UK and London Weather 23/07/12 – 29/07/12

The first week of the IOP has seen some potentially very interesting meteorological conditions for observing urban pollution. The experimental period got off to a warm start on Monday the 23rd of July. Light onshore winds kept the coastal regions on the Southeast relatively cool, but inland temperatures quickly reached 28 degrees C by early afternoon. The warm and sunny conditions continued into the evening with clear nighttime conditions into Tuesday.

The weather on Tuesday the 24th began with some mist and fog patches in the early morning in parts of the southeast including London due to the clear conditions of the previous night, however this rapdily burned away after sunrise for another hot day with gentle winds. As mentioned in the previous blog post “Ozone building up in the summer sun”, these warm, clear and settled conditions have been one of the driving forces behind a moderate to severe pollution event in the south of England this week. By Tuesday the Met Office’s Daily Air Quality Index was predicting moderate (5 on the Daily Air Quality Index) level pollution across the greater London area, and this was accompanied by an Urban Heat island increment of several degrees overnight. It is also worth noting that high pollen levels were also observed in the southeast, which could have respiratory impacts in addition to anthropogenic pollution.

Synoptic conditions continued to be mostly static throughout the middle of the week, with the southern half of the UK still under the influence of a steady high pressure system over western Europe, leading to a calm, sinking airmass over the country with largely clear skies. Meanwhile the Northen half of the UK was experiencing a low pressure system with more unsettled weather, and a cold front dividing the two regimes.

Wednesday was the hottest day of the week, with temperatures approaching 30 degrees C in London by the early afternoon in fair and dry conditions. It was much the same if a little cooler on Thursday as the heat began to subside and there was further haziness and patches of mist and fog.

Interestingly, Thursday the 26th was the day when the Met Office predicted the most pollution, with high (7 – 8) concentration levels predicted across a wide area of central and southern England. It is possible that the past week, particularly Wednesday and Thursday, could be a good pollution case study.

Though it became quite humid on Friday the 27th with a spot of light rain, conditions were mostly fair and warm (high of 24 C and low of 16C) for the Olympic opening ceremony. Afterwards London saw a return to more “typical” British summertime weather with some periods of heavy showers on Sunday the 29th, so look out for that in the cielometer and lidar data.

While there will still be warm periods in London this coming week, it is unlikely we will approach the temperatures of last week. Conditions will be a little more unstable, with greater cloud cover and drizzley conditions anticipiated on Tuesday the 31st. The start of August from Wednesday will be fine and partly cloudy, but right now it is not predicted to rise above a high of 20 degrees C until the weekend.

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