An unstable impulse of oceanic extraction is descending on the Euro-Mediterranean sector, destined to structure itself in a low depression on the Tyrrhenian Sea. This configuration will trigger marked atmospheric instability, associated with precipitation, a temperature drop estimated at 2-4°C compared to the previous days and the return of snow on the mountains.
Mattia Gussoni, meteorologist at iLMeteo.it specifies that during the day of Friday 6 November the cyclonic circulation will trigger widespread precipitation with a predominantly downpour or thunderstorm character. The phenomena will initially affect the North-West, with accumulations of between 10 and 20 mm/24h and local peaks of up to 30-40 mm/24h over Liguria and Piedmont, and will then rapidly extend to the central sectors (Tuscany, Umbria, Lazio) and to the South, in particular over Campania, Tyrrhenian Calabria and Puglia, where average contributions of between 15 and 30 will be recorded mm/24h and storm peaks up to 40-60 mm/24h.
The baric dynamics will be accompanied by a significant reinforcement of ventilation: the winds will first move from Scirocco and then rotate to Mistral, with gusts estimated between 45 and 60 km/h in the western and southern basins.
The wave motion will increase markedly, with very rough seas offshore and a significant wave height of between 1.5 and 2.2 meters on the Tyrrhenian Sea and on the channels of the Major Islands.
The return of snow to the central-western Alps
The concomitant decline in geopotentials at altitude will favor the return of snow to the central-western Alpine arc: the snow level will be around 1500-1600 meters above sea level, with accumulations estimated between 25 and 35 cm of fresh snow above 2000 metres. On the central Apennine ridge the snowfall limit will be at higher altitudes, above 1900-2000 metres, with limited contributions to the ground of between 10 and 15 cm by the end of the event. The instability will also persist in the first part of the weekend: on Saturday 7 November the phenomena will tend to concentrate on the Adriatic side between Marche and Abruzzo (15-25 mm/24h with peaks of 30-40 mm/24h) and intermittently between Campania, Puglia and Calabria (10-20 mm/24h), while in the North-West and in the upper Tyrrhenian Sea there will be large clearings. Maximum temperatures will be between 11 and 15°C in the North, between 13 and 17°C in the Center and between 17 and 21°C in the South.
Stability returns from Sunday
Starting from Sunday 8 November, the rapid rise of an anticyclonic promontory will lead to a general restoration of stable conditions with clear or slightly cloudy skies over almost the entire country, except for residual light rains in Salento and Ionian Calabria (5-10 mm/24h). During the night and early morning, the calm wind and radiation will favor the formation of fog banks along the Po Valley and in the central valleys.
IN DETAIL
Friday 6. overcast skies in the west with scattered rain between Liguria and Piedmont (10-20 mm/24h with local peaks of up to 30-40 mm/24h); clouds without rain in the North-East; snow level in the Alps above 1500-1600 meters with accumulations of 25-35 cm above 2000 metres; maximum temperatures between 10 and 15°C. increasing cloud cover associated with rainfall along the Tyrrhenian coast between Tuscany, Umbria and Lazio (15-25 mm/24h); snow on the central Apennine ridges above 1900-2000 meters with contributions of 10-15 cm; maximums around 12-17°C. South and Islands: widespread rainfall in the form of showers or thunderstorms in Campania, Basilicata, Puglia and Tyrrhenian Calabria (15-30 mm/24h with peaks of up to 40-60 mm/24h); variability with sunny spells on the Major Islands; sustained winds from Scirocco to Mistral with gusts up to 45-60 km/h and very rough seas (waves between 1.5 and 2.2 metres); maximums between 17 and 22°C.
Saturday 7. In the North: weak residual rainfall in Emilia-Romagna (2-5 mm/24h); large clearings in the rest of the sector; maximums between 11 and 14°C. In the Centre: instability on the Adriatic sector between Marche and Abruzzo (15-25 mm/24h with peaks up to 30-40 mm/24h); isolated light showers between Umbria and the interior of Lazio (less than 5 mm/24h); maximum temperatures between 13 and 17°C. In the South and on the Islands: intermittent showers between Campania, Basilicata, Puglia and Calabria (10-20 mm/24h); sunny spells on the Major Islands; Mistral ventilation with gusts up to 40-50 km/h on the sea channels; maximums between 17 and 21°C.
Sunday 8. In the North: mostly dry weather; local fogs on low plains; maximum between 12 and 16°C. In the Center: slightly or partially cloudy along the Adriatic coast; more significant accumulations on the Tyrrhenian coast with absence of significant precipitation; maximum temperatures between 13 and 18°C. In the South and on the Islands: rainfall in Puglia and Calabria (10-15 mm/24h); dry elsewhere; weak or at most moderate winds from the South on the Ionian sector; maximum between 18 and 20°C.
Trend: removal of the unstable structure starting from Monday 9th with large clearings across the entire national territory and stationary temperatures in line with seasonal averages. From Tuesday 10th new disturbance arriving from the west.
