This image is obtained by the infrared channel of the MSG (Meteosat Second Generation) satellite, in geostationary orbit at 36000 km of altitude. The infrared channel can be used even in night-time, since the presence of clouds and of other meteorological structures is detected by a indirect measure of their surface temperature.
Temperature last three hours
The map shows the average temperature of the last three hours, figured out from a network of 40 thermometric stations. The spatial distribution is based only on altitude. That means that differences between two stations located at the same altitude due, for instance, to a different aspect, are not taken into account.
Precipitations last 24 hours
This map shows the precipitations of the last 24 hours measured from 30 rain gauges able to melt snow. The spatial distribution is based on a simple real time data interpolation.
(Issued at 20/12/2014 13:12:06)
Sea level pressure recorded today at 7.00 am. in Aosta : 1021 hPa.
Sea level and 5500 m situation
Colour contours indicate the geopotential height at 500 hPa, while the blue isoline indicates the sea level pressure (slp). The geopotential height at a given value of pressure indicates the altitude above the sea level with this value of pressure. The geopotential height at 500 hPa is given in decametres: if you multiply by ten you get the altitude, usually between 5200 and 5700 m. Low values – grey to green to blue colours – indicate low pressures systems aloft girdling cold air, while high values – yellow to orange colours – indicate high pressures systems aloft, girdling relatively warm air.
Situation at 1500 m
The isolines indicate the geopotential height of the 850 hPa surface in decametres – usually around 1400-1500 m – while the colours indicate the temperature at this altitude in the free atmosphere. It is important to notice that the real value of temperature around 1500 m, in the Aosta Valley or in any region with a complex orography, might be very different from that of the free atmosphere, especially in the bottom of the valleys, where the thermal excursion is usually higher, being colder in wintertime and in the dark hours, and warmer in summertime and when the sun shines. The temperature of the free atmosphere is nevertheless very important, showing the true nature of the air masses.
Situation at 3000 m
This image represents the situation at 700 hPa – around 3000 m – and can therefore be considered representative of the Aosta Valley mountains. The relative humidity is shown by the colours and the wind by the arrows. Grey, yellow and orange colours indicate a progressive nearing to the saturation, favouring the presence of clouds at about 3000 m. The wind vectors are shown only if the wind speed exceeds 10 m/s (about 36 km/h).