D.C. winter forecast calls for above normal snow, higher big storm odds

Even as we bask in abnormally warm weather, December is a mere three weeks away, and so it’s time for our annual winter outlook.

The last several winters have been a thrill for those who prefer mild weather in the Washington region, but they’ve been terribly disappointing for snow lovers. Just 0.4 inches of snow fell last winter, the third-least on record. It was also the second-warmest winter on record; 19 days hit at least 60 degrees in January and February.

We’re anticipating a harsher winter ahead, and one that is much more satisfying for those who love the snow.

Our outlook calls for above-normal snowfall for the first time since the winter of 2018-2019, when Reagan National Airport, Washington’s official observing location, received 16.9 inches.

The primary driver for our snowier outlook is the ongoing El Niño, which is the climate pattern characterized by warmer-than-normal ocean waters in the tropical Pacific. El Niños tend to fuel strong storms in the southern United States that sometimes turn up the East Coast, increasing precipitation and snow prospects in the Mid-Atlantic. Still, every El Niño winter is different: Some produce very little snow, while others bring blizzards.

Ultimately, how much snow we see will depend on the strength of this season’s El Niño and a number of other factors which can be difficult to predict.

How the winter could play out

We’re estimating there will be six or seven accumulating snow events in the immediate area, with a couple more in our colder suburbs to the west and north. This doesn’t include dustings or ice events; we are likely to have some of those, too.

Some of our wintry weather will come from clippers, fast-moving disturbances from the northwest which typically produce light amounts of snow. We will also see juicier storms that pass to our west, which often draw mild air north, changing snow to rain.

What could set this winter apart are coastal storms, or nor’easters, that carry the potential for significant snowfall. Because of El Niño, the odds of a blockbuster storm unloading a foot or more of snow is higher than average, or around 35 percent. The typical chance of a such a storm is around 10 percent.

We do see winter getting off to a pretty benign start. We haven’t received more than 2 inches of snow in December since 2010. Even if we break the streak, we expect the monthly snowfall to be modest. Most of our seasonal snow should fall between January and March, with a focus on February, which we expect to be our snowiest month.

Temperature-wise, we’re leaning toward slightly cooler than normal conditions overall, with a particularly cold February following temperatures closer to normal in December and January.

Outlook details

Temperatures

Overall, we expect temperatures for December through February to range from average to around a degree cooler than the norm.

December: Average to 1 degree warmer than average;
January: Around average;
February: 2 to 3 degrees cooler than average.

Our snowfall projection covers November through April. Overall, we expect slightly to somewhat above-average snowfall.

Reagan National Airport: 16 to 22 inches (compared with a 13.7-inch average);
Dulles International Airport: 25 to 30 inches (compared with a 21-inch average);
Baltimore-Washington International Marshall Airport: 25 to 30 inches (compared with a 19.3-inch average);
Fairfax, Loudoun, Montgomery counties: 22 to 35 inches;
Alexandria, Arlington and Prince George’s counties and the District: 15 to 25 inches.

Qualifiers

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 for 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.

Why predicting winter storms in Washington is so hard

Answers to questions you may have

What are other forecasters predicting for the Washington region?

We polled five meteorologists who specialize in seasonal forecasting, and they also are predicting near to above-normal snowfall for the winter:

Judah Cohen, Verisk AER: 13.3 inches;
Todd Crawford, Atmospheric G2: 16 inches;
Paul Dorian, Arcfield Weather: 20 to 30 inches;
Paul Pastelok, AccuWeather: 14 to 18 inches;
Matt Rogers, Commodity Weather Group: 15 inches.

In addition, broadcast meteorologists for local television affiliates who have released outlooks are also calling for above-normal amounts:

Doug Kammerer, NBC4: 22 to 30 inches;
Mike Thomas, FOX5: 12 to 20 inches.

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 18 winters. We’ve generally been in the ballpark — although we’ve had notable triumphs and misses — giving ourselves an average grade of around 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 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. In 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.

Our outlook for last winter was mediocre. We predicted slightly above-normal temperatures and below-normal snowfall, whereas in reality, temperatures were much above normal and it was practically snowless.

Do you take climate change into account in your winter outlooks?

Since 1970, the average winter temperature has risen between 3 and 5 degrees across the region. Meanwhile, the 30-year average snowfall has declined from over 20 inches in the late 1800s to just 13.7 inches today.

Here’s how much snow has fallen over each of the past 10 winters (full list back to 1887-1888):

	Snow amount (in inches)

We do consider these long-term trends 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 advances allow us to make educated guesses on the overall tendency of conditions, such as how temperatures and snowfall will compare with the average over the period of a month or 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.

How could this forecast go wrong?

The main risk to the forecast is if El Niño becomes so strong that it persistently draws warm air into the area, resulting in a very mild winter without much snow. This was the case during the El Niño winter of 1997-1998, one of Washington’s two least snowy winters on record.

Methodology

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 have proved to have at least some predictive value in the past. And when considered collectively, they help paint a picture of what we believe is most likely to happen this winter.

Although no two winters are identical, we expect this one to share some similarities with those of 1972-1973, 2002-2003 and 2009-2010. 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 experiencing a moderate El Niño event that may strengthen and peak as a strong event. This is our first El Niño since a weaker event in 2018-2019, the last time we saw above-normal snowfall.

One thing that moderate to strong El Niño events have in common are periods where the subtropical jet stream is active. An active subtropical jet often brings storms ashore in California that traverse the southern half of the United States. Sometimes these storms will come up the East Coast and produce heavy snow and/or rain.

It is often during the second half of El Niño when the subtropical jet stream is most active, and we expect that to be the case this winter.

That said, the northern (polar) branch of the jet stream can assert dominance at times, especially earlier in the winter. When the northern stream is dominant, the prevailing storm track shifts to our west. When storms track to our west, they tend to draw warm and sometimes dry air over our region. When it does snow in these situations, a flip to sleet or rain is common.

Total snowfall during moderate to strong El Niños can be feast or famine. They have produced both some of our snowiest and least snowy winters. While stronger El Niños can be stormy, sometimes they draw up so much mild air from the south that they produce mostly rain. If the ongoing El Niño strengthens more than anticipated, that could result in lower snow chances, particularly given very warm background conditions tied to human-caused climate change.

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, tend warm and dry.

We are in the midst of a very persistent negative PDO period. El Niño events tend to drive the PDO index upward, so we might see some movement of the PDO toward the positive side. However, we do expect the PDO to average slightly to somewhat negative this winter which could favor some periods of mild weather.

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 a high-pressure area (negative phase) over or near Greenland.

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 2009-2010.

While a negative AO and NAO combination far from guarantees severe winter weather, our chances of a meaningful snow event are much greater than without it.

We predict the AO to average slightly negative and the NAO to average slightly to somewhat negative this winter. There will likely be periods when both indexes go sharply negative. These windows give us the best opportunity for meaningful snow events.

Past outlooks and recaps

Ian Livingston and Dan Stillman contributed to this report.