Doesn't make any difference what temp it is outside for welding.
You'll find the biggest difference with using flux core vs gas is how much cleaner the welds will be with gas. Using flux core you will need to clean off the slag after every weld before you move on to the next. Typically with patch panels most people do butt joints and this means you are essentially tacking or stitch welding the panels together, each of those tacks will need to be cleaned before and adjacent tack can be layed down. I also find mig with a shielding gas much easier in general to work with. Biggest concern with using a shielding gas outside is even a slight breeze will blow the gas away from the weld puddle so if you go that route see if you can set something up to block the wind. I'm no pro welder, just my two cents.
