Thursday, March 1, 2007
Severe Weather Flying
Dennis Newton’s book reviewed
Newton details the causal factors in air-mass thunderstorm development, the life cycle of air-mass storms, and the hazards present in each phase of that life cycle. He proposes techniques for avoidance based on an understanding of the factors that create air-mass thunderstorms.
Steady-state thunderstorms. Newton calls steady-state thunderstorms the “Mama Bear” to the air-mass thunderstorm’s “Baby”. As he puts it, “the steady-state storm is a genuine killer.” This is not to suggest it’s safe to fly through lesser storms—“no airplane can be said to be certified for flight in thunderstorms”—but Newton warns that the steady-state storm will typically be much stronger than air-mass storms.
“To get a steady-state thunderstorm,” Newton writes, “we have to take the brakes off. We must get the water out of the updraft. The simply way for this to occur is to have the storm develop in an environment in which the wind changes with height…. The more the growing thunderstorm leans, the more water will go elsewhere than right back down through the updraft [and thus reducing the lifting action’s force], and the more the storm can grow.” Newton discusses ways to evaluate the severity of thunderstorms by correlating hail, wind shear and severe turbulence to a sloping radar profile of the thunderstorm cloud. He gives five rules for avoiding steady-state thunderstorms, punctuated by the first rule: “When in doubt, always treat [a thunderstorm] as a steady-state storm.”
Severe thunderstorms. If there’s a Baby Bear and a Mama Bear, there must be a Papa Bear—and that’s what Newton calls the “full-blown severe thunderstorm.” Severe thunderstorms, identified by high winds, torrential downpours and massive hail, and possible tornadoes “require large quantities of moisture and deep unstable layers to form.”
“Once the moisture and instability are there,” he continues, “and the wind field is favorable for steady-state storm development, all we need is lifting. This lifting is often provided, not by a cold front, as you might expect, but by lifting of the low-level jet stream air over a warm front.” Newton goes on to more closely detail the elements that converge to create severe thunderstorms and tornadoes. He then provides very specific things to look for, in radar imagery and other weather products, that indicate a severe storm is forming, all the while strongly encouraging a healthy respect and a wide berth for these most powerful thunderstorms.
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