Golfers are famous for being imaginative when it comes to making up excuses when things go awry for them out on the course, with weather being one of the obvious candidates. Many excuses are rightfully met with at best a friendly chuckle, but when it comes to weather, give the golfer the benefit of the doubt. Different weather conditions do have a bigger effect on golf shots than you might think, and this is something that should be considered when playing at different times of the year.
Consider two scenarios – a cold, dry frosty morning in winter (say 0 °C, RH 80%, with frost on the ground) and a warm, humid afternoon in summer (say 25 °C, RH 70%, strong sunshine). Assume no wind in both cases and we’re playing the same course (so same altitude, say near sea level).
In this case air density and ball temperature are the two factors directly affecting the flight of the ball (if we neglect the effects of the heat or cold on the player and club shaft!).
Air density, in kg/m³, is dependent on air temperature, specific humidity, pressure and altitude. If we assume that altitude and pressure are the same in both scenarios, then only temperature and specific humidity are different. By specific humidity I mean the actual amount of water vapour in the air (grams per kilo of air) as opposed to relative humidity, which is the percentage of water vapour in the air compared to the maximum it could hold at that temperature (warmer air can hold more water vapour than colder air). The air densities for the two scenarios are
Winter 1.286 kg/m³
Summer 1.170 kg/m³
The aerodynamic drag on a golf ball is a force that opposes motion, and is directly related to the air density (i.e. lower density producing lower drag). The percentage difference between the drag on the balls in our two scenarios is just the difference in densities (i.e. around 10%). That means a 10-yard difference for every 100 yards of carry, so a wintertime carry of 220 yards could be around 245 yards in summer, all other things being equal.
But all other things aren’t equal. The temperature of the ball has a big effect on its flight. They say the optimum temperature of a golf ball is around 27 °C, as that’s where the compression of its elastomeric core is greatest. It takes around 6 hours for the ball to fully warm to this temperature to its core, so storing it indoors overnight prior to a round can gain you a few extra yards.
During a round of golf the ball spends most of its time lying on the ground, and is only in the air a tiny fraction of the time. It is therefore the ground temperature that will determine the ball’s temperature, not the air temperature. In winter, with frost on the ground (assume they didn’t close the course!) the ground temperature could be as low as -10 °C and temperature of the ball will fall quickly during the round, reaching its coldest on or before the 18th hole. You could of course keep a ball in your pocket and alternate balls every hole to slow down this cooling process but it will still cool down overall. In summer, with strong sunshine, the ground could be 30 °C or more, so the ball should hold its temperature right throughout the round. As the core materials are more elastic at this temperature, and the ground will probably be harder, the bounce and roll will be much bigger than in winter.
So we have the 10% increase due to different air densities plus the effect of a warmer ball and harder ground (not to mention the physical state of the player). We could be looking at 20-30% longer drives and using around 1-2 irons less in summer versus winter. Taking all of the above factors into consideration, the longest distances will be acheived in afternoon rounds in warm, muggy low pressure systems, while the shortest ones will be in early morning rounds in cold, dry high pressure systems.
Of course in reality in Ireland we get a much smaller spread in conditions throughout the year, with most rounds probably played between 10-20 °C, but it might be interesting to compare your distances now to those in a few months’ time (assuming wind conditions are the same) to see how your club choices vary.
In the meantime, work on the rest of those excuses!
Fergal – Irish Weather Online