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I really thought I was on top of things, then I found this today between two sets of hives. When I saw then, it was about 3:30 in the afternoon and the temp was 57°. I didn't know/realize they would swarm in this cool of temperature.

The magic number is 55. They may go out anywhere above that.

Thanks for the magic number. Trying to deter swarming, I have done the Demaree method on a couple hives. And yesterday did a vertical split using the double screen board. Put the old queen above and let the big hive make new Q. Like Rob referenced. Only with the cold weather the added heat from bees below the double screen board will help.
Just to be on the safe side, I also am making a Russian Scion to place in the one short tree by the bee yard. Hopefully they will avail themselves of that instead of all the 70 foot tulip poplars.

Thanks for the Magic number, Wally. I thought someone told me it was above 70° that they would swarm.

May you have a great weekend!

I checked on weather history for my February 27, 2020 swarm. It was 49F and mostly sunny the day they came out. It was 62F and foggy the day before. The 3 days before that, only one day was below 55(54F). February 2020 was quite warm overall. If Wally is generally correct, tomorrow has the potential to be a busy day.

Keep in mind, it's not the official temp, nor the temp in your back yard. It's the temp at the hive entrance. On a sunny day, that can be 10 degrees above the official temp.

I didn't get the temperature way up in the tree they came out of, but there surely was no leaf cover to create shade.