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About scottd

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    : Charlotte, NC
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    Weather, writing, flying

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  1. Bob, I see you are in Greenville. I'm in Charlotte just "downstream” from you. This isn't usually taught in primary training, but the movement of a "line" of convection is usually controlled by the overall movement of the air mass. The individual cells on that line are typically controlled by the upper level flow (say, 500 mb). The combination of those two "vectors" is the resulting movement of the convection. So, just imagine a train on tracks. The train moves along the tracks by the upper level winds and the entire set of tracks are also moving as directed by the air mass. In the 500 mb image I posted you can see the wind is generally meridional (south to north) while the upper level trough (that U-shaped pattern) is swinging from west to east. There's your train on moving tracks. Hope that helps.
  2. Yes, as others have said this is the symbol for a squall line or more precisely a quasi-linear convective system (QLCS). Notice the formal name doesn't include the word thunderstorm since lightning isn't part of the criteria per se. Many, many years ago, cold fronts were actually referred to as squall lines. Squall lines usually have a bowing or crescent-shape on NEXRAD which is a good sign for strong straight line winds. Tornadoes, hail and heavy rains are typically also possible with the passage of a squall line. They are typical found in the warm sector (ahead of an advancing cold front) of a major weather system or also can be part of a non-frontal mesoscale convective system (MCS). They can be found 100+ miles ahead of the surface cold front. That's because they are usually connected to the dynamics (energy) and instability found in the upper atmosphere eill ahead of the surface cold front. That's why I like to teach pilots how to read constant pressure charts since what's happening at the surface is like only a small part of the story. Like reading the jacket of a novel to know who shot the sheriff. Remember the surface analysis chart that the OP presented is nearly 90 minutes old by the time you see it, so it's kind of "old news" with respect to a squall line.
  3. Yes, I fly in and out of Rock Hill all of the time as an instructor. Pretty nice airport. Didn’t realize it had such an outrageous fee. The other possibility is Monroe (KEQY) just over the border in NC or Lancaster (KLKR). Where is the wedding?
  4. Yep. I like to get ahead of this as well since it kills more pilots than you might think. I wrote about this recently in my blog.
  5. I’ll be there on Friday and Saturday giving three talks. Stop by and say hello. I’ll be hanging around the SiriusXM booth.
  6. They are identical. It's the same feature.
  7. More info here: Specifically it says, "Also, about this time, the FDR data indicated that some small vertical accelerations consistent with the airplane entering turbulence. Shortly after, when the airplane’s indicated airspeed was steady about 230 knots, the engines increased to maximum thrust, and the airplane pitch increased to about 4° nose up. The airplane then pitched nose down over the next 18 seconds to about 49° in response to nose-down elevator deflection. The stall warning (stick shaker) did not activate."
  8. You are welcome. Yes, that's me. I license Pilotworkshops to sell my Skew-T program.
  9. This is a question that I get asked a lot and I'll be discussing this a bit more in my webinar next week. For the sake of argument, what is to follow assumes the aircraft is in visible liquid moisture. First, when the static air temperature (SAT) is warmer than 0°C, you shouldn't expect to accrete ice. Once the SAT reaches about -7°C, almost all aircraft will begin to accrete some ice. The important temperature for determining ice accretion, however, isn't the SAT, but the total air temperature (TAT) or what some refer to as the ram air temperature (RAT). The TAT is the temperature just above the skin of the aircraft. By the way, some aircraft show the TAT and then infer the SAT from that (honestly that's a more sensible approach). But just be careful...when you offer a PIREP, please use the SAT, not the TAT. The TAT is different on different parts of the aircraft. Excluding the prop for now, the immediate leading edge of the wing or horizontal/vertical stabilizer is typically the warmest. That's due to an effect called kinetic heating. Kinetic heating is primarily a result of both friction and adiabatic compression. As the wing moves through the air, the air just in front of the leading edge will "pile up" and compress causing a rise in temperature due to the laws of thermodynamics. While not exactly linear with airspeed, you can use 1°C rise for every 50 knots of airspeed as a quick estimate. So an aircraft traveling at 150 knots will see a TAT of 3°C warmer than the SAT. However, as you move