A glance at Saturday morning shows a broad area of high pressure, extending from the Ohio Valley eastward into southern New England. A mid and upper level disturbance is tracking through the Tennessee Valley; however, the feature lacks any discernible presence at the lower levels of the atmosphere. It is this weak wave that will provide sections of the mid-Atlantic with some light, nuisance snow. As the wave runs into the weak area of high pressure Saturday afternoon, it will effectively run out of juice and fail to spread snow from areas around New York City and northward.
While the mid-level moisture will be there, the necessary low-level moisture will not be, so while the radar may give the appearance of “overspreading snow” later Saturday, it will really show “virga” or precipitation that isn’t reaching the ground.
Based on timing, Saturday’s snow should work something like this: Washington, D.C. around 9 a.m., Baltimore around 10 a.m., Philadelphia around noon, and Allentown around 2 p.m. Accumulation should be very light, only a dusting generally speaking, and some locales may see nothing at all. Saturday night should turn out dry for most as the light snow and flurries track to the north and dissolve.