The first real snow usually finds the Chicago River first, a dark line of water sliding under the bridges while the streets go quiet and white on either side. R. Rojas Landscape, Inc. is out in it from that night through the long tail of March, plowing drives and lots, shoveling walks and steps, and salting the places where meltwater collects and hardens. Snow is pushed to spots that will not turn into an ice dam across a sidewalk when the thaw arrives. A Chicago winter is not one storm but a run of them, and the trick is showing up the same way for the twelfth as for the first.