Extreme Dutch Weather: Squall passing by Rotterdam; July 27 th 2013

Monday 29 July 2013

Squall passing by Rotterdam; July 27 th 2013

The storm season untill now has been somewhat disappointing. Where e.g. 'Estofex' issued several times a Level 2 or even 3 above the Benelux; even untill the moment of this writing it didn't actually work out that way. For last Saturday a level 3 was issued for a change of tornadic supercells. In the morning a very nice squall line covered the width of the Netherlands and a multi layered shelf cloud could be seen.

Some explanation.....

When a thunderstorm has a longer living rotating updraft (mesocyclone) we call it a 'supercell'. A supercell is a relatively rare appearence in Holland; only on a few days a year one or more can be spotted. They can only exist under specific wind conditions. The top of the storm is often not that heigh as that of their bigger brothers in eg. the US. They often bring extreme weather with large hail and even tornado's being possible. A so called 'wallcloud' is a lowering under the stormcloud out of which a tornado can form. The last photo from the 1st of October 2006 shows a wall cloud.

Another type of tornado is not associated with a mesocyclone. It can appear below a stormbase when there are less windy conditions. Although relatively seldom they appear more often than the 'real' tornado. I prefer to call them 'spouts'.

Other weatherphenomena I'm interested in are 'shelfclouds' and 'mammatus' clouds.