After the storm Agnes blasted over Ireland and the UK this week, much weather is forecast as we head into early October. A strong heat dome will re-develop into Western Europe, with a new heatwave for countries underneath. Temperatures will be back into the upper 30s over Iberia and mid-30s over France. Up to mid-20s over the southern UK on Monday.
The heatwave will first develop into southwestern Europe today, then gradually spread into western and central Europe as the heat dome expands across a large part of the continent over the weekend.
The next several days will bring more significantly anomalous temperatures for some parts of Europe, while we are already entering October on Sunday.
Temperatures will reach around 23-25 °C across southern England, mid to upper-20s over Benelux and Germany into central Europe, while southern France will push temperatures back close to 35 °C. Spain and Portugal will experience even higher temperatures.
Keep in mind that, meteorologically speaking, Europe is now heading into its second autumn season month, so these forecast temperatures are extremely high for this period.
Below is a good overview of how strong the upcoming heatwave will develop in Western Europe; we present this on the Meteogram chart for London, UK. Based on two main global weather models, ECMWF and GFS. A Meteogram chart expands across 14 days, representing temperature at the 850 mbar level (approximately 1250 meters above sea level) and precipitation.
The long-term average temperature for the first half of October is around 5-6 °C for London at this level. The temperature will be significantly above normal from Saturday through Monday, Sept 30th through Oct 2nd. Particularly on Sunday and Monday, when temperatures will be around 14-15 °C at this level, around 10 degrees C higher than normal.
This is an extreme temperature anomaly for the UK and the rest of Western Europe in the first days of October. A general rule of thumb translates these temperatures to the ground with roughly 10-14 °C higher values, so expect that peak daytime could reach 22-25 °C in southeast England. Indeed, much higher further south in France.
The first days of October will likely bring temperatures back near the mid-20s for London and the rest of southern and southeastern England. This is all thanks to a new strong heatwave intensifying over western Europe. A new intense heatwave will likely develop late next week after a temporal refreshment with a frontal system on Tuesday.
So, with a strengthening ridge aloft, the heatwave will first spread over Iberia this Friday, then continue into France on Saturday through Monday, reaching the UK, Benelux, and the rest of western Europe by mid-next week.
Generally, when a long period of stable weather is established, a feature we know as the Heat Dome intensifies heat waves underneath. This specific weather pattern brings excessive heat and very high temperatures. Let’s talk about it first.
What is a Heat Dome, and Why it brings Extreme Temperatures?
Let’s review the primary background that caused the development of major heatwaves in Europe this year. When significant heatwave events occurred in the past, in Europe, the United States, and Canada, the Heat Dome is that feature that brings it. Usually, the heat dome is the main and the most dominant feature of summer weather patterns on both continents.
We will use a heat dome term when extremely high temperatures develop. Here is how it works and why it is important to understand.
The upper-level ridge pattern, or warm air mass in the higher altitudes, is the Upper High (or blocking High). It usually forms the heat dome. Such a weather pattern brings high and sometimes record-challenging temperatures for the region.
So, this specific term is used when a broad area of high-pressure parks over a large portion of the continent. Usually, it stays there for several consecutive days or even weeks if the event is particularly stable and extreme.
The heat dome works like a lid on a pot. The extensive dome of heat results in the trapping of a much warmer air mass at all levels underneath, with sinking layers toward the ground. Therefore, the air mass becomes dry and anomalously warm at the lowest elevations and extremely hot near the surface.
A heat wave, associated with a heat dome, creates stable weather and often arid air mass with minimal chances for precipitation or even clouds, as the sinking air parcels in the center of the heat dome result in rising temperatures. This is because the weather pattern develops a so-called Omega blocking High, which reminds us of a Greek alphabet letter.
The example below is this kind of Omega blocking pattern that’s about to develop this weekend over Europe. The omega-blocking pattern engulfs a large part of the continent, with a central heat dome and a low-pressure system on each side. In this historic case from early September 2023 below, one low is over the southern Mediterranean and the other over the Azores.
Typically, drier and warmer weather leads to a significantly enhanced wildfire threat due to developing drought or worsening the ongoing, pre-existing, arid conditions. Such examples were wildfires in Europe and the Pacific Northwest in North America in recent years, especially in Greece this summer season.
Heat dome is often also to blame for being responsible for deadly heatwaves worldwide, as scorching and excessive heat lasts for very long. Such heat dome events brought record temperatures in Italy in July and scorching hot, surpassing +45 °C in Spain and Turkey in August.
The daily average and maximum temperatures under the heat dome are typically significantly above average, too. When the dome of heat is particularly strong, it challenges or breaks existing historical records, as we have seen globally this year. This becomes particularly striking when this feature develops during early summer or autumn/fall.
Let’s dig into the new, potentially another significant autumn season heatwave coming up this weekend.
An Elongated Omega-Blocking Pattern Develops In Western Europe
Over the weekend into early next week, the general weather situation over Europe indicates an extensive blocking high with a heat dome establishing into western and southwestern Europe. This results in strongly anomalous heights, hinting that a more stable period, especially warm to hot weather, will follow.
