Yesterday, a significant temperature gradient was observed along the Po Valley in N Italy. The strong pressure gradient between central Europe and the Mediterranean has caused a significant foehn effect across the Alpine region, leading to a sharp increase in temperatures in the afternoon over SE France, NW Italy and S Switzerland.
Looking at the temperatures (Figure 1) we can see that most of the areas downwind the NW’ly flow observed values above 20°C.
Some temperatures have broken the all time records, like in Turin (27°C, which is 20°C above the climatological average).
These extremely high temperatures were caused by unseasonably mild air coming from the mid-Atlantic/N Africa combined with the catabatic wind (i.e. foehn) flowing down from the Alps towards W Po Valley, Ticino and SE France. Thus, being the temperature at 850hPa (1500m a.s.l.) very mild (around 12/15°C), the warming effect of the air flowing down the mountains slope (1°C every 100m) has caused temperatures to reach 20/25°C in these areas, as well as clear conditions.
On the central/E part of the Po Valley the NW’ly wind wasn’t powerful enough to ‘clear’ the layer of fog/low clouds lying on the area for several days (Figure 2). Thus, in cities like Venice and Trieste, maximum temperatures barely reached 10°C (though being still 2/3°C above the climatological average).
Today’s satellite image (Figure 1) shows widespread clouds over the continent. This is caused by a Tropical Maritime air advection (TM) along the N flank of a High over Spain. All the moisture and warm air is pushed over the Mediterranean region and central Europe. Meanwhile, a deep low over the Atlantic brings unsettled and windy weather across the British Isles. On the E side of the continent cold air flows S from Siberia, though mitigated as it reaches E Europe/Russia.
The temperatures observed at 12UTC today (Figure 2) are significantly above the climatological average for this time of the year across most of the continent.
Indeed, temperatures between 10/15°C are observed over the UK, France, Germany, Italy and Iberian Peninsula (here with peaks of 20/22°C along the E coast). Also in the Balkans and Greece temperature are very mild (between 15/20°C in S Greece).
Only in Russia and Central/N Scandinavia wintry conditions are observed, with values below freezing. However, these temperatures are still ‘mild’ compared with the climatology (e.g. in Moscow 0°C, but it should be -9/-4°C).
The next few days will see a further increase in temperature over all W Europe, with risk of some record-breaking values in France/Spain/Italy (possible peaks above 20°C) in some areas. This is caused by a northward shift of the Jet Stream over W Europe combined with the strengthen of the High over Iberia. Only from next week, the Jet Stream will push S towards central Europe causing a drop in temperatures (but there is still some uncertainty about its effects on a local scale).
This week is seeing very mild and settled conditions over most of the continent due to a strong high pressure set over central Europe.
If we look at the daily maximum temperatures (Figure1), we can see that mostly everywhere (except few areas in N Scandinavia and Russia) positive values are observed, with temperatures above 10 °C from the UK to the Balkans. Peaks above 15 °C are observed in France, Spain, Italy and SE Europe, with 20 °C reached in Spain.
Looking at the satellite image (Figure2) the weather patterns over Europe are still the same of last week: clear sky (except some local fog) due to the strong high pressure over central-southern Europe, fronts moving quickly along the edge of the ridge between the UK and the N Atlantic and a low between Scandinavia and Russia causing snow in some places.
Unfortunately the synoptic condition won’t change later this week, with the ridge on W Europe moving north towards Scandinavia and pushing mild air from N Africa and the mid-Atlantic.
Only from the weekend, cold air from Russia will move SE towards the E Mediterranean leading to a drop in temperatures and snow at sea level between E Europe and the Balkans, but elsewhere it will be still mild and sunny.
It’s likely that February will end with dry and mild conditions in many areas, and it will be interesting to see the temperatures anomalies observed overall in this month over the continent.
Regardless of the ‘significance’ of the anomaly, February 2019 won’t certainly be remembered as a cold month in many areas.
In this article I am going to analyse the temperatures observed in some cities in Europe during January 2019. A former analysis made two weeks ago had shown that the first two weeks of the year have been cold (and snowy) in Southern and Eastern Europe, with observed temperatures lower than in NW Europe.
Now that January has passed, we can see if the trend observed at the beginning of the month has occurred also throughout the last two weeks or if it has changed.
In Figure1 I have plotted the average daily temperatures observed in 17 cities in Europe.
We can see that E Europe and N Europe have observed the lowest average temperatures (Moscow is the coldest: -7 °C). Moving westward and southward temperatures rise, with positive values mostly everywhere (except in the Balkans: Bucharest -1 °C). The warmest cities have been Lisbon, Athens and Instanbul.
Regarding the anomalies of the average temperatures compared with the long-term average (1981-2010), in Figure2 I have plotted the results, in order to determine where it has been colder than the average and where it hasn’t.
We can see how the most significant anomalies (in absolute values) have been observed in Scandinavia (colder temperatures) and E Mediterranean (warmer temperatures). Warmer than the average also in Germany, Iceland and Ireland (though the anomalies are mostly between +0.2/+1 °C). In southern Europe little negative anomalies are observed.
This ‘picture’ is different than what seen two weeks ago, when significant negative anomalies were observed in SE Europe and ‘warm’ conditions were observed in the north (especially in Iceland, UK and Germany).
In conclusion, January has been ‘mild’ in some places (i.e. in central/western Europe, Iceland and SE Europe) and cold (compared with the average) in Scandinavia and Mediterranean region, though in both cases, the anomalies have’t been too significant.
During the last two weeks wintry conditions have occurred in numerous countries, both in W Europe and E Europe. Very cold temperatures were observed in Scandinavia and Russia and snow has fallen in many areas between central Europe, the UK and the Mediterranean region.
However, these weather conditions are changing, with milder air coming from mid-Atlantic and N Africa. Indeed, already today higher temperatures are observed (Figure1) with values above 10 °C in many areas in S Europe (especially S Spain, Italy and E Mediterranean region) and above 0 °C mostly everywhere, except in the Alpine region, Scandinavia and N Russia.
The satellite imagery (Figure2) shows the main features of the weather conditions over the continent.
A high-pressure is setting on W and Central Europe, with bright conditions in Spain, S France and central/N Italy and fog/low clouds between Germany and Poland. Between France, the UK and the N Sea a (weak) low pressure system is causing showers across England and Benelux.
Moving eastward, warm air from N Africa is causing settled and mild conditions in the E Mediterranean and convection is occurring between S Italy and Greece. This is due to a (weak) low-pressure system positioned close to Sicily which is leading to a temperature contrast between the (relatively) cold air from central Europe and the mild air from N Africa. Thus, convective cells are forming on the sea, causing numerous thunderstorms in the area.
Finally, in E Europe and Scandinavia cold temperatures are still observed, with snowfall between Finland and Russia.
The weather conditions for this week will see an increase in the strenght of the high-pressure in central/southern Europe with settled conditions and relatively mild temperatures (though fog/low clouds are possible in the valleys limiting the increase in temperatures). In fact, from Tuesday possible peaks of 20 °C are expected in S Spain, Portugal, S Turkey and Cyprus. Temperatures between 10/15 °C are expected in S France, Italy and the Balkans and close to 10 °C in the UK and Central Europe. In addition, during the night temperatures will be close or slightly below 0 °C especially in the valleys (and in case of clear sky),causing a strong temperature gradient between day and night.
Only in E Europe and Scandinavia it will be still cold, though with values above the average.
On Thursday, colder air from N Atlantic should cause a slight decrease in temperatures (with frequent showers) in Central Europe, though with no snow or ‘freezing’ conditions. However, only from next week (so in 7 days) a more significant change in the weather conditions should be observed, though it is still too early to talk about its possible effects.
This week, the lowest temperatures in Europe have been observed between Russia and the Balkans, with minimum temperatures close to -20 °C in some areas. Instead, in N. Europe, temperatures are not too low for being January, with maximum values above 0°C along the Atlantic coast of Norway up to the Arctic Circle (today maximum values between + 5-7 °C in the Lofoten Islands).
I have analysed and plotted the temperatures osberved in some cities in both Denmark, Sweden, Norway and Finland, to see if December and the first week of January have been colder compared to the climatological (long-term) average 1981-2010.
In Figure1 the main cities are shown. They are both in the mainland and along the coast.
We can see how the lowest average temperatures (as also according to the climatological average) are observed in the mainland and far from the Atlantic Ocean, between N. Norway and Finland, where the warming effect of the Gulf stream is weaker.
The coldest city is Rovaniemi, with almost -20 °C observed in the minimum average values during the last week. The warmest, instead, is Copenhagen, with both minimum and maximum average temperatures observed during the last December above 0 °C. Also Trondheim (along the coast of Norway) is observing temperatures above 0 °C, especially during the last week.
The comparison with the climatological average (Figure3) shows a very clear result. Positive anomalies are osberved mostly everywhere, especially in the minimum average temperatures (both in December and January), with values up to 7 °C (e.g. Trondheim) above the long-term average.
It seems that the most significant anomalies occurr along the atlantic coast of Norway (Oslo, Trondheim, Tromso), instead moving eastward the anomalies are little (1 °C: Helsinki) or negative (Rovaniemi), though Oulu (Finland) observes significant positive anomalies (+3/+5 °C).
These ‘warm’ conditions are due to the very warm air moved northward during the past few weeks (from mid-Atlantic towards the UK and N. Atlantic); however, the areas close to Russia have been more influenced by the polar air moved towards Eastern-Central Europe, observing values closer or below the average.
The weather should be colder the next few days, especially along the Atlantic coast, due to an Arctic maritime air mass moving towards the N. Sea.
Now we need only to wait and see if the second part of January will show colder conditions (for these areas).
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.
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.
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.