N Italy: difference of 20°C in 200km

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.

Figure 1. Maximum temperatures observed in the Alpine region on 03/02/2020. Source: Meteociel

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).

Figure 2. Sat Image of Alpine region on 03/02/2020. Notice the low clouds over NE Italy and clear skies over the NW areas. Source: Sat 24

Early Spring over Europe

Sat Imagery Europe 31/01/2020
Figure 1. Sat Imagery Europe 31/01/2020

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.

Temperature observed in Europe at 12UTC 31/01/2020
Figure 2. Temperature observed in Europe at 12UTC 31/01/2020

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).

W Europe: winter in stand-by

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.

This situation has not changed since last week.

maximum-temperatures-europe-20/02/2019
Figure1. Maximum temperatures observed today in Europe (source: Meteociel).

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.

SATELLITE-IMAGERY-EUROPE-20/02/2019
Figure2. Satellite imagery of today. I have added the main weather features (rain over N parts of the UK and Ireland, High pressure over central-southern Europe, low-pressure system between Finland and Russia). (source: Sat24).

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.

A very mild Valentine’s day

This week a strong high pressure system has set over central western Europe, causing sunny days and mild temperatures. Today, maximum values are far above the average mostly everywhere in Europe, with temperatures reaching 20 °C in the Iberian peninsula (Figure1).

maximum-temperatures-Europe-valentine-day
Figure1. Maximum temperatures observed in Europe today (source:Meteociel).

Temperatures between 10/15 °C are observed in all the Mediterranean region, France, the UK and Germany. Moving eastward values are lower but still above the average of February. Only in Russia and north Scandinavia temperatures are below 0 °C.

The weather today (Figure2) has seen bright skies over all W Europe and central Mediterranean region, with only some local fog at the lowest levels (mainly in the morning). At the edges of the high-pressure ridge, clouds and band of rain are observed in the north Atlantic and E Mediterranean, instead over N Russia and Finland snowfall is occurring.

satellite-imagery-valentines-day-europe
Figure2. Satellite imagery of today. I have added the main weather features (rain, snow, high-pressure). (source: Sat24).

This weather condition won’t change during the next weekend, with still dry and mild conditions in central/southern Europe. Colder air will reach tomorrow the E Mediterranean, though without ‘freezing’ temperatures. From Sunday, colder and moister air from the N Atlantic will try to push the anticyclone eastward, causing unsettled and ‘colder’ weather over the UK, France and Spain. We will see next week if there is going to be a change in the weather patterns, though it seems likely that the high pressure will be still steady for the next few days.

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.

SE England: Was it actually cold in December and January?

The last two weeks have seen frequent snow showers in many areas in the UK, with several centimetres of snow at the higher levels. These episodes have occurred after a long period of frequent rain and mild temperatures throughout the first month of the winter season.

I have analysed and plotted the temperature anomalies observed in December 2018 and January 2019 in London Heathrow. The anomalies are computed considering the long-term averages (1981-2010), which, for London are: December (+8.3/+2.7 °C) and January (+8.07/+2.3 °C).

This analysis is simply focused on having a general overview of the observed temperatures, and on a local area; thus, it can’t be used to determine a wider analysis for the whole country. I haven’t plotted the rainfall, but data can be found in the references.

In Figure1 we can see the daily maximum and minimum temperatures anomalies observed during the last two months.

London-december-january-daily-temperature-anomaly
Figure1. Daily temperature anomaly observed in London in December 2018 (top) and January 2019 (bottom). On the left the anomaly for daily maximum temperatures, on the right the anomaly for daily minimum temperatures. Positive anomaly (red), negative anomaly (blue).

Most of December has been mild, especially in the minimum temperatures, with positive anomalies close to +10°C during the first week (when frequent rainfall has occurred). During the second week, colder and drier air has caused a decrease in temperatures (especially in the maximum values) though only for few days. Indeed, the last two weeks of December have shown mostly mild temperatures (and frequent rain) with only two days with negative anomalies (one of them it’s Christmas). No snow has been observed throughout the month.

January, instead, has shown a decrease in the positive anomaly (especially in the maximum temperatures), with colder and drier air after new year’s eve. The second week has shown settled weather, and temperatures above the average (+3/+5 °C the anomaly in the minimum values). However, from the 15th colder air (both polar maritime and arctic depending on the episode) has reached the UK, causing a strong decrease in temperatures and the first snow of the season in many areas (also in London) between the 21-23 of January and again, after few days with warmer temperatures, on the 31st and 1st of February. The last few days of January have been the coldest of the season so far, with the lowest temperatures observed before the snowfall in the morning of the 31st.

Considering the monthly analysis, thus comparing the anomaly observed in the minimum and maximum average temperatures in December 2018 and January 2019 with the historical period 1981-2019 (Figure2), we can see that December has observed a significant positive anomaly especially in the minimum values (+3.1 °C), instead January has seen values very close to the average, with a slight negative anomaly in the maximum temperatures (-0.62 °C) and positive in the minimum (+0.28 °C).

december-january-max-min-temperature-anomaly-1981-2019
Figure2. Anomaly for mean maximum (left) and mean minimum (right) temperatures for December 1981-2018 (top) and January 1981-2019 (bottom). Positive anomalies (red), negative anomalies (blue).

Overall, December 2018 is one of the hottest since 1981 (3rd for the maximum temperatures and 2nd for the minimum); instead, January has been roughly on average (27th for the maximum and 21st for the minimum temperatures).

In conclusion, even if numerous news had claimed that ‘freezing’ conditions have occurred this winter (especially in January), the actual analysis has shown that it has been a ‘warm’ winter so far, with few cold episodes mainly occurred during the last two weeks.

We will see how February will end in order to sum up the overall winter analysis.

References

https://www.meteociel.fr/cartes_obs/climato2v4.php?code=3772&mois=12&annee=2018&print=1

https://www.metoffice.gov.uk/pub/data/weather/uk/climate/stationdata/heathrowdata.txt

Europe: first week of ‘spring’

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.

Europe max temperatures 4/02/2019
Figure1. Maximum temperatures observed today in Europe. (Source: Meteociel)

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.

satellite imagery Europe 4/02/2019
Figure2. Satellite imagery of this afternoon. I have highlighted the Tropical air (yellow) and the convection (red) in the Mediterranean region; the snow
(blue) at the ground in central Europe and Alpine region, and the low-pressure system (black) in the N Sea. (Source Sat24).

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.