Snow lovers are unlikely to be pleased as we’re projecting below-average amounts for the fifth time in the past six winters. We do, however, think we’ll top last winter’s snow totals — a mere 6 to 10 inches across the metro area.
Although the snow may not amount to much, there should be plenty of storms to track. We predict we’ll have several accumulating snow events in the immediate area over the course of the winter, with a couple more in our colder suburbs. This doesn’t include dustings or ice events; we are likely to have some of those, too.
Most of our wintry weather will come from clippers, which are often moisture starved, and storms that cut to our west, which are predominantly rain. However, when there is enough cold air in place ahead of such storms, the precipitation can start as snow before usually changing over to an icy mix or plain rain. These are tricky forecasts, and we think we’ll have our share of them this winter.
The odds of a blockbuster nor’easter coming up the coast and walloping us with snow is lower than average, but can’t be entirely ruled out.
We see winter getting off to a fast start and lean toward a colder-than-normal December. Our chance of measurable snowfall is typically only about 50-50, but we see somewhat higher odds this year. Remarkably, we haven’t seen more than two inches of snow in Washington during December in more than a decade. Maybe this year can end the streak.
January should provide additional windows of opportunity for snow, while wintry weather may fade in February.
Overall, we expect temperatures for December through February to be close to average.
- December: 1 to 2 degrees colder than average
- January: Around average
- February: 2 degrees warmer than average
Our snowfall projection covers November through April. Overall, we expect slightly to somewhat below-average snowfall.
- Reagan National Airport (DCA): 8 to 12 inches (compared with a 13.7-inch average)
- Dulles International Airport (IAD): 12 to 16 inches (compared with a 21-inch average)
- Baltimore-Washington International Marshall Airport (BWI): 10 to 15 inches (compared with a 19.3-inch average)
- Fairfax, Loudoun, Montgomery counties: 10 to 18 inches
- Alexandria, Arlington and Prince George’s counties and the District: 8 to 14 inches
- Although advances have been made in seasonal forecasting, there is still a great deal of uncertainty and limited skill in developing these outlooks. These remain low-confidence forecasts.
- Note that monthly temperature predictions are less reliable than for the whole season. A cold or warm pattern lingering a week too long or ending a week early can greatly alter a monthly average. Furthermore, it takes only one big snowstorm for us to reach or exceed our seasonal average.
Answers to questions you may have
What are other forecasters predicting for the Washington region?
After we developed our own numbers for this winter outlook, we polled several forecasters who produce their own outlooks to compare. It turns out their ideas are very similar to ours, and there is a strong consensus for near to slightly above-average temperatures and near to below-average snowfall. No outlook calls for substantially above-average snow or below-average temperatures.
Here is a brief summary of their outlooks:
- Joe Bastardi, WeatherBell: Average temperatures and snowfall
- Todd Crawford, Atmospheric G2 (formerly WSI): Above-average temperatures and below-average snowfall (9.5 inches)
- Judah Cohen, Atmospheric Environmental Research: Average temperatures and slightly below-average snowfall (11.6 inches)
- Paul Dorian, CTFV (formerly Perspecta Weather): Average temperatures and near-average snowfall (15 inches)
- Paul Pastelok, AccuWeather: Above-average temperatures and below-average snowfall (8.7 inches)
- Matt Rogers, Commodity Weather Group: Average temperatures and below-average snowfall (8.5 inches)
Several of these forecasters agree that winter will start fast with cold, snowy conditions before trending milder.
“We expect the ‘shape’ of the winter to be front-loaded with cold, especially December, with an increasingly warm (relative to normal) back end, with a potentially early spring and very warm March,” wrote Crawford in an email.
Of the Washington-area television affiliate weather teams, only FOX5 so far has released an outlook. It’s calling for above average temperatures and below-average snowfall (5 to 13 inches), in line with everyone elses expectations.
The National Weather Service’s winter outlook does not include snowfall projections, but it calls for above average temperatures and near-average precipitation for the Washington region.
What is your long-term track record with these winter outlooks?
We have been doing winter outlooks since 2005-2006 and have evaluated ourselves after the fact for the past 16 winters. We’ve generally been in the ballpark, giving ourselves an average grade of around B- or C+, although we’ve had notable triumphs and misses.
Last winter we called for slightly below-average snowfall (10 to 14 inches) and somewhat above-average temperatures (2 degrees above average), whereas snowfall was solidly below average (6 to 10 inches), and temperatures were slightly above average (1.1 degrees above average). We graded our outlook a C+.
Since initiating these outlooks, our best winter forecast preceded the record-breaking Snowmageddon winter of 2009-2010, when we said: “Overall, we find chances for a large snowstorm of 8-12 inches or more are much higher than normal this coming winter.” Our outlook for the winter of 2014-2015 was also quite successful, as we correctly called for it to be cold with somewhat above-normal snow.
