|
Weathercam "image of the day" Valencia, Spain
Student maps & analysis for 22 March, 2000 |
 |
A large anticyclone brought clear skies to much of Europe today. At 0600 UTC, there were two centres of high pressure, one over the Alps (1025 mb), the other over the southern part of the Plain of Hungary (1026 mb). At 1200 UTC, there were centres in the middle of the Plain of Hungary (1025 mb) and over the north-east of Sardinia (1024 mb). A ridge of high pressure from this anticyclone extended across the British Isles.
Pressure was still low off northern Norway, but the depression filled a little. Its central pressure was 970 mb at 0600 UTC and 975 mb at 1200 UTC. As was the case yesterday, an occlusion wrapped right round this Low, from the north of Norway, across Svalbard and round the northern and eastern flanks of the Low across north-west Russia to Latvia. At 0600 UTC, the cold front of this now well-decayed Low extended across southern Scandinavia and southern Scotland almost to the Grand Banks of Newfoundland. A wave on this front began to develop today. Between 0000 and 1200 UTC, it deepened from 1018 mb to 1002 mb and moved from 49°N 38°W to 51°N 29°W. By 0600 UTC on 23 March, it is expected to be at 55°N 24°W and have a central pressure of 977 mb.
Radar images show that a band of patchy rain lay across southern Scotland and Northern Ireland this morning but disappeared around mid-day. They also show that rain fell over Brittany and south-west England during the night and early part of the day. The showers in south-west England died out by mid-morning, but the rain over Brittany became more extensive and heavier as the day progressed.
Yet again, pressure was low over Portugal and Spain. At 0600 UTC, a Low of 1007 mb was situated off Portugal. At 1200 UTC, its central pressure was 1008 mb. A trough of low pressure extended northwards across the Bay of Biscay, bringing the cloud and rain that occurred over Brittany. As on previous days, there was cloud and rain over most parts of Spain and Portugal. Once again, there were snow showers over northern and western parts of Norway. Satellite images show that cumulus and cumulonimbus activity was widespread over the seas to the west of Norway. The cellular patterns of cumulus and cumulonimbus clouds that were mentioned in yesterday's report could again be seen on the satellite images.
The winds over northern Scotland, Scandinavia and the North European Plain were from a westerly point. Over Spain, England and north-western parts of France, they were generally from a point between between east and south. Elsewhere, they tended to be rather light and variable.
Over many parts of Europe, there was a foggy start to the day. Across England, the Low Countries, northern Germany and northern Poland, radiation fog occurred this morning. This type of fog forms when skies are clear, allowing the radiation given off from the ground to escape into space. The ground thus cools and the air in contact with the ground cools, too. If the temperature close to the ground falls to the dew point, dew forms if there is no wind, radiation fog if the wind speed is 1 or 2 m/s. The fog is quite shallow, typically no more than 50-100 m deep, and it dissipates during the morning, when the temperature of the air in contact with the ground rises above the dew point. Solar radiation causes the ground to heat up. The sun may not be visible through the fog, but solar radiation reaches the ground, otherwise there would be no daylight!
Once again, very few CloudWatch participants reported precipitation. Both stations in Spain reported nimbostratus cloud and rain. The CloudWatch school in Finland had snow overnight and early this morning. Beachborough School in the UK reported drizzle at 0900 UTC. So, too, did Bor's School (Sweden) at 0700 UTC. A power station near Roose School (UK) generated cumulus clouds this morning.
Contrails were seen in some places but did not appear to be as widespread and persistent as on previous days, indicating that moisture conditions in the upper troposphere had changed somewhat since yesterday. For upper-air soundings at stations across Europe, click here.
Only from Reading (UK) and Lännbo Friskola (Sweden) were lenticular (wave) clouds reported. Those at Reading were short-lived and developed into altocumulus castellanus for about half an hour (1600-1630 UTC). Where the change in temperature with height (the environment lapse rate) is less than the dry-adiabatic lapse rate but greater than the saturated-adiabatic lapse rate, the atmosphere is said to be conditionally unstable. It is stable if unsaturated, unstable if saturated. Vertical motions are resisted in a stable atmosphere and in an unsaturated atmosphere that is conditionally unstable. If, however, condensation occurs in a conditionally-unstable atmosphere, through wave motion, for example, convection occurs, because the atmosphere has become unstable as a result of the saturation. The wave clouds then grow cumulus-like features that look like turrets or battlements, hence the name 'castellanus'. The 1200 UTC soundings over the UK at Larkhill (station 03743) and Herstmonceux (station 03882) suggest that the lapse rate and humidity conditions were appropriate today for the formation of castellanus clouds over southern England at a height of 2500-3000 metres.
On the chart for your region, you should find a weather station fairly near to you or even very close to you. On the chart for Italy, for example, there is an observation for Malta, and on the chart for Scandinavia you can find observations for Bergen, Oslo and Stockholm. On the chart for Spain, observations for Madrid and Valencia can be seen.
Austria | Belgium | Czech Republic | Denmark | Finland | France | Germany | Hungary
Italy | Jersey | Latvia | Lithuania | Netherlands | Norway | Poland | Portugal | Russia
Spain | Sweden | Switzerland | United Kingdom
