Each year, between the months of August and November, there is one question we are asked more than any other, “What is this winter going to be like?” After last winter’s bitter temperatures, and heavy snowfall… many people are very nervous about what this winter has in store for the Hudson Valley. So we’ve taken a very detailed look through mountains of data, and put together the 2014-2015 HVW Winter Outlook, which looks at the months of December, January and February. Keep in mind, this is a “Winter Outlook”, based on expected patterns and trends, and not a forecast in the traditional sense of the word.
For readers who want to skip the nerdy, technical stuff… we’ve got you covered. We’re going to give you the HVW Winter Outlook up front, so you can get the info you need, without all the mumbo-jumbo. For readers who want to look behind the curtain, and understand the why and how behind the outlook… don’t you worry… we’ve got everything you could possibly want. So pull up a chair, get comfortable, and let’s do this…
Winter Temperatures (Dec, Jan, Feb): 1° – 3° Below Normal
We’re expecting colder than average temperatures across the Hudson Valley this winter. To put this in perspective, the Dec. – Feb. period last winter was 2.2° below normal… and it would have been even colder, but last December was actually slightly above average. Unlike last December, we expect this December to be colder than average, as winter gets off to a faster start. We expect a persistent dip in the jet stream to be focused over the Eastern US, which should allow for a consistent flow of cold, Canadian air into the Hudson Valley. Each time warmer air tries to push into the Hudson Valley, it will quickly be pushed back to the south by the persistent, cold northwest flow. Then there is everyone’s new favorite weather term… the polar vortex. The jet stream will likely be very amplified this winter, and that will present opportunities for the polar vortex to periodically shift further south, and into North America. Just how often, and how severe the ‘polar vortex’ induced arctic outbreaks are… will determine just how cold this winter is as a whole. Our thinking is a more persistent cold pattern, but fewer or less severe ‘polar vortex’ type arctic outbreaks.
Winter Snowfall (Dec, Jan, Feb): 25% – 50% Above Normal
The average snowfall in Poughkeepsie over the last 20 years is 44.1″. For perspective, last winter Poughkeepsie had 60.2″ of snow, which was 36.7% above average. The general range we’re expecting this winter is roughly 55″ to 65″ of snow in Poughkeepsie. When we look at winters with patterns that are similar to what we expect this winter, the result in each case is well above normal snowfall. The precipitation amounts are near normal, but because of the colder than average temperatures… when the precipitation falls, it more often falls in the form of snow. In addition… conditions could favor a negative NAO pattern this winter, and (in general) that pattern favors the development of nor’easters. Snowfall in the Hudson Valley is very dependent on nor’easters. Last year the February blizzard gave Poughkeepsie 21″ of snow, and a week earlier, another nor’easter dropped 11″ of snow. Those 2 storms made up over 50% of the total snow Poughkeepsie saw last winter. So how much snow we actually see, is always a wildcard. But with that said, it does appear that conditions for snow will be much more favorable than average.
Winter Outlook : Behind the Scenes – *Nerd Alert*
A Winter Outlook is nice, but without a detailed explanation, we could just be pulling numbers out of the air. So below is a very detailed (if not nerdy) look at the coming winter.
The first thing we tried to do, is to identify the general pattern that we expect. We feel the answer lies in the ocean… the Pacific Ocean to be more specific. We believe that oceanic patterns such as El Niño and La Niña and ocean temperatures in general, have a tremendous influence on our general weather pattern from season to season. These features go through cycles, and vary greatly from one year to the next. So lets take a look at the ENSO (El Niño Southern Oscillation) chart first:
This chart tracks the El Niño (red bars) and La Niña (blue bars) events since 1950. On this chart, the bigger the spike, the stronger the event. We’ve circled the current pattern at the right end of the chart. Notice how we were in a weak La Niña in 2013, but are now in a weak El Niño. So what we have done is identified all the transitions from La Niña to weak El Niño. There are several instances that are similar to our current pattern (1968, 1990, 2006), and we have boxed out 3 specific occurrences that have a strong correlation (we’ll explain why in a few minutes). But a similar ENSO event alone, isn’t enough to generate a winter forecast. The ENSO looks at the tropical Pacific Ocean, and while the Tropical Pacific is important… the Northern Pacific may hold the key to our winter.
Sea Surface Temperatures (SSTs) can have an influence on the atmosphere above it. Simply put, temperature gradients in the ocean water can create temperature gradients in the air above it… that in turn creates a gradient in the air pressure (high pressure, low pressure)… and thus influences weather patterns. Sound complicated? Look at these images:
The maps above show the 3 month period of Dec 1993 – Feb 1994. On the left are the Sea Surface Temperatures (SST)s, notice the #1 highlights an area of colder than normal SSTs north of Hawaii, and the #2 represents warmer than normal SSTs in the Gulf of Alaska. This supports a ridge of high pressure over the western half of the US and a dip in the jet stream over the east, which would suggest warmer than normal in the western US and colder than normal in the eastern US. Now, the image on the right is the actual air temperatures for this period, and it’s almost exactly what you would expect… warm in the west, cold in the east. Now, lets look at the opposite SST scenario…
This map shows Dec 2001 – Feb 2002, and this time, the #1 area north of Hawaii has warmer than normal SSTs, while the #2 area in the Gulf of Alaska has below normal SSTs. This would support a dip in the jet stream out west, and a ridge of high pressure in the eastern US… which would suggest cooler than normal temps out west, paired with warmth in the east. The right image shows that the air temps that resulted, were nearly a perfect match.
