Our annual winter outlook is here. It’s a time of year where we’ll throw all sorts of data at the wall and see what sticks (even if snow decides not to). Seasonal forecasting is a fickle beast, rooted in often loose science and weak correlations that make such a forecast much less scientific than we’d like. After many hours of pouring over maps and information, models & teleconnections, any patterns we think we uncover are often contradicted by anomalies that disprove anything we’re trying to prove. As such, I always advise taking these forecasts with a very large grain of salt. I build an 8-day forecast every single day. I’ve yet to become comfortable extending that to an 80-day. Until that day comes, know that the following information from here should be digested in the vein of weak correlations versus a concrete “write it in stone” assessment. With that in mind, let’s dive in.
Our first pit stop is almost always the ENSO phase. You’ve heard about it. El Nino, La Nina or neutral. It’s a warming or cooling of Pacific equatorial waters that can have a correlation on large scale patterns across parts of the United States during the winter. Rochester is in the midst of 5 consecutive winters with less than 100″ (our average) of snow. It’s been around 70 years since we’ve had a streak of at least 6 straight. That’s what’s at stake this winter. Our last few winters have featured a stubborn La Nina phase. They didn’t produce much snow, especially our last winter where we barely sniffed out 50″ during the entire season. La Nina is now long gone, zipping right into what is expected to be a moderate-strong El Nino into at least the first part of our winter. Guidance leans more toward weaker El Nino conditions late winter. Logically, if La Nina didn’t feature much snow, El Nino should be what snow-lovers are looking for, right? No, not necessarily.
Since 1950, Rochester has seen a clean dozen El Nino winters labeled as “moderate to strong”, based on our assessments of the seasons as a whole. Of those 12, 8 of them featured less than 100″ of snow. Several of those fairly significantly less. We had 2 winters with slightly above average snowfall and 2 with significantly above average snowfall. Essentially, 2 out of every 3 such El Nino winters are “soft”. Interestingly enough, Rochester’s history suggests weak El Nino winters are more productive for 100″+ of snowfall. It’s worth noting that a transition to a weaker El Nino caliber might be the eventually transition toward the end of the winter season.
NOAA’s winter outlook leans heavily on typical El Nino setups. These often favor relatively warmer temperatures and a general lack of snowfall.
These two features go hand-in-hand. Warmer average temperatures skew storm events more toward liquid than frozen. It most certainly doesn’t prohibit snowfall, simply allowing more precipitation to be exhausted in the form of non-snow. This can occasionally mean more “mixed phase” precipitation events, including ice in lieu of snowfall. It’s something worth watching this season. It would also lead toward more systems producing rain on the front end, transitioning to limited snow on the back end. While this is true of the synoptic or large scale systems, it leads us into our local lake effect discussion.
WNY’s snowfall production comes from a split of synoptic (system) snow & lake effect. The latter of which is much more difficult to pinpoint. It’s highly localized and highly variable. At its root, the basic ingredients are at least consistent. We need a relatively warm lake and relatively cold air moving over it.
Lake Ontario water temperatures are running warmer than average as of this writing. In fact, they’re been doing so for the better part of the entire year. On paper, that’s a plus for those looking for more snow. Here’s the catch: It’s only relevant if we have frequent intrusions of colder air to take advantage of it. Take last year around this time as an example. The lake was again running quite warm. But we didn’t have the frequency and caliber of cold to take advantage, at least locally. In fact, sometimes when the lake runs warm, it’s inherently the result of warmer air temperatures leading up to that timeframe. If that warmer trend lingers, the lake stays warmer…but fails to produce much snowfall. Remember, the outlook indeed favors milder temperatures. Tough to take our current warm lake as a true plus for snow-lovers given a warmer than average overall forecast ahead.
Now, an overall mild forecast does not prohibit arctic blasts. Far from it. But no one knows when, how many there will be, let alone how potent they are. I’m a fan of using Siberian snow cover in the fall as a metric to attempt to predict how active the polar vortex might be in the winter. The long and short is this- If snow cover in that part of the globe is limited in fall, it favors a stronger jet stream that tends to bottle up the cold air in association with the polar vortex. Essentially, the coldest of the cold says locked well to our north. More snow cover allows that jet stream to become more amplified with more southward propagating waves of cold air. We call this the Arctic Oscillation. When it turns negative (more amplified), that’s when winter really lives up to the hype. Siberian snow cover this fall? Pretty meh, relatively in line/more limited than recent prior years that already didn’t help drive much snowfall around these parts.
The implication there is a more zonal jet without the north-south undulations that transport bitterly cold air our way. Think less frequent cold snaps & less capability to tap into the warm lake waters that would support lake effect snow.
WHAT’S IT ALL MEAN? Remember, the above variables are just a few of many, many others that ultimately lead into how much snow Rochester will receive this winter. Heck, both El Nino & La Nina winters plenty of boom and bust individual seasons. I prefer speaking in terms of probability versus absolutes. And probability leads me to believe Rochester’s streak of 5 consecutive winters with less than 100″ of snow is likely going to extend to 6. The inclination is toward a range of 60-90″ of snow. Remember, that’s a projection for Rochester. We cover a wide range of towns and cities. Some will get more, some will get less.
The assessment of milder temperatures & a lean toward less frequent arctic intrusions makes getting to 100″ a tall order. Not impossible, just difficult. Assuming El Nino weakens toward the tail half of the winter season, it’s possible our snow is weighted toward the second half of the season. But even there, a weak early half would make it tough for the second half to compensate sufficiently to get us back into the triple digits. As the Buffalo area can attest to last year, all it takes is one or two big whoppers to really take the edge of an otherwise tame winter. There’s nothing stopping that from happening again this year, even in an ambient environment with more quiet days than wintry.