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Friday, May 10, 2024

The 2023-2024 winter, it's ups and downs and fairy tale ending !

What a crazy winter 2023-2024 evolved into. It was persistently warm after November, as many winters have been during this recent negative PDO cycle combined with the additional push in the background from the impacts of climate change. Unlike the 2015-2016 Super Nino debauchery, it was snowy and there were periods of deep snow cover on the mountains both early, middle and later part of the winter. It all culminated with the incredible resurgence of winter in March and early April. I apologize for the overuse of sports parlance in the blog, but has Vermont weather ever had a more clutch weather performance in the 75-year history of Mad River Glen than what occurred  in the first 8 days of April. The elusive April 2-foot snowstorm happens and then mostly clear skies for solar eclipse viewing was like hitting two grand slams in the same inning. I still have trouble believing it actually happened ! 

As expected, the strong El Nino was the most critical driving factor locally, nationally and globally. With the exception of Alaska, North America was warm as a whole and the area comprised of the Great Lakes, Upper Midwest, Northern Plains and Central Canada was historically warm. Strong prevailing westerlies in the jet stream made it difficult for pools of arctic cold to build, expand and push southward. Clouds were very prevalent especially across the eastern U.S. and this acted as a blanket during the long overnights. Just quickly glancing through some daily weather data, it is very evident that clouds and warm overnight low temperatures statistically powered the milder than average temperatures throughout the winter over a broad area, New England included. 

For the purposes of a weather blog, I try and simplify things with nonacademic analysis (don't think i am capable of anything else anyway) and lots of context. With that mind, we can assess the strength of the recent El Nino with one number, a SST anomaly in a critical region of the equatorial Pacific. This came in at +1.69 C this past winter which makes it substantially weaker than the +2.28 C El Nino of 2015-2016.   We certainly know that the recent winter was a lot snowier than 2015-16, but it was only marginally colder by about 1.5 degrees F during the period beginning in November and ending in March. If you throw April in there the difference would certainly increase. Every significant El Nino brings global temperatures up and when added to the impacts of climate change, the warmth will set monthly land and sea temperature records and set off alarms and this certainly happened this winter. It is common for a healthy El Nino event to warm global temperatures by a very statistically significant quarter of a degree C. This allows the climate denialists to play their favorite game. Take a big El Nino from 30 years and compare it to a recent neutral ENSO winter and like magic, one can make our warming global temperatures disappear ! Climate change, by way of comparison is warming the earth by an estimated few hundredths of a degree C annually, which is scary, but still can very overpowered by a strong ENSO event, particularly an El Nino. 

A bigger distinction I have made regarding this recent El Nino was the state of the PDO. More typically, El Nino's are accompanied by a positive PDO state in the Pacific though it is not an especially dependable rule and there have been exceptions, this year being one of them. The -1.11 and -1.02 PDO that was posted in November and December respectively represents a PDO in a decisively negative state. As the winter progressed, that number weakened but remains slightly negative as of April and has been so now for every winter month dating back to December of 2019. The word decadal is used for a reason and the state of the PDO comes in streaks that can extend out to a decade in length. What makes the recent streak a little more unusual is the persistent negative strength of the PDO which finally weakened to -0.41 as of March, the weakest its been in any winter month since 2019. I bring this up because, I've been of the opinion that the PDO has made weather pattern life a little difficult in Vermont during both this and other recent winters. It has been difficult during this stretch to maintain a cold, wintry pattern for longer than 2 or 3 weeks and the El Nino further limited the reach of arctic chill across both North America and Europe. All that said, it was also my opinion that the PDO would provide us with an assist on snowfall and help guide storms in our direction at the expense of the coast. This turned out to be true and we ended with the warm and snowy winter that was advertised. 

So lets go through it ! November was one of the two months in 2023 that saw below normal temperatures, in Vermont. It also was a month that foreshadowed the personality of the forthcoming winter almost perfectly, especially the March and April section. Snow whitened the mountains initially on November 8th and a cold ensuing week kept that snow in place for several days before a mid-month mild surge melted it away. More snow and cold returned in the days before Thanksgiving and much of it survived through the holiday and weekend when Killington hosted the World Cup skiing events. Three significant elevation events got the lift service part of Vermont's ski season off the ground over the two weeks between November 26th and December 11th. I scored a good forecast over the National Weather service on the first one, Tim Kelley of Jay Peak owned me on the last one and the high country of northern Vermont was in amazing shape in terms of building an early season base. The first event on November 26th-27th resulted in widespread power outages, but the snow was mostly powdery above 2,500 feet. We saw this repeat on numerous occasional throughout the winter and especially during the spring. It was the most elevation sensitive snow year I've experienced in the 20 years of doing the blog. The 2nd event which begin on Sunday, December 3rd had better cold air support on the back end and modest snow though a little less than I had anticipated. The third event really too me by surprise as the pattern appears poised to turn mild by December 10th, but the storm in question managed to entrain enough cold while re-consolidate along the New England coastline. Rain turned to snow by Monday, December 11th and its often events such as those that really make you think the winter would serve up something special. 


