The term aviation weather always carries a tone of doom about it. I mean, when you learn about weather in pilot training the emphasis is always, always on the macabre. So you read stories and hear tales of hair-raising, adrenalin-pumping near-death experiences with spar-busting thunderstorms; gnarly, foot-thick ice adhesions; and airspeed-snatching wind shear. Fun things like that. Ultimately, the brain chemistry of students and even experienced pilots must certainly develop specific physiological responses to the mere mention of aviation weather.
What we all seem to forget is that the weather is usually very good VFR — most of the time. Fronts come and go, and fog may persist for a while, but in a day or so the bad leaves and the good returns. You can count on it.
When the skies turn blue and the sun dries the runways, that's when we all head for the airport. But sometimes good VFR weather can be a pain to fly in, weather-wise. For example, after a front passes, you may have VFR all right, but the wind often perks up — way up — and turbulence kicks in.
No, right now I'm thinking about those rare days when the weather is perfect. What's perfect weather? Everybody may have a different answer to that one, but here's how I'd define it, and I'm sure most pilots would agree:
First of all, there can't be any wind to speak of. Surface winds would be light and variable, in National Weather Service jargon. Ideally, the surface wind would be no more than 5 knots and right down the runway. Translated into operational terms, this means no crosswind adventures and nice, stable approaches on final.
There can't be much vertical motion in the atmosphere, either. No VSI-pegging thermals; no convective forces to lift the air at lower altitudes; and no winds deflected upwards, downwards, or sideways from encounters with hills, lakes, plowed fields, or parking lots. We want our ride to resemble the experience of sitting on a $3,000 leather sofa situated in a large house in an earthquake-free location.
Winds aloft would be weak, too, so that wind shear and turbulence would be negated. Any winds aloft would have perfect, non-turbulent flow and always be at our backs.
Visibility, of course, would be unlimited. We're not just looking for the weather bureaucracy's paltry threshold of "6 miles plus," but at least 25 miles, and preferably more; 50 or 75 miles would be ideal.
It's a given that the sun would be shining. However, there can't be too much sun. This would create glare that could impair our ability to spot traffic and perhaps temporarily blind us if we happen to glance briefly at a reflection or at the sun itself. And yet, it should still be bright enough to require us to sport our favorite pair of aviating sunglasses. Flying's more stylish that way.
Clouds? I'm sorry; on a perfect flying day, there would be no clouds. Well, let's amend that. There can be a high, thin layer of cirrostratus at 20,000 feet or so. A high stratus layer kills glare and keeps the sun out of our eyes, yet still allows enough brightness to take full advantage of the vistas provided by our 75-mile visibilities.
Now that the perfect day has been defined, it's time to concentrate on how, where, and when it's most likely to be found.
Almost by definition, we're talking about the conditions beneath the center, or just to the west of the center, of a large body of high pressure. By large, I mean a surface high that extends the width and breadth of at least one-quarter of the continental United States. A high that big can have isobars 100 miles apart — just what the doctor ordered for weak surface winds. A high's sinking air mass means that compressional heating of air molecules all but eliminates the chances of any significant cloud formations.
Our location beneath or to the west of the high's center means that fronts are far away and that we can fly for several hundred miles in any direction in the same perfect conditions. Why the stipulation about being to the west of the high's center? Because this is the area known as the backside of the high and its characteristics include a southerly flow of warm air (conditions on the front side of a high are more cloudy and turbulent, because this area follows close on the heels of an exiting cold front, and we can't have that) and the slightest hints of an approaching warm front. The southerly flow means that temperatures won't be too chilly for our early morning preflights, and the approaching warm front will oblige us by providing that high cirrus shield we talked about earlier. By the way, you don't want to be too far west of the high's center. That would put you too far on the backside and closer to the unstable air and denser, lower clouds of the warm front.
Highs like these can park themselves anywhere, but for a truly perfect day we'll probably need to be under a high sitting over the interior portions of the United States. In this way, coastal fogs and sea breezes won't ruin our day. Statistically speaking, the geographic location most likely to win the perfect-day sweepstakes would be — drum roll, please — the Southwestern states. The only reason they're the surest bets is that they most consistently meet our astronomically high visibility requirements.
There's only one hitch in this perfect scenario: the clear skies that attend strong high pressure allow a great deal of radiational cooling at night. If temperatures drop to or near the dew point, fog can form in the early morning hours, say between 3 a.m. and 6 a.m. This is less likely in the arid desert Southwest, but watch out in the central and eastern parts of the United States. In any event, the fog should be gone by 9 a.m. at the latest — unless that high cirrus shield is thick enough to prevent the sun from burning it off.
There it is, ladies and gentlemen — the perfect day. It may happen just a few days a year, but now you know the criteria. Let's all vow to take a few days off this summer when that big high moves in.
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