29 miners were killed in an explosion that rocked West Virginia’s Upper Big Branch Mine on April 5, and some experts continue to suggest inopportune weather as the cause.
Looking back at atmospheric conditions in the vicinity at the time of the blast, it seems a sudden, large drop in atmospheric pressure occurred due to a massive low-pressure system moving across the eastern United States. This scenario could have allowed more methane to escape the porous coal formations in Massey Energy Company's coal mine, therefore resulting in abnormal ventilation of gas.
According to 40-year mining veteran and retired professor of engineering at Laurentian University, Lionel Rudd, it makes sense to keep an eye on the weather. He always took note to the fact that a mine’s furnace would slow down when a very cold high-pressure system went through the area. The ventilation systems in a mine are in place to dilute methane, and if the ventilation doesn't keep up with the significant increase in volume of methane to the point where it can become explosive, you have a problem.
To put it more simply, check out this video explanation I came across on YouTube. It explains how air pressure outside a mine can influence air pressure and the movement of air and methane gas inside a mine.
In any case, the true cause of the blast is yet to be determined, but it seems more and more likely that weather will be to blame.