Weather
Many people may think that the weather will have a severe effect on the lifespan of their grill. Many Weber gas grills are made either of stainless steel or cast iron, both of which are made to withstand elements of rain, snow or sleet for many years before they even begin to show signs of rust. The severity of the winter should have no effect on your decision to keep the grill outside. So yes, you can keep the grill outside during the winter.
Prepare
A few small preparatory steps can help ensure that the grill is winterized correctly and protected from the elements. If you are using propane, disconnect the propane tank from the barbecue and either store it in your garage or bring it to the place where it was originally filled up and have it drained for the winter. You should also clean the grill of any charred-on materials from the grill rack and clean the drain pan as well. The more you maintain the grill during the summer, the easier it will be to quickly start up at the beginning of each season.
Cover
If you have especially harsh winters and you still are concerned about leaving the grill outside, invest in a barbecue cover. Covers are usually sold where the grills are available. The covers are recommended to prevent rust and will extend the life of not only the framework of the grill but also the internal parts. These parts include the spark ignite switch, burners and knobs.Moisture will be kept out of the interior grill parts, which can go a long way in preventing rust.
After Winter
Check the gas hoses for loose connections before the beginning of the season. It's possible that the winter may have caused the gas line to freeze or crack, especially at the joints. Connect the propane tank or gas line to the barbecue. Turn on the gas and use a diluted soap solution and apply it to the joints. Look for bubbling near the joint that will indicate there is a leak. If a leak is present, do not use the grill and have a professional replace the hose and reseal the joint correctly.