You don't have boots for those snowy days? Yeah sure, you may have to eyeball a few if your measuring wheel starts to slip in the snow--or you can't pace it off. however--if you have to actually go out to the location be sure to take advantage of that fact. Talk to them if you can. Go after 5 if you can. (TruGreen doesn't do this. ) Leave a nice big packet of literature and lawn analysis. Show that you took a soil sample. Dig through the snow to estimate the percent weeds and the type of grass, in three spots. Try to give them a gift--coupon for a free flower seeds at a local garden store, say or 3 gladiolus bulbs, a rare and exclusive variety, (of course). Get a kit and meter, and get your lovely secretary to do a simplified soil test. A gift creates a psychological obligation on the part of the prospect.
A coupon may be easy, as some stores restaurants and pizza places are desperate to get a new person to try their place of business--knowing that Ms prospect will spend more and probably come back as a repeat customer once they realize what friendly service they get.
On the other hand feel free to use on of the online services or aerial photos.
You should know how much time it takes to cover 1000 sqft from last year's records. Likewise for the average cost of your product per 1000 sqft.