March arrives tomorrow, promising both daylight-saving time and the spring, or vernal, equinox. Daylight-saving time begins at 2 a.m. Sunday, the 9th, when we spin our clocks forward an hour. Mornings will suddenly be darker, evenings brighter. (Europe follows suit on the 30th.) Spring arrives at 12:48 a.m. on the 20th. In March, average highs at BWI Marshall Airport rise from 49 to 59 degrees. Lows warm from 29 to 38 degrees. The record high was 90 degrees, on March 29, 1945.