Winter 2019-2020 was a long time ago. But I revisited anyway

Though we will look back at the 2020 season for too many of the wrong reasons, it still had its moments. It won’t rank as one of the better winters over the past 25 years and most certainly resides in the bottom half of that sample size. With that said, it is probably closer to the middle than the bottom and at least northern Vermont could brag about some some while other locations to the south saw hardly any. 

The above graph is from the ever-popular Mt Mansfield snow stake site. I actually prefer to take a sampling of final snowfall totals from various ski areas around the northeast (sometimes outside of the northeast) but most stopped reporting as of mid-March. “The Stake” at Mt Mansfield apparently can’t be stopped and it always proves to be an invaluable resource for weather and data enthusiasts such as myself. The color coded lines can appear a bit blurry to the eyes but the pink line is 2020 and it runs behind most years this past decade with the exception of the of 2011-2012 and the Super-Nino debauchery of 2015-2016. We were able to keep pace with 2017-2018 for a while but were unable to score another miracle March and instead recorded a rather ordinary to sub-ordinary one. The 5-week "arctic spring" is also notable. More on that below.

Choosing the one single variable that defined the personality of the past winter was easy this year. Hands down it was the Arctic Oscillation (AO). Scientists have officially been tracking that index going back to 1950 and it remains one of the best gauges we have to measure how blocked the jet stream is over high latitude regions of the Northern Hemisphere. When aggregating over a 5-month period (Nov-Mar) the AO this past winter was the 2^nd highest ever recorded. 1989-1990 remains the winner and 1990-1991 had a strong bronze medal showing but 2019-20 both intense and persistent, often challenging the confines of the graphical display while spending all but a few weeks in positive territory. Below is a chart measuring the top 5 +AO years and top 5 -AO years

When you consider those headwinds, 2019-2020 doesn’t look quite as bad. 1989-90 and 1990-91 were decidedly worse snow years based on data from the Mt Mansfield snow stake and 1992-1993 benefitted from of the greatest winter storms of all time. It also shows that Vermont can survive the adverse impacts of a +AO year a lot better than areas farther south. Winter across the Mid-Atlantic was nearly non-existent and ski areas suffered a much milder fate relative to Vermont. Atlanta, GA was nearly 4 degrees above normal over that same 5-month period. 4 degrees may not be a lot for one month but over the course of 5 months makes it one of the warmest winters on record. The same can be said with -AO winters. All 5 winters on the above chart were good snow years but the record year 2009-2010 actually featured a weather pattern that became too “blocked” and many of the best storms missed Vermont and deposited snow on the I95 corridor instead. Atlanta, GA by the way, recorded one of the coldest winters over this same period. 1968-69 was absolutely historic in Vermont and one of the best snow years ever recorded in many locations.

We also spent much of the winter talking about the persistent tightness of the jet stream in the mid-latitude Pacific Ocean. This zonal, fast to east moving consolidated jet stream mitigates the impacts of arctic air over mid-latitude North America and the index that best measures this is the Eastern Pacific Oscillation (EPO) index. The positive index which is defined by a version of this weather map is largely what we saw throughout the winter. Notice the cold over Alaska which was very prevalent through much of the past several months. 

Though the EPO was very positive through much of the winter, once I went through the rather tedious process of parsing through all the daily data I found that the positive value of around +33 was closer to zero than I would have thought. The two winters prior to this recorded values in the mean of close to -60 and the super evil empire winter of 2011-2012 recorded a value of close to +80. In other words, the EPO was an issue but the +AO, based on the aggregated data, was a bigger issue.

If I had to identify a single culprit to the persistence of the +AO/Somewhat +EPO pattern this winter it would be the configuration of sea surface temperatures in the Pacific. More specifically, the massive blob of sea surface temperature warmth that positioned itself south of the Gulf of Alaska. It was a large contributor to what became a negative Pacific Decadal Oscillation season. A negative PDO is not, in and of itself a pattern killer for snow and winter lovers in New England but the persistence of a jet stream level ridge underneath a glaring lack of blocking in the Arctic became the most prevalent adverse variable in almost every update I did this past season. Interestingly, this feature was identified in the  pre-season outlook as a concern but it was pitted against what was, at the time, a glaring lack of sea ice in the Chukchi Sea (regional body of water north of the Bering Strait). As it turned out, the Chukchi Sea quickly froze and we were left with the anomalous body of sea surface temperature warmth described above. Such a sea surface temperature setup is often associated with La Nina winters but not this time. The equatorial Pacific stayed on the Nino side of zero throughout the winter, and though we did see an energized southern branch of the jet stream at times, the weak El Nino did not greatly influence our winter season one way or another. 

November and early December saw the best stretch of pattern fundamentals and the season was off to a promising start. The high country surrounding the MRV did see several small but measurable rounds of accumulating snow and temperatures were 5-7 below normal for November which was colder than 2018. The biggest difference however was the lack of Snowvember. We were teased with the idea of big storms on a few occasions but nothing ever materialized. Thanksgiving was white but just not “deep” white. Still, the persistent cold was promising and it finally looked like the pattern would bear fruit in early December thanks to a bombing area of low pressure along the east coast. Though the storm did deliver several inches to the MRV, the heaviest snow fell across southern Vermont, the Berkshires, Albany, NY and the Catskill Mountains to the southwest. I feel like this storm was an inflection point. Had we bullseyed that sucker, and we were close, we may have remembered this winter very differently. 

