The atmospheric dominoes are in place and there is only one movement left before this “unwintry” winter is transformed into something completely different in a matter of days. In the next few days, we will see snow and we will see cold, yes. But if these days’ models are right (and its reliability is changing for hours) the huge ‘nortada’ next week will only be the simulation of an end of January that can freeze almost the entire country.
One of the strongest polar vortices on record. One of the reasons why the winter is being so mild is that the ‘Arctic Oscillation’ is positive. Very positive, in fact. That is, the polar vortex is strong and, as a consequence, the cold air remains contained in high latitudes. Under these conditions, it is difficult for cold air sleeves to approach areas like Spain. However, ‘difficult’ is not ‘impossible’.
What is this ‘stratospheric sudden warming’? For the past several weeks, meteorologists have been chasing a possible vortex disturbance that was showing up in the models on a recurring basis: a ‘stratospheric sudden warming’. To understand what we are talking about, we have to take into account that air circulation in the troposphere is relatively independent from that of the stratosphere. They are two layers of the atmosphere that usually work with their own logic.
In ‘stratospheric warming’ what happens is that (usually by the seas and oceans) a part of the troposphere heats up rapidly. As the hot air tends to rise, the mass invades the stratosphere causing a profound alteration of the circulation at high altitudes. Come on, the pole, the vortex and the jet streams go completely crazy for short periods of time.
On a practical level, what interests us is that when these “warm-ups” are intense enough, the force of the vortex is diluted and cold air can circulate at low latitudes very easily. That is, we can find a sleeve of polar air that “sweeps” everything in its path. But, and this is important to keep in mind, it may also not happen at all. There are hundreds of examples of “warming flashes” that did not affect the stratosphere.
Is that what will happen in the next few days? Not quite. The meteorological models draw that possible ‘warming flash’ for January 20. However, meteorologists (with the AEMET at the helm) have warned that in the coming days we will see how temperatures drop and the snow level reaches 400 meters in some areas of the country. Something that, curiously, comes just after the AEMET warned of the low levels of snow that we had this year.
However, next week’s wave of cold air does not appear to be directly related to the ‘stratospheric sudden warming’ we are talking about. Rather, it appears that two large high-latitude storms they are modifying the jet stream pointing it directly at our country. We will see the consequences in the coming days because, if everything goes as we hope, we will see the first snow on Sunday the 15th and the following week.
Imagen | ECMWF