You might expect that in an El Nino winter, the chance of freezing nights would go up, since El Nino winters are generally cooler than average. I decided to test that by looking at the number of nights that the minimum temperature got below 32 F and seeing if years with El Nino had more freezing nights than years with La Nina or neutral years. Below you will see a quick graph that shows a test case for Tifton GA in southern Georgia. For each year starting in 1960-61, I plotted the number of nights per winter with min temps below 32 F, and then highlighted in red the El Nino years. The graph shows pretty clearly that there does not appear to be a pattern, with some El Nino years having a lot of freezing nights but others have very few. The years with the most freezing nights are evenly divided between El Nino and La Nina winters.
You might wonder why this is. In El Nino years, the jet stream is located along southern Alabama and Georgia and northern Florida. The jet stream pushes low pressure centers across the region, leading to more clouds and rain. The wet, cloudy conditions keep daytime temperatures low but keep heat from escaping at night, so overnight low temperatures are not necessarily lower than in non-El Nino years. That means you cannot count on having more cold weather to kill off pests, nematodes, and diseases as well as volunteer crops, so if you are a farmer, you need to make sure you are doing your due diligence to manage your fields to minimize the impacts of these yield-stealers on next year’s crops.
I also post below the El Nino temperature departure for the last strong/very strong El Nino we had in Dec 2015-Feb 2016. Note that even in the Southeast, the temperatures were warmer than normal. That may reflect in part the warming trend we are observing in winter temperatures due to global warming, although there are likely other factors as well.