Does weather watch lore stand up to scrutiny?
WEATHER lore tells us that we’re going to have a dry summer this year. That’s definite. The evidence and certainty for this long-range forecast lies in the fact that oak trees opened their leaves this spring before ash trees did.
The old rhyme comes in a number of variations; one version is: ‘Oak before ash we’ll just have a splash; ash before oak we’re in for a soak’. If the oak leafs before the ash, we are set to have just a splash of rain over the summer but if the leaf buds of the ash burst first then a soaking wet summer is guaranteed.
People noted in the past that in some years the oak leafed before the ash while in other years the opposite happened. The annual competition between the two tree species was keenly watched. What it meant was unknown in the past but many felt it had to mean something; a sign, perhaps?
Over time, weather watchers married the summer weather they experienced to the tree bud burst they noted in spring and came to the conclusion that dry summers followed in years when the oak leafed before the ash. Hence the old rhyme: ‘Oak before ash we’ll just have a splash; ash before oak we’re in for a soak’.
So there you have it: we are going to have a dry summer. Or are we? Does the lore of weather watchers stand up to scientific scrutiny?
Unfortunately, the old rhyme does is not in keeping with the facts as we know them. There is no known connection between what happens in springtime when leaves appear on the trees and what the weather is going to be like during the following summer.
Leaf burst is triggered by day length. Leaf opening has evolved to coincide with the day length that occurs between late March and early May. Furthermore, oak is more sensitive to temperature than ash so if the spring is mild oak will respond faster than ash to increasing day length.
April was a cold month this year due to pretty persistent north-easterly wind but March was relatively mild so oak got off to a flying start. In a year when both March and April are cold, oak suffers a set back and ash leafs earlier.
So, whether oak leafs before ash is a matter of spring temperature and has nothing to do with whether or not we are in for a splash or a soak during the summer.
Ash trees were late coming into leaf this year - a sign of a dry summer to come?