Preflight Briefings
Be aware of the distinction between MSL and AGL. Cloud heights associated with airports are customarily given in AGL. But areal guidance products, area forecasts, and PIREPs, use MSL. Also, anything stated as a ceiling or carrying the CIG abbreviation is AGL. Since IFR and MVFR conditions are based upon ceiling height, centralized products will always use AGL ceilings when constructing an IFR/MVFR depiction. If there is any doubt, find the information ahead of time or talk to a briefer.