As we push toward December, and the unofficial start of the winter season, the most common question right now is, “What does this winter look like?” Each year we try to answer that question with our ‘HVW Winter Outlook’. Our winter outlook is compiled by doing extensive research on a variety of atmospheric and oceanic factors that have been shown to influence our weather patterns. These trends, teleconnections, and indicators can give us some insight into the possible weather patterns for the upcoming winter season. We’ve compared our current and projected indicators for the 2020-2021 winter, to all the winters since 1960. We’ve identified several years where the patterns and trends look very similar to our current year, and use those analogs for our winter outlook. Using that data, lets take a look at what we expect for the coming winter season.
Winter Temperatures : Near Average (-1.0° to +1.0° vs. Average)
Winter temperatures are likely to be near normal across the Hudson Valley and northeast. A moderate La Nina has set set up in the tropical Pacific Ocean. This, combined with the overall sea surface temperatures (SSTs) suggest that we will see a winter with the potential to have several fluctuations between warm and cold patterns. Historically, winters with a similar SST pattern have turned out colder than normal, so the potential for a colder than average winter is certainly there. However, winters in recent years have been trending more mild, so we also factored that into our projection. Based off our analogs, December is likely to be colder than average, followed by a milder January and first half of February, before colder than average temperatures return for the back end of February on into March.
Winter Snowfall : Near to Above Average (100% – 133% of Average) 42″ to 56″
Based on the analog years we have identified, we come up with the map shown above, which indicates above average snowfall for the Hudson Valley. However, snowfall can be quite unpredictable. A difference of 50 to 100 miles in the track of 2 or 3 coastal storms, can make or break your season in terms of snowfall. So to account for the randomization of ‘luck’ with regard to winter storms and snowfall… we’re projecting anywhere from near average snowfall to above average snowfall… or 100% to 133% of average. Since 1991, the average annual snowfall in Poughkeepsie is 42.8″, so that would me anywhere from 42″ to 56″ of snow in the Poughkeepsie area. We’ll have to see if this year follows the expectations from the analogs more closely than recent years.
Methodology / Discussion
In previous years, we’ve spent considerable time digging into the methodology behind our winter outlook. If you have viewed any of our previous outlooks, you have a good starting point for how we utilize Sea Surface Temperatures SSTs to infer their likely influence on weather patterns for the coming winter season. You also know that we get quite technical in these discussions. In the interest of saving time, this year we’re going to have a more direct approach. But if you wish to review last year’s outlook for full context of how we develop the winter outlook, please check out the 19-20 HVW Winter Outlook. If you’re a casual viewer, you may want to skip the in depth analysis… the choice is entirely yours.
Otherwise, lets start by looking at the actual SSTs.
This map represents the entire globe’s SSTs compared to average. The blues and greens are waters that are much cooler than average… while orange and red are ocean waters much warmer than average. We have placed an A, B and C over three (3) areas that we like to focus on.
A – Northeast Pacific , B – Tropical Pacific (la nina), C – NW Atlantic Ocean
These three areas all go a long way into helping determine the general jet stream pattern is likely to unfold. The quick rationale is SSTs influence the air above. The air above either rises or falls depending on whether it’s become more or less dense due to the influence of the ocean water below. Those pressure changes then influence upper air patterns, and in effect determine our weather patterns through the winter.
So we’ve seen the actual SSTs… what does the CFSv2 computer model forecast look like for the winter…
Notice the similar pattern of SSTs between the actual SSTs and the computer model projected SSTs for the winter. So if we want to try and predict what the coming winter might hold, we need to locate winters that had similar SST patterns to what we have, and what is projected. Here is what we came up with.
Notice the pattern setup when we combine our analog years, looks very similar to the actual and projected SSTs for this winter. The analog winters that combine to give us the SST patterns you see here, are:
1995-1996 , 1996-1997 , 2005-2006 , 2013-2014 , 2017-2018
These analog years then combine to give us the winter outlook temperature projection and snowfall projection seen at the beginning of the outlook.
Active Tropics : NW Atlantic Ocean
By now, everyone probably remembers that we’ve had a record active Atlantic Hurricane season. The number of named storms has reached 30… with 13 hurricanes, and 6 of those becoming major hurricanes. In trying to pinpoint trends to analyze for the winter outlook, we like to utilize the tropics as much as possible, and have found an interesting trend…
This graphic shows Atlantic Ocean ACE (accumulated cyclonic energy) for the hurricane season, for every year from 1851 to 2020. ACE is effectively a measurement of the total energy output of a tropical system. While the number of storms is important… a more detailed measurement is the combined strength of those storms. An average hurricane season sees an ACE index of around 100. This year, we’ve seen North Atlantic Ocean ACE of around 178, which is well above average. However, if you look at the right side of the graphic, you’ll see the years with ACE over 150… the most active seasons on record. One thing that jumps out to us, is that 3 of the 4 most active seasons since 1950 are:
– 2005, 1995, and 2017… 2020 ranks roughly 8th.
What’s the big deal? of the 5 winters we identified using the Sea Surface Temperature (SST) method… 2005-2006, 1995-1996, and 2017-2018 are three of those winters! So we have strong overlap between the hyper active tropical seasons and the SST pattern that is in place. This simply helps strengthen our winter outlook confidence. When we can look at 2 separate data sets, that compare 2020 to historical trends… and those two different data sets notice the same years being similar… we feel confident that we have a strong analog set for our winter outlook.
Month By Month
When we use the analog data from the 5 winters we’ve identified, here are the monthly temperatures compared to average that result.
The winters suggest that December starts off colder than recent years, with early chances at winter weather events. January remains near average, with slight moderation, but still a similar trend to what we see in December. February would appear likely to be the mildest month of winter, with some ridging in the eastern US trying to pull warmer air into the HV and northeast. But March looks to try and close out the winter in cold and stormy fashion. We’ll have to see if these historical monthly trends continue for the 2020-2021 winter.
Forecasting or projecting 3 to 5 months into the future is a serious challenge. In fact, there are so many variables… the winter outlook becomes a forecast based on a forecast. We assume certain conditions for SSTs, in anticipation that the maps shown earlier will be correct. If certain areas of the ocean are notably warmer or colder than projected… the resulting forecast will be incorrect as well. We’ve seen this several times in the past few years. Where we put together the winter outlook, only to see areas of the ocean be much cooler than expected… and the result was actual temperatures that were much warmer than we anticipated. So while the outlook is based in science, it’s still subject to considerable error. We look forward to seeing if our ideas for this winter begin to unfold as expected, or if we start to see some extra curveballs thrown our way. Either way, we hope you’ll be here with us… along for the ride… as we begin the month of December and unofficial winter season. We thank you tremendously… for all your continued support of HVW. You are what makes the HVW community so much fun to be a part of. We hope everyone stays safe and healthy! “Keep calm, and weather on…”
-Bill & Alex-