Cold weather persisted in a general sense to about the winter solstice but there were two somewhat damaging thaws within the week of December 9^th to 15^th that limited our ability to establish a base. The coldest day of the season was actually December 19^th when the high temperature struggled to reach 5 but we only managed to muster a few inches of snowsqualls and had limited snowcover going into the holiday. At that point, the pattern broke down and much of what was described in the above paragraphs, a very positive AO (unblocked Arctic), a somewhat positive EPO (zonal Pacific Jet) became the prevailing influence on our weather pattern. Christmas was wintry but there were several days around Christmas that were not.

The loss of Rush drummer Neil Peart cast a dark shadow on the early part of January 2020 for me personally. Looking back, I suppose it was a lead indicator of the rough year that was to come.  On the weather side of things, the 10 days that began on around December 29 and ended around January 8^th was one of the better stretches of the season. Though the pattern wasn’t entirely supportive, a once upper Midwest blizzard deposited a mixture of snow and sleet on the MRV and provided a few days of instability leading up to New Years Day. No it wasn’t epic, but we got a bit of all of the necessary ingredients starting with a good base building storm a few a few inches of powder on the 30^th, the 31^st and on New Years Day. Temperatures crept above the freezing mark for a few days on the January 2^nd, and 3^rd but we were able to score some additional snowfall on the 4^th and procured a nice first weekend of the new decade. A few days of snow showers and squalls during the following week gave us a temporary impression that winter was resettling in. Unfortunately, this didn’t last. A very mild weekend January 11^th and 12^th and some rain put a massive dent into the base and put a crimp into the rest of the month. We got a bit of cold weather and snow in the week that followed but the big storm proved to be elusive. The best chance for one came without much cold air support on the last full weekend of the month. I remember talking about walking the proverbial “tightrope” and hoping for the perfect storm track. In the end we kinda fell off the tightrope a bit but did receive a bit of decent snow across the high country while the low elevations got a bit of wet weather. 

February was a tale of the “same story, better result”. It was historically awful for snow along the I95 corridor including all of southern New England and New York City. Boston recorded only a half inch of snow for the entire month and New York City only recorded a trace. As the AO continued to soar, nearly breaching the limits of the visual chart on two occasions, temperatures continued to run above average across much of the United States including Vermont which saw readings 3-5 above average. We did get the snow however, mainly from two different but substantial events. The first on February 6-7 was the best of the season. It was a windy event which proved to be a challenge for some resorts to manage but we got the powder, almost 2 feet of it and we got a few days of cold weather on the ensuing weekend which included a calm Sunday February 9^th. The other big event occurred toward the end of the month. It was a wetter snow event at the low elevations but an overperformer nonetheless with around a foot of snow. We had hoped to score the additional instability snow leading into the weekend but winds remained westerly as opposed to northwesterly favoring the snow over locations such as Stowe and points north. The two storms in February might have made the month a more memorable one but there was a lot of mild weather in the middle of the month. We did manage to avoid much of the rain but not all of it. 

March brought in the Covid19 pandemic so I suppose it was good year to not have our traditional mid-month snow bonanza. The first 15 days made up the last 15 days of the season for most resorts and it featured big temperature surges and occasional rainfall. It didn’t look especially good for a wintry finish to the season but it goes to show that you just never know. I am saying this completely in jest but it is almost as if the pattern waited or Governor Phil Scott to issue his stay at home order and suddenly everything fell into line. The positive AO became completely neutralized and a “well blocked” jet stream emerged. It showed up in the NAO data the best but we also saw blocking over the Yukon which fueled an amazing and persistent stretch of winter-like weather over Vermont in the middle of spring. 

Much of Vermont did see a nice overperforming wet snow of nearly a foot in some places on March 23^rd, but the true “arctic spring” didn’t commence until around April 9^th. It was 5 weeks of remarkable spring cold and some substantial snow. So much snow in fact that Mt Mansfield had a 2^nd peak of snow pack in early May. More on that later. The 5 weeks beginning on April 9^th and ending around May 13^th was roughly 7 degrees below average and much of the high country didn’t see any 60-degree temperatures throughout April. We did see several rounds of snow, some elevation sensitive, some not so much. Though we never did see the epic April powder producer (that would come in May), I would estimate that Mad River and Sugarbush saw at least 20 inches of snow in April. It got even more incredible in early May. Following a spring-tease May 1-3, a massive surge of May cold descended on New England. A storm on May 8^th and 9^th produced 5-10 inches of not wet snow but powder across much of the northern Vermont high country. I will remember May 9^th for as long as I can remember the dates of all my favorite weather events. Sub-zero wind chills, temperatures in the 30’s all day, snow squalls and several inches of snow on the ground throughout the day. It was truly surreal! Then, in a total about face, a heat wave hit Vermont in a span of less than 3 weeks. Most official reporting sites in Vermont hit 90 degrees oddly beating locations such as Philadelphia and Washington, DC that have yet to see 90 degrees this spring (a rarity)

In many ways 2020 has not been a year we would ever hope for. It certainly was not a memorable winter season from a weather standpoint either but will obviously be remembered for worse reasons years from now. The 5-weeks of winter that the Vermont high country saw in spring has brought some optimism and provided a reminder of what CAN BE. I can hope, like the rest of us, that we can come to a resolution as to an appropriate way to face the challenges on the ground and have a ski season we can all enjoy. Look forward to being back next winter to serve the MRV like always. Until then, stay engaged and continue to work the make our community a special one and the world a better place both now and in the future.