Full Earth September, 14th 2012, 11.00 UTC Sourece: EUMETSAT
General Synopsis of North Atlantic and Europe: A Cut-Off Low over Mediterranian has detached from Jetstream further north. Mediterranian Cut-Off Low looks really beautiful! Jetstream at the North is decernible as a band of cloud.
Usually the pathways of low pressure weather systems are strongly controlled by current of the Jetstream. But sometimes the Jetstream slows down or even breaks, so that weather systems can detach (Cut-Off). After that they move independently until they decay or are captured by a trough of a new established Jetstream.
Low pressure systems on Northern Hemisphere are spinning anticlockwise due to Coriolis force. Inside the system air is rising and cooling. If air-moisture is sufficient condensing water vapor starts to form clouds, made of tiny water droplets (or tiny ice crystals in higher altitudes). It might rain or snow. Bad Weather!
For comparison the model calculation chart for windspeed and Jetstream in the higher troposphere:
Windspeed and Jetstream in the higher Troposphere. Source: www.netweather.tv
The mathematic circulation model shows almost perfect all features of reality!
Jens Christian Heuer