I'm assuming that by "northern" you are meaning "above the freeze line"?
The issue is not so much their latitude, but the amount of traffic those airports have. O'Hare, for instance, is one of the busiest hub airports in the US, and Chicago can have some brutally snowy winters because of the Lake Effect. However, O'Hare also holds the record for most weather-related delays in summer as well. The issue is more the traffic than the weather: it is the second-busiest hub in the US, and it is near enough to Midway that when the weather is bad, the number of aircraft in the air over the city makes lining them up for takeoff and landing complicated.
As the day wears on, the delays stack behind one another, and they worsen for that reason.
The best way to fight weather-related delays at any time of year is to always try to fly as early in the day as possible, always try to take a flight that has as few stops as possible, and to avoid changing planes in your airline's major hub airports wherever you can. (That means that on Delta you'll have better luck connecting somewhere other than Atlanta, for instance.) SWA can be a problem in weather sometimes because a lot of their flights are milk runs; they stop a lot. The non-stop flight that we usually take to MCO from here originates in San Diego and makes 3 stops before it arrives here: in Phoenix, Omaha, and Chicago; weather along the route is a bigger problem for them because they are not just flying through it; they are taking off and landing in it. In summer thunderstorm season, the flight that normally leaves here at about 7 pm has often not landed here until after 9 pm, and often doesn't land at MCO until after midnight. (But it is the only evening flight from here, so we deal, LOL).
The other factor to be considered is the airline's turn time: this is the average time that each flight spends at the gate while the plane is loaded and unloaded. When weather delays are a factor, airlines with longer turn times usually fare better because they have built that part of the delay into the schedule. United schedules their flights with long turn times, and they can use that leeway to catch up somewhat when they get behind. (Also, UAL tends not to do that many short-hauls, so they get caught by fewer ground-stops as a rule.)
PS: Personally, I don't take flights that backtrack a time zone when connecting. There is no way I'd go from OKC > MCO via DEN. You'll feel much more sane connecting in HOU or STL, and a quick check tells me that the price difference is normally minimal.
My preferred are St. Louis or Memphis as those are the most direct routes possible to Orlando out of our region. Like a pp mentioned, I had more trouble with the thunderstorms late spring this year than any snow storm ever. 
