NBC’s year-old digital weather network Weather Plus will bring its shared national and local weather approach to the Internet today in an effort to take on Web weather incumbent Weather.com.

Weather Plus is currently in about 90 local TV markets representing 75 percent of the United States. The digital network reaches about 15 million cable homes and draws on the resources of Weather Plus meteorologists and local weathercasters in all of its markets.

The NBCweatherplus.com Web site is the next logical brand extension for the network, which is quickly becoming the de facto weather brand for NBC. MSNBC and many NBC local affiliates have recently rebranded their weather coverage with the “Weather Plus” moniker, and during breaking weather news the youthful diginet is becoming the source for NBC News programs such as “Dateline,” “Today” and “NBC Nightly News.”

The NBCweatherplus.com rollout begins with the 14 NBC-owned stations and will add its other affiliates in the next several months.

In so doing, NBCweatherplus.com intends to challenge The Weather Channel’s Weather.com by putting more local flavor into online weather. The new service also opens another ad sales opportunity for TV stations, since ad inventory on the site will be shared by the stations and the network.

Weather.com is hugely dominant online, with its intuitive URL and strong brand that attracts 26 million unique monthly visitors.

Mike Steib, the general manager for Weather Plus, said he likes his chances. “We have built NBCweatherplus.com on both the same principle and the same assets of our TV network,” he said. “Stations are the best source for local weather information, and that’s what people care about. What viewers have told us over and over again is their No. 1 source for weather info is local news, and the top driver for which news to watch is often the weather they like to watch.”

So Weather Plus will test whether that concept plays out on the Internet, since the new Web service will mix national weather reports with coverage and forecasts from the local weathercasters at its affiliated stations.

For instance, if a site visitor enters a New York ZIP code, the site takes that visitor to a section branded by WNBC-TV, the NBC owned-and-operated station in New York, with pictures, video and a message from the station’s meteorologist. “It’s not a computer that sits off somewhere and says the temperature in New York will be this,” Mr. Steib said. “We believe the meteorologists in the market can best predict and forecast the weather.”

Visitors can also jump to different markets within the site, thereby tying the local station partners seamlessly into the site. Also, when viewers visit the Web sites of the local Weather Plus affiliates such as WNBC or NBC-owned KXAS-TV in Dallas to request weather information, they will be redirected to the portion of NBCweatherplus

.com dedicated to that station. That handoff between NBCweatherplus.com and its local stations means the new site will have a built-in audience from the get-go because weather traffic from the local stations’ sites will be routed to the mother ship at NBCweatherplus.com.

Tom O’Brien, the general manager and president for KXAS, said the new service gives the station one more advantage in a competitive market.

“Every content provider is fighting parity,” he said. “This gives us something no one else has. With weather being a driving factor, this really just adds to the portfolio of products we have to offer. … This is the coordinated product of three platforms.”

NBC will promote NBCweatherplus.com heavily on the NBC affiliates and will introduce a Web and television marketing campaign later this month.

“It will be a substantial and meaningful increase for the TV stations,” Mr. Steib said. “We’re not putting in all this effort to just bump traffic 10 percent. NBCweatherplus.com will be a major player in the online weather space.”

But NBCweatherplus.com will have its work cut out for it trying to drain market share from Weather.com, said Gordon Borrell, president of local media research firm Borrell Associates.

“[The Weather Channel] has created very formidable competition in Weather .com,” he said. “Weather.com and Weather Channel are about as ubiquitous as oxygen. They are on the AOL opening screen, Yahoo weather screen. They are in planes, on ships, on TV screens, on computers, on cellphones and GPS devices,” he said.

It’s also a trusted online brand. Weather.com commissioned a Nielsen study last fall that found that 39 percent of online users rated Weather.com as the most trusted weather source online, well ahead of second-place National Weather Service at 11 percent and the Web site of the local station or newspaper at 8 percent.

Local stations have always been competitors of Weather

.com, said Joe Fiveash, senior VP and general manager of Weather Channel Interactive. “The single other place where consumers go other [than us] for weather coverage is the online or on-air [local station], so this is nothing particularly new, but another chapter in a long-running competition for local users,” he said.

And Weather.com will go more local as it introduces new functionality later this year that will provide conditions every mile and every 10 minutes. Weather.com has tested the service for the past few months and will extend it deeper across the site later this year. “If it’s raining at work and not raining halfway to your house on your commute, you will know that,” Mr. Fiveash said.

The Internet has changed the way consumers obtain weather to an on-demand and personalized model, said Gary Gannaway, CEO of WorldNow, which powers the Web sites for more than 200 local media properties, including local TV stations. “The NBC … effort sure is a great step in helping local stations to extend their local weather franchises. There definitely is a powerful local weather niche that’s there for the taking,” he said.

Tolman Geffs, managing director of investment bank The Jordan, Edmiston Group, also likes the local approach of Weather Plus. “My sense is that [Weather Plus] online will be a home run,” he said. Mr. Geffs previously headed IBS, which provides content for local TV station sites, including the NBC-owned stations.

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