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July 2012 Forecast- Month Ahead Validation

Thundery wintry showers


Here's a recap on my month-ahead forecast for July:
[quote]With pressure often high in the Arctic and low pressure systems taking a relatively southerly track, it will be another cool cloudy wet month, though probably not as cloudy or wet as June was.

July has commenced cloudy and wet, but as we head through the first week the emphasis will shift towards sunny intervals mixed with slow-moving thundery downpours. The 3rd July will have an area of cloud and persistent rain moving through Wales and most of the southern half of England, while northern England, Ireland and Scotland will be bright with showers. Between the 4th and 7th July slow-moving showers will be heavy and thundery, particularly in north-east England on the 4th, though not quite as severe as some places experienced back on the 28th June. South-eastern Britain will see relatively few showers and a fair amount of sunshine in between. Another exception will be northern Scotland which will be rather grey and cool with rain at times. Temperatures will range between 18 and 22C for most parts of the country, not far from the seasonal norm. Sunshine amounts for the first week will probably be close to or just below average, while rainfall will vary widely, though mostly above normal away from south-east England.

During the second week of July the low pressure area will drift out into the North Sea, allowing a chilly north to north-easterly airflow to dominate over the British Isles, with temperatures below normal everywhere. Under the influence of the low, most of central and southern England will see further showers and an increasing chance of longer spells of rain, and the period will thus be considerably wetter and cloudier than average in those areas. Northern and western areas, closer to the high pressure, will turn drier during the second week, with sunshine and rainfall amounts consequently close to normal in the west (perhaps above normal in western Scotland), but much below normal in the east.

There are signs that towards the third week, the low pressure to the south-east will weaken and this will allow highest pressure to transfer southwards towards the Azores. As a result, we will start to see a north-south split across the UK; most of Scotland and northern England will be cloudy and quite cool with some rain at times, particularly in the west, but southern areas will see some drier, brighter and warmer interludes due to being close to a ridging Azores High. Temperatures and sunshine amounts will probably only be close to average though.

Any particularly warm, sunny weather is likely to be reserved for the last third of July. The general emphasis is likely to remain on changeable conditions with low pressure systems tracking across at intervals, but one or two interludes of warm, drier and possibly sunnier weather are likely, most especially over southern parts of the British Isles. On the whole, the last third of July is likely to be statistically near-average for temperatures, rainfall and sunshine, though with the east drier and sunnier relative to normal than the west.

July 2012 is likely to be another fairly cool summer month, with a Central England Temperature of 16.0C. Temperatures are likely to range from 1.0-1.5C below the 1981-2010 average in northern Scotland, to around 0.5C below in most other parts of the British Isles.

It will be another wet month; the first half will be particularly wet in north-east England, while the second half will be wet in the north-west, but not generally as wet as June. Rainfall is expected to range from 40-80% above normal over much of Scotland and north-east England to just 0-20% above in south-east England.

Sunshine will range from near normal in southern England to 30-40% below in north-east Scotland, while other regions will generally have a small shortage of around 10-20%.

I feel that this was certainly one of my better forecasts, with most of the right weather patterns correctly identified- in particular the suggestion of one or two warm dry sunny interludes towards the south in the last third of the month did indeed materialise. However, I somewhat overestimated sunshine amounts during the first week- the low pressure ended up further south than I expected and as a result the weather ended up exceptionally cloudy in most regions rather than just the northern half of Scotland as predicted.


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