away from the immediate leading edge, the kinetic heating drops off quite rapidly. If you've ever flown in visible moisture with an SAT of about -2°C or -3°C, you may notice horns building on the top and bottom of the leading edges with liquid dancing around in between. That's because the temperature at the immediate leading edges are too warm (above 0°C) for freezing to occur. But just above and below the immediate leading edge, it's cold enough to accrete ice. The blades of the prop are moving at a much higher speed and typically don't accrete ice out at the ends. Again, this is due to kinetic heating. Prop ice tends to collect at the hub and then progress colder temps, it can move out toward the ends which will decrease propeller efficiency. Losing thrust is very really limits your options very quickly. If there's anything you can add to your aircraft for ice protection, it's prop de-ice. Not to add complexity, but those surfaces with a high radii of curvature will collect ice more efficiently than a low radii of curvature. So, thin wings will collect ice more efficiently than fat wings. It also depends on the size of the drops. Except for the immediate leading edge, small drops tend to just flow over the wing and don't penetrate the boundary layer above the wing. Larger drops have more momentum and will typically penetrate the boundary layer further back behind the leading edge. In other words, there are other factors besides air temperature that come into play. One last point. It's really hard to define temperature. SAT is the undisturbed air around the airplane (when it's measured by an aircraft, it's usually referred to as the OAT). The SAT is typically measured by an immersion thermometer on many GA aircraft. On the ground in the shade, the thermometer might be very accurate, but when in the air, it may also suffer the same kinetic heating as the airplane's leading edges. When that immersion thermometer gets wet or accretes ice, evaporative cooling can quickly drop the temperature of the probe by several degrees almost instantly. Have you ever flown into a cumulus cloud (at temps above 0°C, of course) and saw the OAT drop by several degrees? That's a wet immersion thermometer. This is a long way of saying that if you are measuring a temperature of +2°C with your immersion thermometer and then fly into visible moisture, you should expect the OAT to drop a few degrees creating a risk of icing. BTW, airplanes don't feel wind chill. Evaporative cooling of moisture (or sublimation), yes, wind chill no. And please, never use the standard lapse rate to estimate the freezing level. When making weather decisions, if you catch yourself using the standard lapse rate, slap yourself in the face! Now, for the tables in your POH, sure the "departure from standard" applies to understand performance. But don't use the standard lapse rate for anything else. Hopefully that helps clear things up.
  10. Just spoke with the Warning Coordination Meteorologist with the National Weather Service in Houston/Galveston. As I suspected, there wasn't a microburst signature evident - the accident and timing were too far away from the location where the plane went down. The only other weather-related explanation would be some significant turbulence during descent as the frontal boundary moved through the aircraft's flight path and caused the freight to shift.
  11. Upon closer examination of an unfiltered NEXRAD loop, you can see what is a secondary line of weak returns (marked by the yellow dashed line) that moves through and ahead of the line of convection. This looks like the radar picked up the cold front as it pushed east-southeast. Could be a coincidence, but this line of "frontal" returns likely reached the aircraft about the time it was in that steep descent. The convective line falls apart pretty quickly once that passes through. Here is the loop...notice how that secondary line moves through the other returns.
  12. Yeah, I'm not as worried as much about the programmatic aspects; it's the user experience complexity that can be challenging. And I am trying hard to minimize the number of preference settings in the app. Those always confuse users. Some apps go crazy with settings. At the moment we are going to treat these kinds of things like "attributes" for a particular overlay...that way, they stay with the overlay and are easy to remember where they are located and what they are used for.
  13. Just as some background... Everywhere a TAF exists, there's a MOS available, but not the other way around. But we are proposing to add the capability to have a switch such that TAFs take precedence over MOS where they are available. The biggest difficulty with TAFs is they have "temporary" conditions. So, technically we could always account for the worse conditions forecast. Of course, temporary conditions could mean temporarily better for the temporary period of time, as well. There's some complexity there that needs to be considered.
  14. Wonderful feedback! It's extra nice when the weather cooperates with the app.