Our worst outlooks were for the winters of 2011-2012 and 2013-2014. In 2011-2012, we called for near-normal temperatures, and it was 5 degrees warmer than average. Several winters ago (2013-2014), we called for a warm winter with slightly below-average snowfall, and it was cold, with snow that totaled more than twice the average.
How is climate change influencing our winters?
Winter temperatures have steadily risen in Washington over the past 150 years, and snowfall amounts are in decline. Since 1970, the average winter temperature has risen between 3 and 5 degrees across the region.
Climate averages or “normals” warmed around 1 to 2 degrees in every winter month between the 1981-2010 and 1991-2020 periods alone.
Meanwhile, the 30-year average snowfall has declined from over 20 inches in the late 1800s to just 13.7 inches today.
We do take these long-term trends into account in our winter outlooks.
Aren’t weather forecasts only reliable out to about eight to 10 days?
It is true that there is no skill in predicting specific conditions, such as the exact temperature and amount of rain or snow for a given day, more than eight to 10 days into the future. However, seasonal forecasting has advanced to the point that we can make educated guesses on the overall tendency of conditions, such as how temperatures and snowfall will compare to average over a month or period of several months. Because of the uncertainty involved, we give ranges and attempt to be as transparent as possible in conveying that these outlooks are indeed low-confidence.
Below are some, though not all, of the factors that we considered in determining conditions for this upcoming winter.
No single factor tells the whole story, nor are the correlations between past conditions and future conditions — which we used to inform the outlook — always strong. But we have chosen factors that in the past as a guide, have proved to have at least some predictive value. And when considered collectively, they help paint a picture of what we believe is most likely to happen this winter.
No two winters are alike, but we expect this winter to share some similarities with the winters of 1950-51 (snowfall: 10.2 inches), 1955-56 (snowfall: 11.3 inches), 1970-71 (snowfall: 11.7 inches). These analogues helped to loosely form the basis of our temperature and snow predictions because the weather in those years had some similarities to the factors below.
Tropical Pacific Ocean
We are currently experiencing a strengthening La Niña event, which is indicated by colder-than-average ocean temperatures in the tropical Pacific Ocean.
In our region, La Niñas, particularly moderate to strong events, are often associated with dry, mild winters with modest snowfall. This is usually because of two primary factors:
1. The frequent presence of a southeast ridge. It is a persistent area of high pressure near Bermuda that pumps mild air into the region and pushes the storm track to our north and west.
2. A dominant northern jet stream and lack of a subtropical jet. Prevalent storm tracks along the northern branch of the jet stream typically cut to our west and/or redevelop as coastal storms to our north, and we are left either warm and rainy, or dry.
Usually in weaker La Niña events, we experience frequent and often brief oscillations from warm to cold and back again, although the cold outbreaks are typically dry. However, not all La Niñas are the same, and there are other factors that drive our weather.
This winter we expect a weak to moderate La Niña to persist throughout the winter, with some weakening late.
North Pacific Ocean
The Pacific Decadal Oscillation (PDO) is a measurement of the intensity and location of sea-surface temperature differences from normal in the North Pacific. When it is strongly positive, it often correlates with a cold and stormy pattern for the Mid-Atlantic. When it is sharply negative, conditions often, but not always, trend warm and dry.
We are currently in the midst of a very persistent negative PDO period. Additionally, La Niña often lends itself to a negative PDO. We expect that this winter the PDO will average negative, perhaps strongly so.
A negative PDO would favor a dip in the jet stream over western Canada with a southeast ridge, favoring a mild weather regime in the Mid-Atlantic, though we expect that pattern to flip at times, usually briefly.
Arctic Oscillation (AO) and North Atlantic Oscillation (NAO)
The AO is a measurement of surface air pressure at the high latitudes over and north of Greenland. Pressures lower than normal indicate the positive phase, and pressures higher than normal, the negative phase.
During the positive phase of the AO, cold air is characteristically locked up over the Arctic by a strong polar vortex, and the mid-latitudes tend to be mild. In the negative phase of the AO, the polar vortex becomes disturbed, and cold air outbreaks become more likely over the mid-latitudes, including the United States.
The AO’s cousin, the NAO, is technically a measurement of the differences in air pressure over the North Atlantic Ocean. It is often indicated by either low pressure (positive phase) or high pressure area (negative phase) over or near Greenland. Often, though not always, the AO and NAO share the same phase, especially when averaged over the course of the winter.
A negative AO in the winter months often correlates with a cold pattern in our region, and supports winter storms when other factors align with it, particularly when we have a negative NAO as well. This was the major factor in our historically snowy winter of 2009-10.
High pressure over Greenland or high-latitude blocking helps push the storm track farther south and east, often creating storm tracks that are cold and snowy for our region. While a negative AO and NAO combination far from guarantees a cold and snowy period, our chances of a meaningful snow event are much greater than without it.
On the other hand, a positive AO and NAO combination typically supports a warmer pattern, with a storm track that will often go to our west. We expect the AO and NAO to average slightly negative this winter. We expect there will be multiple windows when both indexes link up and go sharply negative, enhancing our chance for snow events.