After three consecutive winters that were full of excitement and above-average snow, we’re expecting a return to a more ho-hum D.C. winter, with temperatures slightly above normal and slightly below-normal snow.

Compared with last winter, which averaged about four degrees warmer than normal, temperatures should be slightly colder, averaging about one degree warmer than normal, even if less snow falls.

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January has the best chance to be colder than normal

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Our best chance of feeling the full weight of winter is in late December through late January, when we might see some persistent colder and stormier periods.

February looks to be pretty mild, and the possibility of an early end to winter is of higher probability than usual.

Some snow, but lower-than-normal chances of a blockbuster

We’re not predicting a lot of snow, but we also aren’t anticipating a virtually snowless winter like in 1997-1998.

Overall, we think we’ll have five to six accumulating snowfall events for 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.

Most of our wintry weather will come from clippers and storms that cut to our west.

Clippers are typically moisture-starved and only drop a dusting to a couple of inches of snow.

When storms take a track to our west, most of what usually falls is rain. However, when there is enough cold air in place prior to the storm, it starts as snow before usually changing over to a mix or plain rain. These are tricky forecasts, and I think we’ll have our share of them this winter.

We won’t rule out a classic nor’easter with a southerly track, especially in February and March. However, we are not confident there will be cold enough air in place to get a decent snowfall from these, so unfortunately for snow lovers they may be a wasted opportunity.

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While we’ll have plenty to talk about this winter, we do expect some longer stretches of dry “boring” weather, which I’m sure will be welcome to most residents, while frustrating to snow lovers.

Outlook by the numbers

Temperatures

Overall, we expect temperatures for December through February (relative to 1981-2010 normals) to be slightly (around one degree) milder than average:

December: Around average

January: One degree colder than average

February: Three degrees warmer than average

Snowfall

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

Reagan National Airport (DCA): 8-12 inches (compared with a 15.4-inch average, 11 inch median)

Dulles International Airport (IAD): 14-18 inches (compared with a 22.0 inch average, 16 inch median)

Baltimore-Washington International Marshall Airport (BWI): 12-16 inches (compared with a 20.1 inch average, 15 inch median)

Fairfax, Loudoun, Montgomery counties: 12-20 inches

Alexandria, Arlington and Prince George’s counties and the District: 10-14 inches

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.

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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.

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Common questions

What are other outlets forecasting for our area?

Three local television outlets have issued winter outlooks to date — FOX5, WUSA9, and NBC4 — and all are predicting a slightly colder than average winter. Two of the three (FOX5 and NBC4) are calling for slightly above normal snowfall while WUSA9 is predicting slightly below normal snowfall.

The National Weather Service says the atmospheric setup is too uncertain to make a call, while several private consulting meteorologists favor a cold, snowy winter, including Judah Cohen at Atmospheric Environmental Research (AER), Dave Tolleris at WxRisk, Joe Bastardi at WeatherBell Analytics, and the Commodity Weather Group.

How have your winter outlooks performed in past years?

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We have been doing winter outlooks since 2005-2006 and have evaluated ourselves after the fact for the past 10 winters. We’ve generally been in the ballpark, giving ourselves an average grade around a B- or C+,al though we’ve had notable triumphs and misses.

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Our best 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.

Last winter was a mixed bag. We correctly forecast a milder than normal winter and said chances of a major snowstorm were above normal. Even so, we predicted slightly below normal snow overall whereas actual amounts were about 150 percent of normal.

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Our worst outlooks were for the winter of 2011-2012 and 2013-2014. In 2011-2012, we called for near normal temperatures and it was 5 degrees warmer than normal. Two 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.

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Methodology

Below are the factors that we have deemed most important 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.

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No two winters are alike, but we expect this winter to share some similarities with the winters of 1980-81 and 1983-84. These analogs 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

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We are currently experiencing a weak La Niña event, which should stabilize over the next couple of months and perhaps even weaken in the second half of winter.

La Niña is indicated by anomalously cold sea-surface temperatures in the equatorial Pacific Ocean.

In our region, La Niñas, particularly moderate to strong events, are often associated with dry, warm winters without much snow. This is usually because of two primary factors:

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1) The frequent presence of a southeast ridge. It is a persistent area of high pressure near Bermuda that both keeps us in warmer air masses 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 branches 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 weak 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 Niña’s are the same and there are other factors that drive our weather.

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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 persistent positive PDO period. The PDO has been positive for 33 consecutive months, and even though La Niña usually lends itself to a negative PDO, we expect the PDO to average neutral or positive throughout the winter.

A positive PDO often correlates with upper-level high pressure or a ridge over western Canada (and sometimes up to and north of Alaska), and a downstream area of low pressure or trough over the southeastern United States.

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A ridge in western Canada is a good mechanism for delivering cold into the eastern United States if the cold air is available to tap. However, La Niña is usually indicated by a trough over western Canada. That is one of the biggest question marks this winter. Despite a neutral or positive PDO regime, will typical La Niña conditions win out?

At this time we are mostly agnostic toward the default ridge/trough setup throughout winter. If anything, we expect it to oscillate throughout winter, with no persistent regime.

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 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.

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 think the AO will average near neutral this winter, with the NAO leaning positive. Consequently, while the predominant high-latitude pattern will be amenable to cold outbreaks at times, the upper-level pattern near and over Greenland might act as a mitigating factor, both in terms of cold air and storm track, which we expect to mostly be to our west.

Summer and fall pattern

D.C.’s summer was the third-hottest on record and the fall has also been unusually warm. While correlations between summer-fall and the upcoming winter are weak, we did consider the months leading into winter in selecting analog years for this outlook.

(Capital Weather Gang’s Jason Samenow contributed to this post.)