The Severe Weather Set-up 

The oncoming outbreak threat is driven by a large trough, which transports warm moist air from the Gulf of Mexico upwards throughout Texas, New Mexico, Western Oklahoma and the rest of the midwest. As the trough moves towards the midwestern and eastern United States, it deepens and undergoes cyclogenesis. This creates a very favourable warm sector, which then creates an environment that can support strong, long-lived tornadoes and large hail. As the dry-line passes, it will be the initatior for the thunderstorms and severe weather event.  Theta-E charts from GFSv16 and supercell composites show a very dangerous situation coming up. In the area of Oklahoma, the clouddeck is likely clear enough to allow for more surface heating, which leads to a quicker destabilization. A more instable environment for tornadic and possibly cyclic supercells will be built up. Later in the afternoon, the cells are forecasted to spring up and organise quickly. Observed Soundings show a potentially dangerous situation for many areas. There is a hatched moderate risk for tornadoes in place for the Texas Panhandle. As supercells are starting to fire up. The risk of a dangerous outbreak increases. The first PDS cell could form within the next hours.

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Large parts of Europe are under a high risk of extreme snowfall, light to moderate frost is forecasted. In the Northwest of the Netherlands a windforce of Beaufort 8 is forecasted along with heavy snowfall. In Poland a Red Alert has been issued for many area’s. In Belgium a Code Orange will go in effect for freezing roads and subzero temperatures. In Germany violet codes have been issued for extreme snowfall, freezing rain and subzero temperatures. For the Netherlands a Code Red has been issued for the entire country. Snowdrift, snowstorm conditions and visibility below 500 meters are possible. The following set of figures shows the warnings issued in the Netherlands, Germany and Poland.

The weather warnings issued in the Netherlands (top), Germany (middle) and Poland (bottom)

Blizzard-like conditions in Germany and the Netherlands

As snowstorm Darcy forms it brings with it life threatening conditions of snowfall, frost, windchill and blizzard like conditions. Besides the factors of wind and snow the system also becomes a windstorm, increasing the danger to life even more. The wind- and snowstorm is expected to strengthen the coming night, bringing with it, snowfall up to 15 cm in large parts of the Netherlands and more than 20cm in large parts of Germany. A Code Red is now in effect for the Netherlands along with Violet Alerts for Germany. The snow is settling at a rapid pace and is forecasted to increase in amounts over the coming 24 hours. Winds picking up at a rapid pace and the storm is only forecasted to strengthen the coming night and then track away over the coming days. The temperatures will keep dropping substantually below zero and blizzard like conditions are happening in large parts of the Netherlands and Germany. Western Belgium is dealing with heavy snowfalls but not as much wind and storm as the rest of Europe is and the UK. The snow accumilates very fast, the windchill makes the temperature feel like it is 20 degrees Celcius below zero and combined with the wind and snow it is a life threatening situation. Stay indoors and seek warmth.

Satellite imagery from KNMI (below) on 22:30, the shape of a classic windstorm becoming clearly visible
Upper image is a simulated infrared run from AROME for storm Darcy

Worsening conditions in Germany and the Netherlands

As an heavy rain zone transforms over Europe conditions take a turn for the worst. In Germany and the Netherlands snowdrift has been reported and snowstorm like conditions. Visibility decreasing at a rapid pace and snowfall settling very fast and things turning for the worst. Temperatures are dropping below zero as the wind picks up. This will cause for blizzard like conditions later on in the coastal parts of the Netherlands. The combination of subzero temperatures, light to moderate snowfall and wind up to Beaufort 8 adds up to a life threatening situation for large parts of Europe. In most of the Neterlands the snow has started to fall at a dangerous pace, the windchill factor is increasing along with the temperatures dropping to 2 degrees Celcius under zero. Snowdune formation is likely over the coming hours and day along with strong windgusts along the westcoast of the Netherlands in the coastal area’s up to 8 Beaufort gusts. The blowig snow is caused by a strong easrerly wind with Force 6 on the Beaufort Scale. The temperatures will be cooling rapidly over the next days. In large parts of Germany a snowstorm is undergoing and the sight is decreasing rapidly. Snow is settling very fast and temperatures are dropping te below 3 degrees Celcius under zero.

