What exactly is 'Bomb Cyclone', that is threatening United States?

Washington, Dec 24: Millions of people in the United States are experiencing bone-chilling cold, blizzards and leaving at least nine people dead, knocking out power to over a million customers, and wrecking holiday plans.

Airlines cancelled over 5,000 US flights on Friday as massive winter storms snarled airport operations around the United States and frustrated tens of thousands of holiday travellers.

This storm looks like it will intensify at twice that rate, said Bob Oravec, lead forecaster at the National Weather Service's Weather Prediction Center told AFP.

Meteorologists are calling the weather phenomenon a 'bomb cyclone.' But what exactly is a 'bomb cyclone'? Which states are being affected by it?

Explosive cyclogenesis

Explosive cyclogenesis (also referred to as a weather bomb, meteorological bomb, explosive development, bomb cyclone, or bombogenesis is the rapid deepening of an extratropical cyclonic low-pressure area, according to wikipedia.

The change in pressure needed to classify something as explosive cyclogenesis is latitude dependent. For example, at 60° latitude, explosive cyclogenesis occurs if the central pressure decreases by 24 mbar (hPa) or more in 24 hours.

This is a predominantly maritime, winter event, but some reports claim that it also occurs in continental settings.

his process is the extratropical equivalent of the tropical rapid deepening. Although their cyclogenesis is entirely different from that of tropical cyclones, bomb cyclones can produce winds of 74 to 95 mph (120 to 155 km/h), the same order as the first categories of the Saffir-Simpson scale, and yield heavy precipitation. Even though only a minority of the bombs become so strong, some weaker ones have also caused significant damage.