From 4 to 6 January, low pressure (970 hPa) centered south of Newfoundland in the North Atlantic Ocean moves to the northeast and deepens.
The ECMWF MSLP animation of the North Atlantic Ocean from 4 January at 0000 UTC to 5 January at 1800 UTC shows a deep depression moving rapidly from eastern Newfoundland to Great Britain. It deepens by about 35 hPa per 24 hours until reaching 936 hPa on 5 January at 0000 UTC. Note the high pressure gradient indicated by the packing of the lines in the south of the low center. The associated winds exceed 50kt locally to the south and southwest of the low where the flow converges.
The maximum fall of pressure occurs between 4 January at 0000 UTC and 5 January at 0000 UTC. The pressure varies from 972 hPa to 936 hPa, corresponding to a deepening of 36 hPa in 24 hours.
This rapidly deepening is called an explosive cyclogenesis or "bomb." Indeed, to be in this category, a depression's central pressure in the mid-latitudes must decrease on average by at least 1 hPa per hour for 24 hours. In our situation, the depression has decreased by 36 hPa in 24 hours. This explosive deepening indicates an exceptional situation.