Sleet in Pennsylvania, March 17 to 18, 2002

A wintry mix of snow, sleet, freezing rain and rain occurred across Eastern Pennsylvania from the afternoon of the 17th through the afternoon of the 18th. In Philadelphia and its suburbs snow began falling between 3 p.m. EST and 4 p.m. EST on the 17th. Precipitation was mixed with some rain and sleet from the start in Philadelphia and Delaware Counties. After 8 p.m. EST precipitation fell as mainly rain with some sleet mixed in from time to time into the early morning of the 18th. Little accumulation occurred. Across Berks, Chester, Montgomery and Bucks Counties, the change to sleet and plain rain took longer. Mixed precipitation fell throughout the evening and there were even some pockets of freezing rain in the upper parts of the county. Precipitation fell as plain rain from the early morning on the 18th until it ended during that day. Snow and sleet accumulations averaged 0.5 to 3 inches. Across the Lehigh Valley, snow began falling between 3 p.m. EST and 5 p.m. EST on the 17th. Sleet began mixing in during the evening and mixed precipitation fell overnight. Plain rain occurred from around 5 a.m. EST onward on the 18th. Snowfall and sleet accumulations averaged around one inch as the heaviest precipitation remained south of the region. Across the Poconos, snow began falling between 4 p.m. and 6 p.m. EST on the 17th. Sleet, rain and freezing rain began mixing in with the snow after midnight EST on the 18th. The change to plain rain took most of the daylight hours on the 18th to go from the southern valleys in the early morning to the higher terrain in the mid-afternoon. Snow and sleet accumulations averaged around one inch as the heaviest precipitation remained south of the region. Ice accretions from the freezing rain were less than one-quarter of an inch. Since this event occurred on a Sunday night, no significant accidents were reported. High temperatures from the 14th through the 16th averaged in the 60s north and the 70s south. This probably helped keep road surfaces relatively warm and ice free throughout this event. Most of the accumulations reported were on grassy surfaces. Specific accumulations included 3.3 inches in Palm (Montgomery County), 2.8 inches in Newtown (Bucks County), 2.0 inches in Tobyhanna (Monroe County) and Warrington (Bucks County), 1.0 inch in Mount Pocono (Monroe County), Easton (Northampton County), Springtown (Bucks County), Hatfield (Montgomery County) and Doylestown (Bucks County), 0.9 inches in Albrightsville (Carbon County), 0.8 inches in Allentown (Lehigh County), 0.5 inches in East Stroudsburg (Monroe County) and Wynnewood (Montgomery County) and 0.2 inches in West Chester (Chester County). A strong cold front moved through the northeast on the 16th and brought in considerably colder air. A high pressure system built into eastern Canada and northern New England on the 17th and helped lock the cold air in place, especially at and within the lowest 5000 feet of our atmosphere. Meanwhile a weak low pressure system developed on the old cold frontal boundary in the Tennessee Valley during the morning of the 17th. It moved eastward off the Carolina coast on the18th. Because the low was so far south and weak, the heaviest precipitation remained from the Philadelphia suburbs and southern New Jersey southward with this event. On the other hand, since the low was relatively weak, so was the onshore flow and thus the longer it took to scour the cold air from the lower layers of the atmosphere.