A Break in the Clouds for Europe

If you look at global maps of cloudiness or sun duration, you will notice that Europe stands out as being one of the cloudiest continents. Aside from relatively sunny Spain and Portugal, clouds regularly darken skies across the rest of Europe, particularly in the winter when the jet stream often steers storm systems directly toward western Europe.

So the bout of unusually clear days and nights in late February 2019 likely came as a welcome change in atmospheric scenery. With a strong high pressure system hanging over Europe, skies were remarkably clear between February 23 – 27, a period when temperatures soared. Weather stations in England, Scotland, the Netherlands, and Sweden have all measured record-breaking temperatures for this time of year.

This pair of daytime and nighttime satellite images highlights the many contrasting features of the land surface, features that are often obscured by clouds. In the day image, acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra, some of the most prominent patterns relate to farming. Areas with high concentrations of croplands and few forests, most notably in France and Spain, have a light brown color for winter; more densely forested areas appear darker green.

The warmth and moisture of the oceanic climate of the United Kingdom, northern France, Belgium, and the Netherlands means vegetation in those countries maintains a healthy green color throughout the winter. In the colder, drier continental climate of central and eastern Europe, vegetation—aside from evergreen forests—withers and browns during winter. Aside from the snow-covered heights of the Alps and Pyrenees mountains, the warm weather this winter kept most of the continent free of snow.

By revealing the locations of cities, the nighttime image underscores the human footprint on the landscape. Madrid, London, Paris, and Berlin—all capital cities—also stand out as the brightest cities in their respective countries. Note that thin cloud cover has diffused some of the light from cities in central Europe, making several appear abnormally bright. The image was acquired by the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite.

As shown in the cloud probability map above, it is usually quite cloudy in western and central Europe in late February. The map shows average cloudiness since 1999 as observed by MODIS for seven days before and after February 27 since 1999.

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