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Weather report for primary schools for Friday 9 February 2001
THE HEADLINES
TODAY
Runaway fires in South Africa. The sun appears in Jakarta. The sun still sleeping hidden in Portugal. Another day in paradise in Madagascar. More rain in Zimbabwe. Windy and cloudy in Illinois. Crisp and cool in the British Isles. Expensive vegetables in Japan.
THE WEATHER IN
THE METLINK WORLD TODAY
On this, the last day of MetLinkInternational 2001 that we exchange observations, we begin at the home of the body that organizes the project, namely the Royal Meteorological Society, Reading, UK. Where is Reading? It is 60 km (37 miles) west of London. What was the weather like there today? It was very pleasant, though a little cool for some people. The day dawned frosty, but the temperature soon rose above 0°C and the sun shone. At 0755 UTC, when the author of the daily weather reports, Malcolm Walker, the Education Officer of the Royal Meteorological Society, made the observation that is in the project’s database, there was just a breath of wind from the north (i.e. a northerly wind) and the temperature was +1.2°C. The main cloud type was altocumulus and patches of cirrus could be seen above the medium-level cloud. Quite a number of aircraft condensation trails could be seen.
In the middle of the morning, Malcolm drove to Bracknell, which is nearly 20 km east-south-east of Reading. At Bracknell, he attended a meeting at the headquarters of the Met Office, the UK’s national meteorological service and a generous sponsor of the 1999, 2000 and 2001 MetLinkInternational projects. Between 0945 and 1020 UTC, whilst he was driving to Bracknell, he observed cirrus, altocumulus and a few small cumulus clouds. The outside temperature, according to the car’s on-board thermometer, was about 5°C. When Malcolm drove back to Reading, between 1220 and 1255 UTC, the temperature was about 8°C and the cloud types were the same. However, the number of cumulus clouds had increased considerably and their height had increased a little. The clouds had very-noticeably flat bases, which is a common feature of small cumulus clouds.
When Malcolm left Reading to drive home, at 1530 UTC, he found that the temperature had dropped to 5°C and the cumulus clouds had disappeared. This was presumably because the ground was not now being heated sufficiently to create the bubbles of warm air (called thermals) in which clouds form when the bubbles have risen far enough for condensation to take place. On his way home, however, he noticed two quite large cumulus clouds over the cooling towers of a power station. From these towers, warm moist air was being emitted and the air was rising sufficiently for condensation (cloud-formation) to take place. Have you ever noticed cumulus clouds over and/or downwind of a power station? The clouds Malcolm saw today were almost directly above the power station, indicating that there was very little wind. Had there been much wind, plumes containing clouds would have streamed downwind.
When Malcolm arrived home, at 1550 UTC, he found that the temperature was 3°C. He began his journey at Reading, which is about 40 m above sea level, and his home is about 160 m above sea level. The temperature is normally a couple of degrees Celsius lower at his home than in central Reading, where the Royal Meteorological Society is situated. The difference in altitude is partly responsible for the temperature difference, but there is also an urban heat-island effect. Malcolm’s home is in a village in the country. He has noticed when driving to and from work that the majority of the temperature change between Reading and his home tends to occur within a kilometre or two of the edge of the built-up area.
A car’s on-board thermometer is useful for doing temperature surveys, but some points about the accuracy of the thermometer’s readings have to be borne in mind. The sensor of the thermometer attached to Malcolm’s car is behind the front number plate. In traffic queues, the temperature shown by the thermometer rises a degree or two quite quickly, partly because heat from the engine affects the thermometer’s readings and partly because the hot exhaust gases of other cars reach the sensor. Nevertheless, for studying the general features of temperature distributions around an area, a car’s on-board thermometer is useful. A survey of temperature variations on a showery day can be interesting. The spatial temperature variations on such a day can be quite large — as much as 8° to 10°C when going in and out of the cold downdrafts that descend from vigorous cumulonimbus clouds.
Elsewhere in the British Isles today, the weather was crisp and clear in most places, and aircraft condensation trails (contrails) were observed at Alleyne’s High School in Staffordshire and Radley College in Oxfordshire. The morning was frosty at Cashel in Ireland, breezy with a blue sky at Bedales School in Hampshire, breezy at Casterton in Rutland, cool and dry at Westbourne House School in Sussex, "sunny and dry" at the BBC Weather Centre in London and "sweet" (pleasant) on the Isle of Bute. "A cold start and frosty" was the comment made by the students of Clifford Primary School, Hereford. "A beautiful, clear, frosty morning" was the comment from Delabole Community Primary School in Cornwall. "Crisp and cold with some sun", said the students of Castle Hall Language College in Yorkshire. "Clear, bright and crisp" was the comment from the Medina Valley Field Centre on the Isle of Wight. "Bright and cold, quite a penetrating breeze", said the students of Bryanston School in Dorset.
