Cdash wrote:
If summer is hot, would late December, early January be feasible? Or would it be really cold and snowy?
Most probably yes. Quite cold at least and probably quite snowy at Bryce. Plus really short days. Sometimes a temperature inversion sets in over Moab and it will be 10 to 20 degrees cooler than here in GWS. Zion is usually reasonably "mild" even in the winter, but even there can be cold at Christmas.
Let me throw another idea out there. How about the week of Thanksgiving? Fly into SLC or Grand Junction, CO. rent a car and motel it. No, it's not camping, but motel rates are a lot cheaper then than during the busy season. Although we're close to Moab, we'll often do a motel trip around Presidents Day weekend. Between the savings on gasoline and the cheap motel rates, we're not spending much more than if we were to camp.
March through mid-May and September and October are the best months weather-wise, but also far and away the busiest. What ever you do, do NOT plan on being in Moab on the week preceding Easter. There's a jeep safari that week that makes everything over the top busy. Sometimes heading into Moab from the north means taking 1/2 hour to go the last five miles!