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

UK: sunny day after the snow

Between Thursday and Friday snow has fallen in many areas, especially in England, with more than 10 cm of snow at the ground in some areas.

This was due to the cold air coming from the north Atlantic and later from the Arctic which has caused a decrease in temperatures during the previous days. Indeed, on Thursday morning (Figure1) low temperatures (the lowest of the winter so far) were observed in the country, with values between -5/-8 °C in many areas both in England and Scotland; the lowest temperatures were observed in the Highlands (-10/-14 °C). Only in Cornwall temperatures were above 0 °C, due to the influence of milder air from mid-Atlantic.

Figure1. Minimum temperatures observed in the UK on the last day of January 2019. (source: Meteociel)

The negative temperatures in the morning have allowed snow to set on the ground, especially in the mainland. Snow has fallen since mid afternoon on Thursday until yesterday evening, though with an increase in temperatures yesterday afternoon which has caused mainly rainfall/sleet at low-levels.

Today, due to the brighter conditions, we can appreciate the satellite imagery (Figure2) showing the snow still at the ground in many areas, from Scotland to S England.

Figure2. Satellite imagery (UK) of today. I have used blue arrows to point out the snow on the ground in Scotland, N Ireland, Wales and England. (Source: Sat24).

The satellite image shows also the cold arctic air on the N Sea (causing showers) and moving southward towards Central Europe. On the west instead, south of Ireland, milder air from mid-Atlantic is moving towards the UK. This will cause an increase in temperatures, especially from Monday, with positive values (both minimum and maximum) mostly everywhere, and causing frequent showers between Monday morning and afternoon, and again between Tuesday afternoon and Wednesday.

Thus, if the previous week has shown wintry conditions, with snow in many areas, the next one will see milder temperatures and frequent (rain) showers, due to the change in the type of the air mass (from polar/arctic to tropical maritime).

UK: snow updates

Today the first snow (for many) is falling and in some areas few centimetres are setting on the ground.

Last night a cold front has passed over the UK, bringing showers especially in England. Following the cold front, colder air (polar maritime) has reached the country this morning, causing a decrease in temperatures and brighter conditions. However, due to the unstable nature of the air mass, frequent showers have occurred on W England and Wales from late morning, moving eastward during the afternoon (Figure1).

Some showers, though less intense and organized, have occurred also in N Ireland and W Scotland.

Satellite imagery and synoptic chart UK 22/01/2019
Figure1. Satellite imagery of this mid-afternoon (left) and synoptic chart valid for this afternoon (right). I have added the polar maritime air (blue arrow) and notice the showers in central England due to the trough. Ahead of it, and behind the cold front, bright skies. Finally, along the cold front notice the long narrow band of clouds, which has caused rainfall last night in England. (source: Sat24, Met Office).

The decrease in temperature associated with precipitation has caused snow at low levels or ground levels in many areas across central England and Wales, especially between Bristol and London. Some snow is falling also in N Ireland since mid-afternoon.
Instead, along the coast of England and Wales rainfall is occurring due to milder temperatures (+4/+6 °C).

However, not everywhere snow is setting on the ground. This is due to the slightly positive temperatures (between +1/+3 °C in central England and London area) and to the freezing level set between 400-800 m a.s.l. These conditions represent a ‘limit’ to observe snow at the ground. Thus, some areas have seen only snowflakes, especially if the precipitation is not intense, others are instead experiencing few centimetres of snow (e.g. between Oxford and London).

In addition, the snow we are experiencing is ‘wet’, that is, the temperature in the lower levels of the air column is slightly positive, thus snowflakes tend to melt slightly when falling (in this case around 400-800 m a.s.l where positive temperatures are observed) increasing their liquid content and sticking together forming bigger snowflakes (as seen today in some areas).

Tonight showers are expected on the east of England and English channel, with some snow possible at low levels. Some showers might occur also between N Ireland, N Wales and W Scotland, though with little precipitation. Brighter conditions elsewhere.

The brighter skies will lead to a decrease in temperatures during the night, with frost in many areas (especially where snow is on the ground). Tomorrow morning temperatures will be below 0 °C mostly everywhere in the UK with values between 0/-2 °C (possible -3/-6 °C in the highlands and central/N England); milder along the coast and on W England, with values between (+2/+6 °C).

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.

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

UK WEATHER FORECAST 25/11/2018

A low pressure system positioned southwest of the UK is causing overcast conditions with showers especially in England and Wales (Figure1), with relatively cold air (especially in Scotland) coming from the Northern Sea and milder air coming from mid-Atlantic towards France and Southern Europe (see Italy weather condition).

Figure1. Satellite image of this morning (Sat24).

The weather in the afternoon will see frequent showers especially in S. England and S. Wales and overcast conditions elsewhere
(few showers might be possible also in E. Scotland), though with some sunny moments in N.W. England and N.W.Scotland. On Sunday instead, a new low pressure system formed on the Bay of Biscay will move on central France (Figure2) but it won’t cause a worsening in the weather conditions, with only few showers expected in S. England and drier/sunnier conditions in Wales and Central England. Finally, some showers are expected in N.E England and Scotland due to an occluded front positioned between N.E England and the Northern Sea.

Figure2. Synoptic chart for Sunday midday (Met Office).

Due to the colder air, some snow is expected in Scotland and N. England above (300-500 m). 

The minimum temperatures on Sunday will be between (2-8°C) in England, Wales and N. Ireland (possible frost in N.Wales and central England in case of bright skies). In Scotland values below 0°C expected in the highlands (-1,-2 °C) and between (2-7°C) on the coast. The maximum temperatures will be between (5-10°C) in England (with the highest values observed in the south-west), between (4-8°C) in Wales and N. Ireland and (2-7°C) in Scotland.

Finally, the winds will be mostly easterly and light (especially in England).