Today’s hot-spot was again Melbourne, where the maximum temperature recorded at Trinity College was 37°C. Today was, however, much cooler than of late, with the temperature only 20°C at 0100 UTC (1200 Local Time). The northerly wind that brought hot air from the interior of Australia to the Melbourne area has been replaced by a cool wind from the south. Yesterday was sunny, but today was a contrast, with cloud and some drizzle.
The coldest place in the MetLink world today was again Edmonton in Canada, where the minimum temperature was —19°C and the temperature at 1500 UTC today (0800 Local Time) -10°C. The temperature at Longyearbyen School this morning was actually a shade lower than at Edmonton (-10.5°C) but the minimum temperature was not as low as Edmonton’s. The temperature at Vörå fell to —10.4°C overnight and was —5.2°C at 1105 UTC, when the students made their observation. At the South Pole, in contrast, the temperature today was —38°C! Did you know, by the way, that alcohol thermometers have to be used in places where temperatures fall to such low values? Mercury thermometers cannot be used because mercury freezes at —39°C.
A maximum temperature of 31°C was recorded at Puerto Vallarta in Mexico, where today was, in the words of the students, "a beautiful day". A maximum of 31°C was also recorded at Antananarivo in Madagascar, where there was slight rain this morning but today was, nevertheless, called "another day in paradise". Two Boats School on Ascension Island ‘topped’ both places, with a maximum temperature of 32°C, but here, too, rain fell.
In other parts of the tropics and subtropics, there was a variety of weather. Jakarta saw the sun today (at last!), but at Leilehua High School on Oahu (Hawaii), the weather was again cloudy. The temperature at 1300 Local Time (2300 UTC) was 22.5°C and a wind of 15 km/h was blowing from the south-east. In Bulawayo (Zimbabwe), the weather was again cool, overcast and wet this morning. The temperature was 18°C and a rainfall amount of 12 mm was measured. At Marondera (also in Zimbabwe), the weather was overcast at 0630 UTC (0830 Local Time) and rain was falling steadily. Here, the temperature was 21.6°C this morning.
The weather at Hilton College in Kwazulu-Natal (South Africa) was today cloudy with light drizzle, with the cloud cover (eight oktas) made up of stratocumulus and altostratus clouds. In contrast, the weather at Micklefield School in Cape Town was again sunny, but a wind of 33 km/h was blowing and the students reported "runaway fires because of drought and wind". Unusually for the time of year, rain fell at Addis Ababa in Ethiopia (during the night).
Central and eastern parts of the Mediterranean from Sicily eastwards had yet another sunny day, but, skies were again rather cloudy over much of central and western Europe. The sun shone at Geilenkirchen in Germany, however, and the weather was sunny but windy at IES Vidal i Barraquer in Tarragona, Spain. The students of Portugal’s Escola Secundária Gabriel Pereira reported that the sun was "still sleeping hidden". "Chilly, cloudy" was the comment from Prague in the Czech Republic, where the sky was overcast (with eight oktas of stratus) and the temperature 8°C. Farther east, at Constanta in Romania, the sun shone but the weather was about the same as in Prague, with the temperature there this morning 8.6°C.
The weather was overcast in northern Italy, with light drizzle at Bozen, but it was warm and quite sunny at Versoix in Switzerland, where the temperature was 16.9°C at lunchtime. The weather was also pleasant in Malta, where there were long sunny periods and the temperature was 16°C at 1000 UTC. Another place where the weather appears to have been quite pleasant is Ljubljana in Slovenia, where there was broken altocumulus cloud and the temperature was 12.5°C. The weather improved during the day at Franeker in The Netherlands, where cloud and light rain gave way to sunny weather with just a few cirrus and cumulus clouds. Temperatures were below 0°C again in Scandinavia, after a brief spell of mild weather, and sleet fell at Bor School in Sweden.
