pwk,
Meadow is one of those "borderline" streams. Its temperatures often reach into the 70's, or even 80, during really hot spells. But if the summer is relatively cool, it may have many holdovers during that year, because nights in the mountains often get fairly cool even during July and August.
Also, it does have some feeder streams and springs that can support minimal numbers of trout during hot periods. So it usually does hold some, albeit sometimes very few, trout through the year (unless it is a real blisterer of a summer).
All of that said, this is no spring fed limestoner. Fish often struggle to keep from asphyxiating during the summer. For that reason alone I rarely fish it into July and August.
Ironically, I have caught native brookies in certain locations in Meadow, no doubt migrated from a tributary. And there are reports of wild rainbows being caught too. But these instances are very rare. Generally speaking, Meadow is a marginal stream when it comes to temperatures.
However, there are other streams in the area that have better temps throughout the year such as Dunbar Creek and some small brookie streams in the Laurel Highlands. These are always your better bet to fish during the summer heat.