DISCUSSION: To the first order, the temperate oceanic and continental climate that governs the conditions across much of Europe can be characterized by relatively cool temperatures during the summer months. Over the course of the last few days, however, most of Europe has been under the influence of a significant summer heat wave where many long-standing temperature records have already been challenged. Recently, daily maximum temperatures have risen well above 30°C (~86°F) in southern England, 35°C (~95°F) in most of western Europe, and over 38°C (~100°F) over southern and central Spain. The heat is creating noticeable strain on transportation operations (by virtue of cancellations and delays) in order to maintain safety, and multiple forest fires have ignited, including the recent Greek wildfire that has claimed 92 lives.
So what is the culprit for the development of this heat wave? It all begins with a robust ridge of high pressure that is situated between the middle and upper-levels of the atmosphere. Geopotential height, a measure of the height of a constant pressure surface above the mean sea level, is a useful diagnostic tool and proxy for determining the strength of a ridge or trough affecting a region, and higher (lower) heights usually correspond to warmer (cooler) surface temperatures. During this heat wave, most of Europe has been faced with 500 hPa (~5,500 meters above sea level) geopotential heights that are 2-3 standard deviations above normal for this time of year, which equates to anywhere from 5,800-5,900 m. Specifically, most of western Europe At the surface, maximum temperatures have been 6-10°C above normal. Furthermore, the positioning of the jet stream also favors south-to-north advection of warmer air in the upper levels.
The excessive warmth is expected to continue once again by the end of this week as current Global Forecast System (GFS) model runs indicate the development of another high pressure system and upper-level ridge. Southwesterly winds will once again facilitate robust warm air advection over much of Europe and keep temperatures several degrees above normal as the air above the surface warms considerably. In addition, moisture over western France and the UK will likely yield heat indices that exceed 38°C (~100°F) there while much warmer temperatures are forecast over Spain. Under this level of warmth, it is imperative to stay hydrated and cool to escape potentially harmful heat-related illnesses, especially in regions that are not adapted to very warm conditions.
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© 2018 Meteorologist Brian Matilla