Know When a Forecast Is Likely to Go Bad

Here's one clue that the computer has guessed wrong.

It has been said that weather forecasting is part science, part intuition and a large part memory. That's why computer forecasting is such a boon to pilots. Even the best forecasters from pre-cyber days had only human memories to rely on. Today, computer databases recall all the nuances of temperature, dew point and winds aloft and what the weather is likely to do when specific conditions prevail. The result is far better predictions of what pilots are likely to find, and where. But even the supercomputers cannot factor in everything that nature has to offer. There are times when what you see out the windshield defies everything you expected to see when you checked the computer screen earlier in the day.

There is one truism that I recall from flying and working with Richard Collins when he was editor in chief of Flying. At least in the eastern half of North America, if the wind is more southerly than forecast, or stronger out of the south than was predicted, the weather is going to be worse than expected. The principle is elegantly simple, and almost always on the money. Warm moist air is a weather maker, and in this part of the world it comes from the Gulf of Mexico. When nature conspires to push more of this warm, moist air northward, it is likely that we're in for what usually happens when hot, wet air meets cooler, dry air. The two air masses will either duke it out in convective activity, or they'll mush together in a warm front that is bound to bring low ceilings and rotten visibility.