Amber warning of snow, 18 December 2009
The example below details an event that happened in eastern and south-east England. It would have generated an amber warning of snow with the new warning service.
Cold north-easterly winds brought very cold air from northern Europe to much of eastern and south-east England a week before Christmas in 2009. The cold air formed bands of snow showers as it crossed the relatively warmer waters of the North Sea.
Snow depths of 5 to 15 cm were reported in quite a few areas most exposed to the snow showers being blown inland from the North Sea, particularly in Kent, East Anglia and Lincolnshire.
Compare these typical accumulations of 5 to 15 cm to the accumulations of 20 - 40 cm and more across north-east England and eastern Scotland in late November and early December 2010. While this event was significant, the snowfalls were not as persistent over a number of days as the 2010 event. Although parts of the highly populated south-east corner of England were affected, impacts were not as severe or long lasting.
- Some flights in and out of Heathrow, Luton, Gatwick and London City airports were diverted or cancelled.
- About 200 drivers on the M20 and M2 in Kent were stuck in tailbacks overnight.
- Essex Police dealt with more than 180 weather-related incidents overnight, including more than 20 road collisions.
- One of the worst affected areas was the A12 between Copdock and the Essex border.
- Hertfordshire Police received more than 400 emergency calls through the night.
- Scores of jack-knifed lorries and abandoned cars littered the roads in the worst affected areas.
- Thousands of children started their Christmas holidays a day early as schools closed in many counties.
- A 20 mph speed limit was put in place on parts of the M1 overnight
- The A1081, the main road connecting Luton Airport to the M1, was gridlocked in the early hours of Friday 18 December 2009 due to the large number of jack-knifed lorries.
Based on the new warning system the following assessments would have been made:
- Likelihood - high
- Impact - medium
This would have resulted in an amber warning for snow: