January 2019 in Europe: cold and ‘mild’, but without extremes.

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.

average-temperature-January-2019-Europe
Figure1. Average daily temperatures January 2019 in some European cities. I have grouped them according to the region.

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.

daily-average-temperature-anomaly-Europe-January-2019
Figure2. Daily temperature anomaly observed in January 2019 in some European cities. In blue negative anomaly and red positive; and the bigger is the circle, the more significant is the anomaly (in terms of absolute values).

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).

This change in the weather conditions was due to a different type of air masses moved towards the continent. After the new year’s eve, cold air from Russia moved towards the Balkans and the Mediterranean region on the southern part of a strong high-pressure system positioned between central Europe and the N Atlantic. Instead, after the second week of the month, the cold air was flowing from Greenland and the Arctic (thus from the N Atlantic) causing a decrease in temperatures in Iceland, the UK and central Europe, and causing warmer air to flow from N Africa towards the Balkans and E Europe.

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.

First two weeks of the year: Was it actually colder in S. Europe than in the north?

The first two weeks of January have seen very cold air coming from Russia towards Central-Eastern Europe, with lot of snow especially in S. Germany, Austria (more than 2 metres in the Alpine region) and the Balkans. Also in Greece and S. italy snow has fallen, at sea levels at times.

In northwestern Europe instead, and especially between France, the UK and the N. Atlantic, a strong high-pressure ridge has caused settled conditions for several consecutive days, causing also very warm air towards these areas and Scandinavia.

I have analysed and plotted the daily average temperatures in 17 countries (cities) and compared the results. This analysis is simply focused on considering the main cities, thus it is not a detailed analysis for each country.

The results (Figure1) show that in S. Europe (especially between Italy and the Balkans) the daily average temperatures have been lower than in central-northern Europe.


Figure1. Daily average temperatures observed during the first two weeks of January in Europe. Notice the cities are grouped according to the geographical region.

We can see how Rome and Istanbul observed similar or lower temperatures than London, Paris and Amsterdam (to cite a few). In addition, it is impressive to see that Reykjavik has observed a very similar mean temperature to the cities in southern Europe.

Also the Balkans have observed temperatures lower than in northern Europe, with Bucharest colder than Stockholm and observing temperatures very similar to Helsinki.

However, not all southern Europe has observed low temperatures; the Iberian pensinsula has seen warmer conditions (though with temperatures close to their climatological average), with Lisbon the warmest capital so far. This is due to the frequent flow of warm air coming from the Tropics caused by the high-pressure ridge set (since December) between W Europe and the Atlantic.

In E. Europe (Warsaw, Moscow) the lowest temperatures have been observed (which is also in accordance to their climate); these areas where directly influenced by the polar continental air coming from E/NE Russia throughout the whole period.

If we look at the daily temperature anomaly (Figure2) computed respect to the climatological average (1981-2010), we can see how Reykjavik has observed the highest values (almost +5 °C; the daily mean average temperature in January for the Icelandic city is 0 °C).

Overall, all the area from France to Scandinavia and Iceland has seen warmer temperatures, instead E Europe and S/SE Europe have experienced a colder weather.

Figure2. Daily temperature anomaly (with respect to the 1981-2010 average) in Europe during the first two weeks of this year. Negative anomalies (in blue) and positive (in red). The higher is the anomaly (in terms of absolute values) the bigger is the ‘circle’.

In conclusion, we can say that the new year has brought cold weather in the southern and eastern part of the continent (with snow in numerous and unusual areas); instead, the western and nothern areas (especially the countries along the N Atlantic coast) are still experiencing mild conditions (as occurred also in December).

N. Europe: how’s the winter been so far?

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.

Figure1. Cities chosen in the analysis

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.

Figure2. Maximum and minimum average temperatures observed in December 2018 (left) and first week of January 2019 (right).

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.

Figure3. Maximum and minimum temperature anomaly calculated with respect to the climatological average 1981-2010. December (left), January (right).

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).

References:

I have collect data from: https://www.meteociel.fr/observations-meteo/temperatures.php?region=nor

Italy: December 2018 analysis

The first snow of the season in central-southern Italy is occurring these days, with snow also in unusual places.

