Winter, where art thou? A look at why it doesn't feel like winter yet in the DC region

Alright. I get it. Some people out there are not big fans of winter. They do not like the cold and the snow causes more trouble than it is worth. However, there are a few of us crazies out there that love the small third of the year when we have the chance to get a little snow into the region. We have been hard-pressed to find it since the great blizzard of January 2016. In fact, Washington, D.C. got more snow over 48 hours from that one storm in 2016 -- 17.8 inches -- than they have in all the days since then combined -- 16 inches.

This winter started with so much promise too! Temperatures snapped cold pretty quickly in November and the week before Thanksgiving saw the District pick up their biggest November snowfall in decades. In December, a major snowstorm missed the D.C. region by just a stone's throw with Richmond picking up nearly a foot of snow on December 9 and areas as close as Fredericksburg, Virginia picking up four inches of fresh snowfall. But then the pattern shifted. Temperatures got mild and they've generally stayed mild ever since. Last year we ushered in 2018 with temperatures in the teens. This year, we did so in the middle 60s. So what gives? Is winter over already?

For cold and snow lover across the eastern half of the United States the problem generally lies thousands of miles away from here across the open Pacific Ocean. Here, an abnormally strong and elongated area of upper level winds that we call the Pacific jet stream has absolutely been wreaking havoc on the jet stream pattern across the United States flooding most of the mainland U.S with mild air from the Pacific which remain abnormally warm. Driven largely by a persistent and strong upper level low in the Bering Sea and contrasting with upper level high pressure across the southern Pacific, these features have largely kept the all-important polar jet stream trapped in Canada in recent weeks.

At the same time, an active southern jet stream has kept the storm pattern an active one across the eastern half of the county. Without the influence of the polar jet however, these storms run up the center of the county, dragging warmth up along with moisture to make for wintertime rain. These storms then drag down colder air in their wake. But the cold tends to be very short-lived as the cold air lacks reinforcement.

Another clue can be found by examining a climate signal we call the Southern Oscillation Index (SOI) which is an indicator that tracks the atmospheric response to El Niño, the warmer than normal water temperatures currently present in the Equatorial Pacific. The index is calculated by measuring the difference between atmospheric pressures in Tahiti, an island in the central Pacific, and Darwin on the northern coast of Australia. Just because the ocean temperatures indicate an El Niño is present doesn't mean the atmosphere is always reacting to it. It was certainly to start the fall. A nice drop in the SOI waves into October helped settle the pattern in towards a colder direction by November. However, in December, something strange happened. Despite ocean warmth indicating a clear El Niño present, not only was the atmosphere not responding to it, but it was instead responding in more of a La Niña fashion than El Niño, which is yet another climate signal correlated to warmth across the eastern half of the United States.

For things to change in the colder direction for us, we need to see both the Pacific jet stream start to calm down, and get the SOI to fall back into negative territory, meaning we need to see the present El Niño start to be reflected atmospherically instead of just on the surface of the ocean.

However the warmth was not entirely unexpected. In fact, if anything, I'd say it was the cold in November that was more unexpected than the flip to warmth in the month of December. When we do seasonal forecasting, one of the things we use the most is analog years. This is where you take the expected forecast pattern for the winter and try to find years past that have had a similar pattern. While no two winters are exactly alike, these can at least give you an idea on how things may play out. The combination of our top analog years indicated to us that we were likely going to go through a warm spell in December, while the cold will be more focused in January and February, a trait that is very typical of El Niño years.

This is why, in our own Winter Outlook released back in October, we leaned towards a warmer than normal December. So I'm hesitant to call the recent warmth a surprise, but will say its intensity and forecast longevity are. My initial expectations on January were that we would flip colder for the latter two thirds of the month to lead to temperatures being slightly below normal for the balance of the month. However, weather model guidance now runs out through the middle of January, and while the occasional wave of cold will come across over the next two weeks, the intensity of the cold does not look to outweigh the intensity of the warmth in respective to normal through at least the first two weeks of the month. Because of that, it is going to be hard to close out the balance of the month below normal unless late January turns very cold, very fast. More than likely, the balance of whether our winter outlook will come to fruition or not looks to rest on the shoulders of February.

Despite the recent 'doom-and-gloom' look of January's forecast for snow lovers across our region, there are signs that the real cold of winter is delayed instead of canceled. Leading the pack in these indicators was an extreme sudden stratospheric warming event, which peaked over the polar region during the New Year's Holiday. Forecasters need to have some patience though, as stratospheric warming events tend to be a little slow going when it comes having their effect felt across the United States.

