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).

Italy: Dry and cold in the north, snow in the south

Since Wednesday cold air from E. Europe has caused a decrease in temperatures along the peninsula, with values below the average (especially in central-southern Italy). The cold air, moving above the Adriatic sea, is causing snow on the eastern side of Italy, with more than 1 metre of snow in some areas on the Appennines (e.g. Capracotta in Molise). Some snow has reached also the coast (especially between Abruzzo and Puglia), with few centimetres on the beaches. Snow has also fallen in Sicily at low levels.

Meanwhile, in the north, bright conditions are occurring, with strong winds especially on the Alps, which have caused some wildfires between Veneto and Lombardia due to the very dry conditions (also some were caused by human activities).

Today has been the coldest of the year so far (and since the start of the winter in the south). In fact, both minimum and maximum temperatures are below the average mostly everywhere (Figure1). Negative values have been observed in the mainland along the peninsula, with peaks of -5/-8 °C on the Po Valley and Tuscany, and below -10 °C on the Alps. The maximum temperatures have been below 10 °C mostly everywhere, except in Liguria and Sardinia.



Figure1. Maximum (top) and minimum (bottom) temperatures observed today in Italy. (Source: Meteociel).

The interesting thing has been, as said previously, the snow along the coast of the Adriatic sea. This event is quite unusual (though it can happen every few years) and it is due to the Adriatic sea effect: very cold air (from the Balkans) moves above the warmer sea (picking up moisture), and pushes against the Appennines condensing and leading to precipitation. If the column of air is cold enough (like today), snow can fall also along the coast.

For this reason the snow observed today was significant, because the continuous flow of air from N.E. has led to precipitation on the same areas.

The situation is clearly visible from the satellite image (Figure2).

Figure2. Satellite imagery of today (12 UTC). I have coloured in blue the area along the Adriatic coast interested by snow (source: Sat24).

The cold air should move eastward tomorrow and by Sunday there will be an increase in temperatures especially in the south. Next week cold air from Central Europe should reach the peninsula, but it is still too early to describe the possible effects. In the meantime, we can enjoy this unusual weather in the south.

First week of 2019 in Europe: between cold and mild conditions

The first week of the year is going to see two different weather patterns over the continent. On W. Europe, a strong high-pressure system will be positioned between the UK and N. Atlantic, bringing mild and settled weather in Spain, Portugal, Ireland (and western part of the UK).

Instead, on the eastern side of the anticyclone, a deep low pressure system, positioned between Sweden and Finland, will lead very cold air (polar continental with values between -12/-14 °C at 850 hPa (1500 m a.s.l)) to move southward during the week (Figure1) towards central-eastern Europe. In addition, the cold air will cause the formation of a low-pressure system in the Mediterranean Sea (between S. Italy and Greece) which will lead to snow at low levels and (very likely, due to the cold temperatures) along the coast of the Adriatic Sea.

Figure1. Synoptic chart valid for 00 UTC on Thursday night. I have coloured in orange the mild air moving towards W. Europe and in blue the cold air (polar continental, PC) coming from Scandinavia. Notice the 528 dam line reaching S. Italy and Greece (which means snow at sea level is possible). (source: Met Office).

The cold wave should reach the maximum intensity between Thursday and Friday, instead Saturday and Sunday milder air from the Atlantic should move eastward, pushing the cold air towards E. Europe and Russia.

Thus, during the week, the continent will be ‘divided’ in two parts, with temperatures well below 0°C (also during the day) in Scandinavia, Balkans and Central Europe, with snow expected especially between Poland/E. Germany and Czech Republic, and between Serbia and central/northern Greece and central-S. Italy.

Instead, warm temperatures on the west (possible maximum values between 8-11 °C in Ireland and between 16-18 °C in S. Spain/Portugal), with settled conditions in both Spain, France, Ireland and the UK (except for some low clouds close to the coastal areas and valleys).

UK WEATHER FORECAST 20/11/2018

Today has been cold mostly everywhere, with maximum temperatures below 10°C and overcast conditions with some showers and snow at the medium height.

On Tuesday, the easterly winds will cause still cold conditions and there will be some showers, especially in England, with snow possible at low levels (notice the 528 dam in Figure1 on the south of England).

Figure1. Synoptic chart for Tuesday afternoon (Met Office).

During the night some showers are expected on eastern England and Scotland (snow on the hills), moving westwards during the day (showers possible also in Wales, Northern Ireland and southern England). However, the most important precipitation should be observed in England (North and east). Depending on the intensity of the precipitations, some snow might be possible at low-levels in southern England and Wales between the afternoon and evening. However, it will be wet snow (due to positive temperatures) and it will be difficult to see snow accumulation in the lower areas, instead few centimeters can be expected on the hills.

The temperatures will decrease, especially in southern England, with little difference between minimum and maximum values. In the morning (2-7°C) mostly everywhere, with the lowest values observed in southern England, Wales and highlands. In the afternoon, values between (4-8°C) with the lowest temperatures still observed in southern Egland and Wales (where snow at low levels is possible). Still, due to the positive temperatures (and precipitation not too intense), it’s likely to see only snowflakes at low levels.

Finally, the winds will be easterly over the UK, moderate on the east of England and on the Irish Channel (25-35 mph).

UK WEATHER FORECAST 19/11/2018

Sunday has been bright and chilly in the UK, with easterly winds especially in England. On Monday these will cause a further decrease in temperatures everywhere, due to the continental air mass coming from the east (Figure1). Moreover, this will cause and increase in cloud cover and some showers across the UK, with some snow expected on the hills.

Figure1. Synoptic condition for Monday afternoon (Met Office).

During the night and morning some light showers are possible on the east of England and Scotland, moving westward in the afternoon. Due to the cold temperatures, snow is expected on the hills in both Scotland, England and Wales above 500-700 m (depending on the duration and intensity of the precipitation).

The minimum temperatures will be between (3-8°C) mostly everywhere, with values close to 0°C in Wales, northern England and highlands. The maximum temperatures will decrease, with values between (4-10°C) everywhere (with highest values observed in N.W. Scotland and Cornwall).

Finally, the winds will be easterly, moderate on the English channel and east of England.

Italy: First cold spell of the season

Finally, the first cold spell of the season is reaching the Italian Peninsula.  As we can see in Figure1, easterly winds (Bora, Grecale) coming from the Balkans are blowing over the Adriatic sea, reducing the humidity and causing clear skies in the Po valley. However, these winds are causing the stau effect in Piemonte and Emilia Romagna, where overcast conditions occur. This is happening also along the peninsula, with more clouds on the east coast and bright conditions on the west.

Figure1. Satellite image of this late morning (Sat24).

The cold spell is causing (and will cause) a decrease in both minimum and maximum temperatures, with snow showers especially on the Appennines (low-medium height) and bright (but chilly) conditions elsewhere. The temperatures will plummet especially in the North, after weeks of mild conditions, with minimum values probably observed between next Monday and Tuesday. In Figure2 is shown the comparison between the actual temperatures and the situation observed 24 hours ago (Friday).

It is clear how the main variation is observed in the Alps, Adriatic coast and Sardinia (decrease in 4-6 °C in 24 hours).

Figure2. Comparison temperatures recorded at 12 UTC on Saturday and Friday (Meteociel).