« Learning how to use in-cockpit weather (1): Miles City, MT (KMLS) to North Platte, NE (KLBF) »

After about 45 minutes on the ground in Miles City, we fired up JYMmie again, this time headed for North Platte, Nebraska. We were hopeful that we would get to North Platte, as the weather there was steadily improving, but not at all confident of our success. We headed first toward Gillette, keeping an eye on the weather on the GPS.

We have not had in-cockpit weather available to us before. Before our trip, we invested in a Garmin Aera and XMWeather subscription. There is no training available on how to best utilize such a resource, but here are some nuggets we gleaned:

1. Understand the limitations of the information:

By the time the information is displayed, it is always old, sometimes by as much as 20 minutes, or more.

For this reason, one should not use in-cockpit weather (ICW) as a tactical decision-making tool, but rather for strategic planning. One should not use it to decide where to go between two cells of heavy precipitation. Of course, this rule is not rigid, for example where cells are widely spaced and slow-moving, especially if VFR.

Interestingly enough, here is an example that negates the tactical/strategic rule.

On our return from the Bahamas we were dodging rain showers as we approached the Miami coastline. We were VFR, but it was comforting to use the ICW to confirm that the cells were isolated.

About 56 nm miles out of Fort Lauderdale Executive airport, we are just inside the ADIZ. The scale of 20nm seems ideal for making strategic decisions at JYMmie’s airspeed. The stationary front to the south, with its associated weather, is shown. Note that this image was obtained 3 minutes ago. The information could be significantly older than this, however, and there is no way to know exactly how old it is.

The ICW display shows precipitation density, not cloud density. So, although it appears that there were only isolated clouds, in fact there was a complete ceiling, with isolated showers. We have found that we can usually comfortably traverse green areas. The yellow not so much, if we are to remain VFR.

Watching the cells to our left, we were doing well, until Miami Approach called us up, and made suggestions for a heading for us to fly. Remembering the fact that our information is often old, we followed their advice and were turned directly into what showed as an orange return on our display. We flew into fairly heavy rain with reduced visibility as a result. We were just starting to clear the rain, when we were once again vectored into another orange area! A look out the window confirmed what our display was telling us, so we declined the vector, and remained in the clear for the remainder of the leg.

Looking back along the reciprocal of our course after landing. As always, we were reminded that final decisions regarding any flight rest with the pilot, and not with ATC, and that weather is a fickle mistress!

Here, however, is an example of how ICW is helpful for more strategic planning.

Check out the video below (there is no audio). The green line is the heading we are trying to steer. Do we go to the left or the right of the rain cell?

At first glance, it would seem that we would be able to go to the left, the more direct way. However, the ICW NexRad showed us that we would end up in a dead-end of heavy precipitation and need to retrace our route. It also showed us that we had better options to escape worsening weather to our right.

We steered to the right of the cell.

(More on using in-cockpit weather in later entries)