The polar jet stream breaks in, what will happen in Italy?

Storms with snow arriving in the Apennines? The mix of snow and lightning is not uncommon in spring, more unusual in winter.

The air has become more seasonal in recent days, modest night frosts have returned in the north and also in the basins of the center. However, the maximum temperatures are certainly not typical of January. Wednesday at Rimini 16°C has been exceeded, yesterday 18-20°C stood out in Sicily and 14°C in Trieste.

In the meantime, the snow has returned to whiten the northern and central Apennines, with a slight snowfall above 1200-1500 m which shouldn’t be news in January.

In short, the weather is busier but the situation is not what it should be in January. What will happen now?

Synoptic situation

The surface maps of the next 2-3 days show a promontory of the Azores anticyclone, sometimes scratched by fast frontal passages. In fact, the high-altitude maps show Atlantic flows, e the undulating jet stream. For now we find ourselves mainly with flows from the northwest, but from mid-January the undulation will be more accentuated and with entry of sacs associated with polar air. To keep an eye out in particular for a cold front expected on 18-19, still uncertain in the ensemble scenarios. Equally uncertain hypotheses of cold outbreaks at the end of January.

Saturday and Sunday weather

Saturday in the north low clouds and mists in the morning, partly sunny in the Alps and the Apennines, then increasing clouds of an average type unproductive as rainfall, with the sun filtering through the clouds at times. At the center variability with large sunny areas especially in the Tyrrhenian regions. More clouds in the Adriatic sector, some rain moving between the coasts of Abruzzo and Molise. In the south showers in Puglia, southern Campania and Calabria, in the evening also on the northern coasts of Sicily, the rest of the island being variable.

Sunday morning in the north with clearing mists and then increasing clouds, showers on the eastern Ligurian coast. In the evening, a brief passage of rains that skips the northwest, snow also thick but short-lived in the Alps eastern center, over 1000-1300 m, and the Apennines, 1300-16500 m.

In the center partly cloudy with increasing clouds from the afternoon and with some rain or showers in western Sardinia and Tuscany. Spaces of sunshine also large in the south, with increasing clouds here too and some rain in Campania.

Temperatures decreasing in the maximumdue to the greater cloudiness, the frosts in the north are scarce and local. But it’s not cold in January, during the day 8-10°C in the north, 14-15°C in the center and just under 20°C in the south.

Snow at low altitude next week, that’s where and how much

On Monday in the north the northern currents bring sunshine and clarity, crisp air in the evening and early morning, 11-13°C in the afternoon, 5-6°C above average, anything but cold! In the center and Sardinia rapid passage of showers and short snowfall in the central Apennines, even on 1000 m, however modest quantities. In the south there are showers and thunderstorms from the afternoon. Windy everywhere.

Between Tuesday and Wednesday more accentuated disturbed wave but uncertain in details. Probable showers in the north and sudden snowfall in the Alps over 400-700 m and also the Tuscan-Emilian Apennines, 600-800 m and Romagna over 800-1000 m, even with a fast storm. Estimating now, 10-30 cm in the Alps, 5-20 cm in the Apennines.

At the center of even intense winter storms, snow in the central Apennines above 800-1000 m, estimated at 5-20 cm, strong thunderstorms arrive also in the south and Sardinia, be careful not to confuse hailstorms with snow, expected above 1000 m, except for the local graupel at lower altitudes.

Textbook Rossby wave in the middle of next week, with the polar jet stream breaking into Italy. However, the consequences on the ground are still uncertain. ECMWF map elaborated by METEORED at 300 hPa for Thursday 18 January 2023 at 12 UTC.

In the middle of the week intense and fast cold front

Between Wednesday and Thursday, another rapid passage of the cold front, with uncertain effects and timing: ranging from the brief appearance of snow in the Po valley to the outbreak of the fohn, therefore prudence is imperative. In the center sudden but fast snowfall at low altitude on the Adriatic regionsbuferotti in the Apennines, windy in Sardinia with mistral storms, bora in the Adriatic and tramontana with clear spells in the central Tyrrhenian regions. Showers with snow on the hills also in the south, between Basilicata and Calabria, locally east Sicily, marked windy variability elsewhere.

Friday sunny and clear in the north, colder morning, even -2,-4°C, but up to 10°C during the day. In the center it improves rapidly with the last snow showers in the Apennines, in the south local snow showers in Calabria and northern Sicilyat hilly altitudes, but overall it improves.

End of January: cold intensifying?

After 20 January minimum temperatures in clear decrease, even intense frosts for the first time in winter, with lows -4,-6°C in the north, -1,-4°C in the center instead +4,+6°C in the south. The effects, on the other hand, are uncertain in the latest maps hypotheses of cold from the east to the end of January and even snow in the plains in the north are now emerging, in Siberia, however, the frost is extremebut there’s a lot of uncertainty in ensembles so we’ll stop here for now and talk about it again.

The polar jet stream breaks in, what will happen in Italy?