September 2014 Review - Jyväskylä

Jyväskylä saw a rather warm September in 2014. Most of the month was dominated by sun and clear skies. Those clear skies, however, also led to cold overnight temperatures. As a result, the average minimum was the lowest seen since at least 2009. A cold change eventually arrived late in the month and the rare sight of September snow came along with it.

With only three rain days in the first three weeks, it looked like the month might have been on its way to the driest September on record, but rain associated with the cold change late in the month prevented that from happening. Rainfall was still well below average though.

September averages from the past six years can be seen below.

September averages at Jyväskylä Airport for the period 2009-2014

FMI's September report and other climate graphs indicate that only a very small part in the far north of Finland recorded a below average September. The southern coast as well as the mid-western coast saw temperatures more than 1.5C above the average. Jyväskylä saw a figure almost 1C above the long term average of 8.8C.

A consistent run of high pressure systems over Northern Europe and Western Russia led to warm, sunny and dry weather in Finland. There were five days that topped 20C in Jyväskylä this September. The previous five Septembers saw only six days above the mark. In contrast, this September also saw only two minimums above 10C. This was the lowest number since 2009. 2011 saw eight minimums above 10C.

The clear skies and dry conditions were evident in the monthly extremes as well. The highest temperature of the month was seen on September 5. It climbed to 21.6C then. Only two days recorded in September 2009 were higher than this in the past six years. The 5th was also responsible for the highest minimum of 10.4C. This was the lowest such recording in the past six years.

The overall minimum came on September 25. It dropped to -1.6C then. Again, only two measurements from 2009 were lower than this in the past six years. September 23 saw the lowest daily maximum. The 3.0C recording then is 2.3C lower than the next lowest respective figure seen since at least 2009.

The highest temperature seen in Finland during September 2014 was 23.1C. That was recorded on both the 8th and 9th days of the month, at Kokemäki and Kruunupyy respectively. The lowest temperature was -9.7C, recorded in the north at Saariselkä on the 22nd.

Daily minimums and maximums against rainfall at Jyväskylä Airport for September 2014

As mentioned, the first three weeks in Jyväskylä were exceptionally dry. The first 20 days saw only 1.6mm of rain. Including August 31, on which no rain fell, this is easily the driest three week period seen this year.

FMI reported a total of 28mm at Tikkakoski, compared to my total of 26.6mm. The 1981-2010 average is 55mm. The 26.6mm total was accumulated across nine days of rain. September 21 to 24 was the longest rain period. Rain totalled 18.3mm across those four days. It also included the highest daily total of 13.8mm on the 22nd. The nine day stretch between September 3 and 11 was the longest precipitation free period.

Interestingly, while rainfall was around 50% of the long term average for Jyväskylä, and in fact most of the western half of the country, areas around Joensuu in Eastern Finland and Kemijärvi in the north saw above average totals.

Rare heavy snowfall was seen in Eastern Finland on the 23rd. Joensuu and surrounding areas saw more than 10cm, while Posio, between Kemijärvi and Kuusamo, had a recording of 25cm on the 25th. The previous time a greater snow depth was recorded in September was at Sodankylä all the way back in 1968. Jyväskylä also saw wet snow during the afternoon and evening of September 23, but it quickly melted overnight.