UK weather: Threat of thunderstorms continues
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The UK’s weather has swung from one extreme to another this week, with days of excessive heat followed by localised floods. Forecasters believe the trend will continue through August and September, but that storms won’t interrupt the country’s drought. People can expect more thunder and lightning, but rain isn’t guaranteed to follow every time.
Can it thunder without rain?
The Met Office currently has two thunderstorm warnings for the UK today, one yellow and one amber.
Both suggest significant rainfall could cause flooding and a “danger to life”, but the predicted precipitation ranges between 30 percent and 70 percent.
Some areas that fall within the warning area may still experience the odd thunderclap and flash, but without rain.
Thunder is the product of lightning which, in turn, is the product of excess atmospheric heat and instability.
During a heatwave, the sun bakes the ground with high temperatures for several days, and the heat eventually rises, cooling slightly.
The temperature difference, combined with enough existing instability, creates water droplets that eventually freeze as they continue to ascend.
Those ice crystals either adapt positive or negative charges and settle in the upper and lower parts of the earth’s atmosphere, setting the stage for lightning.
Negative charges lining the cloud’s bottom layer are naturally inclined to interact with nearby surfaces and build energy toward them.
Once this energy becomes too much, positive charges look to reset the balance by meeting them and discharging.
The discharge creates a flash of lightning, which drives a path of least resistance through the skies that rapidly expands and heats the air.
The air then collapses inwards, creating the characteristic boom of thunder.
As the mechanics of thunder and lightning show, thunder and lightning need moisture, hence why they usually come with rain.
Dry thunderstorms come when rain produced by clouds fails to make it to the surface below.
The same heat that creates storms may also cause rain to evaporate before it reaches the ground, but people may still experience lightning.
Weather experts advise people to take extra care during a dry thunderstorm, as strikes can take them by surprise on the ground without the warning of rain.
Which areas will see thunderstorms today?
The Met Office has forecast potentially severe thunderstorms over several areas today, some of which could see up to 100mm in a few hours.
The agency has placed the East of England, London and South East England under an amber warning for high-impact storms capable of causing floods.
Those locations and South West England also fall within a yellow thunderstorm warning that will likely produce a lesser impact, with between 20mm to 30mm of rain.
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