If the trumpets and vials move in tandem, and if the Islamic State (IS) represent the locusts of the fifth trumpet; then it corresponds with the fifth vial which is darkness and gnawing tongues (a symptom of dehydration; article) over the beast's kingdom (Sunni Islam; aka Babylon).  Thus the sixth trumpet and vial would commence after the five months of locusts end.

The last five years of drought in the Middle East have beaten records over 100 years old. article
 
"12One woe is past; and, behold, there come two woes more hereafter. 13And the sixth angel sounded, and I heard a voice from the four horns of the golden altar which is before God, 14Saying to the sixth angel which had the trumpet, Loose the four angels which are bound in the great river Euphrates. 15And the four angels were loosed, which were prepared for an hour, and a day, and a month, and a year, for to slay the third part of men. 16And the number of the army of the horsemen were two hundred thousand thousand: and I heard the number of them. 17And thus I saw the horses in the vision, and them that sat on them, having breastplates of fire, and of jacinth, and brimstone: and the heads of the horses were as the heads of lions; and out of their mouths issued fire and smoke and brimstone. 18By these three was the third part of men killed, by the fire, and by the smoke, and by the brimstone, which issued out of their mouths. 19For their power is in their mouth, and in their tails: for their tails were like to serpents, and had heads, and with them they do hurt. 20And the rest of the men which were not killed by these plagues yet repented not of the works of their hands, that they should not worship devils, and idols of gold, and silver, and brass, and stone, and of wood: which neither can see, nor hear, nor walk: 21Neither repented they of their murders, nor of their sorceries, nor of their fornication, nor of their thefts." (Revelation 9:12-21)

"10And the fifth angel poured out his vial on the seat of the beast; and his kingdom was full of darkness; and they gnawed their tongues for pain, 11And blasphemed the God of heaven because of their pains and their sores, and repented not of their deeds. 12And the sixth angel poured out his vial on the great river Euphrates; and the water thereof was dried up, that the way of the kings of the east might be prepared. 13And I saw three unclean spirits like frogs come out of the mouth of the dragon, and out of the mouth of the beast, and out of the mouth of the false prophet. 14For they are the spirits of devils, working miracles, which go forth to the kings of the earth and of the whole world, to gather them to the battle of that great day of God Almighty. 15Behold, I come as a thief. Blessed is he that watches, and keeps his garments, lest he walk naked, and they see his shame. 16And he gathered them together into a place called in the Hebrew tongue Armageddon." (Revelation 16:10-16)

The sixth trumpet and the sixth vial are the only two passages in the New Testament which mention the Euphrates River.  The news portrayed the Mosul Dam on the Tigris River as very poorly built and difficult to maintain.  What if there were FOUR key dams on the Euphrates River which God graciously sent angels to protect?  Will they soon be relieved of duty so that IS can completely restrict the flow of water in order to control the people, thus enabling an army of 200,000,000 to cross it?

The IS has threatened Turkey to give them control of a dam, and IS now has 49 Turks from Mosul to bargain with. article

"Since January 2014, the Islamic State (IS) in Iraq has succeeded in taking control of several dams. To date, the group controls the Haditha Dam (the second-largest in the country), the Samarra Barrage and the Nuaimiyah Dam. Between January and April, the IS also controlled the strategic Fallujah Dam.
The dams are an essential element of the group’s military strategy. The IS has already proved its determination to use the dams as a weapon by deliberately drowning government forces around the Nuaimiyah Dam. When in control of the Fallujah Dam, the group closed eight of the ten doors of the dam, reducing water levels in the south and flooding land upstream." article

"In April 2014, fighters of the Islamic State in Iraq and Syria captured the Nuaimiyah Dam in western Iraq, despite earlier efforts to defend the site. They then overflowed it to dislodge Iraqi soldiers dug in upstream of the site—and to deny drinking water to civilians downstream." article

"The [Haditha] dam, which regulates the waters of the River Euphrates, is located north of the city of Haditha, approximately 150 miles (240 km) northwest of Baghdad. It is a major source of hydroelectricity for Iraq’s national grid behind Mosul Dam, which was recaptured by Kurdish and Iraqi forces backed by US air power on Monday." article

It would be an interesting twist if the red, yellow and blue uniformed army gathered in the Jezreel Valley was actually invited by Israel to use that area as a base from which to launch a campaign against IS.  Then if Israel launched rockets against Iran's nuclear facilities, this coalition army turned and attacked Israel instead.  There are so many ways this could play out, and several have nothing to do with prophecy.
I'm just continuing to watch for my Lord's return.