The weather was windy, cloudy and humid at Divernon Middle School in Illinois (USA), and it was also cloudy and windy at Forest Hill Parkway Academy in Cleveland, Ohio (USA). At both places, the temperature was well above 10°C. At Moses Lake, Washington State (USA), however, snow was falling and accumulating at 1800 UTC (1000 Local Time) and the temperature was then —1.7°C. The weather at Tokyo (Japan) was considered cold by the students of Keio Girls’ High School and they reported that vegetable prices were high because of the cold weather.
Where would you like to have been during MetLinkInternational? Please tell us.
NOTES
For central England, there is a monthly temperature series that goes back to 1659. To view the data, click here. For other information about the climate of the British Isles, click here. For monthly rainfall data back to 1766, click here and choose data.
There is material for teachers and pupils in primary schools on the Education pages of the United Kingdom’s Met Office. To go to the Education home page, click here. To go to the Curriculum Learning Centre, click here.
There is a great deal of material suitable for primary schools on the website of the BBC Weather Centre. For the basics of weather, things to do, weather games, stunning weather photographs and much more, visit the Weatherwise, Fact Files, Do-it-yourself (DIY) Weather and Weather Games pages. The Education Officer of the Royal Meteorological Society helped develop these pages.
For a wealth of information about the weather, including the current weather in the USA, visit the website of USA TODAY.
Do you want to find climatic statistics? If so, visit the Royal Meteorological Society’s Climate on the web site.
Do you want to find weather charts, satellite images or current weather data? If so, visit the Royal Meteorological Society’s Weather on the Web site.
Weather report for secondary schools for
Friday 9 February 2001
PLEASE READ THIS REPORT FOR SECONDARY SCHOOLS IN CONJUNCTION WITH TODAY’S REPORT FOR PRIMARY SCHOOLS
ANALYSIS OF TODAY’S WEATHER IN THE METLINK WORLD
AUSTRALASIA
The cold front that lay over western parts of Victoria yesterday reached Melbourne today, bringing with it cloudy weather and a change in wind direction. Ahead of the front, northerly winds brought warm air from the interior of Australia. When the front arrived, the wind swung round to a southerly point, bringing to the Melbourne area cool, moist, maritime air. The following table shows the wind and temperature changes that occurred at Melbourne Airport during the period 0900 UTC (2000 Local Time) on 8 February to 0800 UTC (1900 Local Time) on 9 February. Note that the temperature dropped sharply between 0700 and 0800 Local Time and remained thereafter several degrees lower than it had been during the night. The temperature was lowest at 1400 Local Time.
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Sh = showers; LD = light drizzle; LRS = light rain showers. Wind direction in green = possible sea breeze. Wind direction in red = wind from a northerly (warm) point. Wind direction in blue = wind from a southerly (cooler) point during and after the passage of the front. Source of data: US National Weather Service. For the latest weather at Melbourne Airport, click here.
The front can clearly be seen on the satellite image for 0300 UTC (1400 Local Time) and the weather chart showed that this feature was a cold front from a depression centred near 60°S 145°E, a point close to Antarctica. Today, a High of 1020 mb was centred over the Tasman Sea near New Zealand and another High of 1022 mb was centred at 39°S 118°E, some 500 km south of Albany, Western Australia. Pressure was low over northern parts of Australia, with a depression of 998 mb centred at 15°S 116°E. In this depression and, indeed, in a broad band extending from about 85°E to about 170°E, there was a great deal of cumulonimbus activity. Northern Australia experiences its monsoon season from December to March/April and the broad band of cumulonimbus activity is associated with the Intertropical Convergence Zone (ITCZ), the axis of which lies a little to the south of the equator at this time of year.
The winter anticyclone over Asia has declined a little over the past two or three days and today had a central pressure of 1045 mb. Its position was 60°N 96°E but high pressure covered the whole of eastern Asia, as is usual at this time of year. A ridge extended as far east as Japan. The depression nearest to Japan today was centred at 46°E 170°E (Tokyo being at 39°45’N 139°45’E) and the cold front from this depression lay well to the south and south-east of Japan. A trough from a Low over the Bering Sea (near the Aleutian Islands) lay to the north-east of Hokkaido). Winds over the Tokyo area were very light and variable today.
Skies were again clear over India today, with the North-East Monsoon the controlling influence. Only over Sri Lanka and the southernmost part of India was there any cloud today.
