Like most people I always thought of Yiddish as merely a German dialect influenced by Hebrew and thought it arose in Bavaria. Then racially the so-called Armenoid look of European Jews might be from a Mediterranean stock similar to the Sephardim or the Palestinians mixing with the dinariform Central European race. This was Lundman's explanation of the Jewish look because he felt its vault was not really Armenid enough and supposedly the High German influence in Yiddish is closer to the Bavarian dialect than to the Rheinlander. Also I think I remember Ashkenazim have a fair ammount of ancestry from North Italy where people can be quite dinariform that would suggest their route out of the Roman Empire.

But if this is right Ashkenazi Jews emerged as a non-Semitic caste who followed Judaism to distinguish themselves from their neighbours on the Silk Road. Their explanation comes across as garbled though so I don't know what to make of it. The right hand side of the included diagram helped me but its still messy.

http://gbe.oxfordjournals.org/content/8/4/1132.full