NOAA expects La Niña weather patterns through March

Here's last month's summary and the outlook for the next three.

Scott K. Johnson – Dec 18, 2020 5:34 PM | 26

This was the second-warmest November on record, globally. Credit: NOAA

No change in the weather

November’s weather was dominated by high pressure ridges across the US, which is why the weather pattern was so consistent. The only exception was the second week of the month, when a low pressure trough formed in the West. That brought cooler temperatures and some precipitation, particularly farther north. At the same time, the influence of Hurricane Eta produced rain in Florida and up the mid-Atlantic.

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NOAA put a spotlight on Florida this month, where 2020 has so far been the warmest year on record. The state has been on a roll for about five years now, with 65 out of the last 68 months coming in above the long-term average—including the last 31 months straight. The last few years really stand out, as you can see in the chart below.

The trend in nighttime warming has been notably stronger than daytime warming, though that basic pattern is fairly common. As an example, this autumn saw 246 warm records set for daily high temperatures in Florida, but 687 records for warm daily lows. (There were just 19 new record cold daily lows.) Along with long-term warming driven by greenhouse gases, there are a few other factors that help explain this, Florida state climatologist David Zierden said. Combined with sea surface warming around Florida, humidity has trended upward, holding more heat in the air through the night.

Zooming back around, the widespread warm and dry weather pushed drought to cover an additional four percent of the US last month, putting fully 49 percent of the country in that category. A primary area of expansion was the Southeast, where La Niña conditions tend to keep things particularly dry.

Looking ahead

Speaking of La Niña, it is still expected to remain through the winter, but the spring forecast is edging back toward neutral (neither La Niña nor El Niño) conditions. By summer, neutral conditions are now favored.

Still, the outlook for the next few months is dominated by La Niña patterns. The January outlook generally tilts toward above-average temperatures, with the exception of the northwest US up through southeast Alaska. Due to the way the winter jet stream tends to set up during a La Niña, the southern tier of the US is likely to be dry, while much of the northern tier is likely to be wet. The Northern Plains region is an exception there, with equal chances of wetter or drier weather in the outlook.

The outlook for January through March is a stronger version of the same. Cooler temperatures may stretch into the Northern Plains from the Pacific Northwest, and so does the wetter outlook. The area of wetter weather pushes down from the Great Lakes into the Ohio Valley area, which is partly an expectation based on common storm tracks in the past.

All this means that drought is expected to grow across the Central Plains and Gulf region but continue to improve in the Pacific Northwest and in the Northeast.

North of the border, the current Environment and Climate Change Canada two- to four-month outlook covers January to March. Above-average temperatures are favored in the far southeast, with below-normal temperatures most everywhere else. The precipitation outlook is patchy, with above-normal amounts favored from British Columbia into the Prairies, in the Great Lakes region, and parts of Eastern Canada.

No change in the weather

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Looking ahead

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