A late March snowstorm hits the Washington, D.C., region. (Jonathan Newton/The Washington Post)

Summer seemed to last forever and fall has been fleeting. Our first chance of wintry precipitation is already here and the winter season itself is just a few weeks away.

As such, it’s time we present our annual winter outlook.

The last two winters didn’t feature much winter. The winter of 2016-2017 was abnormally warm and practically snowless. Last winter showed more signs of life, with a punishing Arctic blast in late December and early January and then a cold March capped by a snowstorm on spring’s first day. But, overall, it was still milder than average.

Winter will try to make a comeback in 2018-2019.

A snowier than average result for the first time since 2015-2016

This winter we’re predicting somewhat above average snowfall, to the tune of 18 to 24 inches inside the Beltway and up to 30 inches or so in our normally colder areas to the north and west.


(Washington Post Staff/The Washington Post)

We predict February will be the snowiest month, perhaps followed by March, as a more entrenched and persistent wintry pattern tries to emerge. Additionally, we think the chance of a significant snowstorm — 8 to 12 inches or even more — is higher than normal

Overall, we’re forecasting seven or eight accumulating snow events in the immediate D.C. metro area, with a couple more in our colder suburbs to the north and west. This doesn’t include dustings or ice events, as we are likely to have some of those, too.

A late blooming winter, trending colder into February

Although we favor snowy conditions, we don’t think it will be brutally cold. We haven’t had a cold winter in four years (since 2014-2015) and lean toward slightly warmer than average conditions this year.

But you may notice the winter turning more intense with time. We’re forecasting December and January to end up somewhat warmer than average. That said, weather patterns don’t abide by a monthly calendar, and a flip to a colder and snowier period is very possible in mid- to late January. February should be decidedly cold and, if that verifies, it will be the first colder than average February since 2015.

Given the prospects for a cold March, this winter may seem quite long.

Outlook details

Temperatures

Overall, we expect temperatures for December through February (relative to 1981-2010 normals) to finish near to slightly above average (average to one degree above average).

Here is the month by month breakdown:

  • December: Three to four degrees warmer than average
  • January: Two degrees warmer than average
  • February: Three to four degrees colder than average
  • March: We don’t make specific predictions for March, but we do predict it to be colder than average.

Snowfall

Our snowfall projection covers November through April (1981-2010 statistics in parentheses). Overall, we expect slightly to somewhat above average snowfall.

Here are the predicted snow amounts, by location:

  • Alexandria, Arlington and Prince George’s counties and the District: 18-24 inches
  • Fairfax, Loudoun, Montgomery  counties: 22-32 inches
  • Reagan National Airport (DCA):  16-20 inches (compared with a 15.4-inch average, 11 inch median)
  • Dulles International Airport  (IAD): 24-30 inches (compared with a 22.0 inch average, 16 inch median)
  • Baltimore-Washington International  Marshall Airport (BWI): 22-28 inches (compared with a 20.1 inch average,  15 inch median)

(The Washington Post/The Washington Post)

Qualifiers

  • While advances have been made in seasonal  forecasting, there is still a great deal of uncertainty and limited skill in developing these outlooks. This is a low-confidence forecast.
  • 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 short can greatly alter a monthly average. Furthermore, it takes only one big snowstorm for us to near or exceed our seasonal average.

Common questions and answers

What are other outlets forecasting for our area?

Without exception, forecasters in the private sector, including TV forecasters, consulting meteorologists and major weather companies, are predicting a snowier than average winter in Washington. We reviewed nine independent outlooks and all of their forecasts fall in the range of 15 to 35 inches of snow, compared to the average of 15 inches, with the majority in the 20- to 30-inch range.

Most of the outlooks predict colder-than-average temperatures although a few call for near-average.

[Summary of TV forecaster outlooks | Summary of other private sector outlooks]

The National Oceanic and Atmospheric Administration’s outlook from the government does not issue a snowfall forecast, but favors above normal precipitation and near-average temperatures.

[Summary of NOAA winter outlook]

How have your winter outlooks performed in past years?

We have been doing winter outlooks since 2005-2006 and have evaluated ourselves after the fact for the past 12 winters. We’ve generally been in the ballpark, giving ourselves an average grade around a B- or C+, although we’ve had notable triumphs and misses.

