Winter Weather — Eastern Chester, Pennsylvania

2021-01-31 · Eastern Chester, Pennsylvania

Event narrative

Snow began in the county on January 31 and continued into February 1 and 2, when the heaviest snow would fall.

Wider weather episode

A major winter storm affected the mid-Atlantic from January 31 to February 2, 2021. Low pressure tracking out of the Ohio Valley weakened as it moved slowly eastward on the 31st. Meanwhile, as that low weakened, secondary low pressure began to develop off the coast of the Carolinas and tracked northward, just off the mid-Atlantic coast. The low steadily intensified as it moved up the coast in a classic 'Miller B' storm evolution. The result was a significant and unusually long duration winter storm. Overrunning precipitation associated with the initial low over the Ohio Valley impacted the region on the 31st. A cold antecedent air mass allowed most of this precipitation to fall as snow. This produced widespread snow accumulation, though the overrunning precipitation was mostly of the light to moderate variety. Some areas experienced a lull in precipitation on the overnight of the 31st as the secondary low began to develop and a dry slot overspread a large area. In addition, a surge of warmer air both at the surface and aloft caused precipitation to change to sleet or rain in some areas, especially locations farthest south and east such as the Delmarva peninsula and southern New Jersey. However, as the secondary low strengthened, heavy precipitation developed on February 1, with intense banding and areas of extreme snowfall rates of 2 to 4 inches per hour in northern New Jersey and portions of eastern Pennsylvania. Precipitation eventually turned back to snow all the way to the coastline as colder air was drawn in from the north. The secondary low pressure nearly stalled off the mid-Atlantic coast, causing snow to continue into February 2, although by then snowfall rates were much lighter and additional accumulation was limited. Areas where precipitation remained all snow and that experienced the heavy banding saw extreme snowfall totals, with isolated amounts of near 3 feet of snow and a fairly widespread swath of in excess of 2 feet. Snow flurries even continued into February 3 around the backside of the slow moving low's large circulation, before it finally departed and brought an end to one of the region's most notable snow events in years.

Source: NOAA Storm Events Database, event_id 932259. Narrative written by the NWS forecast office that issued the report.