2024 has been the year of persistent warmth and following 3 flooding events over the past 18 months, autumn suddenly turned very dry. We thus head into the upcoming winter in need of some precipitation of off all types to avoid running a further drought deficit. Though they're a few encouraging signs out there in the outlook, one rather bad one looms over everything. In the mean time, the short range outlook appears very encouraging with snowfall in the forecast over the high country over the next 5 days and more snow and cold on the horizon around the Thanksgiving holiday and beyond. With that introduction, lets take the plunge into another season.
Upcoming Snowfall
Going to start by providing a brief outlook for the upcoming storm, a system that is certainly not atypical during the early or later part of the ski season and one that is very reminiscent of a few of the bigger events from last year. While low pressure is stalling out over southern Manitoba, there will be an extended opportunity to gather moisture from the Gulf of Mexico and Atlantic Ocean which will give rise to a more robust coastal low pressure center late Wednesday. Rain will enhance and spread very slowly northward. When precipitation finally arrives midday Thursday, the deeper occluded low will swallow the coastal system allowing the already marginal temps in valley locations to warm a few more degrees and this means mostly a rain event in low lying areas (at least at for a while). Way up above 3,000 feet, precipitation is likely to fall as some wet snow late Thursday and continue through Thursday night but even at this elevation, temperatures are marginal and only support a few inches of very wet snow. Forecast models then are indicating a break in the action before an additional colder round of precipitation arrives for Friday night into Saturday. This should produce snow everywhere (even on the valley floor) though heavier snowfall amounts will remain confined to the high country and the more powdery snow should stay above 2500 feet. Still, the snowfall is expected to persistent at least intermittently through Sunday and where temperatures are the coldest, closest to the summits, snowfall should pile up modestly. By Sunday evening, expect 4-day totals of upwards of a foot while a 1-3 very wet inches can be expected near the valley floor. There is better dynamic support for heavy snowfall over the Catskills of New York and Pocono region of Pennsylvania on Friday. Much of this will melt early next week and should provide some needed drought relief to some very dry areas of the northeast.
I have some deep concerns about the EPO this winter and the presence of the dreaded evil empire in the Pacific Ocean, but its not showing up in the outlook through the rest of November into early December. Quite the opposite is in fact, with a favorable jet stream in the Pacific, opening the door for stronger shots of cold weather and additional snowfall around the Thanksgiving holiday and into the first week of December. We discuss all this in subsequent posts.
ENSO Outlook
In the meantime, lets start with discussing the ENSO situation for the winter. This is one key area where we are exceeding some of the more dire expectations earlier this year. Following last year's strong ENSO event which was approximately a +1.7 C El Nino, the exceptions of a nearly equally strong La Nina appeared to the prevailing view of those that both follow and prognosticate on ENSO. Sea surface temperatures in the equatorial regions of the Pacific have certainly trended in that direction, but after tiptoeing into negative territory, sea surface temperatures have stabilized and have headed back to near neutral levels. This has defied conventional wisdom. The last forecast I read from the NOAA folks continued to predict a weak to moderate La Nina, but I have very little confidence in such an outcome and would favor a more neutral ENSO as a best guess for the winter at this point.
We certainly could use all the help we can get from ENSO neutrality. Many of the coldest winters, especially since Y2K have occurred during these ENSO conditions including the 2002-03, 2003-04, 2013-14 and 2014-15 and some of the biggest torches have occurred during strong ENSO winters of either the El Nino or La Nina stripe - think 2011-2012 and 2015-16. Boy, I would love forecast a cold winter on this rationale and its certainty tempting to run with this as the medium range outlook continues to trend colder. I can't do it however and the following paragraphs detail as to why.
PDO Outlook
Those that have followed the blog might remember that I keep referencing this current adverse -PDO stretch we are in. 2018-2019 was the last relatively neutral PDO winter and was also the last time we had a complete freeze of Lake Champlain. Since then the PDO has become more and more negative with each successive winter. This past October, the PDO nearly set a record recording its second lowest October reading, -2.48. in a dataset spanning over 100 years and a top 10 lowest readings for any month.
The Pacific Decadal Oscillation or PDO is an index that describes the configuration of sea surface temperatures in the mid-latitude Pacific. No, it is not the defining predictive indicator every year, but the continuous negative state keeps relative sea surface temperature warmth in the mid-latitude Pacific with relative sea surface temperature chill both in the higher latitude areas near the Bering Sea and near the Equatorial regions (which would power La Nina, if it were to ever occur). This type of configuration does not encourage the sustaining of favorable jet stream conditions in the Pacific and instead favors the tighter jet stream flow that has a propensity to repel the southward transport of arctic air. There is a nice illustration when comparing October SST's of this current year to those that prevailed before the last cold winter we had in 2018-2019. 1st map shown is 2018 October and the 2nd is the most recent October.