Once again, just when it seems that nothing can go wrong, it all crashes to the ground. The weather pattern did indeed shift and arctic air went into retreat mode as the Arctic Oscillation (AO) turned very positive. I've lost count of how many iterations of this movie we have seen in Vermont.  An amazing week of weather in the early or middle part of December gives way to a lousy, rainy holiday. In this version, the rain came, way too early, fast, heavy and was accompanied by the ugly combination of wind and high dewpoints. The 2nd of two major flooding events in 2023 hit the state on Monday, December 18th. bringing local rivers above flood stage and causing more damage to low lying areas. Much of the snow melted away, though some did remain across the highest elevations. The holiday weather was dominated by clouds, rain, mild weather and some of the worst skiing of the season. The start of 2024 was to start almost from scratch though MRG managed to keep it going in limited capacity, throughout this very ugly stretch. 

Bridge St, Waitsfield - December 18, 2023

January of 2024 wasn't exactly an epic month, but was a nice bounce-back from the holiday. Jet stream blocking at high latitudes powered the AO and NAO well into negative territory for much of the first two thirds of the month and arctic air became a significant part of the weather picture during that stretch. Garden variety cold early in the month set the stage for a nice dry snowfall on the first Sunday of 2024. I had higher hopes for the subsequent storm around the time of January 10th and 11th, a really juicy southern streamer that was consistently predicted to track toward the Great Lakes and bring a surge of milder temperatures and rainfall. I recall thinking that the downstream blocking would ultimately win the day and possibly turn this event into a big snow producer. The southward shift never materialized really but the snow fell anyway, a heavy base building event that exceeded even my lofty expectations. Another snow/sleet conglomeration early on the MLK holiday weekend added more density to an already hefty snowpack ahead of what would be the coldest period of the year. 

The arctic outbreak in the middle of January generated a lot of news and was especially intense over the western high plains and then the central plains and Texas. It brought -10 degree temperatures to Kansas City for a NFL playoff game, but the coldest temperatures recorded in the MRV were in the vicinity of -5 that week which marked the coldest readings of the season. That is the warmest "coldest day of the winter" I can remember and a more rigorous academic analysis might show that the 2024 winter featured the least amount of extreme cold in recorded history in Vermont. Still, the week beginning January 15th was chilly and snowy with snow squalls finally giving skiers some dry more skiable friendly snow. Arctic air went into retreat mode beginning January 22nd but we still managed to squeeze out some winter weather over the last 8 days of the month including some mixed precipitation around the 25th and some snowfall on the last Sunday of January. 

February was a very different kind of month relative to the other winter months in 2023-2024. It was mild much like December but also very dry unlike December. Most of Vermont, even the mountains, saw less than an inch of melted precipitation which is way below average. The dominant weather feature was a jet stream ridge, a very large one, that established itself not far far from the same area that received the arctic cold. The result was a blow torch across the central part of the North American continent with excessive temperatures stretching well into Canada on multiple occasions. The torching wasn't centered over Vermont so although it was milder month, we managed to avoid a total scouring of our snow pack. There were several instances where the torching enveloped all of upstate New York and the Adirondacks, making it as far east as the Champlain Valley only to stop at the Long Trail. This happened on 2 days early and then again later in the month. All that said, it was a quiet month from the standpoint of storminess and this allowed for more sunny days and better visibility following a brutally cloudy December and January. 

I can recall two moments when both the weather conditions and projected weather pattern going forward appeared especially bleak. The first was the December 18th flooding since that event was coupled with the realization that another Christmas holiday was going to be mild, damp and dreary. The 2nd and an even worse moment came during the back half of February. Though colder weather and a bit of new snow finally buried the crust, the EPO index surged in later February and forced any arctic air back into retreat mode while providing western ski areas with a barrage of storminess. With less than 2 feet of snowfall in February, and mild air melting much of that during the last  6 days of the month, winter 2024 appeared poised fade out altogether by early March when more mild weather was expected to arrive. Indeed, the torching in the Midwest was relentless with 70-degree temperatures surging into the Great Lakes on multiple occasions. Once again, that mild air would push eastward into the Champlain Valley and then abruptly weakened before crossing the Long Trail. It was an ugly scene around March 8th with, only limited terrain surviving at MRG, but the weather pattern took a dramatic and surprising March turn as split flow emerged in the jet stream overall while a storm system manage to defy the conventional wisdom of what typically happens with such an energetic Pacific Jet Stream 

