READERS familiar with the mini series House of Cards, now showing on RTE on Sunday nights, may recall the catch phrase of the anti hero Francis Urquhart "You might say that," he likes to say, "but I could not possibly comment". Such must be the response of Weather Eye to those who list the social and commercial benefits of a second civil airport near our capital. But when it comes to the weather factors involved in such an enterprise, any helpful meteorologist will be, in the words of Alexander Pope
Unbiass'd, or by favour, or by spite, Not dully preposs'd, nor blindly right.
Airports come in many shapes and sizes, but they all have one thing in common if they are in the wrong place, bad weather plays havoc with their operations. No airfield, of course, is completely immune from the weather, and even at an ideal location, fog or strong winds will now and then disrupt the schedule. But proper attention to the meteorological aspects of a prospective site may well pays handsome dividends.
Consider, first, an airport sited in a large shallow valley. On cool clear nights, dense cold air slides down the surrounding hills into the centre of this hollow. If there is any tendency for fog to form on such a night, it will make its first appearance in this cold pool of air at the bottom of the valley. Obviously this is not the best location for an airfield.
But neither is a hill top site ideal. When moist air is forced to rise over high ground, the resulting drop in temperature is often sufficient to induce condensation, causing a bank of cloud to form near the crest of the hill. Poor landing conditions will therefore be more frequent at such a site than on the plains below.
Turbulence on landing and take off is also troublesome, and this is most common where there are sudden discontinuities in the topography. As an extreme example, it would be very unwise to build an airstrip at the base of a cliff with the sudden change in shape of the terrain, winds in the vicinity are likely to be very turbulent indeed.
Even when a good site for an airfield has been chosen, meteorological advice is helpful when deciding which way to orientate the runway. Pilots like the wind to blow straight down a runway, since a crosswind a wind blowing at right angles is troublesome and potentially dangerous. It makes sense to consult wind statistics for the locality, so that the runway can be aligned with the direction from which the wind tends to blow most frequently.