PDO indices are cyclic by nature and this current more adverse stretch will ultimately cycle into something else. The PDO is also a better (and certainly not perfect) predictor of temperatures as opposed to snowfall. For coastal areas of New England and the Mid-Atlantic another year without the more constant presence of arctic air is a good enough reason to predict another bad snow year, but many of these years end up being respectable across interior locations as has been the case over the last two seasons.
Snow/Ice Expansion
The buildup of snow across the northern hemisphere is running about average. The October value came in at 18.88 millions of square kilometers which is right in the middle. The buildup of ice in the arctic is slow relative to average but it remains faster than 2016 and 2020. The arctic refreeze time continues to trend slower over the longer term and this IS a direct result of climate change. Every 5 years or so, there's a noticeably larger area of open water that needs to refreeze and the Hudson Bay, which remains 99 percent unfrozen as of this outlook, has open water later into December. 50 additional years with this trend will have a dramatic impact on the personality and climatology of our winters in particular. I hear the skeptics refer to some obscure prediction made a quarter century ago about ice in the arctic and how it was predicted to be ice-free by now. I never saw such predictions at the time, but the changes that have occurred have been dramatic enough and ultimately will lead to an ice-free arctic sometime before the next turn of the century or early in the next one.
In the meantime ice and snow are building in the northern hemisphere in comparable fashion to what has taken place over the last 10 years and without El Nino to ravage the high latitudes, there should be a better expanse of arctic chill over Canada this year when compared to last.
What is the weather telling us ?
My atmospheric tells section is the part of the outlook where I go through the exercise of examining recent weather trends as a means of predicting the future. Undoubtedly there's been some distinctive traits to the recent weather conditions that will help guide us. 1) It has been persistently warm in Vermont. The last time we've had a below normal month was November of 2023, a year ago. The combined impact of the -PDO and climate change haven't helped in this regard but it would be hard to expect any change in this basic theme without help in the form of different forcing mechanisms in the Pacific . We are getting a bit of help from the neutralized ENSO and let's all hope it provides some material impact. 2) It's been very dry over the past 90 days. Southern New England had a historic flash flooding event back in August and Vermont had a similar such event in July. September, October and November have been extraordinarily dry and sunny most areas have not had an event with an inch or more of rain on a calendar day since August.
Digesting all this and comparing these recent observations to previous seasons points you to one similar year in particular - 1964. That autumn featured dry weather in New England, had a building weak La Nina and a negative PDO. Northern Vermont got sporadic bouts of extreme cold but was decidedly below normal on snowfall and Burlington, VT in particular saw one of the lowest seasonal snowfall totals of the last 100 years. Since MRG opened back in 1949, there's been two other bigger negative PDO spans and some of those winters had very good results for northern New England especially on the snowfall side. The last two winters, though certainly warmer than the 1950's or 1970's, saw respectable snowfall amounts, especially over the high country. The king of all negative PDO winters, 1955-1956 was a more respectable snow season and certainly a colder one winter overall.
The Outlook Summarized
My outlook for upcoming winter shows considerable amount of respect for the near record autumn negative PDO values. I can conjure up some optimism on the snowfall side, and I'll conclude with that more upbeat sentiment, but I expect us to struggle sustaining colder weather in eastern North America. We will have to hope that the ENSO-neutral to weak La Nina setup can allow cold to encompass a greater expanse of southeast Canada and that some of this cold can continue to keep winter in place across northern Vermont even as areas farther south are struggling. It's encouraging to see a looser Pacific jet stream set up in the medium range outlook and this should help get us closer to an opening in the near term, I just have concerns about whether such a pattern can sustain for more than 2 weeks. Over the course of the winter, temperatures are likely to be colder than what we experienced during the strong El Nino winter last year but should remain considerably above average. In t this case I would prognosticate 2-4 degrees F above this average over the 4 month stretch beginning in December. I am more optimistic on snowfall side, especially for the possibilities of an upside surprise. If I had to pick a range on snowfall I would choose the 150-175-inch sub-optimal total both recent and more distant -PDO winters have been more generous and I think another over-performance is very possible, especially relative to coastal areas. Lets hope the next few weeks get us off the ground figuratively and on the mountain literally. Enjoy the upcoming season !
