Lake Michigan writes Chicago's winter. A band can set up over the water and come ashore sideways, dropping more on one neighborhood in an hour than the forecast promised for the whole day. MONROE UNIVERSAL SERVICES plans for that arithmetic, plowing drives and lots while the storm is still building rather than waiting for it to finish, then returning to take out what the wind piled back against the north wall. Walks get scraped down and treated, entries are opened, and the stack is set where the melt will run to a drain. When a lake squall gives three hours' notice, being already out there is the entire job.