Met4Cast Weather Guides Section is where you can read and learn about a range of various weather topics at a beginner level. This is a great place to begin if you are learning about GCSEs.



Precipitation
There are several types of precipitation and they vary as a result of changing atmospheric temperatures and convection in the clouds. The most common form of precipitation is rain. This falls from the sky if lower level temperatures are not cold enough for sleet or snow, basically Spring, Summer and Autumn, but often in Winter if we pick up a mild wind direction. Snow, as you have learnt from the Snow Guide falls when certain temperatures in the atmosphere and at ground level are present. Sleet occurs when the temperatures in the lower layers of the atmosphere are not quite as cold as they should be, the snow basically melts as it falls from the lower part of the cloud. Freezing rain is a fairly rare event and occurs due to Temperature Inversion. This is when the upper atmospheric temperatures are milder than the lower level temperatures. The rain particles melt but start to freeze as they hit the ground. This condition can be very dangerous.

Reading Charts
Now onto the hard part - this is what meteorology is all about and it can be significantly difficult to understand, so I will explain the basics. We look at various weather charts or models that indicate the different air pressures, wind direction, rainfall, cloud and other more complicated observations. Our atmosphere is made up of different levels or layers. We measure temperature, pressure and wind direction at various levels of our atmosphere, not just the surface. We measure each layer in units called millibars (mb) or hectopascals (hPa) - both of which use the same gradient so it doesn't matter what you use. Below I will briefly outline the main layers of the atmosphere:

The Planetary Boundary Layer - This is the Surface Layer of the atmosphere, i.e. where we are sitting or standing. This is usually around 1000 hPa to 970 hPa.

The Troposphere - This is the Layer where most of our weather occurs. It can sometimes be called the Boundary Layer, and is around 900 hPa to 700 hPa, slightly further up than the Surface. Thunderstorm Clouds rise up into the Tropopause, a thin layer just above the Troposphere.

At the Tropopause, the process in which air cools as it rises stops. The process in which air does cool in the lower layers is called Adiabatic Lapse Rates. Thunderstorms can actually rise higher than the Tropopause, sometimes into the Stratosphere.

The Stratosphere is even higher than the Tropopause and the lower level of it is called the O-Zone Maximum, where no form of weather can occur due to a lack of moisture.

The Stratopause is a thin layer above the Stratosphere. Temperatures rapidly fluctuate above the Stratopause into the Mesosphere. The Stratopause is outside the ozone layer. This mean gravity begins to fall.

There are a few more levels running up the Exosphere, but it woudld take a long time to explain all of these and there is no need. We read charts at layers between 900 hPa and 300 hPa usually, as these are the parameters in which most of the weather occurs. Some of these layers will be explained in the PDF below, along with how to read the charts and write your very first forecast.

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Severe Weather
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