Extreme heat has already spread to Portugal, Spain and France, where highs have reached triple digits, and the worst is yet to come. Heat Index values, which take humidity into account, could exceed 115 degrees (46 degrees Celsius).
The yellow warning includes London, which is preparing for highs above 90 degrees (32 degrees Celsius) through Monday. While that may not sound hot by US standards, Craig Snell, a weather forecaster at the Met Office, said that’s about 18 degrees (10 degrees Celsius) warmer than the average high temperature in London in mid-July.
“We have a large pool of warm air over Spain and Portugal at the moment. As we head into Sunday a door will open and it will shoot its way into the UK giving an already warm UK a boost,” Snell said.
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The highest recorded temperature for Britain is 101.7 degrees (38.7 degrees Celsius) recorded in Cambridge in 2019. Snell said there was a 30 percent chance that record could be broken.
This is the second instance of excessive heat development in Western Europe in recent weeks as human-caused climate change leads to higher temperatures.
Portugal, Spain and France
Portugal, Spain and France are facing a prolonged bout of unusually high temperatures that began earlier this week.
In France, the heat will last until Tuesday. Thirty-one departments across the country are affected by some form of heat warning, and the government is reactivating a telephone hotline for residents with questions or concerns about the heat.
“The thermometer is rising this afternoon,” wrote MeteoFrance, the country’s national weather service equivalent, in an online forecast discussion on Tuesday. “It shows 23 to 28 degrees [73 to 82 Fahrenheit] on the Channel coast, but everywhere else the highs are generally between 32 and 36 degrees [89.6 to 96.8 Fahrenheit]with locally up to 37/38 degrees [99 to 100 Fahrenheit] in the southwest and in the middle of the Rhone Valley. The heat wave will last several days in the south of the country.”
In the Rhone Valley, temperatures could reach 104 degrees (40 degrees Celsius) in the next few days. In Paris, highs could reach well into the 90s by early next week, while the average high is closer to 77 (25 degrees Celsius). Weather.com is forecasting a high of 100 degrees (38 degrees Celsius) on Tuesday.
The island of Yeu, off the west coast of France, on Monday set a record for the hottest temperature ever recorded after rising to 95.4 degrees (35.2 degrees Celsius).
Shared all-time heat record for the small French island of Île d’Yeu at 35.2°C. This matches the record from 1952.
The heat wave is just beginning. 43-44°C in Spain & Portugal meanwhile significantly cooler in Central Europe (for now). pic.twitter.com/izAu9GO20i
— Scott Duncan (@ScottDuncanWX) July 11, 2022
Sixteen out of 18 districts in Portugal are on prime red heat alert; The two remaining are under a yellow or orange alert. Santarém, the capital in the district of the same name, was expected to reach 113 degrees (45 degrees Celsius) on Wednesday. The hottest temperature ever recorded in the country was 117.3 degrees Fahrenheit in Amareleja on August 1, 2003.
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In Spain, an “extreme heat risk” warranted a red alert for Campiña Sevillana and Vegas de Guadiana on Wednesday, where high temperatures of 44 degrees Celsius (111 Fahrenheit) were forecast. Spain is divided into 50 provinces; the rest are mostly under orange “major” heat alerts and less amber alerts.
In Madrid, the high is expected to hover near record highs or around 105 degrees (41 degrees Celsius) through the weekend.
It will be late this weekend or early next week before the heat reaches the UK
“From Sunday, but more likely from Monday, maximum temperatures could be above 35C [95 Fahrenheit], most likely central and south-east England. Elsewhere, maxima generally range from the high 20s to the low 30s Celsius [80 to 90 Fahrenheit]’ said the Met Office’s deputy chief meteorologist, Dan Harris, in a press release issued by the Met Office.
Weather.com calls for London to hit 90 on Monday and 95 on Tuesday.
Some places, including central London, will not see overnight lows below 70 degrees (21 degrees Celsius). On a day in the 90s, that means homes are struggling to drop below 75 or 80 degrees (24 or 27 degrees Celsius), especially as very few UK homes have air conditioning.
“Population-wide adverse health effects are likely to occur, not limited to those most vulnerable to extreme heat, which can result in potentially serious illness or death,” the Met Office wrote in its alert.
Some computer models have simulated temperatures of up to 104 degrees (40 degrees Celsius) in the UK, which would break the all-time record, but the Met Office notes the potential has waned somewhat.
“Some models had generated maximum temperatures of over 40°C [104 degrees Fahrenheit] in parts of the UK this coming weekend and beyond,” Harris said in the Met Office press release. “Recent evidence suggests the odds have fallen.”
Still, he added, some locations could see highs in the upper 30s Celsius or 100 degrees Fahrenheit on either side.
The heat will ease over Britain and France in the middle of next week but will spread to central Europe, scorching Germany, Switzerland, Poland, Austria and the Czech Republic on Wednesday and Thursday.
What is causing the heat?
Stimulating the heat is something called “cutoff low,” or a low-pressure system that is pinched off by the jet stream. It’s like paddling a boat through a pond and watching a whirlpool throw off the oar and spin aimlessly. In this case, the low is a self-sustaining vortex of counter-clockwise winds wrapped around a lobe of high-altitude chill swirling across the open Northeast Atlantic a few hundred miles southwest of Portugal.
Since it is no longer embedded in a jet stream sink and has subsequently shuttled from west to east, there is nothing that can really propel it forward. As a result, the cutoff low will spend days sitting in place and turning, with southerly winds on the east side of the system pumping African heat north towards western Europe and the UK.
While the heat should end from south to north this weekend into early next week, it marks the latest in a series of European heat events exacerbated by human-induced climate change. Although human influence is not the cause of the hot weather, it is driving more frequent, more intense, and longer-lasting heat waves.
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It’s been just over three years since Europe was hit by an unprecedented heatwave that sent temperatures soaring. Paris hit an all-time high of 109 degrees (42.8 degrees Celsius). Last month, a heat wave broke hundreds of records across Europe.
Snell said the Met Office tracks how many years Britain has reached 35 degrees Celsius (95 Fahrenheit) in a single day. This has happened nine times since the 1970s – four of them in the last decade. “It shows how the frequency of hot weather in the UK is increasing,” he said. “The frequency of these hot spells across western Europe will increase as climate change progresses.”
Karla Adam reported from London.
https://www.washingtonpost.com/climate-environment/2022/07/13/heat-europe-amber-temperature/ Yellow Warning: Extreme heat forecast for UK, Western Europe