Last winter was another mild one, featuring below normal snow over central and eastern parts of the United States; all thanks to the pattern once again featuring troughs of low pressure in the West and a ridge of high pressure in the East. With a reoccurring theme in the past several years, one has to ponder: How much longer can these stretches of lean winters can go across the eastern US before giving? We've already had sign's of winter show itself in just the past month or so, with many areas in the Midwest and Northeast having already seen their first snowfall, even some more impactful accumulations. Still, many from NYC to D.C. have yet to see their first real snow accumulation. Will this be a precursor to the upcoming season, or are we in for a snowier and active winter?
To help us answer that question, let's look at some factors that we believe will have a influence on the pattern this winter. To start, it's always a good habit to look at sea surface temperatures across the globe, with a focus over the Pacific Ocean. This body of water is probably one of the largest influences on our climate here in the United States and is one big key in determining long range forecasts.
(Sea Surface Temperature Anomalies in Degrees Celsius - Courtesy of OSPO/NOAA)
The image you see above shows just how warm or cool the ocean temperatures are compared to what a normal value would be during the middle of December. The reds and orange pigments indicate warmer than normal water, while the blues indicate the opposite. There are three distinct areas we have circled on the map, which caught our attention when working on our winter outlook this year. We'll now take a look at each of these 3 areas in more detail to try and see how they may influence our winter.
This section is focused over the Eastern Equatorial Pacific, AKA: the ENSO (El Niño- Southern Oscillation) region. Warmer than normal waters in this region indicate a"El Niño", while cooler than normal waters indicate a "La Niña". As you can tell from the image, there is a lot of blue in this circled area, which indicates to us that La Niña has been slowly forming over the past few months. However, some smaller pockets of warmer than normal waters are mixed in as well, which indicates that the La Niña is still weak. While it has started to get its' act together the past few weeks, we don't believe ENSO will be a leading factor to winter's impacts. This mean's we need to look elsewhere for other bigger influence to the winter season.
This section is focused over the Western Equatorial Pacific in the Indian Ocean/near Indonesia. You can see waters are warmer than normal in this area, compared to Area #1, and they have been for some time now. But why does this matter? Well, tropical thunderstorms in the Equatorial Pacific like to form where the warmest sea surface temperatures are located. These thunderstorms will travel from west to east along the equator, a phenomenon to meteorologists known as the Madden-Julian Oscillation (MJO). Where exactly these thunderstorms set up, however, is the important factor. Different impacts to our weather pattern can occur depending on where they are located.
(Western Pacific Sea Surface Temperatures in Degrees Celsius - Courtesy of Tropical Tidbits)
The image above actually shows us SSTs (Sea Surface Temperatures in Celsius), and you can see that the ocean is rather warm in the Maritime Continent. The MJO has been active since the summer and we expect it to remain active at times throughout the winter, spending much of its' time in the yellow circled area. For sensible weather over the United States, this supports milder conditions in the East, especially in January and February. With that said, however, the MJO already has made a push to the international Dateline this fall. This actually increases the likelihood of more cold and snow at times in the East this winter, should it continue to move through this area.
This Section focuses on the area known for the Pacific-Decadal Oscillation (PDO). This 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 a few years now and just recently reached record low levels (indicated by cool waters in the northeastern part of the circled area and very warm waters off Japan). While the PDO likely tries to weaken some this winter, we still expect it to remain at least moderately negative for a while. Hence, this is one of the main pattern drivers for winter, which favors mild weather in the East.
We took these factors into consideration when coming up with our analog years (years that have similar conditions as the upcoming year) for this winter. Below is what the trough and ridge pattern looks like (on average) based off the current data:
(WeatherWorks Analog jet stream pattern for the 2024 - 2025 winter)
Our analog years consist of a combination of ENSO neutral/weak La Niña and moderate to strong -PDO winters, with the map you see above reflecting these factors. One feature that stands out is a lack of a strong subtropical jet stream that was in place last winter. A weak subtropical jet stream is supportive of storm systems remaining weaker this year, which translates to a lower than average risk of a major East Coast snowstorms. In addition, a storm track well west of the I-95 corridor through the Great Lakes is favored to occur multiple times this winter. This does, however, increase the risk for more wintry mixed or all rain events in the East, especially closer to the I-95 corridor.
(WeatherWorks Temperature Outlook for December - February)
Our outlook shows above normal temperatures once again across the Ohio Valley and into much of the eastern US. Keep in mind, however, that these maps are a blended average of the winter, and aren't showing you all the details of the season. For instance, we have already seen some notable cold periods in the East in December thus far. Some temperature variability shows up in our analogs as well, with some support for January to at least start off quite chilly. While we think the more persistent cold will eventually set up in the Pacific Northwest and Upper Midwest, the East can see some cold periods at times later in January and into February. But there still look to be longer stretches of milder weather at times.
(WeatherWorks Snowfall Outlook for the 2024 - 2025 winter season)
Finally, we get to the thing everyone cares about: the Snowfall Outlook. After taking everything we talked about into consideration, our thoughts reveal another potential below normal season for much of the East from the Tennessee Valley to southern New England. With that being said, analogs do show that some decent snowfall can still occur at points this winter for the East Coast, with the highest odds occurring in January. Otherwise, we expect a higher risk for mixed events in the Ohio Valley and into the Mid-Atlantic, with New England having the higher probability of reaching normal snowfall for the season. Our analogs do indicate that an early March snowstorm is possible somewhere in the mid-Atlantic or Northeast, so don't let your guard down if it appears winter is winding down toward the end of the season.
Our Long Range team uses teleconnections like ENSO and the PDO, along with other global datasets when updating the extended outlooks in our WeatherRisk® Service. We provide weekly and monthly outlooks on the upcoming season, breaking down potentials for snow threats and explaining the chances of having saltable/plowable type events. For more information on this service, you can email info@weatherworksinc.com or call us at 908-850-8600
