2018-2019 Winter Outlook for DC: Colder, snowier winter for region

Winter is nearly on our doorstep in DC so FOX 5 has crunched the numbers so you know what to expect this year.

Here are the quick highlights:

- We favor a COLDER THAN NORMAL winter ahead.

- After two years with less than 10 inches of snow in Washington, DC we are favoring an ABOVE NORMAL SNOWFALL season in our region.

- We expect NOVEMBER and DECEMBER to be volatile with changes between both warm & cold periods, with the more persistent cold settling in during JANUARY and ESPECIALLY FEBRUARY.

- A moderate EL NINO is forecast for this winter. For Washington, DC five of the eight recorded moderate El Nino cases have featured above normal snowfall (15.4 inches) with an average of 26.9 inches of snow.

- Nor'easters are more favored during El Nino winters. We are favoring at least ONE MEMORABLE STORM (10-inches plus) during the upcoming winter, with history pointing towards February as the month to watch.

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Before we dive into this winter's forecast, let check on last year's forecast (Released Oct. 26, 2017) and see how we did. Here were the top 5 forecast points from last year:

- With a weak La Nina forecast, we favor temperatures this winter to be COLDER THAN LAST YEAR, but also to come in SLIGHTLY ABOVE NORMAL overall.

- While we anticipate MORE SNOW THAN LAST YEAR, we are forecasting average to BELOW AVERAGE SNOWFALL for the immediate Washington, D.C. region.

- We are forecasting JANUARY to be THE COLDEST MONTH with about average temperatures, while we favor slightly above normal temperatures in December and February.

- The ODDS OF AN ICE EVENT ARE ABOVE NORMAL compared to the average winter.

- While one can never be ruled out, A BIG SNOWSTORM IS NOT FAVORED THIS YEAR (big = 10 inches or more in downtown D.C.) due to a weak La Nina. One to two snow events of 4 to 8 inches are more favored.

Seasonal forecasts are difficult and, try as we might as forecasters to nail all the details, the atmosphere is always going to throw us a curveball or two that we just do not see coming. Most forecasters would agree when you are making a winter outlook, you should always start with whether or not we are looking at an El Nino or a La Nina in the central Pacific. The past two winters have both been La Nina winters, meaning cooler than normal waters are present in the central Pacific. Historically, they are not typically kind to snow lovers in our region, and the previous two years have certainly been a little snow-starved.

This fall, ocean waters across that region have already warmed into El Nino territory. El Nino years tend to have a more active subtropical jet, which is a zone of increased winds leading from the eastern Pacific across the southern half of the United States. This jet can lead to the formation of moisture-rich southern storms, which can develop into snow-filled nor'easters if they form in conjunction with cold air riding on a feature known as the Polar Jetstream.

While an El Nino itself does not guarantee a snowy winter for our area, historically it does seem to provide better than normal chances of getting a good snowstorm or two into the Mid-Atlantic region. Historical records for El Nino and La Nina go back reliably to about 1950. Of the 10 snowiest winters in the DC area during that time frame, half of them were El Nino cases. Four of them were neutral, and only a single one was a La Nina year. Since the turn of the century, four of the five above normal snowfall winters our region have been El Nino cases.

In addition, this year's El Nino has the potential to be a very special type of El Nino known as a "Modoki" El Nino. Simply put, this is when the warm waters of El Nino are more central based and typically flanked by cooler waters on either side of it. Of the 11 recorded cases of Modoki El Nino on record, seven of them have featured more than 20 inches of snow for the DC region. Most recently, the winters of 2009-2010 (56.1 inches), 2004-2005 (12.5 inches), and 2002-2003 (40.4 inches) were all Modoki El Nino cases. Our forecast favoring this type of El Nino helped us lean in the snowier direction.

The activity of our nearest star, our sun, also played a large role in our colder than normal winter outlook this year. Solar cycles are periodic on roughly a decadal scale, changing roughly every 10 to 15 years. Winters during times of low solar activity have shown a tendency towards stronger blocking patterns over the Arctic region, which are necessary for transporting and maintaining cold air masses in the continental United States during the winter months.

Currently, we are nearing the end of solar cycle 24. The snowiest winter on record for Washington came near the end of our last solar cycle (23) and start of the current, in 2009-2010 (56.1 inches). Prior to that, solar cycle 22 wrapped up in the summer of 1996 with the preceding winter being the snowiest La Niña case on record with 46 inches of snow. Solar cycle 21 ended in the fall of 1986 with the winter that followed bringing the DC area 31.1 inches of snow. I could go on to farther examples in the 1970s and 1960s as well, but the data does all show that somewhere around each solar minimum the DC region seems to get a pretty big snowfall season.

