The frontal dynamics and the fact we are in the RER quadrant of a jet streak which induces WAA and subsequent divergence aloft which results in low level convergence and lift. This lift causes air parcels to rise to the LCL (lifted condensation level) which forms the cloud base, subsequently, the parcel rises through the positive dynamics and the moist lapse rate. After that we get snowfall from the aggregation of flakes in the atmosphere. Any more questions?