Not a drop of rain had fallen in Feralas during the year and a half that the virtual forest existed -- until last week, when there was finally a chance of showers. Weather was at last introduced to Feralas, and the rest of "World of Warcraft," by game developers.

Rain and other inclement weather had been promised to the millions who play "World of Warcraft" since the massively multiplayer online PC game's launch in November 2004. A rotating team of developers at Blizzard Entertainment actually worked on creating a weather system for five years. Only last week, however, did the game's developers find a way to patch it into the game in a way the meets their expectations -- and that they hope will meet fans' as well.

In the course of preparing that weather, developers have to make decisions about what video game weather should actually be. Should it just be something to look at or should it have an impact? When should it rain and where? And if game designers could decide the time and date of a rainstorm, should they?

"Coming up with the weather system for a world is fun," said Jeff Kaplan, 33, lead designer at Blizzard Entertainment's Irvine, California, headquarters, where the real-life lack of precipitation resembles the old weather-free version of his game. The falling-from-the-sky possibilities are broad when you're designing weather for a video game. "We've talked about how cool would it be when you killed the blood god, that it rains blood."

Blood storms aside, Kaplan said that Blizzard is approaching the change in climate modestly. Last week, three types of weather were introduced to "WoW": rainstorms, sandstorms and snowstorms. They have a chance of occurring in just 11 of the game's 40-plus realms and will crop up with a frequency that has been designed to err on the side of too little.

Inclement weather is by no means new to video games. Rain fell in the opening moments of 1991's "Legend of Zelda: A Link to the Past." It falls regularly during the ever-flowing day and night cycles of the recent "Grand Theft Auto" games. Even among massively multiplayer games, "WoW" has forerunners, including "Final Fantasy XI," where each day (lasting about an hour in real life) can bring storms, and in "EverQuest," in which some characters have the power to repel the weather.

But what "WoW" lacks in innovation, Kaplan thinks it may make up for in immersive authenticity, mostly thanks to the fact that a day in his game matches the pace of a day in the real world. "Rainstorms can last three to four hours," he said. "We wanted to feel like when it's raining it feels like a rainy day, but it's not always a rainy day."

Kaplan said Blizzard's weather team -- game designers accustomed to being the godlike architects of the worlds they create -- talked about a system that would have them decreeing the weather day by day, but opted to set up a program and leave the weather patterns to computerized number-crunching. "If we were to sort of handpick the weather for each day, we would probably do it in such a way that you wouldn't notice that someone was handpicking it, in which case it's like, 'Why go through that trouble in the first place?' " Kaplan said.

Instead, each sub-zone among the 11 where weather is currently available is now linked to a set of variables that allow for the possibility of precipitation. The variables have been set to make the potential weather appropriate, meaning heavy showers are more likely in one region and drizzles in another. As Kaplan described it, the zone is practically asking itself whether there will be weather. "It's sort of randomly picking: 'I'm ready to rain but do I want to rain?' " he said. Duration will be chosen based on an automated system as well, with enough variables to make things unpredictable. "We didn't want it to be such a mathematical formula that somebody could literally sit with a stopwatch, log in, go to a zone and go, 'OK in two, one, go -- it's going to rain.' "

Kaplan has seen gamer requests for rain that isn't just cosmetic but has the effect of rusting armor and muddling travel. Those are even the types of features promised in the upcoming MMO "Dark and Light," whose Web site says winds will slow winged characters and accumulating snow will stymie dwarves. Kaplan is not into that kind of thing. "There's already an oppressive feel when the lightning comes in and the rain starts to hit," he said. "I think that's enough that we don't need to straight-up slow gameplay down." That isn't to say Blizzard isn't considering weather that has effects. "If we ever do add things that would tie directly into the weather, we'd rather do something more as a bonus," Kaplan said. "Like perhaps more herbs grow after it rains."

The weather in "WoW" not only doesn't have any effects currently, it's also not tied into any seasons just yet. Seasonal weather features prominently in Nintendo's "Animal Crossing" series, with games that feature a year's worth of predetermined events for the title's small village and randomly generate weather that is appropriate to the seasons. Kaplan praises that game's weather system highly and admits that seasonal weather could be on the "Warcraft" horizon. "That's on our To-Do-If-It's-Cool list," he said.

Also on that list is the possibility that gamers who kill Hakkar, the blood god, will cause a rain of blood and that a storm of ashes might surround in-game volcanoes. For a zone in an upcoming expansion pack, the team is considering storms of Arcane energy.

They're also thinking about worldwide events. Currently weather is isolated to just one zone at a time, but "WoW" designers are well-versed in creating global wars and holiday-themed happenings. "We could have a monsoon to rain everywhere pretty intensely for about a week," Kaplan said. Or on Christmas it might snow everywhere all at once.

Reaction to the weather has been predictably mixed. Gamers on Blizzard's official message board delivered a range of reactions, from concerns that weather would slow their computers (in a thread titled "WTF!?! Weather?") to a user who experienced a test-run of rain and reported back: "Just like real weather, never really know when it'll hit and never really sure when it'll end. It's a nice addition though, makes it more pleasant."

There's actually a Blizzard staffer watching fan reaction and preparing new weather patterns. He's not a full-time weather guy -- he's also preparing an upcoming worldwide invasion of the undead. But he's the one at the forefront of the "WoW" storm fronts.

" 'Is there too much weather or not enough weather?' That's the big question that we're asking ourselves right now," said Kaplan. "I feel like the jury is still out on the weather." He wants everyone to experience a few weeks' worth or storms before they decide.

After that, bring on the monsoons.