Page 17 - Volume 17 Number 4

Gettingeven darker, “that the weather was getting better?”Improving ConditionsIt’s not good enough to just think the weather will improve when you’re putting passengers or yourself at risk. You’ve got to know. Weather phenomena are hard to predict long- term, but actually pretty easy to examine and understand in the near-term, over short distances.Knowing conditions will get better starts, of course, with a good look at the weather before takeoff. Consistently, about half of all weather-related mishaps occur with no record of a pilot weather briefing. Forget about Temporary Flight Restrictions (TFRs) and other NOTAMs – weather survival is a darn good reason to get a complete briefing before venturing aloft. A proper weather briefing will help you not only know where the bad weather is, but where it is expected to go and whether it will become stronger or more widespread. Most importantly, it will indicate what’s causing the adverse weather to form. This, in turn, tells you to suspect the weather forecast and make a judgment of whether the skies will be friendlier or more hostile, based on the real-world conditions you find aloft. What,then, are some general rules of thumb for improving conditions?Low visibility: Low visibility results from a close temperature/ dew point spread and the presence of condensation nuclei – dust and other particles in the air around which moisture can condense. The amount of condensation nuclei is why a temperature/dew point spread of four degrees may reduce visibility to 10 miles or so in the central U.S., while in the more polluted atmosphere of America’s east coast it might drop visibilities to five miles or less.Are you flying toward wetter air (toward the ocean or the Great Lakes, or to an airport on the shore of a lake or river)? Are you flying toward a city or a typically more-polluted area? Then, absent a major change in the weather (passing through a front), visibility will likely get worse, not better. Ahead of a front, is the wind stronger than expected? That’ll usually add more moisture to the air, meaning deteriorating visibility.To know visibility should improve, you need to know that; you’re flying into drier air with fewer condensation nuclei; the winds ahead of a front are significantly lower than forecast; you’re enteringair with an increasing temperature/ dew point spread; or heading immediately through a front to better conditions beyond.Thunderstorms: Thunderstorms require significant moisture, atmospheric instability and some sort of lifting action propelling low- altitude moisture aloft. To know things will improve, apply the rules about visibility – measurable reductions in water content will reduce the likelihood and extent of thunderstorm activity. Likewise, the atmosphere must be increasing in stability and lifting action must decrease for thunderstorm activity to wane. Are you flying away from the front or squall lines forming the thunderstorm cells? Is the hottest part of the day done, and the air cooling down? Are you flying away from mountains, sunlit plains (that create thermals) or a strong jet stream aloft? Are you already on the “back side,” or upwind of a line of storms, and flying away from them? If so, conditions will likely improve. If not, to press on is hideously dangerous.Turbulence: Turbulence is sometimes hard to predict, but it’s always caused by something. Most frequently (outside of storms), turbulence results from frontalAPRIL 2013TWIN & TURBINE • 15Betterby Thomas P. Turner