IF you liked to plan your life according to statistics, then you may find Sunday next to be a suitable date on which to hold a barbecue or picnic. It was firmly believed at one time that September 15th was the driest day of the entire year; whether this is true, I do not know, but I suspect, for Ireland at any rate, that it is not. Nonetheless, a spell of dry weather at this time of the year is by no means uncommon, and the anticyclone hovering in our vicinity for the past week or so has been kind to us in that respect.
A prolonged period with no rain is commonly called a drought. Meteorologists, however, are pernickety, and recognise types of droughts which are unknown to other people. A dry spell to a meteorologist, for example, is not what it might seem to be: it is a period of 15 or more consecutive days with less than 1 millimetre of rainfall on each. An absolute drought, on the other hand, is 15 or more consecutive days with less than 0.2 mm on each and a partial drought is a period of at least 29 consecutive days with less than 0.2 mm. Somewhat paradoxically, you will notice, absolute droughts, by definition, come along more frequently than partial droughts.
With this abiding passion for taxonomy, meteorologists classify our bad weather as well. A rain day of a particular spot is defined as a day on which at least 0.2 mm of rain is measured, the equivalent of a light shower or a few hours of drizzle. And to you and me a wet day is one on which it rains for most of the time, but to weather people it is a day on which at least 1 mm of rain falls, an amount which roughly corresponds to a fall of light rain lasting for about an hour.
This latter criterion can cause some strange anomalies. The hour of rain, for example may fall during the hours of darkness, so a day that you remember as having been one of unbroken sunshine during your waking hours, may be perversely classified by your meteorologist friend as a "wet day".
Rain is also classified, by the rate at which it falls, as "heavy", "moderate" or "light". Here too, of course, meteorologists have been meticulous, and define each rate in bands of so many millimetres per hour. Broadly speaking, however, moderate rain falls fast enough to form puddles rapidly; light rain does not; and heavy rain is a downpour which makes a roaring noise on roofs, and makes a fine spray as each drop splashes on the wet surface of a concrete road.