This is a textbook Omega blocking pattern we see developing over the European continent on the chart below.
With a strengthening High, a south-southwesterly flow will establish a significant warm plume into Western Europe. Thus, achieving a much warmer air mass in the following days gradually spread north, expanding into western and central Europe over the weekend into early next week.
Starting this Friday over Spain and Portugal and extending into Monday, an extremely anomalous air mass will develop into France, Benelux, Germany, and the southern UK. The warmest and most anomalous air mass will persist for several days, at least until Monday next week, gradually spreading east into central Europe with time.
The heat dome and heatwave will peak in Western European countries through Sunday and Monday. The highest temperature anomalies are forecast over Iberia, France, Benelux, western Germany, and the southern UK.
This will result in temperatures significantly above normal for early October.
Heatwave Brings Extreme Heat Again Into Portugal And Spain From This Friday Through Sunday
With an expansion of the warm plume over southwestern Europe, starting today (Friday), temperatures will rapidly increase over Portugal and Spain. The heat dome strengthens from the south, developing a heatwave underneath.
Peak temperatures across the western and southern part of the Iberian peninsula will already reach mid-30s this Friday, becoming even warmer over the weekend.
Maximum temperatures are forecast to be in the 35 to 38 °C range on Saturday and Sunday, then gradually lower after Monday next week. Temperatures elsewhere over northern Portugal and eastern and northern Spain will be in the low 30s.
Very Hot Weather Returns Into France On Sunday Extends Into Monday With A Peak Around 35 °C Again
With a warm plume developing further north, the first region affected will be southern France. On Sunday, temperatures are forecast to return into the low 30s across southern and western France, with peaks up to around 32-33 °C.
Temperatures will get even higher on Monday as the heatwave peaks, with the maximum temperatures reaching up to nearly 35 °C in the lowlands of southwestern France. Dry, downslope winds from the Pyrenees will significantly help the air mass warm up during peak afternoon hours.
The rest of France should experience upper 20s to low 30s on Sunday and Monday. Further north and east into Benelux and Germany, temperatures will warm up into mid-20s as well. Temperatures will also climb into the upper 20s over Italy and could reach the 30 °C mark on Monday.
Nevertheless, these temperatures are very high for early October.
High Temperatures Expand Into The Southern UK Over The Weekend, With Peak Temperatures Towards Mid-20s On Sunday And Monday
The upper High will gradually expand north on Sunday and Monday, allowing temperatures to warm up significantly across the southern UK. On Sunday, peak afternoon temperatures are forecast to reach just shy below the mid-20s in the south, 16-18 °C in Ireland. A tad higher temperatures are forecast on Monday as the warm wave peaks; highs could locally hit 24-25 °C in southeast England.
As the heatwave center will be further southeast over France, temperatures are not forecast to become as warm over northern England and Scotland. They should remain in the mid-10s on both days.
Overall, temperatures on Monday are forecast to be significantly higher than normal across a large part of Europe. The 2m anomaly chart below indicates those will be the most anomalous over Iberia, France, Benelux, Germany, and most of central Europe.
About 10-12 degrees Celsius under the core of the heat dome, precisely over France on Monday.
Another Massive Heatwave Could Develop Later Next Week Over A Large Part Of Europe
In the chart below, we are reviewing the mid-range trends. The general weather model consensus agrees that another powerful heat dome could re-develop next week, with an extreme heatwave dominating most of Europe. This would bring temperatures at all levels very high for mid-October.
A large heat dome established over the European continent would trap the significantly anomalous temperatures for several days. The chart below shows that the blocking High will be parked and centered over western and central Europe.
Although this forecast is almost a week in advance, the general trends lean into this solution on both global weather models, ECMWF and GFS. So, from Thursday through Sunday (or even longer), extremely warm weather for October could return to the UK, France, Germany, and Italy.
With the position of the Omega blocking pattern as seen on the chart, very warm days would also follow over Denmark and southern Scandinavia, too.
Peaks could well exceed 25 °C in many areas, which is significantly warm for early October.
Below is a Meteogram for Frankfurt in western Germany, which reveals how rapid temperature increase is forecast once October starts. From the long-term average around 5 °C, it will push close to 16 °C, so more than 10 degrees above normal.
Thus, maximum daytime temperatures will be in the mid to upper 20 °C across much of Germany. After a short refreshment, the Meteogram indicates another heatwave will likely follow next week and extend into the next weekend.
This will also allow central Europe to push temperatures around 10 °C above normal, so higher altitudes over the Alps and the Alpine valleys would be very warm, including the nighttime temperatures to be significantly higher than normal due to thick warmth into the mid-levels.
If these conditions are verified, temperatures would be extremely high for mid-October and record-challenging for multiple countries. We will monitor the general pattern evolution as we head into the next week; stay tuned.
