UK: sunny day after the snow

Between Thursday and Friday snow has fallen in many areas, especially in England, with more than 10 cm of snow at the ground in some areas.

This was due to the cold air coming from the north Atlantic and later from the Arctic which has caused a decrease in temperatures during the previous days. Indeed, on Thursday morning (Figure1) low temperatures (the lowest of the winter so far) were observed in the country, with values between -5/-8 °C in many areas both in England and Scotland; the lowest temperatures were observed in the Highlands (-10/-14 °C). Only in Cornwall temperatures were above 0 °C, due to the influence of milder air from mid-Atlantic.

Figure1. Minimum temperatures observed in the UK on the last day of January 2019. (source: Meteociel)

The negative temperatures in the morning have allowed snow to set on the ground, especially in the mainland. Snow has fallen since mid afternoon on Thursday until yesterday evening, though with an increase in temperatures yesterday afternoon which has caused mainly rainfall/sleet at low-levels.

Today, due to the brighter conditions, we can appreciate the satellite imagery (Figure2) showing the snow still at the ground in many areas, from Scotland to S England.

Figure2. Satellite imagery (UK) of today. I have used blue arrows to point out the snow on the ground in Scotland, N Ireland, Wales and England. (Source: Sat24).

The satellite image shows also the cold arctic air on the N Sea (causing showers) and moving southward towards Central Europe. On the west instead, south of Ireland, milder air from mid-Atlantic is moving towards the UK. This will cause an increase in temperatures, especially from Monday, with positive values (both minimum and maximum) mostly everywhere, and causing frequent showers between Monday morning and afternoon, and again between Tuesday afternoon and Wednesday.

Thus, if the previous week has shown wintry conditions, with snow in many areas, the next one will see milder temperatures and frequent (rain) showers, due to the change in the type of the air mass (from polar/arctic to tropical maritime).

Central Mediterranean sea: a deep low-pressure system is causing snow, rain and strong winds.

The cold air moved towards central Europe the last few days has reached the Mediterranean region, causing the development of a deep low-pressure system (981 hPa) between Spain and Italy (Figure1). This is causing strong winds especially southwest of Sardinia, with gusts up to 100 km/h.

In addition, since yesterday rainfall is observed along the Italian peninsula (especially in Liguria and S Italy); last night and this morning, with the colder air approaching the Mediterranean region, snow has fallen on the plains in N Italy (especially E Romagna and Piemonte), but snow showers have been observed also in Genova on the coast of Liguria.

Moving south, the snow limit increases (between 300-1000 m a.s.l in central Italy and 1000-1500 m a.s.l in the south).

synoptic chart 24/01/2019
Figure1. Synoptic chart of today. Notice the low-pressure system in the central Mediterranean sea. (source: Met Office).

The satellite imagery of today (Figure2) shows clearly the different weather conditions on the Mediterranean region, with the low-pressure system on the Tyrrhenian sea, the colder air entering the Mediterranean region from France and the low clouds in central Europe (where very cold temperatures are still observed).

Satellite imagery Europe 24/01/2019
Figure2. Satellite imagery of Mediterranean region today. I have added the main weather features (polar air, snow at ground and fog/low clouds). Source (Sat24).

Tomorrow the low-pressure system will move eastward towards Greece, though it will start weakening. Thus, winds won’t be as strong as today and the weather conditions should see brighter skies by evening, with some precipitation still possible in Sicily and SE Italy (with snow on the Appennines above 700-1000 m a.s.l. due to the colder air).

Finally, temperatures will decrease mostly everywhere, with negative values tomorrow morning in N Italy (especially in the area with snow on the ground) and close to 0 °C along the coast in Central Italy. In the south possible +8/+10 °C only in extreme S Italy and Sicily. The maximum values will be between +4/+8 °C in the north, +5/+10 °C in central Italy and between +8/+13 °C in the south.

Italy: first snow on the northern plains

The first coldwave of the winter has brought snow at low levels and in some areas (especially on the south of the Po valley) on the plains. Overall, temperatures have decreased towards value below the average, especially in central-northern Italy. The maximum temperatures observed on Sunday (Figure1, when most of the snow occurred) where below 5 °C in all N. Italy (except the Ligurian coast), Tuscany and Umbria. On the Alps and N. Appennines maximum temperatures were below 0°C. In central-southern Italy, the temperatures reached values between 10-13 °C and only in Sicily and Sardinia mild conditions were still observed (14-17 °C).

Figure1. Maximum temperatures on Sunday (Meteociel).

Snowfall has occurred mainly between Sunday afternoon and Monday morning due to a low-pressure system moving westward from France and colder air coming from the Balkans. However, only in few areas (mainly in Emilia Romagna) few centimeters of snow have been observed, instead elsewhere the precipitation was too weak to lead to some accumulation.

This is the first coldwave of the season, after the first 10 days of December when temperatures above the average have been observed. The next few days (until Friday, when milder air coming from the Atlantic should cause an increase in temperatures especially in central-southern Italy) will see still cold air coming from the east (though not as cold as the previous one) with minimum temperatures below 0°C especially in the areas with snow at the ground and maximum values slightly below or close to the average mostly everywhere. This will contribute to reduce the significant positive anomaly observed until last week.