The skies over Southcentral Alaska were mostly cloud-free this weekend, but a yellowish haze made it difficult to spot Sleeping Lady and other nearby peaks from popular hiking spots like Arctic Valley and McHugh Creek. Monday was even bleaker.

Why is that?

Part of the reason is dust being kicked around due to a weeks-long dry spell and this year's early break-up, and there is also perennial glacial dust that whips around in the spring, said Bill Ludwig, lead forecaster for the U.S. National Weather Service Alaska.

But researchers from NWS sparked conversations and speculations when they shared a graph containing the results of a backward trajectory analysis to give an idea of what is hanging around the Chugach Mountains.

“Would you be surprised to hear that it originated in China?” Samuel Shea, acting science operations officer of the Weather Forecast Office in Anchorage, wrote on the service’s official Facebook late last week.

The chart was deleted Monday, but in the post, the NWS singled out China using the Hybrid-Single Particle Lagrangian Integrated Trajectory. HYSPLIT relies on archived meteorological observations and short-term forecasts to project where particulate matter will end up or to back-track and figure out likely sources of things in the atmosphere.

What Anchorage residents have been squinting through in recent days likely comes from China, though the results are far from conclusive: “It’s not an exact science,” Shea said. “It’s kind of speculative.”

With a level of accuracy somewhat comparable to an extended weather forecast, NWS traced the source of particulate matter back to Eastern China, following a “W” pattern over the Pacific Ocean.

The sketch may look strange on a map, but so goes the wind: generally from west to east and often unpredictable.

Given China's poor reputation for air quality, a lot of people wrongly guessed that the stuff in the air is pollution.

Shea said the post was removed not because of its content but because of misinformation spread by commenters who assumed the Chinese haze must be from industrial pollutants, an inaccuracy that is "inconsistent with the mission of the NWS," he said.

One of the few things that is a near certainty, Shea said, is that the haze is not the result of industrial Chinese pollution and is in fact not pollution at all. More likely is that the particulate matter is from a series of colossal wind storms recently reported in China or wildfires in the country.

There is also a Russian wildfire currently burning a land area about the size of Los Angeles County – mostly in the Irkutsk and Omsk regions and near Lake Baikal, all parts of Siberia – and that too may be making the haze hazier.

Alaskan forest fires occasionally hurl hazy particulate matter down toward the Lower 48, something that reportedly happened in 2012.

"If we have fires in the Interior, it can make it all the way down there, it smells smoky and their sunsets turn bright red," Shea said. "It's not big forest fires causing problems now."

Whatever the reason, Ludwig said the rainy forecast projected for Tuesday and Wednesday could lead to blue skies by the end of the week.

"The atmosphere is kind of a dirty mixing pot," Ludwig said. "Rain should help clean things up."