Probably a gap between the brickwork and the interior ceiling which allows hot air into the attic. Warm roof deck + snow + cold = ice dams.

This is the sneakiest kind of ice dam in that it lacks all the drama of large icicles but does just as much damage.

If you see it on your siding, it's most likely in your wall cavity. Bad news Bears.

This home is typical of the 40's Cape Cod style. It has little or no soffits and even less ventilation through the roof system.

You can see someone installed a type 750 vent above. This is marginally worthwhile.