Strange and beautiful clouds over the Lower East Side at sunset

Carrie and I were walking up The Bowery on Friday night, after a tremendous Vietnamese dinner at Nha Trang meal at Grand Sichuan on Canal Street - and were stopped dead in our tracks by this sunset/cloud cover combination.

We weren't the only ones. Everybody, tourists and locals alike, had their cellphone cameras out trying to capture this scene:



I hope one of our Air Force vets (there are at least three actively reading enrevanche) can help me out with cloud identification. Right now I am thinking exceptionally rounded altocumulus...

Update: over on Facebook, Heidi sez these look like mammatus clouds. I think she's right.