Winter outlook 2013-14 for Washington, D.C.: Volatile, leaning warm, with below normal snow
BY MATT ROSS
November 13, 2013 at 11:29 am
There is no staving off the inevitable. The trees are defoliating. The sun is setting around 5 p.m. Even when we have bright blue skies and temperatures in the 50s and 60s, it still feels quite chilly in the shade, and not much warmer under a weakening sun. Time for our annual winter outlook.
In short, we favor yet another warm winter with below normal snowfall. However, all winters take on their own character. If we can deconstruct winter into a theme, the theme this winter will be incongruity between temperatures and snow.
While overall temperatures could potentially approach some of our warmest winters in the last 140 years, we don’t expect that it will be one of our least snowy.
This isn’t to say we will exceed normal snowfall. In all likelihood we won’t. We rarely do. The concept of “normal snow” is skewed by our blockbuster winters like 2009-2010. But we think snow totals could approach those we got in the cold winter of 2010-11 (just over 10 inches in D.C.), while this winter should be quite a bit warmer than that one.
Snow at the Capitol – February, 2006 (Kevin Ambrose)
We expect very little stability in our weather this winter, as the pattern should mostly be progressive and fast moving. Cold shots could be quite cold, but short-lived, and they should frequently be preceded and followed by more powerful warm shots.
But we don’t think the pattern will be boring. With the instability will come a number of track-able wintry events, often as cold regimes enter and exit. These will probably be mostly of the tricky variety to forecast, with many mixed precipitation events. Snow to rain, rain to snow, sleet, freezing rain, with greatly varying impact depending on where you live. So, even if you get 12″ in your backyard for the winter, it won’t be tidy. You will slop your way there with predominantly messy events.
Six to eight accumulating snow events is a reasonable expectation this winter, with a few more in the outlying western and northern suburbs. I think our chances of an area-wide 6″+ event are around 35%. It is more probable that our biggest storm of the winter is a 3-6″+ event with the 6″+ amounts relegated to the usual spots well north and west. Our best chances of a more moisture-laden storm coming from the south arrives in late winter when more hostile temperature regimes often put precipitation type and impact into question.
In summary, this winter is likely another victory for those who dislike cold and snow. But it won’t be a complete loss for snow lovers. Despite the warmth, this isn’t going to be another (close to) snowless winter 2011-12 or 2001-02. Most of us (perhaps not the far western suburbs) should exceed our snow totals of the last two winters. But enjoy the snow while it lasts. Whatever sticks won’t hang around very long as warmer air is liable to be lurking around the corner.
Overall temperatures for December through February (relative to 1981-2010 normals): Well above average (around 3 degrees above average)
Monthly temperatures (relative to 1981-2010 normals)
December: three degrees warmer than average
January: two degrees warmer than average
February: three to four degrees warmer than average
* Our snowfall projection covers November through April (1981-2010 normals in parentheses):
Overall: Somewhat below normal
Reagan National Airport (DCA): 6-10” (15.4”)
Dulles Airport (IAD): 12-18” (22.0”)
BWI: 10-15” (20.1”)
Fairfax/Loudoun/Montgomery counties: 10-20”
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.
Importantly, it just takes one big snowstorm for the region to reach “average” or “normal” snowfall and such events are somewhat random and impossible to forecast months in advance (even if we believe the odds of a “big” one are below normal).
What are other outlets forecasting for our area?
Of the outlooks we’ve reviewed, most – not all – are predicting a colder and snowier than normal winter.
Is the current snap of cold weather a predictor of upcoming wintry conditions?
No…but it’s quick-hitting (here today, gone tomorrow) yet intense nature may be fairly common.
Did the Capital Weather Gang reach consensus on this outlook?
Yes. All of the CWG forecasters who take an interest in long-range prediction agreed with the general themes of this outlook. A few expressed some minor disagreements about the month-to-month temperature details (in particular, the mild February).
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 the last 6 winters. We’ve generally been in the ballpark giving ourselves an average grade around a C+ in that span, though we’ve missed important details here and there. Our best forecast preceded the Snowmageddon winter (2009-2010
) when we said “Overall, we find chances for a large snowstorm of 8-12”+ are much higher than normal this coming winter.” Our worst outlook was the winter of 2011-2012 when we called for near normal temperatures and it was five degrees warmer than normal
You can review our past outlooks and evaluations by referring to the links at the bottom of this post.