Could this be the year of extreme snows in the DC region? We see this as a risk but did not go with the big "jackpot" numbers this season. Timing the effects of a solar minimum are tricky and can occasionally be stretched out over a number of years. However, given the emergence of El Nino along with the downtrend in solar activity, we felt confident enough to at least go with above normal snowfall in our region.

While El Nino and the downtrend in solar activity were the primary drivers in our winter forecast, several other weather features over the globe have caught our attention as well. A feature that meteorologist call simply "the Pacific warm blob" (no really, it has its own Wikipedia page) has returned after taking a couple of years off. This feature is believed to periodically enhance in lifting the Polar Jetstream northward in this region, causing it to dip across the eastern United States and bringing cold air into our region. It was believed to be a big player in the polar vortex winters of 2013-2014 and 2014-2015.

Additionally, good snow coverage across northern portions of North American so far through fall should help with the deepening of cold Arctic air masses as we get deeper into winter. Aiding this has been a recent healthy expanse of snow across portions of Siberia over the past week here in October. While difficult to simply explain, a wide enough advance in the snow-coverage field in this region is believed to help provide additional warming of the stratosphere due to a large amount of sunlight being reflected off the snow cover. This additional stratospheric warming can help lessen winds in the upper level of the atmosphere over the Arctic region, allowing what we call "blocking patterns" to develop and maintain their strength. It is these "blocks" in the atmosphere that help steer cold air out of the polar regions and down southward into the United States.

So let's get to it. This winter we are forecasting the coldest winter since the winter of 2014-2015, and are forecasting temperatures to be between 2 and 4 degrees below normal for the season here in Washington. This does not mean we expect every month to be cold. We expect November and December to be volatile for our region, with back-and-forth swings between above-and-below normal temperatures. We expected the colder pattern to win out during the second half of winter with February being the coldest month, which is something that is very typical of El Nino winters.

Snowfall wise, we expect our busiest snow season since the winter of 2015-2016, which was a very warm winter overall but featured the one big blizzard in January 2016 which brought DC 18 inches of the seasonal total of 22 inches of snow that season. This was also our last El Nino, although that was an abnormally strong El Nino season so the warmth was expected. Given the tendency for an active southern storm track with El Nino winters, we are forecasting a higher-than-normal change for a big snow storm (10-inches plus) in DC this winter and favor at least one. As is typical with these types of storms in an El Nino winter, we believe the best odds for such a storm will be in the late January or February time frame.

So what could go wrong this year? Well in going back to examine historical El Nino cases that I thought shared some characteristics to what I expect from the upcoming winter, I came across several cases where winter did not turn out too cold. Two recent examples would be the winters of 2004-2005 and 1994-1995, which both would come in warmer than our current forecast. While both scenarios would still favor more snow than last year, they saw between 10 and 13 inches in DC for the season which would be below both our current forecast and below the seasonal average for Washington. The failure in these years was that those key Arctic blocks needed for sustained cold air transport into our area never really materialized the way we needed them to here in the eastern United States.

Eyeing the Pacific, we will be closely monitoring the intensity of the El Nino as we get into the winter months. Too strong or too weak of an El Nino is not as favorable for snow in our region as they forecast "moderate" events. We will also have to monitor the strength of the jetstream over the northern Pacific as well as a feature known as the Madden-Julian Oscillation, both of which can affect how those blocking patterns develop over the Arctic. While both of these were active and played a role in the previous two years (which were La Nina winters) they typically are not as active in El Nino winters. We will be closely watching them anyway as features which could push the forecast in a warmer and less snowy direction.

Of course, then there is always the risk that we are not cold and snowy enough. The recent winter of 2009-2010, which was the winter of the snowmageddon storms, would be one example to go on. In that El Nino winter, blocking patterns over the Arctic set up early in the season with enough cold air in place in December that DC got its first blizzard of the year just a week before Christmas. If these features, which we expect to be stronger in January, start appearing earlier in December then that would be a colder and snowier threat to the forecast.

In addition, the solar minimum itself presents snowier risks. Four of the past five solar minimums have featured snowfall exceeding our current forecast range.

Well, there you have it! FOX 5's 2018-2019 winter forecast! Remember, while there is science behind every season outlook, nobody is ever going to nail it exactly so take the forecast all in good fun!

Although the past can help us, no two winters are ever exactly alike. The winter ahead will undoubtedly throw us a few curveballs that we will have to take in stride. But at least for the snow lovers in the DC region who have been pretty snow-starved the last couple of years, the winter ahead does seem to be pointing in a snowier direction. Whether warm or cold, rain or snow, we will be here all winter long to help get you through it all!

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