La Nina conditions have strengthened across the Equatorial Pacific with sea surface temperature anomalies approaching negative 1.5 degrees Celsius, (image below courtesy NOAA).
Historically speaking, La Nina winters that have followed either ENSO neutral (average sea surface temperatures) or El Nino (warmer than average sea surface temperatures) winters have produced colder than average Decembers across the eastern United States. Because last winter featured a weak La Nina, the winter of 2020-21 is considered a “first year” La Nina.
I took a handful of “first year” La Nina winter seasons and ran them through NOAA’s climate database and here are how temperature anomalies in December, January, February and March shook out.
December temperature anomalies were much cooler than average across the eastern United States
The colder weather retreated to the northern plains and western United States during January, with above average temperatures common from the south to New England.
February featured near average temperatures in the Washington Area with colder air beginning to make intrusions deeper into the Midwest and Ohio Valley.
March was also cooler than average in the Washington Region and across much of the eastern United States.
Remember that monthly temperature anomalies (or departure from average) by no means indicates that the entire month of January will be mild with no shots of cooler air. When i made my winter forecast, i predicted temperatures overall (December through February) would be milder than average with precipitation near to below average in the DC Area. You can access my winter forecast here.