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

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edof93

I am Edoardo and I am passionate about weather analysis and forecasing. I would like to share my knowledge and to learn more with others (both International and Italian community).

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