DISCUSSION: Within the last 24 hours, there has been a fairly impressive increase in the coverage of deeper convection across parts of western and northwestern Europe. During the last 24 hours, a weak (but slightly invigorated) piece of mid-level energy was propagating across western Europe. As it did so, the surface low pressure helped to shift the larger-scale regional wind field direction from a northeasterly to more of a southeasterly orientation. Hence, this wind direction change helped to increase the influx (i.e., the amount of incoming air from a given region) of warmer air from the greater Mediterranean Sea. As this warm air coming north increased with time, this helped to bolster the overall amount of convective instability as a result of the warmer air closer to the surface being coupled with much cooler air aloft.
This increasing unstable lower-to-upper atmospheric combination led to a regional atmospheric environment which was much more conducive for deep convective development. As shown in the footage above, one such convective storm developed into a severe thunderstorm which exhibited a classic shelf cloud. Shelf clouds often form in convective situations wherein there was effective low-level lift which helped to create the layered cloud deck which was observed as a shelf cloud out ahead of the aforementioned severe thunderstorm.
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©2017 Meteorologist Jordan Rabinowitz