Video instructions and help with filling out and completing How Form 2220 Forecast

Instructions and Help about How Form 2220 Forecast

You may have heard weather forecasters on television talking about a warm front or a cold front approaching bringing with it a change in the weather but what are they going on about what is a weather front and how does it affect our weather a weather front is the boundary between two bodies of air with different temperature and humidity these differences depend on where the air has come from on the globe for example air sitting over tropical oceans becomes very hot and humid while in contrast air over the Arctic becomes very cold and dry that's logical enough but what happens somewhere like Britain where our climate is neither tropically warm and humid nor polar cold and dry over the Atlantic these warm cold air masses often meet just like oil and water they don't mix easily and can become unstable as a result giving us an active area of weather in which fronts form when air mass is first collide it's impossible to know if we're looking at a warm or cold front it's only when one air mass dominates that we can distinguish between the two if the warm air is stronger than the cold air then this is called a warm front you may have seen this on TV as a line with red semi circles along it the semi circles point towards the cold air and the direction in which the front is moving if the cold air has the upper hand then it's a cold front which is shown by a line with blue triangles along it the blue triangles point towards the warm air and again in the direction of movement but what is happening when two opposing air masses meet and what kind of weather does each front produce on a fine day if you see a layer of very high cloud beginning to spread across the sky usually from the southwest in Britain it may mean that a warm front is approaching warm air is less dense than cold air so it tends to ride over the top of the cool air it's replacing this creates a vertical slope to the frontal system with the front first being seen high in the atmosphere miles ahead of the front at ground level as the warm moist air is forced to rise it cools and water vapor condenses into water droplets or ice crystals these form clouds that you see approaching first as high cirrus clouds and then as thicker clouds it's these interactions which form clouds if you're measuring the air pressure is the front approaching you'd see that it's falling this is because the column of dense cold air above you is gradually being replaced with more and more warm and less dense air as the front moves closer layers of cloud also deepen and rain begins to fall a warm front usually produces quite a long period of light and drizzly rain with a shorter spell of heavier rain at the beginning of the front the rain or drizzle will eventually die out once the front has moved through but it will often stay pretty cloudy you might think that a warm front would mean nice warm weather but unfortunately that's not always the case all that rain and loss of sunshine can mean that temperatures are actually lower than they were before the front arrived so why is it called a warm front well the cold dry air mass has been replaced by a warm humid airmass it just doesn't feel much warmer but what about cold fronts warm fronts are easy to spot because you see the leading edge of high cloud approaching on the horizon across clear skies however warm fronts leave clouds behind and the following cold front sneaks in under the cover of the clouds this makes them hard to spot just using your eyes as it's difficult to see any changes that might be on the way but remember that the pressure Falls with a warm front because the air is less dense well the opposite is true with a cold front a cold front is a bit like a wedge the air is colder and more dense than the warm air and it scoops it up causing the pressure to rise and we can spot that using a barometer so what kind of weather does a cold front bring deep cloud layers form as the warm moist air is forced to rise and cool these cloud layers produce lots of rain often in bands and these bands tend to be quite narrow with heavy rain in them sometimes with even hail and thunder once the front passes there's often a dramatic clearance with blue skies bright sunshine as the cold air descends as the front passes temperatures fall at first but they may rise again when the sunshine appears however this sunny weather doesn't always last for very long because if the cold air is warmed it will rise or convect as weather men say and produce sherry rain clouds just cumulus or Kuno Nimbus as we've seen weather fronts can be complicated things and bring with them some very varied weather which is one of the reasons we have such an interesting time of it here in this country we've looked at how warm and cold fronts are formed and what sort of weather they bring but if you want to learn anything more about weather fronts or anything to do with weather and climate visit the Met Office website you you