https://www.severe-weather.eu/global-weather/snow-extent-northern-hemisphere-highest-56-years-winter-cold-rrc/Snow extent in the Northern Hemisphere at the end of November represents an important parameter for the early winter forecast. This year snow extent is running much higher than average and according to existing global estimates, it is now beyond the highest ever observed so far. Winter forecast, especially in its early phase and in Europe, might be strongly influenced by such a large snow extent, although many other factors need attention.
This can be explained by two factors
1. Warming resulting in more moisture reaching continental areas in Eurasia and North America which leads to more snow build up since even if it would be around or slightly above average, precipitation would fall as snow, and more precipitations simply means more snow.
which is seen here that the trend was already going upwards2. Part of it can be explained by changes in the southern hemisphere which leads to weakening of northern polar vortex, since it's getting clear that the HTHH eruption has a more clearer impact on the climate, and that its potential effects were likely underestimated as well as the eruption itself.
https://www.severe-weather.eu/global-weather/stratosphere-polar-vortex-cooling-event-update-cold-anomaly-winter-season-influence-fa/The January eruption of Hunga Tonga in the South Pacific has injected a large amount of water vapor into the stratosphere. That water vapor is now causing significant cooling of the southern stratosphere, continuing into late Fall and early Winter.
We looked at the historical data and found that there is a weak indication of the south stratospheric cooling, coinciding with later stratospheric warming events over the northern hemisphere. But much more research is needed, as other background signals can be at play.
Stratospheric warming during the northern hemisphere winter can mean a heavy disruption of circulation. This causes pressure changes and can unleash cold air from the Arctic into the United States and Europe.
It would make sense for the changes in the stratosphere on the southern side of the planet could also impact the northern hemisphere. As the cooling in the southern hemisphere is substantial, the upcoming winter will be a great real-life “lab test” of the potential global weather changes.
The eruption injected massive amounts of HO² in the stratosphere, especially south of the equator, cooling the southern stratosphere, which in fact might warm the northern one (weakening it, leading to more break outs of cold). This in turn also explains the increase of rainfall on the eastcoast of Australia as tropical winds can more easily reach Australia from the east.
The southern stratospheric region is at record cold levels, strengthening the vortex and keeping it compact, and it is above record levels since this summer already.
