September arrives tonight, the longest month of the year (count the letters). It's also Baltimore's wettest (3.98" on average), probably thanks to a century of passing tropical systems. Average high temperatures at BWI slip from 82 degrees to 73. Average lows dip from 61 to 51. Records range from a high of 101 degrees on Sept. 7, 1881, to a low of 35 degrees, on Sept. 25, 1963. We'll lose 74 minutes of daylight.