Can someone tell me what exactly "snow" mode is?

From what I've gathered (through sparse info), it allows (or keeps) the engine in higher gears while under normal driving conditions...

Can anyone confirm this?

EDIT* So is this like the opposite of "sport" mode?

 

Yes. That's it.

I don't have my manual nearby to see how Lexus explains it, but I've always looked at it as an RPM governor, where Snow Mode restricts higher RPM's in each gear so your wheels are less likely to spin on snow. Conversely, Power Mode allows higher RPM's in each gear before upshifting to the next gear.