I’ve been a little lazy about this whole Divine Strake business. Fortunately, several of my colleagues—John Pike, Andy Lichterman, Hans Kristensen,, John Fleck and Bill Arkin—have been all over the story.
Long story, short (via Hans): DOE is making a gi-normous (about 0.6 kt) conventional explosion that is probably a simulation of a B 61 Mod 11 Earth Penetrating Warhead:
DTRA confirmed that Divine Strake is the same event that is described in DTRA budget documents as being a low-yield nuclear weapons shock simulation designed to allow the warfighters to fine-tune the yield of nuclear weapons in strikes against underground facilities. The Divine Strake event will detonate 700 tons of chemical explosives corresponding to a yield of 593 tons of TNT (~0.6 kt). The nuclear weapon with the lowest yield is the B61 bomb, which has four selective yields down to 0.3 kt.