WASHINGTON - Winter is coming, so let's get right to the point. Here are the top 5 things you need to know about our winter forecast for the 2017-18 season:
#1: With a weak La Niña forecast, we favor temperatures this winter to be COLDER THAN LAST YEAR, but also to come in SLIGHTLY ABOVE NORMAL overall.
#2: While we anticipate MORE SNOW THAN LAST YEAR, we are forecasting average to BELOW AVERAGE SNOWFALL for the immediate Washington, D.C. region.
#3: We are forecasting JANUARY to be THE COLDEST MONTH with about average temperatures, while we favor slightly above normal temperatures in December and February.
#4: Similar to last year, we expect issues with the rain/mix/snow line to cut down on snowfall totals for some events this year. The ODDS OF AN ICE EVENT ARE ABOVE NORMAL compared to the average winter.
#5: While one can never be ruled out, A BIG SNOW STORM IS NOT FAVORED THIS YEAR (big = 10"+ in downtown D.C.) due to a weak La Niña. 1-2 snow events of 4-8" are more favored.
If you're ready to dig a little deeper into what lies ahead this winter, buckle in and we'll break it down for you. But first, a quick recap.
Last Year: A Winter To Forget
Last winter was not a kind one to forecasters and snow lovers alike. A number of climate signals were pointing towards a cold winter with the potential for an above normal snowfall season. Many winter outlooks, including our own, were forecasting this.
While we did not favor a major snow event last winter (the one bright spot in the forecast), we expected a higher than normal number of snow events, similar to the winter of 2013-2014 which featured a high number of smaller, clipper storms.
Believe it or not, the winter began almost as expected, with some bitter cold air blasting into the region in mid-December. On December 16, the District woke up to temperatures in the teens with single digit lows out in the western suburbs.
After a brief break, the cold roared in yet again just after New Year's with parts of the region picking up their first inch of snow on January 8 ahead of single-digit lows recorded at Dulles on January 9. These waves of cold were expected to continue as we closed out the second half of the month and headed into February, but that was not to be the case.
Instead, a shift in the pattern allowed southern warmth to flood back into the region. Just four days after hitting their coldest low of the winter at 15°, temperatures in Washington, DC hit 72° on January 12-- the warmest temperature for that date in over a century. While the cold would come again at times, it was heavily outweighed by mild conditions the remainder of the winter.
There was a noticeable lack of snow as well. It took all the way until the middle of March for most of the region to see their one decent snow event of the year. The event began on the evening of March 13, with downtown Washington waking up to an icy, slushy 2" of snow on the morning of March 14.
By the end of the snow season, Reagan National picked up just 3.4" of snow total, pushing the year into the top 10 for winters with the least amount of snow for the District of Columbia. With only 7.3" seen at Dulles, it became their 8th worst snowfall season on record.
The Remainder Of Fall
All eyes are on the Pacific typhoon season for November, with late October showing several storms in the far eastern Pacific expected to push northward over the next week. Despite being so far away from the United States, the typhoons moving in this manner disrupts the Arctic pattern enough that colder air is move favored over the eastern half of the United States.
This should get November off to a chilly start compared to normal. This matches well with a La Niña pattern, which also favors a cooler than normal November. However, current suggestions are that beyond the first week of November the pattern will take on a more average November look, with the potential for some occasional southern warmth to sneak northward during the middle and latter half of the month. Therefore, we are expecting an average winter.
The Winter Ahead
Given all of the factors discussed above, temperature-wise nationally we are leaning towards cold-focused through the Upper Midwest with above normal temperatures focused in the Southeast and Southwest, a pattern very that is very typical of La Niña. For the Washington, D.C. region, this means slightly above normal temperatures are favored.
This does not mean a warm-dominated winter, however, as we also favor a very variable winter in terms of temperatures with lots of back and forth between cold and mild periods. We don't see this winter as "locked in" cold, but do not see it as "predominantly warm" either. Our analysis favored slightly above normal temperatures in December and February, while January may be closer to average or perhaps even a bit below average.
In terms of snowfall, La Niña winters tend to have more of an inland storm track that brings the best snowfall to the interior as opposed to coastal storms that bring the big snowfall events to the I-95 corridor. The latter tends to be more favored during an El Niño season.
The interior storm track should make for a good ski season for the interior highlands of the Northeast, with above normal snowfall also favored in the Great Lakes region. Coastal cities in the Mid-Atlantic will likely find themselves mixing snow with rain in the bigger events, with the all snow events a little moisture starved therefore coming with smaller snowfall totals.
That brings us to our immediate area. Any winter snowfall map you see like the one above are admittedly guesses, but there is some science and statistics behind the numbers that you see. It is a fact that the most snow Washington, D.C. has ever received in a weak La Niña winter was 17.1 way back in 1964-1965.
Of the 10 weak La Niña winters history in D.C. stretching back to the 1950s, only five of them have seen snowfall above 10". Average snowfall in D.C. during a weak La Niña is just 10.9", so in this regard our 11-17" of snow is above normal for a typical La Niña year-- but still below normal snowfall for the typical snow season.
Historically, these winters have featured several smaller scale snow events (under 4") with one or two medium size (4-8") snow events. The District's three biggest snowfall events during La Niña winters all came during either a moderate or strong La Niña event, and with a weak event favored this winter we are not favoring a major blizzard this season, favoring several smaller events instead.
