Heat Spreads Across the Mediterranean on August 17, Driven by an Upper-Level High

During the day on August 17, temperatures are expected to rise well above normal across a wide stretch of the Mediterranean region, centered on Italy, Tunisia, and southern France. The main driver is a ridge of high pressure aloft, around the 500 hPa level (roughly 5,500 m above the surface). Beneath this ridge, air tends to sink and warm as it is compressed — the common cause behind this widespread heat.

Cause: An Upper-Level Ridge Combined with a Surface High

The main driver of this heat is a ridge of high pressure spreading across roughly 5,500 m in altitude (near the 500 hPa level). Beneath a high-pressure system, air slowly sinks and warms as it is compressed, making it easier for temperatures to rise over a wide area of the Mediterranean.

In addition, a surface high is expected to build from southern France toward Switzerland, bringing continued clear skies and further warming from solar radiation. The combination of this upper-level and surface high pressure is likely to keep the heat going from southern France through Italy and into Tunisia.

Nearby, low-pressure systems are forecast near Poland and near Algeria, with the high pressure ridging into the Mediterranean between them.

A Pattern Common Across the Mediterranean Coast

This kind of upper-level ridge is a familiar pattern behind summer heat along the Mediterranean coast. What stands out this time is that the heat is spreading simultaneously from Tunisia in the southern Mediterranean all the way to southern France in the north.

Forecast Airport Temperatures — August 17

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