Tuesday, May 26, 2009

In Praise of Onboard Weather

Here are a couple of photos from this morning's flight showing the XM Weather display (and specifically the NEXRAD Radar screen) on N631S' Garmin GPSMap 396. The first image shows us over Delaware Bay east of the Smyrna VOR (ENO) near Dover AFB (KDOV) headed toward the LEEAH intersection.

You'll note that the course shown is, for the time being,  nicely free of all those green and yellow precipitation returns.

The next image is a little earlier (note...not yet past ENO) and at a wider scale. I had just accepted a reroute. My clearance would have had me turning left at ENO and going up to Cedar Lake (VCN). The Dover Approach controller said he'd need me to descend from 7,000 feet to 5,000 feet unless I wanted to proceed to LEEAH and thence to Coyle (CYN). A quick glance at the NEXRAD display made this an easy question to answer -- take me to LEEAH! 

The ride was smooth and the precipitation was light as I proceeded through the "alley" where the returns were absent then headed up to the Atlantic City (ACY) area through the region of green (= light) echoes.

Having this kind of information on the airplane provides tremendous confidence and terrific decision support. You know what you are getting into. With the caveat that you must understand NEXRAD's limitations, this is a remarkable enhancement to IFR safety.

About the limitations: At the lower left of each screen image is a data label indicating the age of the information (i.e., Wx -00:06 indicates data six minutes old). In addition, the actual returns might be about five minutes old before the NEXRAD system processes them. So I am looking at precipitation areas that may be, in this case, 11 minutes out-of-date. You must avoid putting yourself into any situation where a rapidly moving cell traps you because you cut in too close to its downcourse side.

This is a strategic tool and a weather avoidance tool -- not a tactical tool or a weather penetration tool. (The latter is the onboard weather radar that the Big Iron carries.) But used for what it is, the NEXRAD/XM Weather/Garmin 396 system is incredibly valuable.


Chip said...

Those photos of N631S aloft between the storms are very cool.

Something of a non sequitur: Solar weather predictions from NASA

Frank Van Haste said...


Thanks for the link to the solar weather page. Interesting stuff. BTW, if you think these screen shots are cool, look at the post dated 6/1 documenting the 5/29 trip from KBDR to KVKX. Still more fun.

Eric said...

Awesome example of the value of onboard weather! Have you considered upgrading to the 496? I know the refresh rate is faster, but I'm not sure it would really impact the value of the weather depiction (other than smoothing out the edges of echos).

Frank Van Haste said...


I don't think that the 496 would provide much, if any, additional functionality as a weather machine. If the portable was to be my primary VHS for navigation then it would certainly be worth it. As it is, the 396 complements the GNS530 nicely. Thanks for leaving a comment.