Clouds

There are several types of clouds, and they are split into 3 catagories, Low Clouds, Middle Clouds and High Clouds.

LOW CLOUDS

Stratus clouds are a kind of grayish cloud that often cover the entire sky. They resemble fog that does not reach the ground. Usually no rain falls from stratus clouds, but sometimes they may drizzle.

Nimbostratus clouds form a dark gray, “wet” looking cloudy layer associated with continuously falling rain or snow. They often bring light/moderate rain.

MIDDLE CLOUDS

“Alto” Clouds

Alto Clouds are middle level clouds that have bases between 2000 and 7000 m (6500 to 23,000 ft.).

Altocumulus clouds are made of droplets of water,  and appear as gray, puffy clouds which can sort of be rolled out in parallel waves or bands. These clouds can result in thunderstorms.

Altostratus clouds are gray or blue-gray that are made of both ice crystals and water droplets. They usually cover the entire sky. In the thinner areas of the cloud, the sun may occasionally be seen. Altostratus clouds often form ahead of storms that will produce a lot of rainfall.

HIGH CLOUDS

Cirrus Clouds

Cirrus clouds are thin, wispy clouds that are blown by high winds into long streamers. These are high clouds, which can be found over 6000 m (20,000 ft). Cirrus clouds usually move across the sky from west to east. They generally mean quite nice weather

Cirrostratus clouds are very thin, high clouds that can cover the sky. They are so thin that the sun and moon can be seen through them

Cirrocumulus clouds appear as small, rounded white puffs.

Cumulus clouds are puffy clouds that sometimes look like pieces of cotton wool or candyfloss. The base of each cloud is often flat and may be only 1000 m (330 ft) above the ground. The top of the cloud has rounded towers. When the top of the cumulus resembles the head of a cauliflower, it is called cumulus congestus or towering cumulus. These clouds grow upward, and they can develop into a giant cumulonimbus, which is a thunderstorm cloud.

Info taken from Wikipedia

 

Severe Weather – The Tornado

The United Kingdom has around 33 tornados per year, which is the second highest amount per land area in the world.

Although still made up of wind, a tornado is a completely different kettle of fish from a hurricane.  A tornado forms over land, it is a violent rotating column of air extending from a thunderstorm to the ground, and in some cases can destroy anything in its path.  Tornados can have windspeeds reaching 300mph, and can often form with very little warning.  Most tornadoes form from thunderstorms. You need warm, moist air  and cool, dry air. When these two air masses meet, they create instability in the atmosphere. A change in wind direction and an increase in wind speed with increasing height creates an invisible, horizontal spinning effect in the lower atmosphere. Rising air within the updraft tilts the rotating air from horizontal to vertical. An area of rotation, 2-6 miles wide, now extends through much of the storm. Most strong and violent tornadoes form within this area of strong rotation.  A funnel cloud is a rotating cone-shaped column of air extending downward from the base of a thunderstorm, but not touching the ground. When it reaches the ground it is called a tornado.

Twisters, as they are often known, are often accompanied by hail. Giant, persistent thunderstorms called supercells spawn the most destructive tornadoes.

These violent storms occur around the world, but the United States is a major hotspot with about a thousand tornadoes every year. “Tornado Alley,” a region that includes eastern South Dakota, Nebraska, Kansas, Oklahoma, northern Texas, and eastern Colorado, is home to the most powerful and destructive of these storms. U.S. tornadoes cause 80 deaths and more than 1,500 injuries per year.  The meteorological factors that drive tornadoes make them more likely at some times than at others. They occur more often in late afternoon, when thunderstorms are common, and are more prevalent in spring and summer. However, tornadoes can and do form at any time of the day and year.

Tornadoes’ distinctive funnel clouds are actually transparent. They become visible when water droplets pulled from a storm’s moist air condense or when dust and debris are taken up. Funnels typically grow about 660 feet (200 meters) wide.

Tornadoes move at speeds of about 10 to 20 miles (16 to 32 kilometers) per hour, although they’ve been clocked in bursts up to 70 miles (113 kilometers) per hour. Most don’t get very far though. They rarely travel more than about six miles (ten kilometers) in their short lifetimes.  Like hurricanes, tornados are classed by windspeed, as hurricanes have the saffir simpson scale, tornados haveThe Fujita Tornado Scale:

Category FO – Gale Tornado Category 40 – 72 mph
Light damage: some damage to chimneys, breaks branches off trees, pushes over shallow-rooted trees, and damages sign boards.

