Weather bombed north-east US feels the chill

Explosive meteorology of Storm Orson sheds snow as pressure plummets

Storm Orson has made an impact on parts of the north-east US, leaving more than a metre (40in) of snow over the past week as it underwent explosive cyclogenesis, dropping 24 millibars in just 15 hours.

Explosive cyclogenesis, or a “weather bomb”, is meteorologically defined as the rapid intensification of a low-pressure system, whereby the central surface pressure falls 24 millibars within 24 hours.

Prior to the birth of Storm Orson cold continental air spilled southward from Canada and collided with the warmer waters of the Gulf Stream, creating a sharp temperature gradient and fuelling the rotation of a cyclone. These events most commonly occur during winter when there is a stark temperature contrast between high and mid latitudes.

Following the worst drought Bolivia has seen in more than 25 years, severe thunderstorms plagued parts of central South America last week. Whilst rainfall helped alleviate drought conditions, more than 75mm of rain fell in just a few hours across parts of Santa Cruz, Bolivia, triggering severe flash floods as water inundated the dehydrated and impermeable ground. Other regions were hammered by crippling hailstorms, leaving at least two fatalities.

Dal Lake, Srinagar. Kashmir received avalanche warnings at the start of February.
Dal Lake, Srinagar. Kashmir received avalanche warnings at the start of February. Photograph: Farooq Khan/EPA

The Kashmir valley in northern India has also been buried by its heaviest bout of snowfall in 25 years, an event that initially coincided with the harsh weather period known as Chillai Kalan , when regional temperatures can drop as low as -20C (-4F).

Incessant snowfall continued to coat the region thereafter, triggering a series of devastating avalanches last week. This was due to a “western disturbance” feeding in – an extra-tropical storm driven by westerly winds originating from the Mediterranean area.

Tamsin Green (MetDesk)

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