|Above: The parched banks of the Danube River in Mariaposching, southern Germany, on Wednesday, Aug. 1, 2018. Many stations in Germany saw their driest July on record, and Wednesday was the hottest day ever recorded at a number of German locations. Image credit: Armin Weigel/dpa via AP.|
The intense heat that has waxed and waned across various parts of Europe this summer is on the move once again, and residents of Spain and Portugal need to be prepared. Temperatures could approach or exceed all-time highs across parts of the Iberian Peninsula from Thursday to Saturday. Intense heat can be expected elsewhere in western Europe—including Germany, where at least 11 stations broke or tied all-time highs on Wednesday.
A ridge of high pressure that’s been lodged over and near northern Scandinavia will be eroding later this week, as a separate ridge builds northward from Africa and a trough approaches Europe from the northwest. This pattern will pull hot, dry air from Algeria and Morocco into the Iberian Peninsula (Spain and Portugal), along with some Saharan dust. By the weekend, a building surface high across Ireland and Britain will help push the scorching air mass back southward across the higher terrain of central Iberia. This will lead to downslope flow across parts of Portugal and southwest Spain that could heat the air even further.
|Figure 1. Temperatures on Friday, August 3, 2018, are predicted to top 35°C (95°F) from southwest Germany across much of France into most of Spain and Portugal, where readings of 45°C or even hotter are possible. Image credit: The Weather Company.|
The expected pattern is so extreme that the surface-temperature predictions of forecast models have to be approached with a grain of salt. Such models often struggle when trying to get a handle on the most unusual situations, especially when surface temperatures have a chance of going “superadiabatic.” A superadiabatic lapse rate means that conditions are warming the surface air even more than one would expect simply from bringing air of a certain temperature down to the surface from aloft. By itself, that descent produces a warming of 10°C per kilometer, or about 5.4°F per 1000 feet.
With that caveat in mind, some of the model forecasts are jaw-dropping. Highs are projected in some model output to approach the neighborhood of 50°C (122°F) across parts of central Portugal northeast of Lisbon. For context, the hottest temperature ever reliably recorded in Portugal is 47.4°C (117.3°F), which was notched at Amareleja on August 1, 2003, near the peak of Europe’s infamous and deadly heat wave of that year. Spain’s all-time heat record of 47.3°C (117.1°F), set in Montoro on July 13, 2017, may also be in jeopardy.
Forecasts from the UK Met Office suggest that 48°C (118.4°F) is possible in Iberia. The Weather Company is predicting that temperatures could reach 47°C by Saturday in the Alentejo and Tejo regions of Portugal, with readings of 40°C (104°F) possible in southern France. The World Meteorological Organization has deemed the all-time high for continental Europe as 48.0°C, set in Athens, Greece, on July 10, 1977. However, a reading of 48.5°C was observed at Catenanuova, Italy, on August 10, 1999. According to weather records expert Maximiliano Herrera, the Catenanuova reading is more consistent with nearby observations than the Athens reading, and thus more likely to be the highest reliably measured temperature in European history.
If you're heading to Spain or Portugal this week, the potentially record breaking temperatures are expected to be inland. ️The heat will be a little less intense at the coast ️— Met Office (@metoffice) August 1, 2018
Watch until the end to see how temperatures compare across the rest of Europe! pic.twitter.com/OMzdZgmQSm
|Figure 2. A house burns on June 20, 2017, as a wildfire approaches Mega Fundeira village after a wildfire took dozens of lives on the night of June 17-18 in Pedrógão Grande, in the Leiria district of central Portugal. At least 47 victims died in or near their cars as they tried to flee the area. Image credit: Pablo Blazquez Dominguez/Getty Images.|
Wildfire a serious threat as the heat moves southwest into Spain and Portugal
The heat-up across Spain and Portugal will bring an intensified risk of wildfire in a region that’s quite vulnerable to it. Iberia experienced two catastrophic fires last year. The first was a complex of blazes in June that killed at least 66 people in Portugal, making it the nation’s deadliest wildfire event in modern records. It was followed in October by a frenzy of more than 7,900 fires that struck northwest Spain and north Portugal, killing at least 49 people. In a freakish circumstance, the October blazes were stoked by winds flowing into ex-Hurricane Ophelia as the storm moved toward Ireland.
Fire weather outlooks issued by Portugal’s national weather agency, IPMA, show increasingly dire conditions spreading across most of the country as the week unfolds. By Saturday, more than half of Portugal is predicted to be in very high wildfire danger, and roughly 20% of the nation is in the highest risk category. For example, the Abrantes municipality in central Portugal is projected by IPMA to hit 45.1°C (113.2°F), with relative humidity dipping to as low as 13%.
|Figure 3. Fire weather outlook issued at 10 AM Portugal time (5 am EDT) Wednesday, August 1, 2018, valid for Saturday, August 4. Image credit: IPMA.|
At higher terrain, such as the Sisteme Central range that extends from central Portugal into northwest Spain, models suggest there could be just enough moisture through the depth of the atmosphere to support “dry” thunderstorms—those that produce lightning but very little rain. Such storms are believed to have triggered at least some of the blazes in the June 2017 disaster.
Update: One mitigating factor in the wildfire threat is that Portugal has had a relatively cool, wet summer so far. WIth spring also on the moist side, vegetation hasn't dried out as quickly as usual, as noted by Portuguese fire researcher Paolo Fernandes (University of Trás-os-Montes and Alto Douro) on Twitter.
For more on the avalanche of heat records set across the Northern Hemisphere in recent weeks—including the all-time records in both North and South Korea set on Wednesday, as discussed by Jeff Masters in our last post—see the roundup from Jon Erdman at weather.com.
Thanks to meteorologist Katie Greening at The Weather Company's office in Birmingham, UK, for background used in this post.