Imagery: Philip
Imagery: AlexR

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Storm Filomena

Storm Filomena formed over the North-Atlantic ocean from the remnants of a big dynamical-low. These spun up again and underwent  a new cyclogenesis. Forming a new storm-depression. This got the name Filomena by AEMET. As storm Filomena approached Spain, it brought a north-east circulation with it. This caused very cold temperatures to occur in the country. This NE circulation brings polar air straight from Russia to Spain, which then causes an extreme drop in temperatures. Storm Filomena is the sixth named storm on the 2020-2021 windstorm season names list from AEMET, MeteoFrance and the Meteorological Service of Portugal. Filomena has brought freezing temperatures with subzero days and heavy snowfall over Spain ever since she came ashore. The storm is expected to weaken and dissipate in the coming days, but the cold spell stays.

People skiing in the streets of Madrid due to the heavy snowfalls     Author: unknown

The Snowfall

As storm Filomena passes over Spain it brings heavy rainshowers with it. These rainshowers then turn into snow due to the extremely cold air temperatures. In many parts of Spain cars can be seen delved under in snow. In Madrid record amounts of snow fell in 24 hours time. With 35-50cm (even in the regions of Madrid). This is the heaviest snowfall in Spain since March 1971. For large parts of Spain there are still Yellow and Orange warnings in force due to the severe snowfall and a severe coldwave. This amount of snowfall in Spain is rare and with it, it brought new cold records for many area’s in Spain.  As the cold spell continues, additional snowfall is possible in the area’s. Salt trucks and shovel trucks are having a hard time keeping up with the amounts of snow falling, making it very hard to keep the roads clear of snow. Many cars are snowed in and people cannot leave their homes in some places. Many people went outside to ski during this rare phenomonen.

People trying to unbury the cars under the extreme layer of snow as many places in Spain are struck by severe cold and snowfall   Author: unknown
Snowtruck preparing to clean the roads once more in Spain due to the heavy snowfalls and Siberian like temperatures.  Author: Europa Press

Author: AlexR (17 years old Climate Physics Enthusiast)

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Cyclogenesis

When Odette formed, the depression was still quite small and weak. Weathermodels were suggesting a potential heavy-storm forming from it. On the 25th of December, As the occluded front started spiraling very tightly, the winds got accelerated. Over the next seven hours, she deepened incredibly fast. Creating a strong, but local windfield. This would then aim at the NW of Belgium and the entire province of Zeeland. Cyclogenesis is the process of the formation of an extratropical cyclone and occurs when a warm and a cold front meet. These can start to occlude and form a low-pressure system. A select few of those actually become windstorms.

(Figure 1) A small storm-depression which has formed in the North Sea and has been given the name “Odette” by KMI   Charts: @KNMI

Landfall of the storm

On the 26t-27th of September Odette made landfall in the Netherlands, with the full windfield on Zeeland and northwest Belgium. As Odette came ashore, gusts were reported of over 110 km/h. The winds blew on the coast with such a force, that the whole dune was blown on land and whole parts of beaches were slammed away. (See figure 3). KMI issued a code orange for the coast and West-Vlaanderen. With gales topping the 11 Beaufort, it made the storm earn the title of a very heavy storm. Whole parts of beaches were swept away by the sea. In Hoek van Holland (Netherlands), a wind gust of 114 km/h was reported. In Zeeland, the storm had sustained Beaufort 10 for two hours long. Making it a heavy storm for the Netherlands. The damage caused by Odette was massive because the incredibly strong winds at the low level forced them into a very small area. Due to the English Canal, the Venturi Effect took place. Because of the narrower space to move through, the air got crushed into itself and forced to flow faster. This caused stronger winds in the areas directly impacted. The total damage estimate is still unknown.

(Figure 2) Odette causing a huge swell of the Belgian coast. Photo: @Belga

The Damage

After Odette ravaged through northwestern Belgium and Zeeland, Netherlands, the true extent of the damage became clear. Whole parts of the beach swept away, small beach-houses destroyed. destroyed sailing yachts and small boats, sand blew off the beaches and onto roads of the cities and villages. Trams cannot move due to the sand and cars that are completely buried in the sand. The following set of photos depicts the damage Odette caused.

(Figure 3) Sand has blown all over the road and railway between Oostende and Westende (Belgium)   photo: @Belga
(Figure 4) Cars buried beside the tram line between Oostende and Westende (Belgium)                photo: @Belga

(Figure 5) Small beach houses destroyed by storm Odette  Photo: @Belga
(Figure 6) Dike of Oostende after storm Odette                     Photo: @Belga

Author: Alex R (17 years old Climate Physics Enthusiast, future UU Physics and Climate Physics student)

