Rapture Explicitly Posttrib?

Is a posttribulational rapture explicitly taught in Scripture? A participant in a Facebook group discussion has cited two statements made by John Walvoord: 

1) "The fact is that neither pretribulationism and posttribulationism is an explicit teaching of Scripture. The Bible does not in so many words state either."

2) "Both pretribulationists and posttribulationists are confronted with the fact that the Scripture does not expressly state either view."

Then this individual claims that Walvoord's statement is only partially true:

"It is A FACT that pretribulationism is not an EXPLICIT teaching of Scripture. However, it is a FACT that the Scripture teaches a rapture AFTER the tribulation." (All capitalization his)

The idea of posttrib explicitness is based on his assumption regarding the "context" of the Mathew 24 Olivet Discourse. But what does this alleged rapture passage actually say?

And He will send forth His angels with a great trumpet and they will gather together His elect from the four winds, from one end of the sky to the other. Mat 24:31

This person's expectation (among other things) is that the gathering is the rapture, and that the elect is the church. His "context" is derived from superimposing a prewrath-posttrib assumption onto the text. One might just as easily (even more so) make a case that this passage refers to Israel's final gathering. 

Given this, John Walvoord was right: neither posttrib nor pretrib is explicit in Matt 24.  

For more see a previous post: Conclusion to Messiah's Lecture on Israel