I searched but wasn't able to find an answer to my question. I live on the East Coast of Canada where temperatures can reach -30 C at some points during the winter months and over 30 C during the summer months. I was thinking of making a small device which would operate outside year round. I'm wondering what the maximum/minimum operational temperatures would be for an Arduino? I'm very new to this so forgive me if this is a silly question 
From the Atmega 328P summary datasheet, -40°C to 85°C. So that'll pretty much apply to any 328-brained clone, too.
Depending on which board you are using, you might want to check other component datasheets, but I would hazard a guess you'll be fine.
Sweet!
Any idea where I can get some info on making a weather proof enclosure? 
Silicone+Plexiglas?
Silicone sticks to acrylic (Plexiglass) very poorly. If you wanted to use acrylic, best bet would be to use solvents designed for acrylic (i.e. weld-on products) to assemble the box, then use a rubber gasket to seal it.
Probably easier and cheaper to buy a sealed, weatherproof project box. IP65/NEMA4 stuff should be fine:
Ahh, perfect!
Keep in mind that temperature extreams tend to be as hard on the power source as on any of the electronic components. If using batteries be sure to research their performance at your required temp range.
Lefty
The summary and the datasheet show -40 to 85degC operation and all the specs
in the table specify a temperature range of -40 to 85degC but the Absolute Maximum
rating for the operating temperature is -55 to 125degC. Quite a large difference in
range.
Also don't forget that these temperatures are usually junction temperatures not ambient
temperature (although it unclear from the table). I am not sure what the thermal resistance of the ATmega is or how much power you are dissipating in the package.
As was mentioned you should look at the power supply components. In addition to
the batteries I would look at the caps. Are they electrolytic? At low temperatures
electrolytic caps loose a lot of capacitance and you may have excessive ripple
until the ESR heats the capacitor up.
(* jcl *)
Since he said it needs to operate year long, It probably will have an external non-battery power source...
It probably will have an external non-battery power source...
If that turns out to be the case then internal strip heaters in the enclosure could help with low temperature operation and possibly fans for summer cooling?
Lefty
I was thinking solar for power. This device only needs to be operational during the day so solar is a perfect power source!
Well solar by itself is not a very reliable/stable voltage source, you will most likely require a battery that the solar array can keep charged.
Lefty
Although I guess I'll have to get crafty with the enclosure to include a solar module of some kind.
edit: lefty - I don't have any experience with solar (or much of this really) 