While 450 and 144 propagation differs a bit, the map at
VHF Propagation Map will give one an idea from where signals are coming from. Maybe the map, updated hourly, will offer a hint on where to investigate. Warm days and cool nights equal temperature inversions. Results have been amazing these past few months.
In early June I was sraying in a second floor room at Congress Hall on the beach in Caoe May talking to some friends on 440 reoeaters in the Philadelphia area... using a VX6-R HT. The tropo lasted hours each evening.