Europe: a beautiful satellite image of today, with very different weather conditions

If we look at the satellite imagery of today (Figure1) we can see different weather conditions across the continent.

Between the UK and Scandinavia we can see the cold air coming from the Arctic, visible for the scattered cumulus clouds on the N Sea caused by instability (ocean surface is warmer than the air mass, thus the warm air lifts up in the atmosphere and condenses forming clouds and precipitation); these are causing scattered showers (mainly snow) in Scotland and E England, as well as a decrease in temperatures in the UK, Norway and N France.

On the west (in N Atlantic) a deep low-pressure system (989 hPa) is moving towards Ireland, though it will weaken before reaching the coast (between tomorrow and Saturday), so no severe event is expected.

On the southern part of this cyclone, less clouds and calm conditions are due to a high-pressure west of Spain, which is leading to a warm air advection from mid-Atlantic towards the Iberian peninsula (maximum values of +14/+17 °C today between Portugal and S Spain).

Instead, from E Spain to the Baltic region, a long and narrow tail of clouds stands for a cold front moving southeastward (causing rainfall and snow between France, N Italy and the Alpine region ); this is simply the front of the arctic air mass which is ‘pushing’ towards central-southern Europe.

Moving eastward, we can see how between S Italy, the Balkans and Turkey the weather conditions are ‘calm’, with clear skies (notice the snow at the ground between Greece, Serbia and Romania). Here, a high-pressure is causing settled (and relatively) mild conditions (maximum temperatures between +12/+15 °C in S Greece and Turkish coast).

On the northern side of the anticyclone, we can see another band of clouds (between Ukraine and Russia) which is related to a warm front moving eastward and causing snow at ground level (due to the negative temperatures at surface).

The warm front in E Europe and the cold front in central Europe are related to a deep low-pressure system (976 hPa) positioned between the Baltic sea and S Finland. This is causing intense snowfall in the area and quite strong winds on the Baltic sea, and it is leading to very cold air from NE Russia towards central Scandinavia, where temperatures close or below -30 °C are observed.

Figure1. Satellite imagery of today. I have added the different type of air masses and weather systems. Tropical maritime air (yellow), high pressure (orange), Polar Maritime air (purple), Arctic air (blue) and Polar continental air (dark blue). (Source: Sat24).

Thus, today has been fascinating on a meteorological point of view, and also the next days will be interesting due to the fast change in the weather conditions over Europe.

UK (but not only): Beast from the east? Attention to the ‘fake’ news.

In the last few days numerous news stories have reported the possibility of a very cold spell in the UK (usually called ‘the Beast from the East’) with snow and very low temperatures which should occur from this weekend.

However, up to now, the ensemble models are not seeing any of these dramatic freezing events (not only in the UK , but also in Europe), but only cold spells which can occur during every winter. In fact, in order to be as cold as last year (when, between February and March, for more than 10 days very low temperatures and snow where observed both in southern and central Europe), the air mass should come straight from Siberia/NE Russia where the coldest temperatures are observed (usually between -30 °C/-50 °C). Thus, the type of air should be Polar Continental (that is coming from the polar region, originating on land), which is the coldest in Europe and can cause snow and low temperatures also in the Mediterranean Region (e.g. in February 2018 between 10-15 cm of snow fell in Rome).

This week instead, even if colder air will move towards the UK and Central Europe, it will mostly come from the Arctic (Figure1). Thus, it will bring snow showers (especially in Scotland and N. England between tomorrow night and Thursday), but no severe event is expected.

Figure1. Synoptic chart for Thursday afternoon. I have added (blue arrow) the direction of the air mass (from the Arctic) and the areas where snow showers are likely in the UK (blue stars). Finally, notice the 528 dam line over Scotland and E. England which shows how snow can be possible at low levels. (Source: Met Office).

It will be a normal cold spell (as usually occurs in January), with snow at low levels and frost (the latter especially in the mainland between Thursday afternoon and Friday morning).

Temperatures will be only few degrees below 0°C during the night on Thursday (-2/-4 °C in some areas), and above 0 °C during the day mostly everywhere (0/+4 °C).

In addition, already from Friday afternoon, the arctic air will be replaced by a ‘milder’ polar maritime air mass from the N Atlantic, which will cause an increase in temperatures (especially in Wales, N Ireland and W England), with values above 0 °C mostly everywhere; snow will be replaced by rain except in Scotland (mainly Highlands) and N England (Pennines).

Finally, for the next week, air from N Atlantic is still expected, with cold (and wet) conditions at times, but without causing freezing temperatures and deep snow as shouted recently. It will be simply winter.

UK: when is the weather going to be less ‘boring’?

Today has been mild all over the UK. Both maximum and minimum temperatures (Figure1) have been well above the average, with no values below 0 °C (except on the Highlands this afternoon).

Figure1. Maximum (left) and minimum (right) temperatures observed today. (source: Meteociel).