So, now that we’ve established the basic idea of how Sea Surface Temps (SSTs) play a role in the general weather pattern during the winter… let’s take a look at the projected SSTs for December – February of this coming winter:
Notice how similar this forecast map looks to the first scenario above (Figure 2)? The model is forecasting cool SSTs north of Hawaii (#1), and warm SSTs in the Gulf of Alaska (#2). In the scenario above, with these conditions… we saw a very cold winter across the eastern half of North America.
So now, let’s go find other years where the SSTs look as close to the CFSv2 model’s forecast. Below are the 4 winters that most closely resemble the forecast:
While none of these 4 “analog” winters look exactly the same… or exactly like the projection for this winter… they are very similar in many ways. All four have a cold pool of water north of Hawaii (#1), all four have a warm(er) pool of water in the Gulf of Alaska (#2), and all have an El Niño in effect. We mention the El Niño again, so lets take another look at the ENSO chart.
We mentioned earlier that we boxed the 3 years that closely resemble the current ENSO pattern and labeled them 1, 2, and 3. You will also notice the number 4. Well, those 4 numbers represent the 4 Sea Surface Temperature (SST) “analog” years we just showed you in (Figure 5)… or the 4 years with the SSTs that most closely resemble the SSTs projected for this winter. It is rather interesting, that 3 of the 4 SST analog years, are also 3 years where we went from a La Niña to a weak El Niño… kinda cool how everything is tied together.
So now that we have 4 winters (’76-’77, ’93-’94, ’02-’03, ’09-’10) that experienced similar patterns and oceanic conditions, lets look at what happened in those years. Let’s combine these 4 winters, and take their average. First… temperatures:
When you take the average of the 4 analog winters we’ve discussed, the result is a very cold winter for the eastern half of the United States. A ridge of high pressure dominates the pattern out west, while a large dip in the jet stream allowed cold Canadian air to dominate these winters. These winters were roughly between 3° and 5° below average in our area, and provide the basis for our 2013-2014 winter outlook. Now lets take a look at the precipitation in these winters…
The average winter precipitation over these winters is a much less dramatic. Dry conditions on the west coast, as well as in the Great Lakes and Midwest, are offset by a general near to slightly above average precipitation in the Mid Atlantic and Southeast. While it’s not dramatically wetter in our area during these winters… snowfall was still well above average, because when the moisture fell… it fell more often as snow. How much snow? Well… Poughkeepsie statistics are a bit lacking prior to 1990… so we can’t tell you how much snow fell in the 1976-1977 winter (although it is regarded in the weather community as one of the harshest US winters in the past 50 years), but here’s a graph showing Poughkeepsie snowfall since the ’91-’92 winter:
So with last winter still fresh in most of our minds, you can see that we saw 60.2″ of snow in Poughkeepsie (5th most out of the last 23 years). We have placed arrows indicating the years that correspond to the analog winters we have been discussing. The winter of ’09-’10 ranks #10 on this chart, which is not too impressive… until you consider that was the winter of ‘Snowmageddon’. Two blizzards passed just south of the Hudson Valley, and a 3rd hit in late February, bringing over 30″ of snow to parts of Orange and Sullivan counties, while ‘only’ dropping 10″ in Poughkeepsie. So ’09-’10 was certainly no walk in the park. The winters of ’93-’94 and ’02-’03 rank #1 and #2 respectively over the last 23 years, with snowfall amounts that are head and shoulders above the other winters. If this winter follows the historical trend… snow lovers may have a lot to look forward to this winter.
One final set of factors, are things we refer to as ‘wildcards’. These are things that could play an additional role in our winter:
- First, the pattern from last winter never truly changed. The eastern 2/3 of the United States has been well below normal in 2014. Just think back to our summer recap, and how relatively cool it was in the Hudson Valley. The pattern doesn’t need to change, it just needs to continue and strengthen.
- Second, October snow cover in the northern hemisphere is near record highs this year. Snow cover acts like a refrigerator, helping keep air masses colder as they head south. Additionally, the colder air temps are believed to have impacts on a teleconnection known as the Arctic Oscillation (or AO), which is instrumental in allowing features like the Polar Vortex to shift south. This could help cool our winter temperatures even more than expected.
- Third, parts of the Great Lakes were ice covered into June this year, and the lake waters are still running about 3 to 6 degrees below average. Similar to the snow cover, the colder waters help to cool the air above it. This could have an additional cooling effect on our air masses this winter.
- Finally, the waters right off the east coast are expected to be well above average. This could have significant impacts on the development and track of nor’easters this winter. Storms feed off warm water, and tend to track along the strongest temperature gradient. We just experienced a nor’easter that lasted for 3+ days, and many of the drivers that led to it’s development and track are expected to be in place this winter.
So in summary… to create our winter outlook, we identified the winters with oceanic temperature patterns most similar to the pattern expected to be in place this winter. Those winters have produced some of the coldest temperatures and heaviest snowfalls in Poughkeepsie history. So based on what occurred in the past, it is our belief that this winter will be both much colder… and much snowier than average.
We hope you enjoyed the 2014-2015 HVW Winter Outlook. We know it was a bit in depth and comprehensive. Please keep in mind, that while our Winter Outlook is based off a lot of research and historical trends… it is not a forecast. If the ocean waters don’t behave as we expect them to, the result could be much different than envisioned above. Your encouragement and support for us has been tremendous, and motivates us to provide you with the best weather information possible. Thank you so much… and we look forward to helping you through what promises to be a wild winter.
-Alex & Bill-