Exactly one year ago the first snow arrived on the peaks of Campigna. The comparison with 2019 is merciless. On Monday the maximum peak touches the ridge, at an altitude of 1658 meters, it was 14 ° C. The Romagnolo October continues to dress in summer, with t-shirts and shirts still in vogue and sweaters and coats forced to leave in closets. Ironically it can be said that more than October 22nd is the 82nd of August. In the last ten days in Forlì the maximum has been constantly above 20 ° C, with the peak recorded on Monday of 26.1 ° C, a temperature that normally can be felt at the beginning of September. And the situation is not likely to change. A decidedly anomalous scenario, which on the one hand may seem pleasant, with the possibility of spending more hours outdoors, on the other it is worrying for the effects that can have repercussions on nature, delaying the normal vegetative phases and causing an increase in the insects.
Pierluigi Randi, meteorologist from Emilia Romagna Meteo and Meteocenter and vice-president of the Ampro association, it is a month of October that has very little in autumn, at least here in Romagna. What is happening and what is this anomaly due to?
Undoubtedly, apart from a temporary and relative fresh phase at the beginning of the month, subsequently abnormally high temperatures were observed for the rest of the period. The sinking in the Atlantic of deep areas of low pressure, has activated for a long time very hot streams of sub-tropical origin that have fed robust anticyclones that from North Africa have then invaded the Mediterranean, bringing stable conditions and with progressive temperatures rising up to the excesses of the last period. Even in the last few days the scenario has repeated itself: depression sinking on the Iberian peninsula and Morocco / Algeria, with response of very hot currents that have invaded the peninsula, assisted in this by the presence of a high pressure on the Balkans. It is a model of circulation that is not abnormal in autumn, but the temperatures observed due to the influx of very hot air masses in relation to the period are anomalous.
A heat that may seem pleasant and that delays the end of what can still be called summer. But it is inevitable that it brings a long series of problems …
Exactly. An example we have at this time in the Italian north-west, where the passage of a 'normal' Atlantic perturbed front, but on very warm low layers and unusually high temperatures of the Italian seas, has triggered severe regenerating and almost stationary storms due to excess of energy available for convection, with large amounts of rain. But it could also happen other areas, including ours, even if in these circumstances and with this type of circulation it is always the north-western areas of the peninsula that risk the most. If we limit our gaze to our region the consequences are, for now, concentrated on excessively high temperatures, low rainfall (the anti-cyclonic component of the hot influx prevails) and an alteration of the vegetative cycles, in a period in which the flora should " prepare "for the winter dormancy.
When is a return to normal expected?
Despite the peak intensity was touched on Monday, with maximum temperatures between 26 and 27 ° C on the internal Romagna and on the 24 ° C on the coast (ie 7/9 ° C above the climatological norm of the third decade of October), the thermal field will remain above normal again for a few days, at least until day 28, with temperatures always high apart from the effects of intermittent stratified cloudiness which may at times limit the daytime temperature rise. Then we see a colder signal indicatively starting from day 29, but whose size and duration still appears uncertain, thus requiring confirmation.
We are now at two-thirds of meteorological autumn and we have seen very few rains. What is the rainfall deficit?
In the month of September we found a pluviometric deficit (compared to the climatological norm of the period 1971-2000) of about 25%, which is added to a shortfall of about 50% in October until October 22, so, considering so far the meteorological autumn, we can attribute to this part of the 2019 season an average deficit between 35 and 40% depending on the area. In reality it has happened even worse, such as in the years 2001-2006-2009-2011 (to remain in the new millennium), but it is clear that until now the autumn is proving to be stingy with rainfall, moreover in the season that should be the wettest of the year.
What can we expect for the last part of the season?
To date, the signs that can be seen on long-term trends concern average scenarios with a thermal trend closer to normality and a recovery in rainfall, even if it is difficult at the moment to predict whether these will eventually rebalance the shortfall accumulated so far. Obviously these are "scenarios" on a rather wide scale, so they must be considered with the right caution.
Is it already possible to have a trend for the coming winter?
Still on the subject of seasonal scenarios, the predominant signal is a positive winter governed by Nao (North Atlantic oscillation), therefore with lower pressure than the norm on the North Atlantic (including Iceland and the United Kingdom); and higher pressure on the Mediterranean area and central-eastern Europe, which would imply a mild and not very rainy season. However, there is considerable uncertainty about the exact positioning (at a medium quarterly level) of the high sub-tropical pressure band, which could, especially in the second part of the season, observe a greater tendency to migrate northwards, which would expose the Balkans and the central Adriatic and southern Italian regions, with continental cold returns from the north-east. It is no coincidence that many winters characterized by a largely positive Nao were sometimes also relatively cold on these areas, so the uncertainty appears to be greater precisely in the Mediterranean area and the Balkan sector, where the ensemble spread of many models appears to be the highest.