Does a smart app exist that will let me use Accuweather for outside temperature, and when the outside temp drops below a threshold the thermostat will switch from heat to emergency/aux heat? Just the opposite for when the temp goes above that same threshold.
Not sure about accuweather, but there is Wunderground integration. I use WebCore for a similar need, I have a roof heating wire for my gutters up here in the North East to prevent icedams … I have a piston that checks to see if any snow has fallen in past 48h or will fall in next 24h AND that the temp is below 38F if so turn on the heater - otherwise turn off the heater
BTW with WebCore Wunderground’s API is built into the smartapp
My Ecobee does this for me automatically.