The basic concept of ASII is the identification of:
As the time evolves slowly to the 18th November, the big depression (a.k.a. Quimburga) moves in over the North Sea. The dry intrusion gives some sign of the still ongoind cyclogenesis and the deepening of the surface low.
On the 17th November at 21UTC the first signs of the RaCy are observed. The baraoclinic leaf is recognised and is analysed as a wave. The F represent the cloud fibres as a result of the Jet. Another indication of RaCy!
In the afternoon of 18th Novemeber the severe development has started. A Dry intrusion runs into the depression. Over the highlands of Scotland some L mark the lee clouds. This development of the RaCy continues.
At 19th November 09UTC something very interesting can be observed as was before already mentioned sevral times in this case, namely the second development just south of the Alps. In the image we see this areaa marked with DI for dry intrusion. In the cold air behinf the RaCy some Cbs have developed over.