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Metcheck Forecast Room - Meteorological Discussions
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Sometimes, the front page articles just aren't big enough to cover all our thoughts and ramblings on the developing weather.
By using graphical analysis from the weather models, as well as full forecasting terminology, you can see how events are being discussed here at Metcheck. The discussions aim to provide unparalleled access to forecasters thoughts and you may even start talking like us too ;-)
Here are the latest discussions from the Metcheck forecasters.
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| Current Discussions (PREMIUM ONLY) |
| Radiation Fog - What Is It? |
We often get to this time of year and begin to hear the word 'fog' mentioned in forecasts. Fog can have some serious implications on every day life, depending on how thick it is and where it's located. With high pressure being the outlook for the foreseeable future there is a reasonable risk that fog will become a feature of the weather. Here we take a look at what fog is and what kind of conditions you need to get fog...
Starting with what fog is first.
There are different types of fog, but we are specifically looking at radiation fog, the fog that develops on long clear nights during autumn and winter.
Fog is essentially a cloud that is in direct contact with the ground. It can vary in density and also height. Fog (like a cloud) is made up of tiny water droplets. Sometimes you may see a shallow layer of fog in a valley or over a marsh land. But then fog can become very dense indeed leading to very poor visibilities and during the winter can last all day long.
So what are the ingredients to get fog formation?...
1) Saturated air is required at the surface. Just like when a cloud develops moisture is needed and the same goes with fog. If the atmosphere near the earth surface is very dry then fog won't develop. So a moist landmass is required. What can be helpful in creating fog is a late afternoon rain shower to wet the ground.
2) Clear skies allow the surface temperature to cool off at a higher rate. This process allows the surface temperature to reach what is known as the dew point (the temperature at which air is saturated). When this is reached the atmosphere is very moist and fog can then form. So clear skies are a must!
3) Light winds are very important indeed. Strong winds allow drier air from higher up in the atmosphere to mix with the air near to the surface and as we mentioned before a moist air mass is required for fog to develop. So any dry air coming into the equation will either stop fog from developing or disperse it.
So if you combine the above together you need; moist atmosphere, clear skies and light winds. These conditions are all usually possible in association with high pressure. High pressure (anticyclone) during autumn and winter will bring a threat of fog if the above conditions are present. Find below a surface pressure chart which may lead to fog development;
The high pressure is bringing light and variable winds and depending on the cloud amounts beneath the high pressure, clear skies at night are likely.
So if you notice clear skies after dark, light winds and a rising humidity level you may well just wake up to a dense fog by morning.
Discussion Added : 03 October 2007 |
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