AFRICA AND ASCENSION
Once again, as satellite images show, skies were clear over North Africa, apart from a few patches of cirrus and altocumulus cloud and, unusually for this time of year, an area of low cloud over Ethiopia. The ITCZ was very weak over the Atlantic Ocean today, and the majority of what activity there was on it occurred between the equator and about 5°N. Over the Gulf of Guinea, there was hardly any ITCZ activity at all. There was, though, plenty of cumulus and cumulonimbus activity over central and eastern parts of southern Africa, with rain or drizzle at all MetLink stations in the region. The only MetLink school in southern Africa with fine weather today was the one at Cape Town, where skies were clear. A High with a central pressure of 1021 mb at 39°S 28°E was the dominant weather influence over southernmost parts of Africa today. At Cape Town, which lay between this High and a shallow Low of 1007 mb that was centred at 30°S 17°E, there was a fresh south-easterly breeze of 33 km/h.
Ascension Island lay on the northern edge of the trade-wind zone, with winds from the south-east, and satellite images show that patches of cloud over the tropical South Atlantic were scattered. The cumulus and cumulonimbus build-up over Ascension today may have been associated with strong heating of the island. The sun is high in the sky at mid-day at this time of year in the latitude of Ascension (8°S).
To obtain the latest South African Weather Bureau chart showing fronts and isobars over southern Africa and the Southern Ocean, click here.
NORTH AMERICA AND HAWAII
At 0000 UTC today, there was a High of 1032 mb over the North Atlantic Ocean between Newfoundland and the West Indies, its centre at 35°N 70°W. A Low of 1010 mb was present south-west of the Great Lakes and this Low deepened by 0600 UTC, when it possessed two centres, one of 1006 mb over Lake Michigan, the other of 1002 mb over Oklahoma. In association with the developing Low, there was a broad band of cloud and precipitation extending from Quebec Province to northern Mexico. It was windy at the MetLink school in Illinois, the direction being south-westerly (i.e. from the south-west). Pressure was high (1041 mb) west of Hudson Bay and also (1030 mb) over Montana and Wyoming, while a Low of 1000 mb brought cloud and precipitation to Oregon, Washington State and southern parts of British Columbia. A High of 1038 mb was centred at 42°N 152°E and a weak trough of low pressure brought overcast conditions to Hawaii. A ridge of high pressure maintained fine weather at Puerto Vallarta.
As satellite images show, there were many cumulonimbus clouds today over eastern, western and southern parts of Brazil. This is the wet season over the tropical parts of South America south of the equator.
To obtain a recent weather chart from Environment Canada, click here and then choose the chart you require. For charts of North America made available by a German source, click here. For weather maps, satellite pictures and precipitation maps supplied by USA TODAY, click here.
EUROPE
Today’s weather chart for 0000 UTC shows numerous centres of high and low pressure over north-west Europe and north-eastern parts of the Atlantic Ocean, with Lows of 1004 mb at 49°N 1°W, 1000 mb at 56°N 6°E, 990 mb at 66°N 20°E, 978 mb at 73°N 32°E, 1003 mb at 67°N 26°W and 1006 mb at 61°N 19°W, as well as a complex depression (with centres of 988 and 989 mb) between Newfoundland and about 50°N 20°W! The chart shows centres of high pressure at 64°N 16°W (1014 mb), 61°N 8°E (1009 mb) and 41°N 21°E (1025 mb). A complicated pressure distribution indeed! The fronts of the complex depression in mid-Atlantic lay well to the west of Europe. During the day, however, they moved eastwards, bringing rain to Portugal and south-west Ireland. A front from the Low over northern France brought cloud and precipitation to northern Germany, southern Sweden and southern Finland early in the day, but this front moved eastwards during the day and weakened.
In association with the Low at 73°N 32°E, there were northerly winds over Spitsbergen. Winds were also northerly (from the north) over most places in the British Isles for much of the day, but they changed to southerly over Ireland and western parts of Scotland and Wales by the end of the day. Winds were from points between west and north over Scandinavia all day today and rather variable over other parts of Europe.
Satellite images show that ice covers much of the Gulf of Bothnia (which lies between Finland and Sweden). They also show cumulus activity south of Spitsbergen, where cold air streamed southwards over a considerably warmer sea. The temperature at Longyearbyen School this morning was -10.5°C. The water temperature south of Spitsbergen was about 4°C. Thus, the cold air was heated strongly from below and became unstable, hence the cumulus formation.