Category F1 –  Moderate Tornado Category 73 – 112 mph
Moderate damage: The lower limit Category 73 mph– is the beginning of hurricane wind speed, peels surfaces of roofs, mobile homes pushed off foundations or overturned, and moving autos pushed off roads.

Category F2 –  Significant Tornado Category 112 – 157 mph
Considerable damage: Roofs torn off the frames of houses, mobile homes demolished, boxcars pushed over, large trees snapped or uprooted, and heavy cars lifted off ground and thrown

Category F3 –  Severe Tornado Category 158 – 206 mph
Severe damage: Roofs and some walls torn off well-constructed houses, trains overturned, most trees in forest uprooted, and heavy cars lifted off ground and thrown.

Category F4 – Devastating Tornado Category 207 – 260 mph
Devastating damage: Well-constructed houses leveled, structures blown off weak foundations, and cars and other large objects thrown about.

Category F5 – Incredible Tornado Category 261 – 318 mph
Incredible damage: Strong frame houses are lifted off foundations and carried a considerable distance and disintegrated, automobile sized missiles fly through the air in excess of 100 meters, and trees debarked.

Category F6+ –  Inconceivable Tornado Category 319 – 379 mph
The maximum wind speed of tornadoes is not expected to reach the F6 wind speeds.

Tornadoes can be classified into one of three types:

Weak Tornadoes Category F0/F1
These tornadoes account for 74% of all tornadoes. They cause less than 5% of tornado deaths. Their lifetime is usually 1 – 10+ minutes with wind speeds less than 113 mph.

Strong Tornadoes Category F2/F3
These tornadoes account for 25% of all tornadoes. They cause nearly 30% of all tornado deaths and may last 20 minutes or longer. Their wind speeds are clocked between 113 and 206 mph.

Violent Tornadoes Category F4/F5
These rare tornadoes account for less than 2% of all tornadoes. However, they cause 67% of all tornado deaths nationwide. They may last for one hour or more with wind speeds greater than 206 mph.

Hurricanes

Hurricanes, cyclones, tropical storms, typhoons….these are all the same thing, but are named differently depending where on earth they are formed.

A storm that is created in the North Atlantic Ocean, the Northeast Pacific Ocean (east of the dateline) or the South Pacific Ocean (east of 160E) will be called a Hurricane.  The same kind of storm that forms in the Northwest Pacific Ocean, west of the dateline, will be called a Typhoon.  A Tropical Cyclone will form in the Southwest Indian Ocean.  These kind of storms can cause catastrophic damage if they reach land.

How do they form?

In the case of a hurricane, the storm begins life in tropical regions. They form there because they need warm water of at least 26°C, high humidity with moist air, light winds, and very warm surface temperatures. Summer and the early fall months are perfect for hurricanes to brew up in the oceans around us. Most of the Atlantic hurricanes brew up on the coast of Africa. For that the northern hemisphere hurricane season is considered through the months of June and November.  Continue reading

How does it snow?

Most precipitation that falls to the earth actually starts off as snow. The process of water forming into snow begins high in the earth’s atmosphere.

I have often heard the term “too cold for snow“.  This is in fact a myth, how else would the poles have so much of the white stuff?  As long as there is some source of moisture and some way to lift or cool the air you can get snow. It is true, however, that most heavy snowfalls occur with relatively warm air temperatures near the ground, typically -9°C (15°F) or warmer, since air can hold more water vapor at warmer temperatures.  However, the snow can still reach the ground when the ground temperature is above freezing if the conditions are just right. In this case, snowflakes will begin to melt as they reach this warmer temperature layer; the melting creates evaporative cooling which cools the air immediately around the snow flake.  As a general rule though, snow will not form if the ground temperature is above 5°C.

Snow forecasts are better than they used to be and they continue to improve, but snow forecasting remains one of the more difficult challenges for meteorologists. One reason is that for many of the more intense snows, the heaviest snow amounts fall in surprisingly narrow bands that are on a smaller scale than observing networks and forecast zones. Also, extremely small temperature differences that define the boundary line between rain and snow make night and day differences in snow forecasts.

This is part of the fun and frustration that makes snow forecasting so interesting.

What shapes our weather?

Britain is an Island, and as such we are obviously surrounded by water, which massively influences our weather.

Northern Ireland, Wales and western areas are generally milder and wetter than other parts of the country, and are also generally windier. The weather in these parts of the Uk is mostly down to the influence of the Atlantic Ocean. In the east however, the weather is usually drier and colder than in the west, and here in the North East our weather is shaped by the continental polar air mass.  Generally speaking, the South East of England is thought to have the best summers of anywhere in the UK, while the North of Scotland  generally experience the colder weather.

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