For much of this winter season, the polar vortex winds at 60°N have been racing around the stratospheric polar region. During February alone, these west-to-east winds were two times stronger than normal for that time of year. However, the latest forecasts suggest that the polar vortex is about to switch gears with a major vortex disruption to happen this weekend. Read on to find out why the polar vortex could be bottoming out early this season.
Observed and forecasted (NOAA GEFSv12) polar vortex wind speeds at 60°N (bold blue line) compared to the natural range of variability (faint blue shading). Since mid-November, these stratospheric winds have been stronger than normal (thin blue line). However, that’s about to change as the latest forecasts (issued March 3, 2025) indicate the winds at 60°N are going to dramatically decrease over the next few days (bold purple line), indicating a polar vortex disruption. The big question is whether these winds will rebound toward their normal strength before the end of the season. NOAA Climate.gov image, adapted from original by Laura Ciasto.
Stratospheric pit stop
At the time of writing this post, the polar stratospheric west-to-east winds are still speeding around the Arctic [footnote #1], but forecasts suggest they are not only going to come to a screeching halt by the weekend, but they are then going to strongly reverse direction. When this wind reversal (i.e., winds become east-to-west) occurs at 60°N and 10 hPa (~19 mi/30 km above us), it’s called a sudden stratospheric warming. As the name suggests, these major polar vortex disruptions are linked to incredible stratospheric temperature increases over a short period of time [footnote #2]. For this upcoming event, temperatures in the mid-stratosphere could increase as much as 45°F (25°C) in less than 5 days.
Observed and forecasted (NOAA GEFSv12) polar cap temperatures compared to the natural range of variability (faint orange shading). Since October, these stratospheric temperatures (bold red line) have been colder than normal (thin red line). This is expected because strong polar vortex winds act as a barrier between cold Arctic air and warmer mid-latitude air. As the polar vortex becomes disrupted, the stratosphere will warm quickly and intensely (bold pink line), hence the name sudden stratospheric warming. NOAA Climate.gov image, adapted from original by Laura Ciasto.
Sudden stratospheric warming events usually come in two possible flavors in which the polar vortex either displaces off the pole or splits into two smaller vortexes. This particular event may be a bit of both. The initial warming event kicks off with the polar vortex shifted toward Europe, but the forecasts also show pieces of the vortex splitting off from the main lobes several days later.
Evolution and forecast of stratospheric conditions. Earlier this week (March 4 2025; left panel), the polar vortex winds (vectors) were situated closer to the pole keeping the relatively cold air (light shading) isolated from the warmer surrounding air (orange/red shading). By March 10, 2025 (middle panel), the GFS forecast indicates the polar vortex will be nudged farther off the pole, with warmer air flooding the Arctic. The average winds around 60°N will become east-to-west, characterizing a sudden stratospheric warming. This disruption to the polar vortex is expected to continue through at least the next two weeks with smaller lobes of the vortex periodically splitting off (e.g., March 13, 2025, right panel). Current forecasts suggest that the stratospheric winds will not recover this spring and become west-to-east again. If so, this event will be classified as a final warming instead of a mid-winter sudden stratospheric warming. NOAA Climate.gov image, based on Global Forecast System data provided by Laura Ciasto.
Will the polar vortex rev its engine again?
One of the big questions regarding this polar vortex disruption is whether the stratospheric winds at 60°N will recover and become west-to-east again, extending the polar vortex season (and its ability to influence weather patterns) into late spring. Forecasts [footnote #3] do not currently show a recovery, so this pit stop may be the end of the vortex’s racing season. If this turns out to be the case, then it would be classified as a “final stratospheric warming” rather than a major sudden stratospheric warming.
As we discussed in last season’s post, final warmings occur every spring as sunlight returns to the North Pole and the temperature differences between the equator and pole decrease. As a result, the west-to-east winds that are maintained by that temperature difference decrease and transition to east-to-west winds. This transition usually happens sometime in mid-April, but there have been 5 years since 1958 when final warmings occurred before March 15. Like this year, those years corresponded to winters without a mid-winter sudden stratospheric warming [footnote #4].
A potential stratosphere-troposphere fender bender
Differences from average atmospheric thickness (“standardized geopotential height anomalies”) in the column of air over the Arctic for the stratosphere and troposphere. Since the beginning of the year, low-thickness anomalies (purple shading indicative of a stronger than average polar vortex) have dominated the stratosphere but only periodically coupled down to the troposphere. Latest forecasts show a dramatic change with thickness anomalies increasing (orange shading), consistent with a polar vortex disruption. These stratospheric anomalies are preceded by tropospheric anomalies of the same sign, hinting at a nudge from below. However, it’s too soon to tell whether these stratospheric anomalies will then drip down into the troposphere again. Standardized anomalies are based on departures from the 1991-2020 Climate Forecast System Reanalysis climatologies and have been divided by the standard deviation. Data are from the Global Forecast System observational analysis and forecast.
Regardless of whether this is the final warming or the vortex decides to ride again, both have the potential to impact our weather this spring. Disruptions to the polar vortex can communicate down to the troposphere and disrupt the jet stream. These disruptions to the jet stream can bring colder than normal Arctic air down into the eastern United States.
Now this doesn’t mean you need to bring your winter tires back out while your garden tools continue to collect dust. First, it’s too soon to tell whether this vortex disruption will make its way down to the troposphere as the latest forecast doesn’t show much stratosphere-troposphere interaction after the onset of the warming event. Second, though the impacts of March sudden warmings are very similar to those in mid-winter, spring is coming, so any Arctic air brought down in the US won't "feel" as cold compared to if it happened in January because we are in a warmer part of the year.
Even if the polar vortex season ends early this year, we’re hoping to have at least 1 or 2 more posts (including a guest author) so stay tuned!
Footnotes
[1] We spent several posts this winter talking about the strong, but sometimes stretchy, polar vortex and what that has meant for our winter weather. If you’re interested, please read more here, here, and here.
[2] The sudden increase in temperature over such a short period of time occurs for a couple of reasons. As the polar winds weaken and reverse direction during a major sudden stratospheric warming, there is a component of the air that moves poleward and descends rapidly over the Arctic and pressure increases. As the air descends it warms: this is one of the reasons why the temperatures can increase so impressively during a major warming event. Furthermore, the polar vortex winds act as a barrier between cold Arctic air and warmer mid-latitude air. When the winds/barrier weaken, warmer mid-latitude winds can enter the polar stratosphere and contribute to increasing temperatures.
[3] We show the American GEFS model in these posts, but the ECMWF model currently doesn’t show a vortex recovery in the next several weeks either.
[4] The link between winters with a sudden warming and late season final warmings (and correspondingly, years without a sudden warming and early season final warmings) is thought to be due to the tug of war in the stratosphere between dynamic and radiative processes that control the strength of the polar vortex. In particular, if a sudden warming occurs during mid-winter, the polar stratospheric winds will be pulled towards returning to a west-to-east flowing state to balance the stratospheric temperature gradient created by lack of sunlight over the pole. If this recovery of the stratospheric winds to west-to-east flow occurs, it provides potentially weeks to months of additional time for planetary waves to interact with the winds, extending the timing of the final warming until much later. On the other hand, if the sudden warming occurs near the spring equinox, when sunlight has returned to the pole, the stratospheric winds feel no radiative force to return to a west-to-east state, and so often the winds will stay east-to-west (corresponding to an early season final warming).