Hope all my readers are having/have had a great holiday.
A paper of mine, "Siwa and its significance for Arabic dialectology", should (inshallah) be appearing in ZAL soon-ish. Basically, there's a whole lot of Arabic influence on Siwi, including things you wouldn't expect to be borrowed, like Arabic's rather unusual method of forming comparatives from adjectives. However, this influence shows clear signs of deriving, not from any dialect currently used in or even particularly near Siwa, but rather from a more archaic one, with some resemblance to the dialects of other Egyptian oases quite distant from it and some features not attested in any other Arabic dialect of Egypt or Libya. In the 1100s, according to al-Idrisi, Siwa was inhabited both by Berbers and by sedentary Arabs; I suspect that the Arabs got assimilated into the larger Berber community and that much of the Arabic element of Siwi derives from their now-extinct dialect. If this sort of thing interests you, have a look (you can download it from the link at the beginning of this paragraph) and please feel free to comment on it here or by email.
3 hours ago