December 2007

So why so much rain?

Some that watch Cwmparc weather station may question why we record such high rain totals in Cwmparc when stations a few miles south record much less. Where is the rain gauge? Under a waterfall?

This is something that perplexed me when I started taking records manually in Cwmparc - at that time using a glass instrument to measure the rainfall. I quickly noticed that sometimes two inches or more had sometimes fallen into my gauge when maybe only half an inch had fallen less than 20 miles away. I also noticed the nearest weather station to Cwmparc - Nantymoel - only a few miles to the South West as the crow flies - often recorded less rainfall - sometimes quite large amounts - particularly for a station so near.

Firstly I have to say the instruments I use are good ones, they are calibrated well, and sited to do the job they are meant to do well. But there has to be a reason so what was it? This is where I quickly learned an important lesson in topography.

The station to the South West of me is over on the other side of the Bwlch mountain - the first mountain in a series that the moisture laden sub tropical air from that direction encounters on the way to and over the Brecon Beacon's. As our wettest weather comes from the South West to Westerly quarter weather systems - and more important winds - pass over Nantymoel weather station first. But as the moisture laden wind approaches the Bwlch mountain air is forced up the steeply sided mountain that has a top height of 1600 foot. Simply put this warm moist sub maritime air is pushed up into the colder air above, where the moisture rapidly condenses into thicker clouds. Just over the other side of the mountain, on the other slope at 770 foot is Cwmparc weather station. And of course it here that the results of all that condensation is seen - in the form of heavy rain. Comparing conditions with the Nantymoel station and mine it can often be observed that it is dry in Nantymoel - while raining at Cwmparc.

Often was the case when I worked by the seaside about 15 miles away as the crow flies - for me to hear it is raining at home - even though I was basking in sunshine. Amazing isn't it. The price we pay for living on high ground. Weather here is all to do with Topography that give us very localised weather. Of course this means the recorded rain for Cwmparc being so very localised is not a general indication for South Wales in general.

More normal patterns to the North and East.

One feature that has been obvious in this apparent warming world of ours has been the milder winters here in Wales - and also in Northern Latitudes in general. As an avid watcher of weather web cams it was with disbelief I watched last year as a whole winter of well above average temperatures in Russia and Scandinavia were observed. There have been a run of recent winters in Russia that have been much warmer than the norm. Cause for concern although weather patterns rather than global warming seems to have been the cause.

One essential ingredient for snow lovers here in the UK is for these far distance shores to cool off substantially. No good having a wind all the way from Siberia if the air is not cold enough to provide us with enough cool to give snow lovers the snow they desire.

Cold lovers will be pleased to hear this year there has been an astonishing u-turn in weather patterns with the cold now well established in places that were last year - at least temperature wise - well above normal for time of year. Arctic sea areas have been freezing well after record ice loss reported during the last summer, and has more than made up for the losses with ice in most places being the same - or above last years level. Rovaniemi's Sillat river is now frozen and unlike last year when the snowman in Rovaniemi's Lordi's square had to be constantly patched up due to the warm temperatures, everything remains frozen. Good news indeed for those jetting off to Lapland with the children to visit Father Christmas. Svalbard in Norway's Arctic circle is much colder than last year and most parts of Northern Norway have had good snow cover. St Petersburg, Russia is well below zero as I write and the canals frozen - and Kemerovo, Russia is deep in snow.

Alaska is in the deep freeze and is in general much colder than during the same period last year. As I have mentioned in previous blogs weather patterns have this year been much different than for some while - so don't be deceived if the first half of December in the UK are more Atlantic driven and warmer. The winds and heavy rain of the last few days, and of the coming week to ten days, were to expected with a rapidly cooling Canada and Northern America. With temperatures as low as -20C in some places leaving these shores and heading towards the UK over a warm sea, a simplistic explanation is that moisture is picked up as the air moves over a warm ocean, depressions form, and the huge temperature differences between the north and us make for violent winds. The reason being that air will always try to equalise Of course the air is much warmer when it arrives into the UK. It is fact the UK at the latitude we live is a battle ground between the cold arctic air and warmer tropical air.

One things is becoming all the more certain this winter - and that is for there to be periods when the cold air will win - and for snow lovers to rejoice. But will the snow arrive in time for Christmas? Look out for my next blog when I will try to give an indication of the chances on Christmas snow.

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