in the north-east such as New York and Boston - places still recovering from last weekend's storm. However, there is some uncertainty as to whether the storm will remain out at sea by this stage.

The storm system is forecast to strengthen rapidly as it moves out into the Atlantic on Saturday.

The term 'bomb cyclone' or weather bomb describes a storm that undergoes explosive cyclogenesis, where its pressure drops very quickly - by 24 millibars or more in 24 hours. Such storms can bring very strong winds, heavy snow, and coastal impacts, making even a short-lived event potentially disruptive.

Bitterly cold Arctic air is locked across the eastern half of the country. Temperatures across many eastern states will be as much as 15C (59F) below the January average.

A freeze warning in Florida warns of potentially record-breaking cold weather Saturday night. Hard overnight frosts will extend to coastal areas which very rarely experience freezing conditions.

Snow and ice already on the ground are unlikely to thaw, making the region vulnerable to any additional snowfall.

The US National Weather Service notes this could become the longest-lasting cold spell in several decades.

The unusual positioning of the jet stream has created persistent northerly winds, driving Arctic air into regions that rarely see such cold, from the Midwest to Florida.

Overnight lows have hit -27C (-17F) in parts of Ohio, while Florida's Panhandle experienced frosts of -5C (23F). The combination of these winds with snow still on the ground has helped the cold linger and intensify, making conditions feel even harsher.

The current pattern is likely to keep temperatures well below average across the eastern US for the rest of the week.