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>> Weatherweb Reporters << Thunderstorms across the UK What causes them? By Emily Hall in Birmingham 19:35hrs 28/06/2012 Temperature: 22C Weather: Cumulus clouds Parts of the country today saw hailstones the size of golfballs in addition to severe flooding and thunderstorms. Thunderstorms are caused by convection when moist air passes over warm ground, causing the air to become unstable and to continue rising into the upper atmosphere. This is exactly what happened today with temperatures in the mid-twenties across the country and a series of fronts carrying moist air in from the Atlantic. Hail forms in cumulonimbus clouds which develop from strong updraughts, causing the cloud tops to often reach the top of the troposphere (about 10 km high). Droplets of water that are caught in updraughts are taken high up into the top of the cloud where they freeze to balls of ice. If these updraughts are continuous, the ice balls are kept at the tops of the clouds and can keep increasing in size with layers of water freezing on their surfaces. When the hail is heavy enough, or the updraughts reduce in strength, they fall to the ground without time to melt. >> Comments on this story << >> Add your comments below << Your name Email (not shown in posting): Location: Your comment): Security question: What colour is the sky? (the answer is blue but remove the 's)	>> Latest comments on this musing << [Scroll down to add your comment and see what others say] >> More from Weatherweb Reporters << Moon research continues By Garry Nicholson in Darley Dale, Derbys 17:45 13/06/2013 Upcoming period of interest Tropical Storm Andrea By Garry Nicholson in Edgbaston,Birmingham 15:30 06/06/2013 First Atlantic storm of Hurricane season Review of May 2013 By Garry Nicholson in Darley Dale, Derbys 18:30 03/06/2013 A mixed month – often cool with glimmers of early summer [click here for a full list of Weatherweb Reporters stories] >> Simon's Weather Musings << Severe, Extreme or Inconvenient? By Simon Keeling in Wombourne, Staffs 10:00 18/06/2013 Let's have a meeting! Central Europe roaster this week By Simon Keeling in Wombourne, Staffs 13:40 16/06/2013 A taste of some hot summer weather [click here for a full list of Simon's weather musings] >> Captain Bob's Dispatches << Month Ahead By Captain Bob in Kingswinford 15:30 15/06/2013 Some fine spells, but rain too Seasonal Outlook By Captain Bob in Kingswinford 11:00 19/05/2013 July looks best [click here for a full list of Simon's weather musings] >> Around the webcams << Latest webcam pics (add yours) >> Learning channel << Summer 2013 - Latest guidance >> Forecast channel videos << Tuesday's Look Ahead 18/6/13 Monday's Look Ahead forecast 17/6/13 Sunday's Look Ahead video 16/6/13 Saturday's Look Ahead video 15/6/13 Friday's Look Ahead - August high?