Understanding Pressure Patterns


Welcome to our new and improved weather guide to Understanding Pressure Patterns & Reading Weather Charts. If you don’t know much about weather forecasting, and you’d like to learn how you can give it a go yourself, you’ve come to the right place. Once you’ve read through these guides, you will then have the knowledge to look at the forecasting models, and have a go at forecasting yourself. The first thing we need to do is familiarise ourselves with Pressure Patterns and what they mean, by doing so it’ll make reading the weather charts far easier.

Click Image to View

High Pressure

High Pressure is often associated with warm, sunny days during the summer months, and cold, foggy days during the winter months. However, during the winter if High Pressure is placed correctly, it can mean days of cloudy, dull weather. High Pressure systems are often large and slow moving. Winds circulate in a clockwise direction around the center of an area of high pressure. You will commonly hear weather forecasters on the TV saying “A ridge of high pressure” this generally indicates settled, calm weather. So in general, when high pressure is in charge, we can expect little in the way of rain and calm winds. During the winter months high pressure can bring cloud, fog and frost, during the summer months it brings warm, sunny weather.


Click Image to View

Low Pressure

Low Pressure, as you might have already guessed is the complete opposite to High Pressure, whilst High Pressure brings settled weather, when we have Low Pressure in charge we’re likely to see wet and windy weather. Low Pressure is caused by rising air, its this rising of the air that allows water vapor to move upwards forming clouds. The deeper the area of low pressure the faster the air rises, and as this air rises colder air rushes down to take its place, creating wind. Wind circulates in an Anti-Clockwise direction around the center of a low pressure system.

Weather Charts

Now that we know the two different types of weather patterns and what weather we get from them. We can now talk about spotting them on weather charts. The lines on the weather charts are called Isobars, and these lines show equal pressure. We can use these Isobars to see how deep an area of low pressure is or how high an area of high pressure is. Pressure is measured in Millibars (MB) we can also use them to tell which direction the wind is going to be coming from. Remember, High Pressure circulates clockwise around an area of High Pressure, and Anti-Clockwise around an area of low pressure. High Pressure is marked with an H on the pressure charts, and low pressure is marked with T.

The arrows on the chart above show us which direction the wind will be coming from in a setup like this. With High Pressure to the South-West of the United Kingdom and Low Pressure to the North East of the United Kingdom, we see winds coming in from a North/North Westerly Direction. Here is a second map showing something different.

The above weather chart shows high pressure to the South of the United Kingdom and Low Pressure to the North. When a setup like this develops we usually see slack mild Westerly winds and areas of rain and showers moving Eastwards.

There are several different weather models that we use to get a more accurate picture of what the future weather could hold. Generally anything beyond 5 days becomes very changeable, the further out you look, the more unreliable the models become. When you click on the different models below you will see numbers, these numbers represent the number of hours until that pressure pattern happens. But as I said, anything outside of 5 days must be taken as gospel. The three main models we look at are the GFS, ECM and the UKMO. The UKMO are charts that the UK Met Office provide to the public.

GFS

ECM

UKMO

Generally, we’ll look at the 500hPa charts to get a general idea of the pressure patterns we can expect. We then click on the “Niederschlag” tab on the GFS chart to see predicted rainfall across the United Kingdom and Europe

So that’s the basics of weather patterns and weather charts. I’ll be covering the weather charts again in the other guides when i’ll be focusing on the types of patterns we look for, for particular weather events. Thanks for reading.

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7 Comments on “Understanding Pressure Patterns”

  1. phoebe shikuku Says:

    this information is quite timely for my course work,am a meteorology student and appreciate greatly you posting me with more information about weather and climate to boost my learning

    Reply

  2. Julezyme Says:

    Very interesting, succinct, and informative!

    Reply

  3. ros Says:

    As a retired person (not a student) I would like to know the measurements (or numbers) for “high pressure” and “low pressure” – to simplify – what is 1-10 for low pressure, and what is 1-10 for high pressure.?? Many thanks

    Reply

  4. Claire Says:

    Awesome information. I have just started my introduction to meteorology. I have always been interested in the weather and like to go out and research storms storms. and its nice to get to know people that are interested in the weather .

    Reply

    • Daniel Smith Says:

      Hi Claire!

      Goodluck with the Meteorology, i’m sure you’ll cover pressure patterns in much more detail than on here! Who knows, maybe you’ll be giving me a few lessons a couple of months down the line! 🙂

      Reply

  5. Pebshamboy Says:

    Thank you Dan, well explained, I actually understood that. Maybe I`ll get the courage up to make a forecast one day !!

    Reply

  6. colinb Says:

    Hi, iam a newbee but uterly entranced as to how the weather works, my question is how do the low preassures form, what instigates them, and how does the jetstream influence it.

    Reply

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