If I want to know whether or not there could be enough surface moisture to allow for significant precip in a nonmountainous area in the SE during winter, the direction of 500 mb flow will tell me a lot. For fun I will often look at 500 mb flow before looking at the surface. If I see, say, WNW 500 mb flow at Atlanta, I know right off the bat that the chances of the sfc map showing sig precip at that point in time at Atlanta is going to be extremely low. Even W flow is quite often too dry. However, if I see SW or even WSW flow, then I know there's a decent chance that significant precip is then or around then falling in the area. I've written about this in BB posts in the past. When I looked for major KATL wintry events by searching numerous old wx maps going back to the 1950's (when H5 maps were already available), I learned that I could just look at the H5 maps and search for WSW to SW flow (though with the rare closed H5 low I'm more cautious). If the flow is WSW to SW, I know to then look further at that period (sfc maps). If W to WNW flow, I then know I don't even need to look at the sfc.
If, say, there's WSW flow, I'll then need to look at the surface to see if there's favorable low level flow to allow for precip. If there's, say, a high to the W imparting a dry NW low level flow, then I can be pretty sure there's still going to be either no or very little precip. despite the rather favorable WSW 500 mb flow.