Alright!
In that case, just find a school yard or some Mall or Plaza parking lot. Usually, the maintenance crews will keep these lots clean and free of snow, for you to cycle. Just plan it properly. Most schools don't open their doors until 7 am. You'll have to find out the exact time that your nearest school opens for their teachers. Try to beat that time!
If teachers are allowed entrance at 7am then you must leave at 6:50 am. The goal is to get you onto the snow-free lot for a minimum of at least one hour of riding time per day, during the week. During the weekend (on Saturday), you'll put in 100 minutes of riding time. Fifty minutes in the morning and fifty minutes late in the afternoon, before dusk.
At first, make a schedule and pace yourself. Only ride four times per week. Like maybe M-W-F and either Sat. or Sun. on the weekends. Do not ride everyday, at first!
Sample Schedule:
If the school opens to teachers at 7:30 am, then you get there at 5:50am. Ride in the lot for 15 minutes continually and then break for 7 minutes. Do this 4 times. When it gets to the point where you feel that you no longer have to take a break, then don't take a break. Just keep on going! Leave ten minutes before teachers are suppose to arrive.
Once you've cut your weight down to about 270lbs and riding has gotten easier, keep riding. However, now extend your rides. Plan trips. Try to find a riding buddy for security reasons.
Find a bicycle co-op, so that you can learn how to fix a flat, or anything else on your bike.
Once you're working. Save up enough money to buy a really nice bike, like a Jamis Quest, or a Cannondale CAAD 10, or something. Join a road bike club and become a weight weenie, just like the rest of 'em! Take pictures of yourself now. Then after you lose weight, show your roadie club members those same pictures. Show them how much tenacity and determination you have!
They'll respect you! They'll respect you both, for your level of determination and your relentless ability to accomplish your goals!
Good Luck!
PS.
At your current weight, I wouldn't advise you to ride on slippery surfaces. Either walk the bike to the school yard or plaza, or stay home and wait for the weather to break. Always ride on sturdy ground. Never ride under slippery conditions!