Our outlook for last winter was pretty good. We correctly called for slightly warmer than average conditions and below average snowfall — although we missed on some of the month-to-month specifics.

Our best winter forecast preceded the record-breaking Snowmageddon winter (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 normal. Four winters ago (2013-2014), we called for a warm winter with slightly below normal snow and it was cold, with snow more than twice the average.


People gather on the banks of the tidal basin to check out cherry blossom trees covered by a spring snow fall in Washington on March 21. (Melina Mara/The Washington Post)

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 in the past as a guide, have proven 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 1913-14 and 1923-24. These analogs helped to very 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 likely currently experiencing the infancy of a weak to moderate El Niño event that should persist throughout the winter, and perhaps beyond. El Niño is a phenomenon in the central and eastern tropical Pacific Ocean in which ocean temperatures are warmer than normal. In recent weeks, ocean temperatures in this region have warmed significantly.


Animation of sea surface temperatures from normal over time in the tropical Pacific Ocean. (NOAA)

One thing that most weak to moderate El Niño events have in common is periods where the subtropical jet stream is active. An active subtropical jet stream is indicated by storm systems hitting the California coast and traversing across the southern half of the United States. Often these storms will come up the East Coast and produce snow, but even when they don’t, we are frequently far enough south in latitude to be affected.


(The Washington Post/The Washington Post)

It is often during the second half of El Niño when the subtropical jet stream is most active and we expect the greatest chance of meaningful snow events.

That said, the northern (polar) branch of the jet stream can still assert dominance at times, especially in weaker El Niño events. 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 situation, a flip to sleet or rain is common.


(The Washington Post/The Washington Post)

All other things being equal, El Niño tends to slightly favor above normal snowfall in Washington, but more for moderate events than for the weak and strong. This event is predicted to straddle the line between weak and moderate.

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.

After a multiyear persistent positive PDO period, we are experiencing a more neutral period. Often, though not always, El Niño events tend to have a strengthening effect on the PDO toward the positive phase. As such, we think the PDO will average slightly above normal for the winter, but less so than in El Niño winters that occur during more positive PDO periods.


The Pacific Decadal Oscillation over time. (NOAA)

A positive PDO often correlates with a zone of high pressure or ridge over western Canada (and sometimes up to and north of Alaska), and a downstream area of low pressure or dip in the jet stream over the southeastern United States. A ridge in western Canada is a good mechanism for delivering cold into the eastern United States.

Arctic Oscillation (AO) and North Atlantic Oscillation (NAO)

The AO is a measurement of surface air pressure difference from normal 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.


Jet stream pattern during the positive AO (left) and negative AO (right) (University of Washington)

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 an upper-level low pressure area (positive phase) or upper-level 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.


(The Weather Channel)

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 predict the AO and NAO will average slightly above normal this winter, which will somewhat limit windows in which the storm track and available cold air are favorable for snow. That said, we expect there will be a window from late January to early March in which both indices go sharply negative, enhancing our chance for snow events.

Other factors considered

2018 will be one of our wettest years on record. We expect this wet pattern to persist, particularly since El Niño events often lend themselves to wetter than normal conditions anyway. Consequently, we expect precipitation to average above normal for the winter, which tilts the odds for snowier conditions.

Capital Weather Gang’s Ian Livingston contributed to this outlook.

Past outlooks

2017-2018 winter outlook recap

2017-2018 winter outlook

2016-2017 winter outlook recap

2016-2017 winter outlook

2015-2016 winter outlook recap

2015-2016 winter outlook

2014-2015 winter outlook recap

2014-2015 winter outlook

2013-2014 winter outlook recap

2013-2014 winter outlook

2012-2013 winter outlook

2012-2013 winter outlook recap

2011-2012 winter outlook

2011-2012 winter outlook recap

2010-2011 winter outlook

2010-2011 winter outlook live chat

2010-2011 winter outlook recap

2009-2010 winter outlook

2009-2010 winter outlook recap

2008-2009 winter outlook

2008-2009 outlook live chat

2008-2009 winter outlook recap

2007-2008 winter outlook

2007-2008 winter outlook recap

2007-2008 winter outlook

2006-2007 winter outlook

2005-2006 winter outlook