It's no secret the central and eastern US had a lackluster winter season last year, thanks to a persistent ridge of high pressure and one of the warmest January/February's on record. But already this year, we've seen snowflakes fly across parts of the Midwest and interior Northeast through early November; some places even reporting measurable snowfall! With that in mind, it's easy to conclude that this year features signs of a snowier year across the East without looking at any data at all. But how much higher can we raise the bar this year? To find out, let's start by looking at sea surface temperatures across the globe.
(Courtesy of Tropical Tidbits)
The image above shows the sea surface temperature anomalies as of late October. The reds indicate warmer than normal water, while the blues indicate cooler than normal water. We circled the major anomalies that caught our eye when coming up with our winter outlook. We believe each of these areas will play a vital role in how the winter pattern shapes up. Let's take a closer look...
Area 1 the warmer normal waters in the equitorial Pacific indicates we have a fairly healthy El Niño developing, which is the opposite of the La Niña (cooler waters in the same region) that was in place the last three years. At first glance, it appears we are on our way to a strong El Niño for this winter and that will dominate our weather pattern. Well, looks can be deceiving as we like to look at what is called the Multivariate ENSO Index (MEI) to measure the true impact El Niño and or La Niña is having on the weather pattern.
(Courtesy of NOAA)
The chart above shows MEI values of some of the strongest EL Niños we have ever had that are averaged over two-month periods. The positive red values indicate El Niño, the black numbers indicate neutral conditions, and the blue negative numbers indicate La Niña. The bottom row shows the true strength of this year's El Niño so far and you can see this year's El Niño is much more comparable to a weak to moderate strength El Niño than a strong one. We expect the pattern to eventually behave like a moderate El Niño this winter, which is more favorable for snow along the East Coast.
Area 2 indicates what is happening with the Pacific Decadal Oscillation (PDO), which is simply a measurement of how warm or cool the sea surface temperatures are in the Northern Pacific. The PDO has been in its negative phase for quite some time now and it is just coming off of near-record strength (indicated by very warm waters near Japan). Despite recent indications of weakening, we expect the PDO to have a significant impact on at least the start of winter by increasing the risk of a trough in the western United States with an overall mild start to winter in the East.
Finally, Area 3 refers to what is called the Indian Ocean Dipole (IOD). Simply put, this is based on sea surface temperature anomalies in the Indian Ocean. Right now, the IOD is in its positive phase and is expected to stay this way for the first part of winter. So why does this matter? Well, this favors convection (thunderstorms) occurring near Africa and the western Indian Ocean. When this occurs, this increases the risk of mild, Pacific air being transported into the eastern United States and decreases the risk of sustained cold.
We took all of these factors into account when coming up with analog years (years with similar conditions as this year) for this winter. Below is what the trough and ridge pattern looks like (on average) based off that data:
(WeatherWorks analog jet stream pattern for the 2023-2024 winter)
All of our analog years were El Niño winters and the map above certainly has an El Niño feel to it. One thing that stands out this year that's different than the last few years is the presence of a strong sub-tropical jet stream. This favors a stormy winter across the South and up along the East Coast. However, at the same time, the polar jet stream is displaced much further north than in the last few years, which limits persistent cold in the Midwest and East.
(WeatherWorks temperature outlook for December - February)
It follows that our seasonal outlook shows above normal temperatures across the northern US, including the Ohio Valley and Northeast. However, keep in mind that these maps are a blend of the winter as a whole, and they are not telling you all the details of the winter season. For instance, we're starting out chilly in November, but after mid-month, we expect Midwest/Northeast to trend above normal... that likely continues into some of January. Cold and snow during El Niño winters in the East is notoriously known to be backloaded, and this year is no different as we expect the best risks of persistently cold temperatures to occur later in the winter, especially during February.
(WeatherWorks snowfall outlook for February 2024)
The map above shows that February is indeed favored to be the snowiest month of the winter in the East, with many areas in the mid-Atlantic likely exceeding their monthly snowfall averages. In fact, we would not be surprised if 70 - 80% of the season's snowfall occurs after January 20th for many along the East Coast. Also, we feel this period is the greatest opportunity to see high latitude blocking near Greenland (-NAO), which would certainly increase the risk of a significant or even major snowstorms.
(WeatherWorks snowfall outlook for the 2023-2024 winter season)
Taking everything we have discussed into consideration, we believe the majority of snowfall this season in the Mid-Atlantic occurs in a few larger storms later in the season, which for some can be enough to exceed normal seasonal totals. New England can still cash in on winter storms, though we expect sharper cut-offs in snow amounts due to high pressure from Greenland blocking later in the season. Unlike the past few seasons, the upper Plains and Great Lakes see lighter events due to a more suppressed storm track. Not to be left out is the Ohio Valley, as more snow than last year is expected, though the best chance to reach normal seasonal totals is in eastern areas closer to Pittsburgh.