Several signs are pointing to Apple refreshing its MacBook Air ultraportable lineup soon — perhaps as soon as this Wednesday.

Ming-Chi Kuo, an analyst at Concord Securities, said that Apple has placed orders for 380,000 revamped MacBook Airs with Intel Sandy Bridge chips this month. Her comments came out in an AppleInsider report. Meanwhile, MacRumors reports that Twitter user @chronicwire said Apple is due to release the new Air on Wednesday.  [Update: Now Chronic Wire is saying Apple will announce unlocked iPhones on Wednesday, not MacBook Airs.]

Kuo’s information jibes with our last story on the Air refresh, which predicted that Apple would introduce new models in June or July. The new Sandy Bridge chips would be a significant improvement in computing power and battery life over the last-gen Core 2 Duo processors the Air is currently sporting.

I can’t really vouch for @chronicwire’s reliability, but I’ve heard from several Apple store employees that the company has been significantly winding down existing MacBook Air stock to prepare for a refresh. Even if the new Airs don’t hit streets this Wednesday, they’ll certainly be coming sometime soon.

Apple already upgraded its Macbook Pro line with Sandy Bridge chips in February and refreshed its iMacs in May. With competing ultraportables and other laptops already adopting Sandy Bridge chips, Apple can’t sit still and let the Macbook Air age ungracefully.

Last year’s Macbook Air redesign was a big improvement over the original version of the Air, which was criticized for being slow and underpowered. Apple also made the new Air cheaper, offering the 11.6-inch model starting at $999 and the 13-inch model at $1,299.