Weather Forecast For December 2025. Get the monthly weather forecast for london, london, united kingdom, including daily high/low, historical averages, to help you plan ahead. The forecast average is within the la niña threshold but shows a weak to moderate event.

Federal forecasters expect a la niña climate pattern to form in the coming months, according to a report released thursday — offering a potential picture of what the weather could look like. Our long range forecast (which is updated on a daily basis) provides an indication of how the weather might change, or be different from normal, (i.e.