Bob Henson ·

Above: Temperatures at 850 millibars, about a mile above ground level, are predicted to be more than 12°C (21.6°F) above average over parts of central Europe at 12Z (8 am EDT) next Thursday, June 27, 2019. Such readings would correspond to surface temperatures of 35°C (95°F) or greater. This forecast is from the 12Z Thursday, June 20, run of the GFS model. Temperatures at right are in degrees C. Image credit: tropicaltidbits.com.

A vicious heat wave next week could produce all-time highs at multiple European cities. This heat wave—which will be unusually strong for so early in the summer—will gin up some of the hottest June temperatures ever recorded in western and northern Europe.

The European and GFS forecast models are in strong agreement on the development of a blocking ridge of high pressure from near Greenland into western Europe. The setup is related to a negative phase of the North Atlantic Oscillation (NAO) that has prevailed since late April and that could intensify next week. Often a blocking high over Greenland leads to cooler, cloudier conditions in western Europe, but in this case an upper-level trough is positioned over the eastern Atlantic, west of France. The Greenland high will arc around and to the north of the trough and into western Europe. This topsy-turvy pattern, known as a rex block, can last for a number of days.

Figure 1. The 12Z Thursday run of the GFS model shows a highly contorted jet-stream pattern at the 250-mb level (about 34,000 feet) by 00Z Tuesday, June 25, 2019, with a cut-off upper low just west of the continent and a strong jet stream at higher latitudes well to the north. The setup will allow hot air to sweep across much of Europe. Wind speeds at right are in knots; multiply by 1.15 for miles per hour. Image credit: tropicaltidbits.com.

“In a negative NAO, it depends where the trough over the Atlantic sits,” explains Leon Brown, head of global meteorological operations for IBM Watson Media and Weather. “A little further west and you get a plume of heat from Africa to western Europe (as next week), or a little more to the east and the heat keeps across central and eastern Europe with northwest Europe much cooler. There can be a sharp divide, especially for western Iberia, France and the U.K.”

Brown adds: “Next week is interesting since the upper trough may become a slow moving cut-off low for a few days. If so we may see several plumes or heat episodes moving from Iberia to France and reaching the U.K. to southern Scandinavia. These plumes normally don't last that long though over the west and destabilise with some severe storms and local flash floods as the upper trough moves eastwards. Next week may last a bit longer and perhaps until the weekend, by which time the heat would have time to build and break some June records!"

Figure 2. Forecast high temperatures in Europe for Monday, June 24, and Thursday, June 27, 2019. Similar readings are expected on Tuesday and Wednesday during this long-lasting heat wave. Temperatures are in degrees C; 30°C = 86°F and 35°C = 95°F. Image credit: TWC Europe.

An unusually early heat wave

Much like the eastern U.S., Europe tends to get its hottest temperatures of the year later in the summer, in July and especially toward August. All-time national records, some of which may be challenged next week, include:

Austria: 40.5°C (104.9°F), August 8, 2013

40.5°C (104.9°F), August 8, 2013 Belgium: 38.8°C (101.8°F), July 2, 2015

38.8°C (101.8°F), July 2, 2015 Czech Republic: 40.4°C (104.7°F), August 20, 2012

40.4°C (104.7°F), August 20, 2012 Denmark: 36.4°C (97.5°F), August 10, 1975

36.4°C (97.5°F), August 10, 1975 France: 44.1°C (111.4°F), August 12, 2003

44.1°C (111.4°F), August 12, 2003 Germany: 40.3°C (104.5°F), July 5 and August 7, 2015

40.3°C (104.5°F), July 5 and August 7, 2015 Liechtenstein: 37.4°C (99.3°F), August 13, 2003

37.4°C (99.3°F), August 13, 2003 Luxembourg: 39.9°C (103.8°F), August 8, 2003

39.9°C (103.8°F), August 8, 2003 Netherlands: 38.6°C (101.5°F), August 23, 1944

38.6°C (101.5°F), August 23, 1944 Switzerland: 39.7°C (103.5°F), July 7, 2015

Some of these all-time June records are even more likely to tumble:

Austria: 38.6°C (101.48°F), June 20, 2013

38.6°C (101.48°F), June 20, 2013 Belgium: 38.7°C (101.7°F), June 27, 1947

38.7°C (101.7°F), June 27, 1947 Czech Republic: 38.2°C (100.8°F), June 22, 2000

38.2°C (100.8°F), June 22, 2000 Denmark: 35.5°C (95.9°F), June 29, 1947

35.5°C (95.9°F), June 29, 1947 France: 41.5°C (106.7°F), June 21, 2003

41.5°C (106.7°F), June 21, 2003 Germany: 38.5°C (101.3°F), June 27, 1947

38.5°C (101.3°F), June 27, 1947 Luxembourg: 36.1°C (97.0°F), June 22, 2017

36.1°C (97.0°F), June 22, 2017 Netherlands: 38.4°C (101.1°F), June 29, 1947

38.4°C (101.1°F), June 29, 1947 Switzerland: 37.3°C (99.1°F), June 21, 2003

In France, the highest fully reliable June temperature is 41.5°C (106.7°F) on June 21, 2003 at Lézignan-Corbières, according to Etienne Kapikian (Météo-France). Other June readings as high as 42.2°C are less reliable, Kapikian said. “I think that we can reach at least 43°C or possibly 44/45°C in the upcoming heat wave. I wouldn't rule out a new all-time national record,” said Kapikian in an email. Official forecasts are not yet this hot, he noted, which is common when heat waves are still a few days out.

“Currently, June 2019 in Germany is only narrowly behind the three hottest Junes (1889, 1917, and 2003) since at least 1881,” said German meteorologist Michael Theusner in an email. “And with the upcoming extreme heat wave, there is a very good chance we will break the 2003 record. The eastern parts of Germany have their hottest June already, and, Berlin/Brandenburg and Saxony by a margin of 1K [1.8°C].”

Early-season heat waves are especially dangerous

Heat waves are especially dangerous when they occur early in the summer, before people have had time to adapt to the seasonal heat. A 2015 report from the World Meteorological Organization and World Health Organization on heatwaves and health notes:

“Heatwave timing appears to have a notable effect on the level of mortality. Heatwaves occurring early in the summer have been shown to be associated with greater impacts on mortality in the same population than later heatwaves of comparable or higher temperatures (Hajat et al., 2002; Kinney et al., 2008; Anderson and Bell, 2011). The impact of high temperatures later in the summer is sometimes diminished after an early heatwave.

“In Europe, heatwaves occurring in June result in relatively high mortality compared to later in the summer, while most high-mortality events in southern Asia appear to occur early in the summer before the summer monsoon."

Figure 3. A resident of the "Montplaisir" retirement home in the French town of Lyon has a drink in an air-conditioned room on August 18, 2009, during a visit from French Secretary of State for the Elderly Nora Berra (not pictured). During the European heat wave of 2003, thousands of elderly people in France died from the soaring temperatures. Image credit: Jean-Philippe Ksiazek/AFP/Getty Images.

Europe’s biggest heat-wave catastrophe occurred in the first two weeks of August 2003. Great Britain saw its first 100°F readings in more than 300 years of recordkeeping, and similar temperatures were widespread across Europe. Adding the various national counts implies that more than 50,000 people died as a result of the 2003 European heat wave. Later estimates brought the toll as high as 70,000, though the exact number is difficult to discern. No heat wave in global history has produced so many documented deaths.

A landmark 2004 study led by Peter Stott (University of Reading) found that human-produced climate change made heat waves on par with the European disaster of 2003 about four times more likely to occur.

Thanks to Maximiliano Herrera for providing European national weather records.