Wednesday, December 1, 2021

"Fall" and hurricane season end, so here's the winter outlook!

Meteorological Fall Comes to an End

As the calendar turns to December and minds collectively turn towards the end-of-year holiday season, meteorologists see a changing of the seasons. While the official start of winter is when the winter solstice occurs (December 21), "meteorological winter" for climate record-keeping purposes starts December 1 and runs through the end of February. That means the record books are closed on autumn. We'll have more detail in the November climate summary in a few days, but preliminary data indicates that the average temperature for fall this year was 65.1 degrees, which is above the long-term average of 64.4 degrees. Rainfall, however, was below normal, totaling 8.92" for September-November versus the average of 11.70". 

Winter 2021-2022 Outlook

So what does the crystal ball look like for winter, perhaps the most anticipated season of the year? Early prognostications are driven primarily by the state of El Nino-Southern Oscillation (ENSO), but there are many other factors that make it pretty unpredictable, especially in the south. What is likely is the current La Nina climate pattern - an oceanic pattern that features cooler than average waters in the central Pacific Ocean - will continue through the winter. In fact, it's a "double dip" La Nina after the pattern dominated last winter, receded this summer, but reappeared in the fall. The typical impacts from a La Nina pattern are shown below. The Mid-South tends to be in the battle zone between wetter conditions to our north and drier to our south, while temperatures tend to be above average.

Typical impacts over North America during a La Nina winter. (NOAA)

The official Winter Outlook from NOAA is very close to what we would expect from a La Nina pattern and is shown below. There is a 40-50% chance of temperatures averaging above normal and odds of wetter than average conditions dip as far south as west TN. 

The temperature outlook for December-February 2021 from NOAA.

The precipitation outlook for December-February 2021 from NOAA

Remember that these are predictions of average conditions over a three-month period. That means there can certainly be cold spells in an overall warm pattern, or rainy periods in a dry month. In fact, you will certainly remember the Arctic outbreak last February that occurred in a very similar overall pattern to this winter. Other factors and atmospheric patterns will dictate the day-to-day conditions.

Atlantic hurricane season also ends

The start of December also means that the Atlantic hurricane season has also come to an end. It also marks the first time that the pre-defined list of 21 storm names has been exhausted in consecutive years. The 2021 season featured exactly 21 named storms (the third most in a year), seven hurricanes (five of which classified as "rapidly intensifying" during their life cycle), four major hurricanes, and eight U.S. landfalls. It was also the sixth consecutive "above normal" season and seventh consecutive season in which a named storm formed before the official start of the season on June 1. (NOAA's outlook published in May called for 13-20 named storms, 6-10 hurricanes, and 3-5 major hurricanes.)

Erik Proseus
MWN Meteorologist

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