DISCUSSION: Several trees were downed in Poland late Saturday night when warm down-sloping winds reached speeds of nearly 70 miles per hour (mph). These winds in Europe are known as the Foehn wind, and typically occur on the leeward (downwind) side of a mountain range. Winds off the Mediterranean Sea and Atlantic Ocean are forced to rise up the mountain where the air then cools and condenses, as it passes over the mountain top the air has dropped all of its moisture on the windward side and thus is now much drier. Due to the difference in adiabatic lapse rates of moist and dry air, the air on the leeward side of the mountain becomes warmer and as it sinks it becomes compressed and speeds up. This is why the leeward side of mountain ranges all across the globe are typically arid. The speed of the Foehn wind can reach dangerous speeds as we saw in Poland over the weekend. But, it’s not just the speed of the wind that is remarkable, it’s also the change in the temperature. As mentioned earlier, the air on the leeward side is drier and warmer, sometimes 25°F (14°C) warmer! Which in the winter months can lead to rapid snowmelt and sublimation. However, rapid snowmelt wasn’t the concern in Poland late Saturday night, it was the strong winds.
Many reports of downed trees were seen all across Southern Poland in the region of Aleksandrowice Śląskie. Regional Road 960 in this area was closed for several hours as crews scrambled to clear the roadway from fallen debris. Some rain showers may affect the cleanup effort today before colder air returns later this weekend.
To learn more about other high-impact weather events from across Europe, be sure to click here!
~ Meteorologist Jake Keiser