I haven't flown that much with ADS-B, and not at all with any kind of weather. That said, ErgonomicMike's explanation seems reasonable, but has caused me to suggest something else.
It would seem there should be a list of all the current ADS-B towers, in light of the importance ErgonomicMike, and likely others, put on the towers, could iFly create a layer (so they could be turned on/off) in order to display them on our map, even when we aren't receiving an ADS-B signal? This would allow us to use the availability of ADS-B towers as part of our pre-flight planning. In addition, I can't imagine that whether or not an ADS-B tower is working won't soon be (if it isn't already) part of the NOTAM system. Therefore I would further suggest that iFly have a unique color to alert us to towers that are NOTAMed out of service, or predicted to be out of service.
Something like:
Solid Blue ADS-B tower is the known location of a tower.
Flashing Blue ADS-B tower is a tower that iFly is gathering data from.
Yellow ADS-B tower is predicted to be out of service sometime in the future, touching the tower would give the text of the NOTAM.
Flashing Yellow ADS-B tower is predicted to be out of service sometime in the future, and iFly is gathering data from the tower.
Red ADS-B tower is NOTAMed out of service at this time.
Flashing Red ADS-B tower is NOTAMed out of service at this time, but iFly is none the less gathering data from it.