However, though the temperatures are pleasant, the weather is seeing overcast conditions mostly everywhere. In Figure2 we can see the satellite imagery of this afternoon. It is quite impressive: a deep low-pressure system (987 hPa) just north of Scotland and moving towards the Northern Sea is causing very strong winds (and frequent showers) in N. Scotland and N. Atlantic (gusts of 100 km/h), as well as a decrease in temperatures in this area (Figure1). Instead, the rest of the country, as well as Ireland, is seeing overcast conditions (with drizzle or light rain in some areas) with weak winds.

This is due to a high-pressure system positioned just south-west of the UK which is leading warm and humid air from mid-Atlantic (mostly Tropical maritime) towards the UK.

Figure2. Satellite imagery of today (12UTC). (source: Sat24).

The cold front, related to the low-pressure system (and which has caused showers today in Scotland) is moving southward this evening, causing a decrease in temperatures (especially from tomorrow evening when the skies will be clear mostly everywhere). Showers will be very rare, with dry conditions mostly everywhere.

However, temperatures won’t drop significantly, with values close or slightly below 0°C between Tuesday evening and Wednesday morning (especially in Scotland, N. England and Wales).

In addition, no rainfall is expected this week (until Friday) because of the semi-stationarity of the high-pressure system between Spain and the UK. Indeed, it will move northward from tomorrow, and the maximum pressure values would reach Ireland by Thursday, causing settled weather mostly everywhere.

In conclusion, this week will be still quite ‘boring’ with no interesting weather phenomenon on the country and also looking at the ensemble forecasts no significant change in temperatures or precipitation is expected for the next week.

Italy: Dry and cold in the north, snow in the south

Since Wednesday cold air from E. Europe has caused a decrease in temperatures along the peninsula, with values below the average (especially in central-southern Italy). The cold air, moving above the Adriatic sea, is causing snow on the eastern side of Italy, with more than 1 metre of snow in some areas on the Appennines (e.g. Capracotta in Molise). Some snow has reached also the coast (especially between Abruzzo and Puglia), with few centimetres on the beaches. Snow has also fallen in Sicily at low levels.

Meanwhile, in the north, bright conditions are occurring, with strong winds especially on the Alps, which have caused some wildfires between Veneto and Lombardia due to the very dry conditions (also some were caused by human activities).

Today has been the coldest of the year so far (and since the start of the winter in the south). In fact, both minimum and maximum temperatures are below the average mostly everywhere (Figure1). Negative values have been observed in the mainland along the peninsula, with peaks of -5/-8 °C on the Po Valley and Tuscany, and below -10 °C on the Alps. The maximum temperatures have been below 10 °C mostly everywhere, except in Liguria and Sardinia.



Figure1. Maximum (top) and minimum (bottom) temperatures observed today in Italy. (Source: Meteociel).

The interesting thing has been, as said previously, the snow along the coast of the Adriatic sea. This event is quite unusual (though it can happen every few years) and it is due to the Adriatic sea effect: very cold air (from the Balkans) moves above the warmer sea (picking up moisture), and pushes against the Appennines condensing and leading to precipitation. If the column of air is cold enough (like today), snow can fall also along the coast.

For this reason the snow observed today was significant, because the continuous flow of air from N.E. has led to precipitation on the same areas.

The situation is clearly visible from the satellite image (Figure2).

Figure2. Satellite imagery of today (12 UTC). I have coloured in blue the area along the Adriatic coast interested by snow (source: Sat24).

The cold air should move eastward tomorrow and by Sunday there will be an increase in temperatures especially in the south. Next week cold air from Central Europe should reach the peninsula, but it is still too early to describe the possible effects. In the meantime, we can enjoy this unusual weather in the south.

UK: Where is winter?

If we look at the temperatures observed today, we can see how the values (especially maximum) have decreased since last week. In fact, the maximum temperatures (Figure1), are between 3-8 °C in the UK, with negative values on the Pennines. Instead, in Ireland, temperatures are higher, between 6-10 °C. The decrease in temperatures, especially in S. England, is due to a cold air mass moved southward towards Central-Eastern Europe.

Figure1. Maximum temperatures observed this afternoon (source: Meteociel).

However, the cold air has reached mainly only the eastern part of the UK (and not at all Ireland), causing a decrease in temperatures towards value close to the average or slightly below. Until Sunday, minimum values (especially in England) will be close or below zero (possible -3/-4 °C in some areas) and maximum temperatures will remain between 3-7 °C mostly everywhere.

Thus, the significant element is the positive anomaly seen during the first month of the winter season, when there have been only few cold events.

Indeed, if we look at the temperatures observed in some cities in the UK in December, we will see how the average minimum and maximum temperatures have observed values above the long-term average. I have analysed data of some cities in the UK and plotted their anomaly referring to the long-term average 1981-2010 (Figure2).

Notice that this is a general analysis (it doesn’t consider all the weather stations and local orography in detail), but I think it’s interesting to notice the overall view of December.

