A ridge in the jet stream allows a bubble of warmth to slip north over Scandinavia. (Weatherbell)

For the third time this summer, parts of Europe will soon be dealing with another heat wave. Temperatures will climb some 20 degrees above average in spots beginning this weekend, baking much of Eastern Europe and Scandinavia in unseasonable warmth.

The culprit for the hot weather will again be a strong area of high pressure aloft, or heat dome, that will set up an atmospheric squeeze-play of sorts between low pressure on either side. This will draw a flow of unusually warm air northward.

On Saturday, the heat will begin to crank up across most of Europe before consolidating over central Europe on Sunday. By Tuesday, a bubble of significant heat will pinch off and settle over Scandinavia, while the rest of the dome will settle south and reorganize over the Balkans.

The sweltering conditions are set to arrive in Germany on Sunday, when Frankfurt could hit the upper 80s. Then they will be within a degree or two of 90 on Monday, Tuesday and Wednesday — pretty impressive considering the average high there this time of year is just 71 degrees.

Most late-August nights in Frankfurt drop into the middle 50s. July tends to be the hottest month there, and indeed it was — during last month’s heat wave, Germany recorded an all-time record high of 108.7 degrees.

It’s a similar story in neighboring Poland, which will be ground zero for the heat midweek. Warsaw will also flirt with 90 degrees Wednesday, up 20 degrees above its average high of 69 degrees. Warsaw hasn’t hit 90 or higher since June 30.

Lodz, a city of 700,000 in central Poland, could see overnight lows Monday and Tuesday that come close to eclipsing their average daytime high temperature. In Paris, highs will be in the upper 80s to near 90 from Saturday through Tuesday.

The French capital already saw two intense heat waves this season, making this one particularly unwelcome. Paris typically spends most of August in the mid-70s. Even London will be 15 degrees above normal to start the workweek.

More heat for Scandinavia before this system moves into the Arctic

The heat wave may be especially anomalous in Scandinavia. Bergen, Norway, will climb into the mid-70s next week, up from average highs of just above 60. Trondheim will dance between 75 and 80 degrees during a time of year when its nights are ordinarily dipping into the 40s. Stockholm will peak near 80 degrees Tuesday, well above its average of only 65. From there, a wisp of warmth will slip up the Norwegian Sea, scooting into the Arctic before dissipating.

It could enhance sea ice melt heading into early September, and sea ice extent is already running near a record low.

The surge of warmth will bulge the atmosphere upward as the warm air expands. This will raise the halfway point of the atmosphere, above and below which rests half of the atmosphere’s mass, upward by 800 feet.

That’s significant enough to place this high-pressure area in the top 3 percent of mid-level highs for intensity.

Climate change’s potential role

Climate studies show that heat waves such as the upcoming European event are becoming more likely and severe as the overall climate warms in response to human activities.

An attribution analysis of the July heat wave that set records in France, Germany, The Netherlands and other areas found that climate change made the heat wave at least 10 times as likely to occur, compared with a climate without an increased amount of greenhouse gases.

The report, from World Weather Attribution, also found that by raising global average surface temperatures, climate change boosted the heat wave’s temperatures by up to 5.4 degrees.

“The July 2019 heat wave was so extreme over continental Western Europe that the observed magnitudes would have been extremely unlikely without climate change,” the report stated.