The window well
Finishing a basement legally means putting windows in it, and putting windows in a basement means cutting openings below grade. Every one of those openings (the egress well, the lookout sill, the old glass-block replacement) is a spot where the yard can hand its water directly to the room behind the wall.
How a well becomes a funnel
A window well is a steel or plastic tub holding the earth back from a hole in the foundation. It stays dry three ways: a gravel base that drains, a cover that sheds, and grading that sends surface water around it rather than into it. Each fails quietly. The gravel silts up over the years; the cover cracks or walks away; the landscaping creeps until the lawn tips toward the well. In a fast melt or a summer downpour, a well that has lost its drainage fills like the tub it is. The window at the bottom was never designed to hold back standing water.
Why spring finds them first
Snow gets shovelled and blown against the house all winter, and wells sit at the wall; many spend February buried. When the melt comes, the snow inside and above the well melts last and drains worst, straight down against the frame. An egress window that seeps every March is not a window problem; it is a drainage problem wearing a window as its exit. The fix lives in the well and the grading, and the finished room inside pays until it happens.