Why Storms aren't Sodding Off

Weather has been crazy recently for the south of UK, and at the moment, severe weather warnings have been put in place for the South-West and more than 200 homes have been evacuated in Devon and Somerset. So what exactly is going on?

What’s happening in the UK?

Parts of England have probably had their wettest January in more than 100 years. Our weather is dominated by a jet stream, a narrow band of fast flowing air high in the atmosphere driven by temperature differences in the cold air to the north and warm air to the south. With the contrast a lot stronger this year, a strong jet stream has been driven over here from the Atlantic. The variations in the jet stream are what drive the development of storms. Usually, it would oscillate in large waves, creating more varied weather patterns, but this time, it’s stagnated into a particular pattern that caused a strong and straight pattern – meaning a stormy one.

How are storms formed?

Winter storms derive their energy from the clash of two air masses of different temperatures and moisture levels. They usually form when an air mass of cold, dry, air moves south and interacts with a warm, moist air mass moving northwards. When the two air masses meet, it is called a front. If cold air advances and pushes away the warm air, it forms a cold front. When warm air advances, it rides up over the denser, cold air mass to form a warm front. If neither air mass advances, it forms a stationary front.

In a thunderstorm, the action of warm air rising and cold air sinking (convection) plays a key role in the formation of severe thunderstorms. If the warm surface air is forced to rise, it will continue to rise, because it is less dense than the surrounding air. In addition, it will transfer heat from the land surface to upper levels of the atmosphere through the process of convection. What’s key for thunderstorms are the formation are instability (unstable air) and moisture.

How do blizzards form?

Blizzards typically occur when the jet stream sags well to the south, allowing cold polar air from the north to clash with warmer, humid air to the south. Due to the conflicting air masses, high winds develop and storms can erupt, sometimes turning into full-blown blizzards. It is a long-lasting snowstorm with very strong winds and intense snowfall. You need three things to have a blizzard; cold air at the surface, lots of moisture, and lift. Warm air must rise over cold air.

Thanks for reading!