Plane & Pilot
Tuesday, October 6, 2009

Top Mistakes In Convective Environments


How to stay safe in bad weather



Pulse-type thunderstorms are easy to avoid as long as you can remain visual. In this flight to New Orleans, we watched this thunderstorm develop from over 50 miles away and move north into our route. It was obvious from looking at the XM-based satellite weather that we needed a deviation. Because the storm was moving north, we asked for a deviation to the right on the upwind side of this slow-moving cell.

Wouldn’t it be a dream come true if you were able to set the NEXRAD loop in motion and have it continue to run beyond the current time, playing out what might happen in the next six hours? That would certainly eliminate much of the convective guesswork. There’s no doubt that all pilots would love to take a peek at the future NEXRAD image. The simulated reflectivity product (www.nssl.noaa.gov/wrf/refl_loop.html) is an example of a forecast that’s the next best thing to the NEXRAD crystal ball. Simulated reflectivity is an hour-by-hour, model-based forecast that will help you visualize all aspects of the convective environment, including thunderstorm onset and dissipation, speed and direction of movement, organizational profile and intensity, just to name a few. But because it’s a model-based forecast, it’s subject to serious errors. Be sure to use this product in concert with other official NWS weather forecasts.

Fly Upwind
Once confronted with a thunderstorm, some pilots make the wrong tactical decisions. Of course, most understand that staying out of the visible cloud boundary or flying underneath the base of the thunderstorm is the first rule in thunderstorm avoidance. By staying out of the visible cloud, you’ll likely keep clear of the truly ugly parts of the thunderstorm. It’s widely known, however, that severe or extreme turbulence, hail, lightning and strong straight-line winds can exist outside of the visible thunderstorm boundary. Most of the time, these elements occur downwind of the thunderstorm; in other words, in its primary direction of movement.

Flying upwind of the cell helps the pilot in several ways. First, this keeps the aircraft on the side of the tiger that has no teeth. While there can be an occasional outflow boundary down low on the upwind side, most of the time, the air is glassy smooth, especially above 10,000 feet. Second, the cell is moving away from your position or route, so any latency you might see in your satellite-based weather is magnified because what you see on your display has likely already moved away from that point. By the time you get to this position five minutes later, the cell has moved off, keeping you safely out of harm’s way. Flying on the downwind side of convection provides just the opposite effect, with latency making it difficult to judge where the convection might be in five minutes.

Choose Your Help Wisely
When down low, stay away from any visible rain shafts and stay out of the rain curtain of larger storms. If you have no onboard radar or satellite-based weather in the cockpit, enlist help from ATC. Be very careful here; pilots often take directions from ATC that may not be in their best interest. Controllers don’t see what you see. Approach control weather radar is typically fairly fresh, but controllers can’t see a building cell about to unleash its fury in the next five minutes. Also, they’re primarily concerned about how your deviation will fit in with their current traffic flow and airspace; they’re less concerned with taking you on the upwind versus downwind side of a thunderstorm. Be assertive and refuse any clearance or instruction that takes you into an area that doesn’t keep you in visual meteorological conditions in a convective environment.

The Enroute Flight Advisory Service (EFAS), better known as Flight Watch, is another outlet for pilots flying in challenging convective environments without any onboard weather. Flight Watch can be reached on 122 MHz and should be used as a strategic tool 50 or more miles from reaching the nearest convective activity. It’s not what you can see outside of your windscreen that’s the most critical; it’s the convection you can’t see that might be lurking behind it. General guidance is typically useless. Be sure Flight Watch offers a route from your present position with specific waypoints or navaids that will minimize your exposure based on the current radar and forecasts.





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