Pressure – What exactly is it?

You will have heard a million times forecasters talking of high or low pressure systems, but what exactly are they, and how do they affect our weather?  A huge amount of air is pushing down on us at all times, the gases in the air are made of tiny molecules that although we can’t see them, are taking up space and have weight.  The reason we can’t feel this is because our bodies also have air, which pushes outwards and this creates a balance between the two.  Warm air molecules move quickly and push each other apart, meaning the air gets lighter and rises.  Cooler air molecules move slowly, and they take up less space than the warm air molecules, and as the air becomes denser and heavier it sinks.  Air pressure is the weight of the air pushing down on the earths surface, when air warms up it rises, when air cools and sinks there is high pressure.  Air pressure varies all over the planet as different areas receive different amounts of the suns warmth.  Pressure is measured with a barometer, and is recorded as millibars (mb).  There is a difference between absolute pressure and sea level pressure.  You can find your sea level pressure with a quick google search by typing in your location.  My weather station records the actual pressure where I am, and will be different to those nearer the sea.  Where there are hurricanes/typhoons the pressure at sea will drop very low, as these storms from from low weather systems.

High Pressure

As stated, when the air cools it sinks, and this means there is more air pushing down on the earths surface, thus the air pressure rises.  As the air sink it becomes warmer and drier and the clouds disappear, so areas of high pressure usually bring warm dry weather with clear skies.  In weather maps, high pressure will be depicted as red.

Low Pressure

When the air warms it rises, leaving less air pushing down on the earths surface, and this leads to the pressure going down.  Areas of low pressure, which are usually described as a depression, bring rain, wind and storms, and changeable temperatures.  As high pressure is shown as red on weather maps, low pressure is shown as blue.

So generally, high pressure = good, low pressure = bad.  Here in Britain, when we have typical weather for the seasons, we will have high pressure in spring/summer, and low pressure in autumn/winter.  The reason we haven’t had the typical weather patterns lately is because of the jet stream, because it has been sat to the south of the UK for much of the past 18 months it has allowed low pressure to sweep right across the UK, usually in summer it sits above us, therefore drawing away low pressure above us and allowing high pressure to build.  This is the kind of weather we have been seeing lately, the jet stream is in its more typical place for this type of year so the low pressure is being dragged north of us.  Let’s all hope it will stay there throughout July and August!



Hottest day recorded, and broken 3 times this week! will it last?

So Saturday saw the hottest temperature I have recorded at 27.6c, Tuesday then broke that record at 28.7c, and today we have reached 29.8c, with a good chance we will top 30!  The question everyone is asking is will it last?  The answer is yes, it certainly could, potentially until the end of July believe it or not.  This has been the longest real summer weather we have experienced since 2006, and many have welcomed it with open arms, myself included.  The reason as I have explained previously is the Jetstream (Jetstream is explained elsewhere on the site) is currently situated well to the north of the UK, pushing away all low pressure and allowing high pressure to pretty much dominate the entire country.  Northern Ireland has recorded the hottest temperatures of this current spell, reaching 29.9c, which is only just under a degree hotter than the hottest ever record.  The chances are that will be well beaten this weekend though.  Some coastal areas, South Tyneside included will find temperatures dropping over the weekend with some cloud rolling in off the North Sea, that is not to say it will be cold by any means, it will still be in the 20s and will feel very warm in the sunshine.

The rest of the month appears for now to remain largely warm and dry, there is the chance of a few showers, which you would expect this time of year, but by no means a washout.  All in all enjoy the weather, make sure you wear suncream mind even in cloudier conditions, I can testify how easy it is to get caught out by the Rudolf look I am currently sporting after strolling yesterday morning in cloudier conditions!

Summer arrives in style!

So after forecasts of a heatwave for over a week, the good weather began on Friday as high pressure built over the UK, and yesterday we hit this years high, in fact, the highest I have recorded since having my weather station (records began December 11 2011).  The top temperature was 27.6c and was reached at 14.30, and it was by anybody’s reckoning a glorious summers day, we had wall to wall sunshine and not a cloud in the sky.  Many are in agreement that this will be our best weather since July 2007, and although there are signs that the weather may break down by the 15th this is not a certainty, and also even if it does it will not be a washout like we have had in recent years, and the weather should stay around average for the time of year.  All will become clearer as we get closer to the time, all forecasts and models are more reliable a few days before hand.  Check back for more info on what to expect over the next few weeks

Summer ready to arrive?

After much debate over whether we will have to endure another washout summer, and it did actually look like a bit of a damp squib until recently, it is now fairly certain that from the end of this week at least we shall experience some glorious summer weather.  All charts now seem to be in agreement that from around Friday temperatures will rise and blue skies and sunshine are on they way, and could actually stick around for a while.  Some say we could have the hottest July temperatures since 2006, which I have to say would be very welcome after last years washout.  The chart below gives a brilliant indication of what is to come:

A brilliant sight to see :)


That chart is for the 10th July, so you can see how well the UK is looking for this time.  Let’s just hope it continues until autumn, and is followed by a nice snowy winter!

The reason the weather is set to improve is again down to the position of the jet stream, which is set to head well north of the UK, allowing high pressure to build from the continent.  This picture is taken from Matt Hugo, and shows the position of the jet stream and how it allows the high pressure to reach us:

In summer, high pressure from the continent brings warmth and summery weather, whereas in winter it brings cold and snow.  Weather systems from the Atlantic (low pressure), regardless of season bring with them  wind and rain, and while we would expect these kind of weather systems to dominate through autumn or springtime, the position of the jet stream over the past few years has meant we have had Atlantic weather a lot more than usual, and this caused a lot of the flooding throughout last year.  In short, if everyone blows north we may be able to keep the jet stream well clear of us, and the summery weather will remain!