Aircraft condensation trails were observed over southern England today. They occur when the upper troposphere is moist, as it was today ahead of the Atlantic Low’s fronts which approached the British Isles during the day. An explanation of contrails is provided below. This explanation is taken from an illustrated sheet called Science in the sky, produced by the Royal Meteorological Society. If you would like to receive the contrail sheet or, indeed, any of the other three sheets, please write to Malcolm Walker, Education Officer, Royal Meteorological Society, 104 Oxford Road, Reading, RG1 7LL, UK. The other three cover, respectively, rainbows, cumulus clouds and hooked cirrus clouds.
CONTRAILS
The exhausts of aircraft engines are hot and moist, the water vapour in them coming mostly from combustion of hydrogen in the aircraft's fuel. Behind an aircraft, exhaust gases cool rapidly, mainly from mixing with their surroundings but also to a small extent as a result of radiation loss. This cooling takes a finite time (a fraction of a second), so there is normally a gap of some 50 to 100 m behind an aircraft before a contrail appears. The water droplets that are produced freeze very rapidly if the temperature is low enough. The resulting trails of ice crystals persist and spread if the atmosphere at contrail level is moist enough. Contrails (and water droplets) form when the saturation vapour pressure with respect to liquid water is exceeded. They persist when the air is saturated or supersaturated with respect to ice. Once formed, contrails are distorted by upper winds and spread by diffusion, and curtains of ice crystals can sometimes be seen falling from them. Persistent trails often form large patches of fibrous clouds that look like cirrus, cirrocumulus or cirrostratus. Thus, old contrails sometimes cannot be distinguished from these clouds.
Supercooling is a normal occurrence in the atmosphere. Clouds composed of water droplets can persist at temperatures well below 0°C, even at temperatures below -30°C. At temperatures below about -40°C, however, all cloud droplets freeze very quickly. On long-haul routes, commercial aircraft usually reach altitudes of 10 to 12 km, where temperatures are typically below -40°C. Planes on these routes therefore tend to leave contrails behind them. Over the British Isles, trails rarely form below about 8 km in summer, 6 km in winter. When the weather is as cold as it often is in mid-winter in Alaska, Siberia and central Canada, contrails can even form at ground level. Indeed, airfields in these regions have sometimes had to be closed when low-level clouds (ice fogs) composed of aircraft-generated ice crystals have proved persistent.
The rapid reduction in pressure that occurs immediately behind an aircraft causes condensation trails to be produced adiabatically at wing surfaces and, particularly, wing-tips. Such trails often have a wavy appearance, consistent with the occurrence of complex vortices (twisting rotating eddies) behind the aircraft.
Through a pair of binoculars, have a close look at an aircraft that is making a contrail. Can you see a gap between the plane and the beginning of the contrail behind it? Can you see trails from the aircraft’s wing tips?
NOTES
For central England, there is a monthly temperature series that goes back to 1659. To view the data, click here. For other information about the climate of the British Isles, click here. For monthly rainfall data back to 1766, click here and choose data.
Did you know that hourly measurements of wind, temperature, pressure and sea conditions recorded by the sensors of the automatic weather stations that are aboard data buoys on the North Sea and eastern North Atlantic are available on the web? To obtain the latest observations, click here. When the page has loaded, click on the yellow diamonds to obtain data for individual buoys. Please note that temperatures are by default given in degrees Fahrenheit, pressure in inches and winds in knots. For metric data, choose, on the page containing the data for the buoy you selected, ‘metric’ on the ‘Unit of measure’ drop-down menu and ‘Greenwich Mean Time (GMT)’ on the ‘Time Zone’ drop-down menu. Then press ‘Select’.
For satellite images of superb quality, click here and follow the links for the images you wish to see. From this website, maintained by the United Kingdom’s Met Office, you can obtain satellite images covering Europe, Africa, The Americas and Asia/Australasia.
For upper-air soundings made at stations in Europe, click here. For upper-air soundings made at stations in the USA, click here. For soundings from other regions, scroll down either the Europe page or the USA page and follow the appropriate links. Each sounding is provided in tabular form or as a Postscript file or as a GIF image.
For a radar view of the weather over the British Isles, click here.
Do you want to find climatic statistics? If so, visit the Royal Meteorological Society’s Climate on the web site.
Do you want to find weather charts, satellite images or current weather data? If so, visit the Royal Meteorological Society’s Weather on the Web site.