Figure2. Maximum (left) and minimum (right) temperatures anomalies observed in some cities in the UK during December 2018 compared with the 1981-2010 average. The dots increase their size according to the temperature scale, that is, the bigger is the dot the more is the anomaly.

We can see how all the UK has observed values well above the average, especially the minimum temperatures (close to + 5 °C in Wales). Only in eastern England, along the coast of the N. Sea, negative anomalies are observed (Norwich -0.2 °C anomaly in the minimum temperature).

Thus, we can see that up to now in the UK winter has shown very few episodes with cold weather, and the temperatures observed these days are nothing exceptional. Next week, colder air should move towards the UK from Greenland and N. Atlantic, causing a decrease in temperatures compared with the next weekend, but it’s still to early to describe the event in details. Thus, we will see how January will be, maybe changing the mild trend observed during the last month.

References: 

I have used the data from both Meteociel and Met Office

First week of 2019 in Europe: between cold and mild conditions

The first week of the year is going to see two different weather patterns over the continent. On W. Europe, a strong high-pressure system will be positioned between the UK and N. Atlantic, bringing mild and settled weather in Spain, Portugal, Ireland (and western part of the UK).

Instead, on the eastern side of the anticyclone, a deep low pressure system, positioned between Sweden and Finland, will lead very cold air (polar continental with values between -12/-14 °C at 850 hPa (1500 m a.s.l)) to move southward during the week (Figure1) towards central-eastern Europe. In addition, the cold air will cause the formation of a low-pressure system in the Mediterranean Sea (between S. Italy and Greece) which will lead to snow at low levels and (very likely, due to the cold temperatures) along the coast of the Adriatic Sea.

Figure1. Synoptic chart valid for 00 UTC on Thursday night. I have coloured in orange the mild air moving towards W. Europe and in blue the cold air (polar continental, PC) coming from Scandinavia. Notice the 528 dam line reaching S. Italy and Greece (which means snow at sea level is possible). (source: Met Office).

The cold wave should reach the maximum intensity between Thursday and Friday, instead Saturday and Sunday milder air from the Atlantic should move eastward, pushing the cold air towards E. Europe and Russia.

Thus, during the week, the continent will be ‘divided’ in two parts, with temperatures well below 0°C (also during the day) in Scandinavia, Balkans and Central Europe, with snow expected especially between Poland/E. Germany and Czech Republic, and between Serbia and central/northern Greece and central-S. Italy.

Instead, warm temperatures on the west (possible maximum values between 8-11 °C in Ireland and between 16-18 °C in S. Spain/Portugal), with settled conditions in both Spain, France, Ireland and the UK (except for some low clouds close to the coastal areas and valleys).

Alpine region: strong winds, snow and spring on the same day.

A high pressure system is positioned on W. Europe (Figure1) causing settled and mild conditions between Spain, France and the UK. Instead, on the eastern side of the anticyclone, colder air from Scandinavia is moving southward towards central Europe and the Balkans.

The pressure gradient between France and Italy is causing an increase in the wind speed especially on the Alpine region, with northerly winds blowing on the eastern side of the anticyclone. The gusts, especially at high altitudes (above 2000-2500 m) and on the southern side of the Alps are pretty strong, reaching 80-100 km/h (between Trentino Alto Adige and Veneto).

Hopefully the winds should not cause damages to the forests already hit by the strong winds in November.

Figure1. Synoptic chart valid for today (12 UTC). Notice the quick change in the pressure values between central Europe and N. Italy (from 1032 to 1024 hPa).
(source: Met Office)

The northerly winds are also causing the Stau effect. That is, overcast conditions with showers are observed in the northern side of the Alpine region (manly between Austria and Switzerland), with snow above 800-1000 m. Some clouds and showers have also reached N. Italy (especially between Lombardia, Trentino Alto Adige and Veneto). However, sunny and mild conditions are observed on the pre-Alps and in the Po valley due to the fohn descending from the Alps (Figure2).

Figure2. Satellite imagery of today (12 UTC). I have coloured in blue the wall of clouds (stau effect) and in orange the fohn blowing on the southern side of the Alps. (source: Sat24).

The fohn is causing a strong temperature gradient between N. Italy (especially N.W. Italy) and Switzerland-Austria. Indeed, there is a difference of more than 10 °C between the southern and northern side of the Alps (Figure3), with values between 10-15 °C in N.W. Italy (peaks of 20 °C in Liguria) and only 3-5 °C observed in Switzerland and Austria.

Figure3. Temperatures observed this afternoon in the Alpine region. (source: Meteociel).

This weather condition should last until Wednesday, when a cold air mass from Russia should move south-westward towards central Europe and the Mediterranean region, causing a strong decrease in temperatures (especially in the areas where mild conditions are observed today).

However, there are still uncertainties on the correct direction of the cold air and on its possible effects (in terms of temperatures and precipitation) especially in the Mediterranean region and W. Europe; thus, it would be better to wait Monday/Tuesday to check the output of the weather prediction models.