Last winter was historically mild and snowless
We do not expect a repeat of last winter, which was mostly a no-show, ranking as the seventh warmest on record.
To the delight of many and the despair of some, less than three inches of snow fell at all of the three major airports in the region over the entire winter. Reagan National Airport saw just 0.6 inches, the third-lowest amount on record.
The last time we experienced serious winter weather was in January 2019, when we were blanketed by a somewhat rare 10-inch snowstorm.
A snowier winter than last winter is a safe bet
It is hardly going out on a limb to say that the upcoming winter will be colder and snowier than last. But that certainly doesn’t guarantee a cold and memorable winter. In fact, we think it will end up mild overall, but not without some sharp cold snaps and wintry precipitation.
We expect more snow than last year, though a little less than the average of 15.4 inches at Reagan National Airport. Overall, we think we’ll have several accumulating snow events even in the immediate D.C. metro area, with a couple more in the outer suburbs. This doesn’t include dustings or ice events, as we are likely to have some of those, too.
Expect mixed precipitation events and tough forecasts
Most of our wintry weather will come from clippers and storms that cut to our west, though we can’t rule out a classic nor’easter charging up the East Coast.
When storms take a track to our west, most of what usually falls is rain. However, when there is enough cold air in place before the storm, it starts as snow before usually changing over to a mix or plain rain. These are tricky forecasts, and we think we’ll have our share of them this winter.
While we’ll have plenty to talk about this winter, we will still have our typical stretches of dry, “boring” weather, particularly in December.
We think our best chance of feeling the full weight of winter is in late January, when we might see a persistent colder and stormier period, with another more modest opportunity in late February.
Overall, we expect temperatures for December through February to be slightly to somewhat above average (by about two degrees):
- December: Three degrees warmer than average
- January: One to two degrees warmer than average
- February: One to two degrees warmer than average
Our snowfall projection covers November through April. Overall, we expect slightly below-average snowfall, though around the median:
- Reagan National Airport (DCA): 10 to 14 inches (compared with a 15.4-inch average, 11-inch median)
- Dulles International Airport (IAD): 14 to 18 inches (compared with a 22.0-inch average, 16-inch median)
- Baltimore-Washington International Marshall Airport (BWI): 14 to 18 inches (compared with a 20.1-inch average, 15-inch median)
- Fairfax, Loudoun, Montgomery counties: 12 to 20 inches
- Alexandria, Arlington and Prince George’s counties and the District: 10 to 16 inches
Answers to questions you may have
What are other forecasters predicting for the Washington region?
There is a reasonably strong consensus among forecasters in private industry and the media for below-normal snowfall and above-average temperatures this winter.
We interviewed via email seven forecasters who either own forecasting businesses or represent larger companies. All but two predicted just 10 inches or so for the winter. The two outliers are calling for more than 20 inches.
Among the media meteorologists, here are the outlooks from the different television affiliates:
The National Weather Service is calling for somewhat above-normal temperatures and near-normal precipitation; it does not issue a specific snowfall forecast.
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 15 winters. We’ve generally been in the ballpark, giving ourselves an average grade of around B-minus or C-plus, although we’ve had notable triumphs and misses.
Last winter we called for somewhat below-average snowfall and somewhat above-average temperatures, and there was hardly any snow and temperatures were historically warm. We self-graded our outlook a “C” but noted we were one of very few outlets that correctly called for below-average snowfall.
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 five 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.
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.
- 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.
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 1971-1972 (snowfall 16.8 inches), 1999-2000 (snowfall: 15.4 inches), 2008-2009 (snowfall: 7.5 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, while we experience frequent and often brief oscillations from warm to cold and back again, 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 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 fairly persistent negative PDO period. Additionally, La Niña often lends itself to a negative PDO. We expect that this winter that the PDO will average negative, though we don’t expect it to be extreme.
A negative PDO would favor of 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 a 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 2009-2010.
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. This was the case last winter; the AO reached record-breaking positive values at times.
We expect the AO and NAO to average positive this winter. That said, we think there will be a window, perhaps lasting a couple weeks, when both indexes link up and go sharply negative, enhancing our chance for snow events. We think this is most likely to occur in late January. Outside of that, flips to negative should be briefer but can deliver snow chances with the right timing.