The WeatherBlog is currently receiving a lot of questions about El Niño, which is this year - or was it La Niña? What is all this again and what does it mean for the Alps? Haven't we covered this topic before? Yes, we have. To start with: there is still no clear, statistically definitive correlation between El Niño and the Alpine winter that anyone can agree on.
What is el Niño?
Let's dig a little deeper: One of the slightly larger cogs in the global weather engine is a flow pattern over the Pacific Ocean at the level of the equator, called the Walker circulation. At the equator, the trade winds at the surface blow roughly from east to west, due to the Earth's rotation and such.
These winds push the surface seawater to the west, creating a kind of waterlog on the east coasts of the continents (in the Pacific this would be the east coast of Australia/Southeast Asia). On the west coasts of the opposite continents (in the Pacific, the west coast of South America), the surface water that has been pushed away is missing and cold deep water (rich in nutrients, liked by fish and therefore also liked by fishermen) rises to the surface. There is now a temperature gradient from one edge of the ocean to the other.
On the warm side (Asia, Australia), warm, humid air rises, the weather tends to be stormy and unstable and often erupts in the form of hurricanes and cyclones. On the cold side (South America), the air sinks and the weather is comparatively calm.
This "normal state" of the Walker circulation is the neutral phase of ENSO, the El Niño Southern Oscillation. If the Walker circulation is particularly strong because the east-west temperature gradient of the surface seawater is more pronounced than usual (cold in the eastern Pacific, warm in the western Pacific), this is referred to as La Niña, the cold ENSO phase.
El Niño is the warm phase of ENSO. The temperature gradient in the ocean disappears or reverses (warm in the East Pacific, cold in the West Pacific), which leads to the Walker circulation also weakening or reversing, or shifting.
We don't know exactly why this happens, but it happens with a certain irregular regularity. El Niño phases cannot yet be reliably predicted using models. In order to estimate developments, the sea surface temperatures of certain parts of the Pacific Ocean near the equator are observed, from which various indices can then be calculated. If the index swings in one direction or the other over several months, this heralds a certain ENSO phase.
We are currently in an El Niño phase and the current episode is expected to peak in the winter of 2015/16. The whole thing is, at least in terms of the magnitude of the SST (=Sea Surface Temperature, because you don't want to write out sea surface temperature every time) deviations, comparable to 1997/98, the last really strong El Niño, which has burned itself into the collective memory, at least in the USA, as a phase with particularly chaotic weather.
Roughly speaking, El Niño manifests itself in the west of the USA in the form of warmer, wetter conditions than usual. To emphasize this again, there are no effects here that can be painted as a colorful blob on a map. Somehow, of course, everything is always connected, but, as usual, it's not that simple.
Here you can follow what's happening right nowut. .Current ENSO advisory from NOAAGood, detailed explanation.
And when will'it finally be winter?
Our Dutch colleagues have been seeing the winter apocalypse approaching this weekend for some time, sometimes over the entire Alpine arc, sometimes, as now, only in the west in a totally apocalyptic form. Our in-house oracle has also been distributing hints and teasers on the internet regarding a possible PowderAlert on Friday.
So what's going on?
The now very zonal general weather situation is being disrupted in its persistent westerly flow. A wedge is forming over the east coast of North America, which will become stronger over the next few days and move eastwards. As is usually the case with waves, this rather large wave in the current of the westerly drift does not remain alone in the otherwise smooth atmospheric ocean, but produces further waves. Relevant for us is a trough over Central Europe that shovels cold air towards us. A low pressure development in the Mediterranean that was present in the models until recently has now disappeared again, which means that most of the precipitation is expected in the northwest. As usual, we'll leave the details to the oracle and, in the meantime, join in the general sigh of relief that can be heard from the ski resorts: November summer is coming to an end and, for the first time, the signs are not bad for seasonal weather in the medium term. We would like to remind you that typical seasonal weather in November is not the same as typical seasonal weather in February. FC Stubai sums up this topic in the following self-explanatory graphic:
