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| Cold air aloft brings heavy showers Heavy downpours, hail and thunder By Garry Nicholson. | |
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| Tweet Topic Started: 18 May 2015, 06:58 PM (71 Views) | |
| Audi-Tek | 18 May 2015, 06:58 PM Post #1 |
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Cold air aloft brings heavy showers Heavy downpours, hail and thunder By Garry Nicholson in Darley Dale, Derbys 18:30hrs 18/05/2015 Temperature: 10C Weather: Shower An upper trough will reside across north-western Europe on Tuesday, driving an area of low pressure at the surface, centred in the northern North Sea. A very showery west to north-westerly pattern will affect Britain. The chart below is the forecast 500mb chart for midday. It shows temperatures of below -30C at this level in the atmosphere, which is around 5.5km, or roughly 18,000ft above sea level. This results in a steep lapse rate, in other words, a rapid fall in temperature with height, creating very unstable conditions up through the atmosphere. In these conditions, air will rise readily, forming rapidly growing cumulus clouds, which continue to grow into cumulonimbus clouds, capable of producing heavy showers, including thunder and lightning and also hail. Snow is also likely on the tops of the Scottish mountains. Daytime surface heating of the land means central and eastern regions will see most showers by afternoon, but showers forming over the (relatively) warm sea means windward coasts are likely to have showers from the word go. Despite the showers, the air mass is quite ‘dry’, so very high rainfall totals are unlikely from any one shower, and sunshine should break through in between. It’s a classic ‘four seasons in one day’ – although the ‘summer’ option may be rather elusive for most of you! ![]() Link ........... http://www.weatherweb.net/wxwebtvgarrysnotebook.php?ID=1362 |
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9:35 AM Jul 11