The Monday March 11th event was probably the best of the season and it also marked the beginning of an incredible late season 4-week stretch. Though it didn't quite land on the  Ides of March storm, the 30 inch snow on March 11th was yet another season saving event and one that followed a miserable stretch of weather. The initial storm took shape while all of New England was enveloped in mild air and this event would have brought more rain were it not for the ability of robust southern branch energy  in the jet stream to re-consolidate the storm over the Mid Atlantic. Cold air was limited but the newly energized coastal system managed to suck enough cold air to create a powdery event for the northern Green Mountains. It was the first of many very elevation sensitive events over this stretch with only a few gloppy inches falling in the Champlain Valley. 


Following a succession of more spring-like day prior to St Patrick's Day, the weather pattern turned cold as blocking reemerged at high latitudes, mainly over upstream areas of Alaska and portions of the Arctic this time. Both Sugarbush and Mad River Glen were hit with snow squalls on multiple days beginning on the 19th. It was fascinating weather actually because any snow that fell in valley locations would melt with a few hours of partial sunshine while the snowfall continued to pile up over the mountains with fresh powder on a ski succession of days. A reinforcing shot of even colder air enveloped northern New England appropriately on the first day of spring. This was timed perfectly with an incoming weather system that produced widespread snow for the entire state of Vermont on Saturday March 23rd. This was probably the least elevation sensitive event of the season and one of the coldest with over a foot of snow falling at MRG atop the powder that fell during the week.

The receding El Nino and weakening PDO certainly seemed to help revive an ailing winter season, but who was to expect what was to happen on the first full week of April. It's hard to get Vermont weather to cooperate fully in any season and the only good bet for April typically is clouds and mud. After a pretty innocuous start of the month on the 1st and 2nd, with afternoon temperatures approaching 50, colder arctic air moved south out ahead of a big approaching late-season winter storm. Like many of our bigger snow producers, a good snowfall was contingent on a strong low pressure area located over Lake Michigan, transferring energy to an ideal coastal position and then having that storm lead us to glory. There were some questions as to how efficiently that transfer would take place but it all worked out in the end with heavy snow falling on April 4th while conditions continued to turn colder as snowfall piled up. The snow over performed on the front-end but disappointed a little on the back end with snow showers confined to the Adirondacks at the expense of the northern Green Mountains. Still, the elusive April storm was in the bag and the snow was deep from top to bottom, albeit a little dense at the bottom. 

Like magic, clouds vanished on Sunday April 7th making for a beautiful spring day of skiing atop almost two feet of new snow. Clear skies continued for the big day on April 8th and the scattered high cirrus clouds remained scattered creating a near perfect situation for the solar eclipse. Lots of corn snow, terrific visibility and afternoon temperatures in excess of 50. Just an incredible stretch of weather in what is typically not a very incredible time of the year. Clutch !  


The season concluded with well over 200 inches of snow at most of the northern Vermont resorts and well over 300 inches at Jay. What stands out more about the 2023-2024 winter was the elevation sensitivity of most of the snow. Burlington which serves as the most reliable first order station in the state recorded 61 inches of snow, well below the normal 87 inches. Meanwhile, the Mt Mansfield snow stake peaked well above average, recording a depth of over 90 inches prior to the April 8th solar eclipse. Warmth centered over the Midwest/Great Lakes/central Canada region and even stronger warmth across western Europe was another major headline. The strong El Nino is a known contributer to high latitude warmth while climate change continues to push land and sea temperatures higher. With all these warm weather headlines, it might seem as if it wasn't cold anywhere in the world and that's not quite true. Portions of Scandinavia had a cold winter while eastern areas of the Eurasian Continent saw multiple outbreaks of brutally cold air. I bring this up because SST forcing in the Pacific, stemming somewhat from the state of the PDO has been very unfavorable for North American cold in recent winters. I was encouraged to see the PDO index weaken over the past few months and hope we can go into next season in a more neutralized state. The extremely positive PDO values have been a consistent theme over the last several winters and when added to the headwinds of climate change and a big ENSO year (in any direction) attaining sustainable cold weather is challenging. With that, I can sign off for the 2023-2024 winter. Hope everyone enjoys the summer weather and returns to MRG in good health for another good ski season in 2024-2025 !