However, December has not seen any relevant episode, except before Christmas, when some snow fell in the Po valley (especially in Emilia Romagna).

I have extracted data from the main cities in Italy and plotted the results in order to have a general overview of the maximum and minimum temperatures observed in December and compared with the long-term average 1971-2000 (there is no data for Aosta in N.W. Italy).

Regarding the average maximum and minimum temperatures observed during the last month (Figure1), we can see how the highest temperatures are observed in the south (mainly Sicily and Sardegna) with average temperatures between 14-16 °C. Instead, in the north, except for Liguria, the maximum values were below 10 °C on average.

Regarding the average minimum temperatures, only in few cities (regions) the values are below 0°C, with Bolzano the coldest one.

Figure1. Average maximum (top) and minimum (bottom) temperatures observed in December 2018 in the main italian cities. Each color is related to a single city.

Considering now the comparison of the observed temperatures with the climatological average (1971-2000), we can see how southern Italy (mainly the regions along the Adriatic coast) have observed negative anomalies in both the minimum and maximum values (Figure2). Instead, in N.W. Italy the most significant positive anomalies are observed especially in the maximum values (more than +2 °C in Lombardia), instead in N.E. Italy the anomaly is less (between +0.5/ +1 °C).

Figure2. Temperature anomaly of the maximum (left) and minimum(right) temperatures observed in Italy in December 2018 calculated with respect to the climatological average (1971-2000).

The positive anomalies in N.W. Italy are mainly due to the frequent episodes of fohn, caused by a strong flow of northerly winds towards the Alpine region, which have caused sunny and dry conditions in the southern part of the Alps and mild temperatures (the last episode occurred few days ago). Instead, in southern Italy more rainfall and overcast conditions (as well as the easterly winds) have contribute to the (little) negative anomalies.

Italy weather analysis Autumn 2018

In this article I am going to analyse the temperatures observed in Autumn 2018. I have extracted temperature data (minimum and maximum) for each main city in every region in Italy, and plotted the results. To notice that this is only a general overview, which doesn’t consider differences between mountainous regions and the plains or the local climate.

The anomaly is calculated with respect to the long term average 1971-2000 for each city.


It is clear how all the three months have observed temperatures anomalies well above the average (for both max and min temperatures) mostly everywhere. Only in southern Italy negative anomalies (-0.5/-1.0 °C) have been observed (especially in September); instead in the north (in particular in the N.W. Alps), the anomalies have reached +5 °C especially in September and November. This is strictly related with what found in the Autumn analysis in N.E. Italy.

In summary, the last Autumn has been very mild especially in the north, with continuos significant positive anomaly in both maximum and minimum temperatures due to the presence of the high-pressure positioned in the western Mediterranean (in September) and to the southerly winds (in October and November) which have brought lot of rain but very mild temperatures.

References

https://www.meteociel.fr/climatologie/villes.php?code=16120&mois=10&annee=2018

N.E. Italy: A very mild autumn

Related to the analysis I made for November 2018 in Treviso (N.E. Italy), one of the warmest recorded since 1973, here I am going to analyse the temperatures of the last 3 months, that is September, October and November (‘SON’ from now onwards) in order to evaluate if Autumn 2018 has been above or below the long term average (1981-2010) in Treviso.

In Figure1 the maximum and minimum temperatures average for SON in each year are shown. Like for November 2018 analysis, we can see how the average minimum temperatures tend to increase more in the last 20 years than the maximum values and Autumn 2018 shows the highest values.

Figure1. Maximum and Minimum average temperatures for SON since 1973. The dashed lines represent the 1981-2010 average for minimum (blue) and maximum (red) temperatures in Treviso.

In fact the long-term (1981-2010) Autumn average temperatures in Treviso are (9.63/18.76 °C) and the last Autumn has recorded (13.03/21.06 °C). The magnitude of the anomaly can be seen in Figure2, where the temperatures anomalies for each year (Autumn) are shown (for both maximum and minimum average values).


Figure2. Temperature anomaly for average Maximum (left) and minimum (right) temperatures in each Autumn since 1973. Anomalies higher than 0.5 °C (red), lower than -0.5 °C (blue) and between 0.5-0.5 °C (green).