The Health Risks During A Heat Wave
During an extended period of very warm weather, generally surpassing +35 °C, it is physically challenging and presents an enhanced risk for health.
Hot weather, particularly in extended periods – heat waves – is uncomfortable but presents a significant health risk.
Who is most at risk?
Scorching hot weather is uncomfortable for most people. The following groups are particularly threatened by the very high temperatures we encounter during heat waves:
- elderly people aged over 75 years
- babies, young children
- people with chronic/long-term health conditions, such as diabetes, respiratory disease, circulatory disease
- People who are obese
- People taking certain medicines
- people who work outdoors, in hot/poorly ventilated areas, or engage in physical activity in hot weather
- socially isolated people
- people who are not acclimatized to hot weather, such as tourists from northern countries
Always stay cool, hydrated, and healthy in scorching hot weather
Staying hydrated is one of the most crucial things during extreme heat. Consider taking these precautions and measures to stay healthy in scorching weather:
- Drink plenty of water! – A human’s body cools through sweating; on a sweltering day, an adult may lose up to several liters of water. Keep drinking water, and avoid drinking alcohol, hot drinks, and drinks with high sugar content, as they can worsen dehydration. A regular intake of water is a good way of preventing dehydration.
- Keep your body cool; stay out of the sun if possible. Eat small meals, preferably fruit and salads. Wear light-colored and loose clothing made from natural materials like cotton. Take a cool shower or a cold bath if you feel hot. Also – keep your workspace and living space cool. If you do not have air conditioning, shut the curtains and blinds during the day. Stay in the coolest room, and avoid using the stove and oven as much as possible. If your home gets too hot, go to a cooler place – a library, shopping center, cinema, or swimming pool.
- Keep your food safe! – Keep food that needs refrigeration adequately stored! Food spoils rapidly at high temperatures, and you may risk food poisoning if the food is not stored correctly.
- If you need to go out in the sun – protect your skin and use proper sunscreen and clothing to avoid sunburns. Cover your head correctly.
- Know your body and have a plan – Ask your doctor if you have any health conditions that may increase the risk of heat-related illness. Call and consult with your doctor if you are feeling unwell. Call emergency help (know the number!) if you feel unwell!
Common heat-related illnesses with symptoms: What to do if it happens?
WHO considers these symptoms’ descriptions and treatments below as informative only – consult with your doctor for details and professional advice:
Dehydration
Dehydration occurs when the body loses too much water to maintain normal functions. Symptoms include dizziness, tiredness, irritability, thirst, dark yellow urine, loss of appetite, and fainting. Drink plenty of water or diluted fruit juice. Avoid coffee, alcohol, and sugary drinks. Move to a cooler space to cool off. If you feel unwell, call your doctor or emergency room.
Heat rash
Heat rash is an itchy rash caused by excessive sweating. Move to a cooler, dryer environment, and keep the affected areas dry. Hydrating creams may make the condition worse. Consult with your doctor.
Heat cramps
This happens during strenuous activity when the body sweats and loses water and salt. Heat cramps manifest as muscle pains or spasms. If this happens, stop all activity, move/lie down in a cool place, and raise your legs slightly. Drink water or diluted juice. Have a cool shower or bath, and apply ice packs. Refrain from returning to strenuous activity for several hours. If heat cramps do not subside, seek medical help.
Heat exhaustion
Heat exhaustion is the condition in response to losing excessive amounts of water and salt due to dehydration. Symptoms include heavy sweating, pale skin, fast and weak pulse, fast and shallow breathing, muscle weakness or cramps, tiredness and weakness, dizziness, headache, nausea or vomiting, and fainting.
If heat exhaustion occurs, the body needs to be cooled and rehydrated by moving to a chilled place, lying down, having a cool shower or bath, and placing cool packs under the armpits, groin, or back of the neck. Rehydration should be done by taking small amounts of cool fluids. Medical help is advised if symptoms do not abate within an hour.
Heat stroke
Heat stroke happens when the body temperature reaches 40.5 °C, a severe and life-threatening condition! Immediate first aid in lowering body temperature is critical, and an immediate call for an ambulance! Find more information on heatstroke here.
High relative humidity during a heatwave can also significantly affect the body, as it also becomes physically challenging for those working outside. After high rainfall events, strong heating will help evaporate the soaked grounds, resulting in higher humidity than normal as well.
We use a Heat Index chart to represent the real feel of scorching hot temperatures and high humidity. These graphics indicate what is the real feel of temperatures based on what the temperature and humidity are.
As we see, when air mass has a temperature around +35 °C, humidity below 60 percent is much less challenging than once the humidity is very high, e.g., above 80 %. Thus, the real feel temperature would be near 50 degrees Celsius.
With even higher temperatures close to the 40s, such sweltering hot air becomes hard to handle with even lower humidity, 50 to 60 percent.
Stay safe!
Wxcharts, Pivotalweather, and Meteociel, provided images used in this article.
See also:
A Violent Atlantic Storm Agnes blasted Ireland and the UK on Wednesday, September 27th