Severe thunderstorms have affected the Mediterranean this week. On Monday, a surface low-pressure system in the Mediterranean in conjunction with an upper air cut-off low, led to thunderstorms over north Africa. Their intensity was aided by the hot precursor conditions.
Algeria and Tunisia were notably affected by the thunderstorms, with some hail accumulation layers as a result. When so much hail forms, it starts to lay down sheets of hail, covering the ground like snow. Hail accumulations of up to 3cm were reported in Oum Ladjoul and Hammam Sokhna in Algeria, and there were hailstones of up to 3cm in diameter in Makthar, Tunisia. Thunderstorms continued in the region through the following day, with further hail accumulations, notably in Ouled Bousmir, Tunisia, where there was a layer about 2cm deep.
Later in the week, another surface low developed, this time over Sicily. Thunderstorms broke out across parts of central Italy on Wednesday morning. These led to some severe downpours, with 52.1mm of rain falling in just over an 1 hour and 10 minutes in the city of Ascoli Piceno and 62.3mm falling in less than 1 hour and 50 minutes in the town of Mosciano Sant’Angelo. Other regions were also affected, with 46mm of rain in 36 minutes in the Sicilian town of Bagheria, as well as heavy rain being recorded in Algeria and Tunisia.
There were severe thunderstorms elsewhere in the world this week, notably parts of the north-east US. On Tuesday evening, a supercell affected Dane county, Wisconsin, and as a result, a tornado warning was in force. According to radar, a tornado did occur, but there were no confirmed reports of it touching the ground. However, this supercell also led to some severe hail. Around Madison, baseball-sized hailstones were reported. At 7cm in diameter, these would have been twice the size of those reported in Tunisia.
The following day, severe storms continued in the north-east US, and spread into Ohio. During this outbreak, even bigger hail was reported, with softball-sized stones being seen near Kansas City – stones as large as 11.5cm in diameter.
Tornadoes were also a big player in these storm outbreaks, with about 20 across the US this week, primarily in Wisconsin, Kansas, Iowa and Minnesota.