Date of publishing: 26th of December 2020

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In Northwestern Europe a white Christmas is likely to happen in the higher parts of the Ardennes (400m and above). The GFS weathermodel is suggesting a possible snowfall of 20-40cm on the highest peak in the Ardennes. Much less snow is forecasted to fall below these area’s because of the temperatures being too warm for snowfall. But this should change as Bella arrives, bringing much needed polar air with her and cooling down the lower 400m too. This should allow for snowfall in the lower area’s in the Ardennes too. In Germany the lower levels could be getting snow starting on Monday. The GFS only shows an increasing amount of snow for Germany. For France the snow could be of much lesser proportions until at least next week Wednesday. The snow forecasted for France is anywhere inbetween 0 and 2cm of snow. Storm Bella keeps bringing gusty winds and cold weather until the parent low she is part of, weakens but stays higher up.  Causing a West Based NAO as suggested by all four weathermodels in the long range. This West Based NAO blows all the very cold air with snow potential from Scandinavia away and up unto the North Atlantic Ocean. This West Based NAO is not the most favourable situation for a white winter in the short term. Although it is a good sign for later on in the year. In January this would have been the jackpot for snow. Denmark is forecasted to be right on the east side of the core from Bella, which allows very cold polar air to flow onto the country. This should favour snowfall in the area by next week. New Year’s eve should have the big shift into the winter weather for large parts of Northwestern Europe.

Southern Europe

In Southwestern Europe the snowfall potential is mostly for Portugal and the Pyrenees. Portugal will profit a lot from the West Based NAO and get the full polar air blown over. Loads of snowfall is possible in inland Portugal because of this. For next week, Bella should bring very cold air to Portugal, also allowing snowfall inland and the higher area’s. For Spain, snowfall is not very likely because of the lower 400m being too warm for snowfall. Sleet is a low possibility in many area’s of northwestern Spain. For Italy, a small low pressure area, which is forecasted to form from Bella, could cause problems for traffic in the form of ice on the road. For other area’s of Italy wind could be a slight disruption for daily life. The southern parts of Italy are going to receive a more southwesterly flow from Bella, bringing with it cooler winds, yet warmer temperatures because of subtropical air from the southwest being blown in. For Greece snow is possible in only the mountainous area’s higher up than 400m because of a very strong southwesterly flow Blowing subtropical air all over the country. Warming the lowest 400m up. Turkey will be getting the full hit of the Subtropical air, so snow should only be possible higher up than 700m. For Switserland, a lot of snowfall is possible in the whole country as The Alps cool down the air in the lower 400m massively because of their immense height. The Alps might even get the jackpot in terms of snowfall on the peaks by next week.
(Figure 4) Bella (Dark blue and purple, Low pressure) weakening and a strong subtropical airflow for large parts of Southern Europe.

Benelux

In the Benelux, Bella is forecasted to arrive this weekend. Bringing strong gusts and colder temperatures. The storm is forecasted to have an average sustained wind of 7 to 9 Beaufort. The gusts Bella is forecasted arrive with in the Benelux, are anywhere between 75 km/h and 90 km/h. Over sea or right at the coast, the gusts are possible to reach >100 km/h up north in Ameland and southwest in Hoek van Holland. As Bella passes over, she brings cold polar air with her. Significantly cooling the area. After this she will weaken and cause slight instability in the area. This should allow for some extensive snowfall to occur in the Ardennes. For western Belgium the chance on any form of snowfall will be from no to small for the coming week. For central Belgium the snowfall chance is forecasted to be high for a small strip of the country. Brussels in it. For southern Belgium, the snowchances range from small to high. With especially the Southeast having a high chance of snowfall.  Luxembourg will have a high snow chance starting today. This will only get higher the more time passes as of up to 20cm of snow could be falling in Luxembourg by next week if the ECM run verifies.

(Figure 5) Snowchance map for the Benelux by the GFS model. (Green: No chance | Light Blue: Very small chance | Darker blue’s: Small and moderate chance | Purple: Big Chance | Pink: Very high Chance). Source: Noodweer.be

Summarised

Overall, a nice week with winter weather in many area’s of Europe. Is it either sleet or actually centimeters of snow. It does not matter a lot. The winter still has until mid March. Due to a Greenland Blockade forming, a depression above Iceland is forced down. This depression has been named Bella by Met Office, the British Meteorological Institute. A white Christmas is a nice Christmas gift for Scandinavia. Making the countries white for the most part. In Southern Europe the weather is expected to be softer than the rest and should bring less winter weather. Portugal and Switserland are the lucky ones in this area. With Portugal getting blasted with polar air from Greenland. While a high pressure blockade forms there.

Great week ahead for many in Scandinavia and Northwestern Europe.

