Winter storm Stella is hitting the northeastern United States. The USDA has food safety tips to keep in mind when you are preparing for a severe weather emergency.

Many people think that storing food outside when it’s cold is safe, but it isn’t. Outdoor temperatures can vary, and food can be exposed to unsanitary conditions and animals. Instead, make ice by filling buckets and cans with water. Leave them outside to freeze, then use this ice to keep food cold in coolers or your refrigerator or freezer.

If the power goes out, keep refrigerator and freezer doors closed as much as possible A refrigerator will keep food cold at safe temperatures (below 40°F) for four hours. And a full freezer will keep temperature below 0°F for 48 hours; 24 hours if it is half-full. Put meat and poultry one one side of the freezer, or on a tray to stop any thawing juices from dripping on other foods. Dry or block ice can be used to keep a freezer cold. Fifty pounds of dry ice will help a fully stocked 18-cubic food freezer cold for two days.

When the weather improves and the power goes back on, make sure you check the temperature inside the refrigerator and freezer. Discard any perishable foods, such as meat, poultry, seafood, eggs, or any leftovers, that have been above 40°F for two hours or more. Check every item separately. Don’t taste the food to check if it is okay. Discard any food that has an unusual odor, color, or texture, or that feels warm to the touch.

If frozen food still has ice crystals, it is safe to refreeze. Any food in the freezer that is partially or completely thawed can be refrozen if it has ice crystals or if it is 40°F or below. Check the temperature using a reliable food thermometer. And remember, when in doubt, throw it out.