When convection or thunderstorms are expected, convective outlooks will be issued on the website in a similar way to how advisories are issued. All convective outlooks are issued after discussion with @Ben_Weather to ensure they are as accurate as they possibly can be.
All convective outlooks cover a period of 24hrs starting at 6am and ending at 6am on the following day.
Due to the hit & miss nature of thunderstorms we use a % risk of lightning within a 25 mile radius. For example, being in a 30% risk of lightning risk zone means there is a 30% risk of lightning striking within 25 miles of your house, it doesn't guarantee you will see a thunderstorm.
When conditions look favourable for severe thunderstorm development, a black dashed circle will be drawn onto the graphics, this highlights an area where severe storm development is possible, although not guaranteed. Severe thunderstorms are characterised as having at least one of the following;
When severe weather is likely, a product might be issued to cover one of the following weather extremes;
There are three levels. These are threshold based graphics and are triggered when a certain criteria is reached. Below is the criteria for each level and weather type.
Level 1
Wind 60-70mph | Rain 50-60mm in 24hrs | Fog Visibility below 100m.
Level 2
Wind 70-90mph | Rain 50-90mm in 24hrs | Fog Visibility below 50m.
Level 3
Wind >90mph | Rain >90mm in 24hrs | Fog N/A
Snowfall is a separate graphic and there are two of them. The first is a snowfall probability graphic, this is issued 2-5 days ahead of a potential snow event to give a percentage chance of falling snow in a particular area.
1 day before a snow event, a more specific snow graphic will be issued to cover accumulations.
These forecasts & graphics are threshold based so will sometimes differ to the warnings issued by the Met Office which take into account potential impacts. This should NOT be used as a replacement for official Met Office weather warnings but as a guide to potential weather severity alongside them. You can view all official warnings by clicking here.