(CNN) -- As a volcanic ash cloud hung over parts of Europe on Thursday, weather experts said air travel in the region, and increasingly the world, will be affected by how the wind blows.
With no major storm system on the horizon, the weather --specifically the wind -- in Europe could play a significant role in how the cloud acts, CNN meteorologist Brandon Miller said.
The ash cloud, swept in from a volcanic eruption in Iceland, has affected thousands of flights and closed some of Europe's busiest airports.
"The volcanic ash is transported primarily by upper-level winds," Miller said. "Once the ash is ejected into the atmosphere by the volcano, the only real forces acting on it are gravity and wind."
Although wind patterns were pushing the plume westward Thursday, that could change if a storm occurs or if the winds began to stagnate, according to Patrick Murphy, warning coordination meteorologist at the National Aviation Weather Center in Kansas City, Missouri.
"If there were a situation where the winds would become very weak, which could allow the ash to sit, that would allow the ash to stay in stronger concentrations," Murphy said.
Such a case could cause the ash to build up and create poor visibility, said Bill Burton, associate coordinator at the Volcano Hazards Program of the U.S. Geological Survey.
At the worst, "It would create maybe a fine, thin cloud layer, if you could see it at all," Burton said. "It may dim the sun a bit, maybe create a whitish haze at the most."
As prevailing winds continue west to east, the ash will continue to cut off flight routes, Miller said.
"This fine volcanic ash can rise extremely high in the atmosphere, up to 50,000 feet, where planes cannot fly over them," Miller said. "At this height, the winds can be very strong and can therefore transport the plume of fine ash several hundred miles."
About midday Thursday, the ash cloud extended from Iceland "clear down to near the English Channel," Murphy said.
"If you were right under the plume right now, it'd be the same effect of having an overcast sky," Murphy said. "It wouldn't be a blackout, but if there were thick enough concentrations, it would obscure visibility."
Miller said the dispersion of the cloud will make it less dangerous as it travels.
It's very unlikely that United States skies would be affected, but northern Europe may not be out of the dark soon.
"The other problem is that the volcano is still erupting and still transmitting the ash into the atmosphere," Miller said. "As long as the volcano is erupting, the ash will continue being transported by the wind, and flight disruption will continue."
The flight cancellations go beyond visibility concerns, Burton said. "The problem is with the silica in the ash. Silica is like glass, so basically the glass content of the magma melts onto the hot metal" of the aircraft engine.
"The ash could be confined to higher elevations. There's also sulfur dioxide in the ash, which could act as an irritant to people. That is a possibility, but that's a very fine part of the ash," Burton said. "The prevailing winds are the big story here."