Several countries in Europe experienced their hottest Septembers on record, including Austria, Belgium, France, Germany, Poland, and Switzerland. This occurred despite a major cool down with snow in the Alps during the third week of the month. 

For Europe on the whole, September 2023 was the warmest September on record. Across the entire region, temperatures were 2.51°C higher than the 1991-2020 average, and 1.1°C higher than 2020, the previous warmest September.  

Below is the temperature anomaly map for the month of September.

In France, September was a whopping 3.5 C above normal, smashing the precious record! Some individual locations in the country saw temperatures up to 6 C above normal for the month. In other locations, the month of September was warmer than either July or August. 

Germany saw its hottest September since records started, nearly 4 C warmer than the average. Most of Belgium was warmer in September than either July or August. 

Poland saw temperatures more than 3.5 C above normal for the month as well, with September 2023 being the hottest since records began. Austria also experienced the warmest September in history. Temperature s soared over 40 C (104 F), especially during the heat wave in the early part of the month. 

The primary cause of the extended heat was an extremely persistent high pressure system dominating the atmosphere in southern Europe. These areas of high pressure pump warmer air from the south into the region and are associated with reduced cloud cover, which allows the temperatures to further climb. Look at the departure from the long term average in mid level pressure below. 

The location of this area of high pressure result in the clockwise winds bringing warm air from the south into the heart of Europe. Since this is the average pressure over the course of the month, this indicates that a majority of the time the winds were out of the south like this, consistently dragging warm air into the region.

The greatest temperature anomalies during September were in France, which is no surprise given the location of the high pressure.

October has started out warm as well, and that will continue, especially in Western Europe, for the next five days as well.

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