This is my area of expertise. I'm happy to field any questions.

First question: Is this a new phenomenon? Or has distant desert been seeding our clouds for centuries?

Second question: If it is new, why? If it is old, why are we just tumbling to this?

Thanks in advance. (And what do you do, by the way? Climatologist?)

(Er, "distant desert sand been seeding...")

Ooh me too. Tiny salt particles (which become airborne when sea foam/bubbles pop and gain altitude in updrafts) actually function better than dust as cloud condensation nuclei (CCN), and the air above the Sierras generally would not be short on CCN. So while it's super cool that specs of Sahara dust are embedded in snowflakes in the Sierras, it's the moisture content of the air that will limit or enhance snowfall there, not the availability of CCN. That said, the type and amount of CCN can affect us in the form of visibility (Seattle's clearest days are with east winds, which is due to a combination of low salt particles and low humidity, for example) as well as -- to a limited extent -- cloud and precipitation patterns on the short-term local scale ("cloud-seeding" is based on this premise).

@wxPDX: are we coworkers? Are you slogging at work, too? For shame...

Errybuddy in Africa, the Middle East, and Asia, take your carpets outside and beat the devil out of them, please. Winter snowpack in my part of the western U.S. is currently about 50% of average.

The Sahara dust also feeds the Amazon, which has poor soil.

@2: 1) not new; 2) Dust as cloud condensation nuclei isn't a new research topic (try a google scholar search on "dust ccn")...what seems newsworthy about this Science article is that they've been able to track and prove the specific source of some CCN in a specific region: instead of claiming that dust from the Sahara could seed clouds in the Sierras, they're saying dust from the Sahara DOES INDEED seed clouds in the Sierras. (Disclaimer: I only read the abstract and the article you linked; I don't have a Science subscription.)

Thanks G_g, I agree with everything you said. I don't think we work together, because I'm able to access the paper. Basically, they did an aircraft campaign to take in-situ samples and data. They ran mass spec and did TEM analysis (though when I did TEM on cloud aerosols, that gave us composition, so I'm not sure why they did mass spec on some of it). They found typical dust & biogenic particles, then did some HYSPLIT back trajectories. They note that the trajectories passed over several dust regions which likely contributed. Cleverly, they used CALIPSO observations in conjunction with the back trajectories to see when the parcel(s) picked up their dust, and how the particulate matter was lofted for long range transport. That part is cool and I might crib it for my own research. I'd say the use of LIDAR w/ HYSPLIT, and that the dust went westward in the mid-latitudes (instead of eastward in the tropics, which is the usual way Sahara dust reaches the US) is what got this paper into Science. But I disagree with the authors when they say remote aerosol influence on precip formation hasn't been a focus of study -- it definitely has.

@2 I am an atmospheric scientist. I've done climatology, but now do mostly cloud microphysics and aerosol transport. There's connections between the two via radiation effects. The biggest uncertainty in the 2007 IPCC estimates of global warming were attributed to cloud-aerosol interactions, so there's a lot of study on this topic.