Exteriors have many advantages over interiors. They can impart a bigger sense of scope and more production value. You can work with fewer lights (if you're shooting days). They often cost less to rent. But they have one significant disadvantage - you're at the mercy of the elements.

If you're prepping an exterior-heavy shoot, ask: what time of day is it in most of the scenes, and how season-dependent is the script?  If the script takes place at night, the ideal time to shoot is in late December, when you'll have 14 hours or more of darkness.  For "daytime" scripts, the best month is in June.  Season-dependency is also important.  If the story is set in the wintertime during the day, then you can't shoot it in June but you may be able to shoot it in February, when there's more light than in December.

If you're outside in cold/inclement weather, make sure everyone dresses sensibly.  Windburn and sunburn can hit exposed skin even on mild days, and hypothermia is no joke.  If the cast has to work in skimpy or non-weatherproof clothes, make sure someone stands nearby with coats, blankets and coffee.  See if the costume designer can provide silk undershirts and long-johns.  Silk retains body heat without adding bulk.

Some things you should buy or rent for the shoot:

• Sunscreen
• Hand/face cream and lip sealant
• Waterproof spray-on sealant for boots and gloves
• Hand warmers - these little pouches heat up when shaken
• Coffee, hot chocolate, hot water - rent a large coffee maker and/or a cambro (a large thermos)
• Hand towels - great for keeping hands and faces dry
• Vitamin C, nuts, instant oatmeal, Cup-o-Noodles soup - keep these by crafty
• Rubber mats - for keeping rain/snow/mud off the floors of your interior holding area

If you can't get a building nearby for people to stay warm in, rent an EZ-up tent with sidewalls and a heater.  There are several heater models available, including electric, kerosene, and hybrid-powered.  My favorite is a "blower," which has an electric ignition but uses gas flame to blow a hot stream of air into the tent.  To power your heater and coffeemaker, you'll need to run cable to your tent.  If you can't tie into a nearby indoor breaker box, budget for a small (6500W putt-putt) generator and enough cable to keep it away from set.

Keep rain and snow off your gear with the following:

• Cellotex - a heat-resistant, expensive, wire-mesh reinforced waterproof film.  Electricians clip it to lights to keep moisture away.  Buy the roll and return unused portions, or buy partial rolls
• Extra flags and c-stands - for rain hats
• Visqueen (waterproof plastic), tarps and additional stands - can be used to build temporary tents.  (You can sometimes rent visqueen and tarps, or buy and return unused portions as above)

Also remember that things take more time during inclement weather.  Stay safe and good luck!