Best Wishes and a very Merry Christmas from Alex

Author: Alex R. (17 years old Climate Physics enthusiast, future UU physics student. Specialised in Severe Weather and the dynamics behind them, especially tornadoes.)

Date of publishing: 24th of December 2020

The post Europe Winter Weather Forecast (part 2) (24 December to 4 January) appeared first on Force Thirteen.

The Cold Front

As a cold front is passing over Germany, The Benelux and parts of France, rain is brought with it in the boundary zone between the warmer air and the cold northerly air. In some places there already has fallen more than 25mm of rain. Once the front passes over the wind can suddenly change in direction. Once the cold air starts to really gain terrain the temperate can drop multiple degrees celcius an hour. After the midnight the wind can pick up quite quickly in the Benelux, UK and France. Bringing gusts from 60-90 km/h. Once the winds become northerly, colder air is blown in very fast. Storm Bella is forecasted to arrive this weekend. (Figure 1) The cold front tracking over the Benelux and northwestern Europe. Bringing a change in airflow from southwest to north. Bringing cooler air with it. The white arrows show the airflows from southwest and north. Blue line is the cold front.

Greenland Blockade and Storm Bella

Storm Bella, which is currently located over Iceland should bring polar air down to big parts of Europe. The Northwest of Europe, Northeast and Alps are likely to get some form of sleet. Due to a Greenland blockade, which is forecasted to form as suggested by the weathermodels for the past two weeks. This causes a low pressure area to drop down from the Polar Vortex. This low has been named Bella by the Met Office. The storm is forecasted to impact the UK and Beneleux with storm force. This low-pressure system causes the polar air to be drawn from Scandinavia. This should allow for some serious cooling in the lower 400m. The ECM weathermodel forecasts Bella to reach 975 hPa at her core. GFS goes deeper and shows 970 hPa is possible in the core of this system. The ridge, which is currently located over the North Atlantic is expanding and attempting to reach Greenland and form a very strong blockade. This blockade causes some serious warming in the Stratospheric Polar Vortex (SPV), which in turn can trigger a Sudden Stratospheric Warming. This ssw suggests a stronger winter is possible starting in January. Once this blockade forms over Greenland, it will bring a northeasterly airflow. Bringing polar air from the North Pole with it. As Bella drops down towards Europe, the models show warm air from the southwest going up towards the northeast over Russia. Warming up the “Russian Bear” we all want so badly in Europe. If this blockade settles well, we could be looking at long term winter weather with possibly a lot of snow in the lower area’s.
(Figure 2) ECM 96h (12z) run showing Bella (Purple and pink, which is low pressure) and the Greenland Blockade forming (Red and Orange, High pressure)

Scandinavia

In Scandinavia, the storm Bella, which is currently situated over Iceland, is forecasted to bring a lot of snowfall and a white Christmas for many. The airflow here is moist and polar, changing rainshowers into snowshowers. Some slight thunderstorm activity is possible as a few cold- and occludedfronts pass over. Only bringing more precipitation in the form of hail and snow. The winds will come from the north/northeast, bringing more snow with it A white Christmas is to be expected in large parts of Scandinavia. This area of Europe is the one with the jackpot this December, getting loads of snow in a short period of time. Perfect if you like the winter and snow. If you have children, it would be a beautiful time for them to see a white Christmas for Scandinavia. It is usual for the time of year to have slightly warmer than average temperatures in both Scandinavia and Europe. For this year it has been the warmest November on record in Europe.

Northeastern Europe

For Northeastern Europe a slight polar airflow comes in from Bella from the southwest, but nothing much. The ECM weathermodel forecasts a slight subtropical airflow into parts of North- and South- eastern Europe. Bringing softer conditions than usual. 1-6cm of snow is possible somewhere in the next week. As an occluded front passes over with convective activity snowfall is possible in some area’s. Northeastern Europe could deal with strong winds and colder weather the coming days before having a rise in temperature because of Southwesterlies. But once Bella comes in it should cool again in the Northeastern parts of Europe. Whilst the East keeps getting more subtropical air from the southwest. Around Russia’s border more than 6cm is possible, if the temperatures are cold enough with enough precipitation. This is because of the subtropical air collides with the polar air. This massive difference in temperature could create instability in the area with a lot of rain in the forecast. A white Christmas is not forecasted for this area. By next week it could even be warmer than this week, due to the airflow changing from cold and west, to warm and southwest. Small depressions forming from the parent low could bring snow from time to time.

(Figure 3) The ECM 72h (12z) run showing Bella (Pink, Purple and Black, Low pressure) and the North Atlantic Ridge pushing up to Greenland (Red and Orange and Green, High Pressure)

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