Answer:
La Niña, because the jet stream is displaced northwards
Step-by-step explanation:
La Nina is known to be a cool phase that affects the average ocean temperature. During this period the surface wind becomes stronger and there is lesser rainfall over the areas of the central tropical Pacific to which the Southern United States belongs.
Hence, when the southern United States experiences periodic occurrences of severe cold and drought conditions, the weather phenomenon most likely causes this and why is "La Niña, because the jet stream is displaced northwards."