Frost come in many different guises

20th February, 2015

After what has been a relatively mild few days here in the east, it looks set to turn chillier again next week. Having spent long periods of the week basking in mild and sunny days, it would appear we can expect colder nights once again with a strong risk of a frost.

Frost can be a tricky thing to forecast, mainly because there are so many variables to our weather that will determine whether frost has an opportunity to form. For that reason it is often difficult for experts to forecast a ground frost more than a few days in advance.

Frost is actually quite a broad term and can take several forms.

Ground Frost

We experience a ground frost when the temperature of the ground, objects and trees falls below freezing, causing water to freeze and ice to form. To measure for a ground frost forecasters place a thermometer 5cm from the ground and if the temperature at this point hits 0°C then a ground frost is recorded.

Gardeners will often take a keen interest in the chances of a ground frost occurring, as well as those of a grass frost. This occurs when natural surfaces, such as grass, freeze and man-made surfaces such as concrete do not.

Air Frost

In modern meteorology, experts measure the lowest level of the atmosphere at a height of 1.25 metres (roughly 4 feet) above the ground. When the temperature as measured in this way falls below 0°C then an air frost is recorded. This will be measured by placing thermometers in a double-louvered screen, with the bulb of the thermometers at the 1.25 metre standard.

Hoar Frost

A hoar frost is something we typically associate with a frosty morning following a clear and chilly night. It is composed of many tiny ice crystals and forms through the same process as dew, but when surface temperatures have fallen below freezing point. This can take two forms:

  • White Frost: Composed of globular ice, a white frost occurs when dew forms and is then subsequently frozen once the temperature reaches 0°C.
  • Feathery Frost: Consists of what appears to be feathers or needles and occurs when dew forms after temperatures have already fallen below freezing.

Glaze and Rime

  • Rime: This is a rough, white deposit and is formed when super-cooled water droplets of fog freeze upon contact with vertical surfaces as it drifts past.
  • Glaze: Many people mistake glaze for a wet surface, making it incredibly dangerous. It occurs when super-cooled rain or drizzle comes into contact with the ground when its temperature is well below 0°C

Our team have been trained by the Met Office and are highly skilled when it comes to the interpretation of complex forecast data. At the first sign of freezing conditions we will immediately take action to protect our clients' sites from the threats of snow or ice.

If you would like more information about the winter maintenance services we provide, please click here or call us on 01728 633900.

Thermometer in the snow

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