Why do you think the cold front in figure 1 developed

Sir Alexander Fleming (6 August 1881 – 11 March 1955) was a Scottish physician and microbiologist, best known for discovering the enzyme lysozyme and the world's first broadly effective antibiotic substance which he named penicillin.

For this discovery he shared the Nobel Prize in Physiology or Medicine in 1945 with Howard Florey and Ernst Boris Chain.