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Sea fog in the English Channel

During the afternoon of 5 April 2009, an area of sea fog moving from the southeast encroached on the south coast of the Isle of Wight. Miss Stella Ulrich was walking along the cliff path at the time and took a series of photographs, three of which are reproduced in this article. The photographs (Figures 1(a)-(c)) were taken about 600m from St Catherine’s Point lighthouse, looking approximately towards the south. The elevation is about 140m above mean sea level (amsl). The first picture (Figure 1(a)), taken at 1458 UTC, is looking southeast, where the forward edge of an area of fog can be seen in the distance, several kilometres away. About the same time, fog could be seen in another photograph (not shown) taken looking east, covering the top of St Boniface Down, near Ventnor, about 7km distant. In Figure 1(b), taken at 1504 UTC, the advancing edge of the fog is just about to cover the lighthouse. In Figure 1(c), taken one minute later, fog is advancing up the cliff towards the observer. The Met Office surface analysis for midnight on 5 April (Figure 2(a)) shows an anticyclone of 1027mbar northwest of Iberia with a ridge covering the English Channel area. Also seen in the analysis is a trough over the south coast of England. This is related to the front-like feature discussed later. The geostrophic flow over the area of interest was westerly at this time. By midday on 5 April, the analysis (Figure 2(b)) shows an anticyclone of 1025mbar centred near Texel on the coast of the Netherlands. This is the same anticyclone seen on the chart for 12 hours earlier, it having transferred rapidly northeastwards. The geostrophic flow over the area of interest had now reversed to become easterly or southeasterly. Over the western English Channel, there was a slack southeasterly flow. Sea-breeze flows developed along most coasts. Inland over England, convection developed during the morning beneath a capping subsidence inversion near 1500m. (a)