[Update, Monday 5/10: NWMLS data back online after extended outage.]

Windermere Real Estate, John L. Scott Real Estate, Redfin and other real estate brokerages throughout the Seattle area have been unable to update their Web sites with new listings and other crucial property information for the past three days due to technical bottlenecks at the Northwest Multiple Listing Service. A technology upgrade of the NWMLS's Internet Data Exchange was supposed to be completed yesterday, but as of this morning real estate companies in Seattle said they still were not receiving the feed.

That's bad news for both home buyers and sellers who rely on the Web to research or market properties. And it comes at an especially bad time, given that many real estate companies prefer to list new homes for sale on Friday and promote open houses for the weekend.

With the data feed down, Redfin CEO Glenn Kelman said they've been unable to display properties on the site or post new listings. "Changes in a status of a property are not being reflected on any of our Web sites, and new listings aren't showing up on our Web sites," said Kelman. "It is like what happens to produce in the fridge when you haven't been to the grocery story in awhile."

Kelman said the issue is a real problem for home sellers. If someone posted a home for sale on Wednesday through the MLS, that listing would not appear on any of the Seattle area real estate Web sites that are NWMLS members.

Pat Giles, vice president of marketing, interactive marketing and information systems at John L. Scott Real Estate, said agents can manually add the property to the company's Web site. However, she said the property would appear without an MLS number. In terms of the full data feed, Giles said they had not heard when it would be restored. "It is out of our hands," she said.

Findwell CEO Kevin Lisota, whose online real estate company also relies on the NWMLS data feed, said the outage comes at an especially bad time. "This is exactly the wrong season for this to occur," said Lisota, adding that he was last told that the feed was to be live at 8 a.m. this morning. However, it still wasn't live as of late this morning.

"We’re getting inquiries from many users of our site wondering why they haven’t seen any new listings or email updates in the past three days," he said. "I would imagine that all of the other NWMLS brokers are getting the same questions right now, from both buyers and sellers, as we patiently await the new data feed.”

It is unclear when the data feed will be restored, and some real estate companies say they've had a difficult time trying to get through to the technical team at the NWMLS. Representatives at the NWMLS could not be reached this morning.

"Of course, we are annoyed that they are going through these problems, but we are also empathetic," said Kelman. "We've been through the same kind of situations and we're just hoping to get it up soon."

The outage has been a hot topic on the Redfin forums where some users are wondering when they will be able to see properties again.

"Wow... this is an epic against someone... especially in this town...," wrote one contributor. "If this happened at eBay, Paypal or any other e-Commerce site heads would roll. Millions of dollars are leaving out the window right now... They should have set this up on the side then hit a switch to see if it worked..."