Welcome to another incoming weather season powder and Mad River Glen enthusiasts. Never does it cease to amaze me how fast the descent in to winter takes place. It was only about 7 weeks ago when much of northern New England was finished a multi-week stretch of gentle 70-80 degree warm autumn weather. As of the middle of November, deep snow has enveloped the high country of northern Vermont. Perhaps not enough to call it Snowvember 2, but enough to send the snowpack at the stake at Mt Mansfield soaring to a mid November record.
Drought concerns have unfortunately replaced the run of recent flooding events over the past few years. October was a healthy wet month over all of northern Vermont with most areas procuring 125-200 percent of normal rainfall and this has finally begun to ease drought conditions and we can only hope that a season featuring heavy snowfall will end any drought entirely. Temperatures have been up and down throughout the calendar year. The cold start to 2025 gave way to a mild March. Bouts of cool weather in both May and early June gave way to record heat right after the summer solstice. This was then followed by warm weather in July which gave way to a cooler finish to the summer season in late August and early September. The foliage season, from a color standpoint was stunted by the dry weather but the times of first frost/freezes have been relatively normal and the Vermont landscape has the "ready for winter" look.
Last winter exceeded many preseason expectations and it seems to have also fueled a better set of expectations for the current year. Last year was also one which defied expectations regarding ENSO with much of the season remaining relatively neutral. A weak La Nina has finally developed this summer and although some gradual strengthening has been observed, conditions remain just a shade under what I would consider to be a "moderate" ENSO event. Personally, I consider strong ENSO events of both varieties to have adverse impacts on winter weather for different reasons. Strong Pacific forcing during El Nino events often inhibit the southward progression of arctic air even as they strongly fuel the southern branch of the jet stream which can in turn lead to many east coast snow events. La Nina winter seasons are very often characterized by a strong buildup of cold over Canada but the stronger Nina seasons have been known to feature persistent southeast ridging over the North American continent. This can have the impact of severely limiting the winter below 39 N (let's call this Baltimore, MD) while Vermont repeatedly fends off inland runners that often produce some snow followed by ice and rain. I find the weaker La Nina winters preferable for this very reason. We want a jet stream capable of allowing for a buildup of arctic cold across the northern latitudes of North America, but not one strong enough to entirely eliminate the concept of split flow in the jet stream. We've really seen La Nina go both ways in Vermont and the relationship I was alluding to in this paragraph is hardly perfect. We've had some of our most historic snow seasons during significant La Nina events and also some of the worst seasons. I've also watched over hyped weaker La Nina winters become big disappointments. All we can do is use the data we have and make the best probabilistic-based guess.
There's a happy ending in this story. The snowiest winters at MRG and northern Vermont more generally have featured similar ENSO conditions. The two standouts are 1970-1971 and 2000-2001 which are easily top 5 winters in our 76 winter dataset and maybe top 2. 2016-2017 was another winter with a similar La Nina. We had some incredible periods of snow with two extended blowtorch interruptions. 1996-1997 was similar in that regard and featured the "extension" with deep snow well into the middle of spring. The winter's of 1988-89 and 2011-12 serve as a reminder however that this relationship can break down quite easily. Overall though, we are in a good place from the standpoint of ENSO with the chances for a snowy winter more elevated.
The Pacific Decadal Oscillation (PDO) and state of sea surface temperatures in the Pacific continues to sing a less happy tune. We managed to record some of the highest indices I've ever seen over the summer months, but have managed to bring the values down considerably in the recent months. The situation in the eastern Pacific, closer to Norrth America has been encouraging perhaps suggesting that the index might be ready to flip. What was most encouraging was an area of warm water that seemed to be developing over the Gulf of Alaska though that has been neutralized in recent weeks. It's the central Pacific which seems to be the driving force behind the positive values with very warm water concentrated near the IDL (180 Longitude). In totality, the changes in the eastern Pacific make the story look more encouraging than prior winters but the warmth in the central Pacific can't be neglected. I would imagine it playing a disruptive influence on the jet stream, shortening the duration of colder patterns which is somewhat typical during most La Nina winters.
