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reached around 50cm in places, making it the most significant accumulation in the region since December 2010. These events demonstrated that despite a warming climate, significant snowfall remains possible when wind direction, air mass and local geography align. Episodes of lying snow cause

at high altitude close to the Welsh border (Peak District exceeds 1000 mm per year), but much of the region is drier in the lee of the mountains (South and East Midlands as low as 600 mm per year). Snowfall across the Midlands is variable, from about 6 days of lying snow per year in the lower Severn

of the jet stream is also crucial in determining where the boundary lies between cooler air to the north and hot, humid air to the south. Looking ahead: Thunderstorm risk and heat on the horizon The forecast for the coming days remains finely balanced. A filament of the jet stream currently over Iberia

temperature at 0.1 m, 0.3 m and 1.0 m below the ground level • Relative humidity at 1.25 m above the ground • Amount of rainfall • Depth of lying snow • Mean wind speed, mean wind direction and maximum gust at 10 m above the ground • Atmospheric pressure at the station level and reduced to mean sea

Frequency June–November 2011 2009 2006 2007 2008 2010 2005 PDF: Probability that the number of tropical storms will lie within given ranges CDF: Probability that the number of tropical storms will exceed a given number © Crown copyright 2011 Tropical Storm Outlook 04 05 Climate and forecast

Ocean High pressure Low pressure Antarctica Figure 1. Air mass source regions. The processes that warm or cool the air mass take place only slowly, for example it may take a week or more for an air mass to warm up by 10 °C right through the troposphere. For this to take place, an air mass must lie

diagrammatically in Fig.1. Points C and E represent two different sets of environmental conditions with temperatures TC and TE, respectively. The diagonal lines at these points represent mixing lines between the environment conditions and those in the engine exhaust plume. The latter point lies far to the top

, has also contributed to intense rainfall and the risk of landslides, while low-lying coastal regions have faced the threat of storm surges and flooding. Climate change context It is worth noting that the conditions fuelling Melissa’s development, particularly the above-average sea surface

conditions and the potential for thundery showers, the latter half of the period hinges on the behaviour of tropical systems and shifting pressure patterns. A tale of two systems At the heart of this week’s forecast lies a dynamic interplay between low pressure to the west and high pressure over

Characteristic (ROC) Curve. The further the plotted curve lies above the diagonal line the higher the level of skill. Figure 2 below shows the results of the turbulence SIGWX verification. The new SIGWX forecast is indicated by the blue line, orange is the manual SIGWX currently produced by WAFC