May 2015 Review - Jyväskylä

Jyväskylä saw a cool May in 2015. The typical first burst of summer just never came. It was the coldest May, in fact, since 2008 at Jyväskylä Airport. The cooler temperatures weren't seen during the nights, but during the days, as maximums were well below figures from recent years.

Jyväskylä wasn't the only location in Finland to endure an extended spring. Almost all of the southern half of the country experienced below average temperatures. The southern coast and inland between Helsinki and Turku saw the biggest difference below average; up to 1.5C. Parts of Lapland, however, especially in the east, were slightly more than 1C above average.

Rainfall was above average at Tikkakoski, but there was very little storm activity throughout Finland during the month.

May figures from the previous seven years are shown below.

May averages at Jyväskylä Airport for the period 2009-2015

With an average maximum of 13.5C, May this year was 4.6C cooler than the May of 2013, and 1C cooler than the next coolest figure from last year. The Finnish Meteorological Institute recorded an overall average of 8.7C for the month, against 8.5C from my recordings. The 8.7C figure was the first below the 1981-2010 average of 8.9C since 2008.

The highest recording of the month at Tikkakoski came on May 25 when it reached 18.9C. This was well below figures from recent years. The next lowest respective figure since 2009 is 22.4C in 2011, while 2009, 2010, 2013 and 2014 all recorded days above 25C. The coldest maximum was also the lowest seen in May in the years since 2009. May 2 reached only 5.1C, just below 2014's 5.2C on May 4.

The highest minimum of 10.0C on May 27 was above the respective recordings from 2011 and 2012, but still quite far below last year's 14.1C and 2010's 15.2C. The coldest temperature overall was recorded on the 4th. The -3.0C recording then was one of only two minimums below zero during the month, and sits in the middle of the past seven years.

Extremes in Finland for the month ranged from -12.4C at Enontekiö's Näkkälä station on May 5 to Mikkeli's top of 21.7C on the 26th. The absence of any hellepäivät, or days above 25C, was the first instance for a May since 1998.

Daily minimums and maximums against rainfall for May at Jyväskylä Airport

Rain measured 53.6mm at Tikkakoski during the month. FMI recorded a total of 51mm. Both figures are above the 1981-2010 average of 44mm, but well below last year's 124.6mm, which was only just below the overall record.

May 13 was the wettest day when 22.7mm fell. It was also the wettest day of the year to date, and only the second day of the year with a total above 10mm. There were 20 days of precipitation, but the 14th of the month was the only other day to see more than 5mm. It was also part of a 10 day rain streak. Dry weather during the month was scarce. The longest dry streak was only two days, which occurred three times.

Despite the high number of rain days and the whole country recording above average rainfall totals, storm activity was rare. FMI reported only 331 groundstrikes. This is the third lowest figure for a May since 1960. In comparison, FMI reported over 25,000 lightning strikes for May in 2014.

May 2015 Review - Sydney

May in 2015 at Sydney Airport saw average temperatures a little closer to the long term figures when compared against the previous two years. They were still higher than average though. Rainfall was more than four times last year's figure, and the month was the wettest May of the past few years, but it still fell short of the average.

May averages since 2009 are shown below against the long term values.

May averages at Sydney Airport for the period 2009-2015 plus the long term average

Other than 2011, Sydney Airport hasn't seen an average minimum for May below the long term figure since 1984. 2006 was the prior year for an average maximum below the 20.0C average. The Bureau of Meteorology recorded average figures for May of 12.6C and 20.7C.

The highest temperature for May 2015 was 28.6C on the 5th. This was the hottest May day since 2007 and the seventh highest on record at the Airport. The warmest minimum was also unusually high. The May 3 recording of 19.0C, more typical of figures in March, was one of the highest on record as well. May 2 and 4, with minimums of 17.5C and 16.5C were also higher than the highest May minimum between 2009 and 2014 of 16.3C. 2012's figure was 14.3C, almost 5C less.

The lowest temperature of the month was 7.3C. That recording on May 14 was the coldest May temperature since 2011. Since 2009, only 2011 saw temperatures lower than that; there were four daily minimums below 7.3C then. The coldest day was the final day of the month. It only reached as high as 16.5C. This was, however, the second highest respective figure since 2009.

Daily minimums and maximums at Sydney Airport for May 2015

Rainfall totals for Sydney Airport were below average during the month. The calendar month saw 77.2mm while the Bureau recorded 85.8mm. The long term average is 98.6mm. 2014 saw far less with only 18.0mm. According to Bureau records, the 85.8mm total is the highest May total since 2011.

There were 13 days on which precipitation was recorded at the Airport. The wettest was May 2 when 27.2mm fell. The 1st and 22nd also recorded a daily figure above 15mm with respective totals of 17.2mm and 20.2mm. The longest dry streak was nine, from the 4th to the 12th, and is now the second longest dry streak of the year. May 19 to 23 all saw some precipitation, making it the longest run of rain days.

Wind gusts at the Airport were up during May this year comparing with 2013 and 2014. The strongest gust of the month came on the 22nd when a southerly at 87km/h was recorded. Earlier on May 13 there was a southwesterly at 69km/h recorded also. Both of these were higher figures than any gusts during the two previous Mays. May 18 was the calmest day when a strongest gust of only 22km/h was recorded. The south-southwesterly gust was the lowest strongest daily gust in exactly one year; May 18 in 2014 saw a strongest gust of 20km/h.

FMI changes forecast for Jyväskylä - summer on hold again

Where is summer in Finland? When will it arrive? Well, after predictions last Thursday and Friday by the Finnish Meteorological Institute it appeared that warmer temperatures above 20C would finally arrive in Central Finland tomorrow and Wednesday. On Saturday May 30, however, the slate was wiped clean and no longer was there the potential for the 25C barrier to be broken this week. Now the coming 10 days look more like what has been seen in Jyväskylä during the recent two weeks.

Such dramatic changes in forecasts are not that rare in the world of meteorology, especially for weather four or more days in advance, but this particular change is very disheartening. The potential for days above 25C in Jyväskylä ranges from mid-May until the very beginning of September, and for every day that we delve deeper into the summer without such weather, the less hopeful people are that it will come.

Despite the lack of 20C-plus days, Saturday May 30 was a beautiful day in Jyväskylä. It reached a top of 18.1C at Tikkakoski in the afternoon, making it the equal fourth highest maximum seen so far this year.

Another forecast error occurred on the last day of May. On the 30th there were predictions for rain during the morning and middle of the day for Sunday. These predictions on Saturday night had a confidence level of 90% and showed the potential for more than 5mm. A small band of rain did move north through Western Finland, but it was much less widespread than the predictive images shown through FMI's rain radar on Saturday night. In the end, nothing at all was recorded at Jyväskylä Airport.

The rest of Sunday also turned out quite nicely. The 16.7C maximum was more than 2C above Saturday's temperature prediction and pushed the run of consecutive days above 15C to seven.

Sunshine on dandelion flowers in Jyväskylä during the afternoon of May 31

According to forecasts now, tomorrow looks likely to be the warmest day of the next 10. Saturday June 6 could reach 17C, but all other days up until June 10 aren't predicted to go higher than 16C.

This kind of weather isn't really that unusual for Finland. Summers can be highly unpredictable and often have cool periods. Even the back half of June last year, for example, saw a 12 day run below 18C. At least in 2014's case, by June 12 Jyväskylä had already seen 15 days above 20C, seven of which also exceeded 25C. Let's hope warmer temperatures arrive in Jyväskylä soon...