It is clear how this Autumn has observed the highest average minimum and maximum temperatures (+3.55/ +2.33 °C respectively) since 1973, with October the warmest recorded for the maximum values (anomaly +2.46 °C) and second for the minimum (anomaly +3.78 °C); also September was very mild, the 4th warmest for the maximum values (anomaly +2.78 °C) and 3rd for the minimum (+3.09 °C). 

Considering the historical analysis, though this Autumn has been the warmest since 1973, however it is not the only one observing high temperatures (especially for the minimum values). In fact, from (Figure3) we can see how the years with minimum values above the average (anomaly higher than 0.5 °C) have consequently occurred since 2008, with no Autumn recording negative anomalies in the minimum average temperatures. Instead, in the 70s and 80s, most years observed lower values. Regarding the average maximum temperatures, there is more variability, with some ‘cold’ years in the 00s and ‘hot’ years in the 80s.

Figure3. Occurrence of hot (red) and cold (blue) years (autumn). Maximum temperatures (left), minimum temperatures (right).

It would be interesting to understand why the minimum temperatures observe a higher (positive) anomaly than the maximum values and for more consecutive years; it might be due to an increase in the overcast conditions during the night which might have led to a decrease in the radiative cooling at surface.

References

https://www.meteociel.fr/climatologie/villes.php?code=16098

November 2018 in N.E. Italy. Close to the record for high temperatures.

November (in Italy) has just finished with colder air coming from eastern Europe, which has caused a decrease in temperatures especially in the north.

However, these few days of temperatures below the long term averages are not enough to reduce the (significant) positive anomaly recorded in N.E. Italy during the last month. 

Related to the previous historical analysis made for Treviso, in this article I am going to analyse the temperatures observed during November 2018 and compared with the long term average (1981-2010).

To notice that the average (for both minimum and maximum temperatures) is computed on a monthly basis, thus the 10-day average is not considered (the first week of the month has a higher long term average temperature than the last one), which would have led to a more robust analysis to determine the significance of the daily temperature anomaly .

This analysis is focused on comparing November 2018 with the previous ones, considering the overall monthly average temperatures (thus between maximum and minimum values), and on computing the daily temperature anomaly in the past month in both minimum and maximum values, being conscius that its ‘significance’ cannot be quantified in a precise way because of the above mentioned limitation.

Regarding the daily analysis, in Figure1 the daily temperature anomalies (for both maximum and minimum values) are shown, considering a long term average of (4.6/12.7 °C).

Figure1. Max (top) and min (bottom) daily temperature anomaly referred to the long term maximum and minimum averages in Treviso. Positive anomaly (red), negative anomaly (blue).

It is clear how only in few days temperatures below the average occurred and the positive anomaly is observed especially in the minimum values. In fact, though we can’t exactly quantify the significance of this anomaly, the overall analysis shows how the positive difference from the monthly mean is not counterbalanced by negative anomalies. For the minimum temperatures, 13 days have recorded values 5 °C above the average, instead the same negative anomaly was never observed.

Regarding the maximum temperatures, the magnitude of the positive anomaly is lower. This might be due to the overcast conditions observed in the first week of the month, when the southerly winds caused prolonged rainfall events limiting the solar radiation and thus, an increase in the maximum temperatures.

However, November 2018 (in Treviso) has been the second warmest since 1973 (Figure2). 

Figure2. Comparison of the deviation in the average November temperatures from the long term average (1981-2010). Deviation equal or above 0.5 °C (red), between -0.5/+0.5 °C (green), below -0.5 °C (blue).

The plot shows the temperature deviation for each November and it is clear how November 2018 has the second highest anomaly (+2.79 °C). The warmest November occurred in 2014 (+3.84 °C) and the third one in 2002 (+2.74 °C). Interesting, as mentioned in a first analysis , how since the 00s there are no months observing values below the average (deviation bigger than -0.5 °C), with most years observing a significant (positive) anomaly.

November 2018 has shown as average minimum and maximum values : +8.5/ 14.4 °C, thus, respectively, (+3.9/+1.69 °C) above the long term average. This confirms what shown previously with the daily analysis, where the most significant anomalies are observed in the minimum temperatures.

We will see how December will be, though for the next few days no cold spells are expected and temperatures will increase (again) towards values above the average, even if without reaching the positive anomalies observed in November.

References