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 current/past conditions and future conditions always strong. But we have chosen factors that in the past have proven to at least have 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 1990-91 and 1996-97. These analogs helped to 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 have medium-high confidence we are going to experience our second consecutive neutral without an El Niño or a La Niña. Neutral winters occur about 30 percent of the time.
The Southern Oscillation Index is an indicator of a La Niña (orange) and El Niño (blue) conditions. When the magnitude is within -0.5 and 0.5, it is an indicator of neutral conditions – as in the present. (NOAA)
Conventional wisdom dictates that without an El Niño or a La Niña, the tropical Pacific is not a major player. We somewhat disagree. While the Pacific is a more important driver of our winter weather in La Niña and El Niño events, it is still a huge basin of water, and in its current state will still have a marked impact. Often, neutral winters will take on the characteristics of the previous winter or winters. Last winter we also had a neutral winter, with La Niñas in the two winters prior to that. We believe until we get another El Niño event, winters will continue to take on La Niña characteristics; the most important of which is a storm track to our north and west, as opposed to the frequent southern track we get in El Niño events, which is more conducive to above average snowfall.
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, it often, but not always, tends toward warm and dry. Measured monthly, it oscillates in predominant cycles that can last two-three decades. From the late 1940s to mid-1970s we were in a predominantly negative PDO cycle, and from the mid-1970s to late 1990s a predominantly positive PDO cycle. We are now in a negative decadal phase of the PDO that started in earnest in 2007.
Chart of the Pacific Decadal Oscillation (PDO) over time (NOAA)
39 out of the last 40 months have had a negative PDO, though lately it has been somewhat weakly negative. Often an El Niño will help “force” the PDO to go positive. However since we do not expect an El Niño event this winter, we expect the PDO to default to its current decadal state and average negative for the winter, though perhaps not markedly so.
A negative PDO often supports a persistent area of low pressure in or near the Gulf of Alaska with a ridge over the Aleutian islands, and a trough over western Canada. This is usually not a good sign for snow lovers as an area of low pressure farther west over the Aleutian Islands is the preferred setup for wintry weather in our region. But because the negative PDO may be a little weaker this winter, we expect that patterns driven by the PDO will be less stable and more changeable than they might be in a more sharply negative state.
North Atlantic Oscillation (NAO)
The NAO is technically a measurement of the differences in air pressure over the North Atlantic Ocean. However, 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. A negative NAO in the winter months correlates with a cold pattern in our region, and supports winter storms when other factors align with it. This was the major factor in our historically snowy winter of 2009-10. High pressure over or near Greenland – sometimes called a “blocking high” helps push the storm track further south and east, often creating storm tracks that are cold and snowy for our region. While a negative NAO far from guarantees a snowy period, our chances for any substantial snow event are greatly diminished without it.
Chart of the North Atlantic Oscillation (NAO) over time (NOAA)
We believe the NAO will be variable this winter, perhaps near normal in the averages. We do not expect it to be a major driver of our weather. During periods when it is negative we will tend toward colder temperature regimes, and our chance of snow events materializing will increase. But because we will have a predominant storm track to our north and west, its importance is greatly diminished.
Our recent weather patterns, both upper air and surface, are less important winter predictors than in the past. First, they have been quite variable. For about a month now, particularly in our backyard, we have had very little stability in our weather with very warm days followed quickly by cold days and vice-versa. We expect this to continue in November and through winter, with warm and cold regimes often flipping in a matter of a few days. However, in recent years, when you have a similar number of above normal days and below normal days, the warmer days have tended to be warmer than the colder days cold. So in the means, we end up warm.
Our analog years often exhibited quite different fall and winter patterns, both from each other and from ours so far in 2013. As such, they offer looser guidance than in most past outlooks. But, despite some pattern dissimilarities between those analogs during their respective winters, the actual weather conditions played out similarly: Very warm with somewhat below normal snow.
Persistence is the idea that weather patterns and themes persist until something significant comes along to dislodge them. This was a greater factor than usual in forecasting the upcoming winter, with other factors more uncertain than usual. We believe until we experience another El Niño event, our winters overall will continue to be warmer than normal, with below normal snow, and a prevalent storm track to our north and west.
2012-2013 winter outlook
Jason Samenow, Matt Rogers, Wes Junker, Rick Grow, David Streit, and Dan Stillman contributed to this post.