SST Anomaly
The buildup of snow and ice has managed to proceed in a fairly typical way this autumn. One has to make statements adjusting for the fact that climate change has had a material impact on ice coverage across the arctic regions during the late summer months. With that qualifier in mind, we managed to retain ice well this summer relative to recent prior summers. We then proceeded to begin building ice over the arctic regions on schedule, but in recent weeks, notable anomalous warmth in the arctic has slowed the expansion of ice and we again are challenging record lows for November for coverage. Snowfall has been better and expanded at a relatively normal pace. The coverage of snow across the northern hemisphere was rounded to 18 millions of square km which is average. Recall last year that we were very slow to freeze the Hudson Bay which still showed some open water even in late January. Interestingly, both years that were uncharacteristically slow were exceptional snow years in Vermont (2011 and 2025). I have entirely no explanation for this and only point it out because it is likely to be another slow year unless the expected cold weather in eastern Canada early this December can expand the ice very rapidly.
Our next section tries to "count cards" or assess some of the recent characteristics in the weather pattern as a means of predicting the future. I find there are times it's easier to simply go through this exercise than trying to lean too heavily on some poorly understood variable which can sometimes become the "hot item" in seasonal weather prediction. I've been watching a few things this fall with one being the drought which has had such a broad impact on upstate New York and interior New England. Though the water deficits remain, the weather pattern has turned in accordance with what we might expect in a La Nina season. Interior sections of the northeast are seeing precipitation and should continue to see such in December. I'll preface the next statement with some caution, but it's very encouraging to see eastern North America be a favorite spot for cool weather in a relative sense. The warm almost always outweighs the cold because again, climate change, but the long wave weather pattern can still have propensity to focus the warmth or the cool weather in certain locations and it seems, for the time being that eastern North America is the spot. Last winter turned out to be surprisingly cold also as you might recall, but in the period from March through July, western North America was the cooler part of the continent. By the middle of August, we saw a switch and in spite of a very warm interruption in late September and early October, the cool train has been on the schedule more than the warm one.
Going to bring one more item to the seasonal forecast discussion and that relates to what make last season so spectacular. Can we pull off the trick again? It's a bit cruel to the snow lovers along the coast, but it proved be decisively important for us the last few seasons. Once again, can we kill the coastal storm ? This relationship has been utterly fascinating to me and certainly educational. Even as widespread cold gripped huge swaths of the eastern United States last year, a coastal storm and big city snow never really materialized. Models advertised several times, the internet hypesters climbed on board a few times and in the end snowfall was very limited. Not the case however across Vermont where every clipper seemed to over-deliver which is a striking contrast to all those winters where it seemed the clipper might be gone for good. The reality is that the clipper and the coastal have a relationship and both can't occupy the same space and there are winters where one is preferred over the other. It's a bit beyond my pay grade as a non-PHD level to do an appropriate analysis as to why this is. My intuition tells me it's a local sea surface temperature thing in the coastal Atlantic but I can't say this with confidence. I can say I am watching closely however. We saw two "Miller-A" style coastal storms in October. Those types of events are usually good for everyone, especially for us, but we didn't see any of that last year. Do we see more of that this year or is it a continuation of the trend we saw last year with limited coastal snow. It will hurt some feelings, but coastal pain is MRG's gain.
With all that said we can make a forecast for the winter. Though promising sustained cold weather would be a bridge too far, I tend to believe the following winter will more closely resemble 2024-25 than the three mild winters prior to that. We managed to isolate the mild weather last year to November, March and the Christmas holiday and with November hitting the books as a cold month, we will likely face a milder period either later in December or in early January. Still, with the ENSO under control, the PDO situation a bit adverse and the propensity of the long wave pattern to support relative chill in eastern North America, a winter with closer to normal temperatures appears more probable than an above normal winter. Regarding snowfall, we can hang our hat on two important items. The first is the weaker La Nina and the snowy winters that have occurred in similar ENSO years such as 1970-71, 2000-2001, 2007-08, 2010-11 and 2016-17, the second is the similar sea surface temperature configuration in the coastal western Atlantic Ocean which would suggest it's another clipper over coastal situation. This latter part of the statement is some hypothesizing on my part, but so is seasonal forecasting as a whole. You expect to get surprised and hope it comes in the right direction. Enjoy the Thanksgiving holiday folks and welcome to another season.
