UK Weather - Winter 2011/2012

[Simon Culling]

Hello Orion, the fohn or foehn effect is a common occurance in the UK and in many locations, but does not reach the magnitude recorded in such places as the Alps or the Rockies. It occurs most frequently with the wind direction between south and west and is most noticable on the east coast of Scotland (particularly the Murray Firth) and on the North Wales coast. This type of weather situation is responsible for many of the highest recorded temperatures in the winter months.

On a smaller scale, any range of hills can have a small local effect on temperature. For example the Downs to the south of London (only reaching 800-900ft amsl) can locally enhance the temperature by 1 or 2 degrees centigrade on the lee side (usually the London side in a SW wind), particularly in summer and with a bit of sunshine!

The western slopes of the Scottish Highlands receive significantly more rain than the eastern slopes quite simply because the prevailing wind direction is SW. Conversely, on ocassions the wind will come in from the east and the eastern side will drain the air of its moisture and produce a fohn effect in the western Highlands. This reverse effect is most likely synoptically in the spring.

The pdf below contains some interesting facts re foehns in the Alps...where I am heading on Friday.

http://www.google.co.uk/url?sa=t&rct=j& ... sJAy6S7jyQ

[Orion]

Thanks for that, Simon. Have a good trip.

[Michael]

UK are getting "our" SW wind across the equator

[stepr]

I occasionally witness a foehn effect here, when the wind is SW or SSW, although it's fairly weak, it can raise the temperature by 4-5C. The reaction is a drop in humidity and usually a strong, dry gusty wind, but a fairly mild, or even warm wind, depending on the situation.

As for the weather recently, a little cooler these past few days, and perhaps a frost tonight, albeit light, in some parts, but back to milder, perhaps warm weather next week.

[stepr]

Looking at the forecast patterns, there is no suggestions of a reprieve from the drought afflicting the south of the country. Through the weekend, and into early next week, a strong high pressure system looks like influencing the British Isles, so dry, sunny and warm in general. No rain forecast for the areas that need it, except perhaps tomorrow but even then, no guarantees.

Certainly even though my area has had more rain in general than the southeast this winter, the soil on the cactus bed in the garden has been truly arid this winter, it's usually pretty moist in the winter, not dusty like it has been so far.

Next week we can except perhaps temperatures of 15-18C maximum, which once again signals a warm start to Spring.

[Michael]

One aspect looking at UK maps often is the constant low pressure to the west,giving SW winds predominantly there for long periods,youd think at that latitude more cold NW outbreaks be likely,look at 50S here,more mobile.

[Willoughby]

Interesting to hear of a drought being declared in SE UK.

Video:
http://www.abc.net.au/news/2012-03-12/d ... uk/3883374

[Simon Culling]

The winter as a whole was warmer and drier than average for England + Wales, but the rainfall distribution was very much slanted towards the north and west with the south east remaining very dry.

Average CET for the winter was 5.1*C (+1.0*C) and the EWR was just 210mm, which is only 83% of the average. This follows two drier than average years over England + Wales and hence the drought worries. Yesterday, a further seven water companies obtained drought orders to come into effect in April, banning the domestic use of hosepipes. See the BBC report below:

http://www.bbc.co.uk/news/uk-17340844

However, it is easy to overdramatise a situation like this and the media always fall into this trap. Certainly the rainfall of the last couple of years has been lower than average, but our consumption is still rising and the water companies (all privatised) increase their revenues by selling more water. They seem to want to have their cake and eat it as well.

[Simon Culling]

Michael, the normal meandeing of the jet stream in northern lattitudes results in the SW flow that you mention with the centre of the average lowest pressure somewhere near Iceland and the high located near the Azores.

However, in the last couple of years this pattern has not been so prominent as we have seen many episodes (lasting up to a couple of months at a time) of anomolous high pressure ridging in the central Atlantic which produces more of a NW flow into western Europe. This was what happened in Nov + Dec 2010 and gave us all that cold weather. The jet stream has either been further north and occasionally much further south than normal meaning that the UK (and western Europe) have been drier than average, hence the drought worries currently affecting large areas of western Europe.

When the current La Nina phase ends, the nornal pattern should reassert itself and then the heavens will open....probably just in time for summer.