By popular request – well, one anyway – I have commissioned a guest post from the SF (Statistics Freak, my husband) on March’s weather. The SF is the brains behind our extensive weather statistics, gathered over nearly 14 years. I don’t want the fame going to his head but I know I can count on my readers to provide their usual balanced and judicious comments. There’s a surprise for you at the end of the post. Over to you, SF.
I will give you our normal monthly weather report and then talk about my weather statistics in general.
Weather assessment for March
First as usual a quick reminder of our subjective weather assessment: we assign each day a plus if it’s fine, a minus if it’s bad and a zero if it’s indifferent or we can’t decide. In March, there were:
Pluses – 20
Zeros – 7
Minuses – 4
March has been a sunny month and the latter part has also been unseasonably warm. We had a barbecue on the 25th, the first day of summertime, and that is a record in our 15 years. The cuckoo arrived on the 26th, also a record.
The graph shows the percentage of plus days each March for the past 15 years (the line is the trend). This is the second best March only beaten by March 2003.
Our rainfall stats go back to August 2004. The average for March since then is 72.4mm but this March only gave 19mm. It rained 4 days against the average 10.9.
The deficit is worrying. Since last (wet) July the only month when rainfall has exceeded the average is December. So far this year we have had 40% of normal rainfall.
We had 3 nights of frost. March normally varies between 2 and 12.
The most interesting graph in my statistics is the “Running 12 month rainfall”. At the end of every month I put down the rainfall over the previous 12 months so it is the annual precipitation measured on a monthly basis. The first point on the graph is July 2005. As you can see it starts at 650 mm and rises up to around 900 mm and going above 1000 mm on several occasions. Today it is down to 560 mm. I find astounding the almost 100% difference between the highest and the lowest.
Generally speaking it rains quite a lot down here. As a comparison I can mention that at Stockholm in Sweden the average annual rainfall over 100 years is 650 mm and it has never over the 100 years rained more than 800 mm in any one year.
I think the difference lies in the number of rainy days per year. As you can see from the graph above it is around 100 – 130 rainy days per year. I cannot get hold of the corresponding figure for Stockholm but I suspect it to be much higher. One’s opinion about a rainy climate is formed more by the number of rainy days than the actual annual rainfall.
Another surprise for people (especially Swedes) who think we swim in our pool all the year, is how cold it is here in the winter. This graph shows the number of frost nights per winter. The average is 44 which makes this winter quite normal in spite of the cold spell in February (I have anticipated 2 frost nights for April this year).
As you have seen from our plus/minus/zero graphs we have made the Excel spreadsheet put in a trend line. The general trend seems to be that the winter months are getting worse and the autumn months September/October and April are getting better.
We do these statistics for fun and it is very interesting to see the reactions of friends whom we occasionally ask to fill in for us in our absence. They have no problems with writing down the reading of the rain gauge but to subjectively decide if it is a plus or a minus or a zero seems to create all sorts of mental contortions. We have to tell them “Just ask yourself if it was a nice day or not.”
Thanks very much, SF. Now, here’s the surprise – a photo of the SF, just in case you were all wondering what he looks like. Now you can picture him slaving over a hot computer to bring you the monthly weather stats.