We believe moisture-rich storms that do make it into our region this season will come with enough mild air that we are seeing mixing problems east of I-81 corridor, similar to the mess our region saw with the mid-March storm last year. West of I-81, conditions seem more favorable for a more typical snow season, and I believe the highlands of West Virginia will be just fine in regards to snow this winter.
Given the temperature outlook, January is the month we favor for seeing the most snowfall of the forecasted amount. However, much like last year, the threat for snow and ice events will likely linger through the first half of March. The risk for ice storms is greater in a La Niña winter as well, and we will have to be on guard for these particularly during the latter half of the winter and into early spring.
Making The Winter Forecast
Let's kick off the winter forecast with the same disclaimer I give every year: WINTER FORECASTS DO NOT TEND TO BE TOO ACCURATE. The fact of the matter is there is no one meteorological feature we can look to that is going to give us a clear picture of what the winter holds.
Instead, winter forecasts are a mixture of various model forecasts and climate signals, and then revisiting past winters to see what those with similar features held for our region. The simple fact is no two winter seasons are alike, and the upcoming winter is sure to hold its own surprises. Needless to say, the confidence in this forecast is on the low side when compared to something like a 7-day forecast.
The best indicator we have is whether or not we are looking at an El Niño or La Niña pattern if one is in place. This weather feature has to do with ocean temperatures in the equatorial Pacific and whether or not they are above normal (El Niño) or below normal (La Niña) and is a major player in winter in the United States.
Historically speaking, El Niño events have brought some of the snowiest winters to our region, while La Niña winters have not tended to be as kind to snow lovers in our region. Similar to last year, the vast majority of models are forecasting a weak La Niña for the upcoming winter season.
Data from the National Weather Service shows that weak La Niña winters tend to bring slightly above average temperatures to our region during the winter. Much of this has to do with high pressure over the Southeast which tends to allow some Gulf warmth to occasionally push northward into the D.C. region.
The position of the jet stream is also important, as during a La Niña it tends to be just north of our region. This means that winter storms that for tend to track either up through the Great Lakes region or up the western edge of the Appalachian Mountains. These storm tracks place the Washington, D.C. metro region on the eastern side of the storm, which is the warm side of the storm where precipitation tends to be either more of a mix or completely rain.
Are there exceptions? Absolutely. The problem for snow lovers is that historically as far back as La Niña/El Niño records go (1950), you can count on one hand the number of major snow events the region has seen during a La Niña winter.
According to the National Weather Service, only twice in any La Niña winter has Washington, D.C. recorded a single snow event that dropped more than 10" of snow. The most recent major La Niña storm occurred over two decades ago, the blizzard of January 1996. No single storm during a La Niña since the turn of the century has dropped more than 10" of snow on the District. Only 24 percent of all La Niña years on record feature above normal snowfall.
Looking at recent history, there have been seven La Niña winters since the year 2000 and together they only average just 8.1" of snow a season. Only three of those years had seasonal snowfall above 10" total, with most years featuring a below normal number of measurable snowfall events.
Statistically, history is working against us. But could this be one of the rare La Niña seasons that surprises with a lot of snow? To try and answer this question we looked at the spread of ocean temperatures across the North Pacific, a feature known to forecasters as the Pacific Decadal Oscillation or PDO.
Although data is limited, the two weak La Niña cases with above normal snowfall featured colder ocean water along the western United States coastline. This is known as a -PDO pattern. Unfortunately for snow lovers the current forecast is calling for more of a neutral PDO look, which is more typical of the years with below normal snowfall.
Other factors considered when making this forecast that we will not go into as much detail into are the so far average expanse of snowfall in Siberia this year, global wind anomalies (known as GLAAM) that are more typical with a weak La Nina, as well as the current levels of solar/sunspot activity. All these factors support our winter forecast.
Hope for snow lovers!
In our analysis, one feature did show up historically that may give some hope to the snow lovers in our region. Years with a similar overall pattern to the one we are forecasting this winter tended to favor a blocking pattern over Greenland. Known as the North Atlantic Oscillation (NAO), when this block is in place (-NAO) cold air can become trapped in the East Coast of the United States.
Many of the largest snowstorms in Washington, D.C. history have come when this feature is in place. The block itself helps buckle the jet stream, allowing storms to take a more southern track which is necessary for bigger snows in our region. IF the DC region is going to get more snow, this feature needs to be active throughout the winter months. In our region, one big storm is often all that is needed for an above average snow season.
There you have it! Our official FOX 5 Winter Outlook for the 2017-2018 winter season. Please keep in mind as you go forward that an outlook is more of a guide than an actual forecast. There is a lot of science and research that goes into it, but at the end of the day, Mother Nature is her own beast and she really does not care about what one little forecaster thinks she is going to do this winter. She is going to do her own thing.
Just like the weather forecast can change from day to day, there is still plenty of time for things to evolve as winter draws closer. So enjoy the read, but do not write it off as a guarantee!
Winter officially begins on Thursday, December 21 at 11:29 a.m. and stretches all the way until Tuesday, March 20 at 12:16 p.m. We will be with you every day this winter to keep you up to date on any winter weather that comes our way, no matter how much or how little!