These graphs show the departure from the 100-year average of the daily maximum and minimum 
temperatures from 1950-1998 for BWI airport.

The shaded blue regions represent colder than normal temperatures and the shaded red areas are warmer than 
normal observations.

The dashed lines separate the seasonal boundaries.  For a given year, winter is defined as December of 
the previous year through February of the current year.

These diagrams clearly illustrate that it is normal for the weather to deviate from the mean from day to 
day. In addition, the year to year differences can also be quite dramatic for a given month or even season.