Starting in December, NavCanada is changing the abbreviation used for the term “below”. Currently it is “BLO”, but the new one will be “BLW”.

AIC 27/09 has the details:

Beginning 17 December 2009, the Canada Flight Supplement (CFS) will print the abbreviation “BLW” for “below” in all text and charting instances. The abbreviation “BLO,” currently used for “below,” will be replaced with “BLW” throughout the publication.

Visual flight rules (VFR) charts will adopt the same change from “BLO” to “BLW” in all charts published after December 2009, in accordance with the publication schedule for VFR charts.

This makes sense to me. “BLO” seems more like “blowing” than “below”.