hey guys im doing a project were my arduino needs to be outside.... through winter. i live in PA so it could get pretty cold out. probable a 20-30°F average. im gonna put the arduino in a wooden box a seel it up good so water doesnt get to it but other than that will it be too cold for it to function correctly.
The Arduino itself is not particularly sensitive to the cold (at least not to those temps), but the power supply might be, if it's being powered by a battery.
Depending on how much hardware you need to include you might consider buying a gasketed enclosure and save yourself the work of building and sealing a wooden box. It will also hold up better to temp and humidity changes over time. Small plastic marine junction boxes are cheap and readily available at most home stores, larger NEMA 4, 4X, 6, and 6P enclosures can be found at electrical suppliers or online.
Other than that, your most likely issue will be with condensation if you seal the box when it's warm and humid and then place it in a cold environment. Although I'm honestly not sure how much of an issue that might be in a sealed enclosure since pressure inside the box decreases with temperature which lowers relative humidity. . . hmm. It's been too long since chem 101 and all that gas laws nonsense, but you'll probably be fine as long as you don't seal it up inside a sauna :).