Forecasters are watching for the stratospheric warming to have two effects. The first is to split the famous polar vortex and the second is for the stratospheric warmth over the pole to work its way downward into the lower layers of the atmosphere. This is a process that is not instantaneous, and could take a few weeks to occur in a manor more favorable for us here in the eastern United States.

One of these features, the polar vortex split, has actually just recently occurred, with weather observations showing the vortex has split into several weaker pieces. The most intense piece will focus on Europe in the short term, where temperatures are forecast to take a dive and stay on the cold side for the vast majority of the next two weeks. Another distinct piece looks to be present over the Bering Sea which is helping to enhance and drive that Pacific jet stream that we referenced earlier. A much weaker piece is forecast to be just north of Maine this coming weekend, but is overtaken by the warm pattern before it can strengthen.

What does that mean? No polar vortex outbreak is in the cards for the United States just yet. That does not mean we will not see one come across before the winter is done, but the high atmospheric pattern says it is not in the cards at least through the middle of the month.

So when might we start to start to see the effects of the sudden stratospheric warming take a tool on our region? I spoke to Matt Rogers, a long range forecast specialist and president of the Bethesda, Md. based Commodity Weather Group, and he tells me he sees similarities between the current event, and one seen in February of last year. "This year's stratospheric warming event is occurring faster than last years, which peaked during the middle of the month of February," he said. "The Polar Vortex split occurred around February 11-12th last year, but the cold effects of this were not felt until about three weeks later, in early March."

Indeed, I do remember last year there was talk of winter having a very early end. Much of late January and early February was warm. And we mean of record-breaking proportions. On February 21 2018, D.C. recorded its earliest 80-degree day on record. Winter was seemingly over by just about every sense of the word. However, far above our heads, stratospheric warmth was pushing downward into the lower atmosphere, setting events in motion that would start to bring the cold back into March.

And boy, did winter ever come roaring back. We had our coldest March since March 2014, and the third coldest since the turn of the century. More snow fell on the first day of spring in D.C. than we had at any other point in that entire winter, and the cold kept coming, with April registering at the second coldest of the 2000s.

Matt believes we could see something similar evolve in the coming weeks that happened last year. "My take is that the pattern missed a window to develop more quickly into a cold pattern due to tropical forcing disconnects and an initial stratospheric warming impact over Europe instead of the United States, which we saw happen last year as well," he told me via an email. "We will get another try at it, most likely by the final week or so of January, which would set up a colder potential for February. Weak to moderate El Niño climatology tends to favor February as the coldest month of the winter, so we still have plenty of time."

Weather models may be picking up on this threat as well, as for the first time in quite some time this morning's long range weather model guidance from both the American and European weather modeling camps show agreement on a colder pattern by the end of the month. Additionally, this morning's run of the European model finally showed some softening of the strong Pacific jet stream that has hampered our region for so long, which is something that needs to happen if we are going to start to bring some cold air into the eastern half of the United States.

I was asked this morning about whether or not I thought it was time to write off winter, but I think it's far too early to do so. While meteorological winter is nearing the midpoint, recent winters (including last year) have shown us that winter can extend well into the spring months on occasion. Also working in our favor here as Matt mentioned is the El Niño, the majority of which tend to be back-loaded in winter on snowfall. And look to the winter of 2015-2016 as an example. Many people forget just how incredibly warm that winter was as a whole. It was one of the warmest on record here in the D.C. region. But we had a couple weeks of cold in late January that timed out with a storm to give us one of our biggest single storm snowfalls on record, and an above normal snow season. All from just one storm.

The key in my opinion does lie in February though. When we wrote our outlook, it was the month we expected would be the snowiest, and the month to finally break us out of the curse of below normal snowfall winters that we have been stuck with for the last couple of years in D.C. But as a forecaster, I need to see the pattern start to shift by the end of the month. I need what we see in the long range models to become what we see in the mid-range models and then eventually the short range models as January continues to push forward. That doesn't mean I'm writing off snow for January either, I just do not see any suggestions at this time that it will be the case. If the stratospheric warming and polar vortex split fails us, and cold fails to materialize by the end of this month, then my concerns will begin to build that winter may be at a loss.

But we are not there yet, far from it in fact. Just as Matt said, there is still plenty of time left to get this winter pattern started. But snow lovers like me will need to pack our patience in the meantime.

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