Went out to do the final drop chart check with the 270 AM and 140 NABs @ 36xx FPS. Wind was 7 to 12 mph @ about 25% value. I had to guess at wind speed as the battery on my weather station conked out. Target was at 430 yds, LRF'd. First two shots with 1/2moa dialed landed 1.5 moa down wind. Hmmmmm, guessed the wind wrong. Horizontal spread was less than an inch. Vertical spread was 1 MOA. Huh. Cranked in some more windage. Next two shots were again dispersed about an inch horizontal and 4" vertical. The wind was the gusty wind before it really starts to blow ahead of a thunderstorm. Cold front passing through............ Temp dropped 10 degrees almost instantly. I was on the lee side of the lava flow at a spud field edge. I was only paying attention to the wind at the shooting table and ignored down range wind. Very bad idea. The wind blew over the lavas then swirled down to the base for the last 350 yards. Before I got a 600 yard shot off the big wind came blowing over the target holder and cleaning off the shooting table.