It's a morning just made for "Grimm." A thick, damp blanket of fog is shrouding the Portland metro as dawn breaks in early April. And in Clackamas County, near Oregon City, the cast and crew of the NBC show are hard at work, filming the "Grimm" Season 3 finale.

The mists are eerily atmospheric, a perfect fit for a series about a Portland Police detective with the magical ability to see the supernatural creatures who lurk beneath a seemingly normal surface.

By about 8 a.m. the fog begins to lift, and bursts of sunshine break through. Which also makes sense. After all, everyone is gathered here for the happiest of reasons –- to film the wedding of Monroe (Silas Weir Mitchell) and Rosalee (Bree Turner.)

“It’s a brilliant location,” says Mitchell of the log house tucked amid the trees. Driving to the location, he adds, felt special with the mist all around. It was appropriate, he says, because “this is an event.”

But, as fans of "Grimm" know, even glorious occasions like weddings can be fraught with danger. Especially when you get various Wesen –- as the supernatural creatures are known –- together. Add the presence of best man Nick Burkhardt (David Giuntoli) -- whose status as a Wesen-chasing Grimm is bound to put wedding guests on edge –- and you're begging for trouble.

Which isn’t to say the happy couple are admitting that there’s anything to worry about. “We’re in our perfect little world of love and acceptance,” says Turner.

Indeed, for now, everything is sunshine and flowers. The wedding is happening in a historic log house, which is decorated to look like a cross between Northwest Rustic and Black Forest Traditional. From the back deck, you can see and hear water flowing by. During filming breaks, actors and crew members head out there to hear the birds and breathe the fresh air.

Inside, it's close quarters, with actors and extras seated in chairs, looking toward the front of the room, where the bride, groom, best man and Nick's girlfriend, Juliette (Bitsie Tulloch) stand to run through blocking for the scene, guided by director Norberto Barba, also a "Grimm" executive producer.

Steve Oster, one of the show’s producers, says that while other places were considered for the wedding –- Timberline Lodge and Silver Falls State Park, for example -– this log house was ideal, because it was only about an hour from Portland, and felt like it was located deep within a forest.

Huge lights shine down on the cozy, polished wood interior, but it’s still chilly early in the day. Space heaters are set up here and there to warm the high-ceilinged living room. The lead actors wear parkas over their fancy wedding wear, tote coffee cups, and take swigs out of a Thermos. During this rehearsal, Tulloch wears warm boots beneath her red coat, and Turner wears a down jacket over her elegant white wedding dress.

As rehearsal begins, Mitchell solemnly walks from the rear of the room toward the altar, then does a comical stumble over a small step, as the other actors crack up.

Turner descends a rough-hewn staircase on one side of the room, and walks to the altar. “I’m legitimately nervous,” she says.

After the rehearsal, the actors disperse to wait until they’re needed for filming. Upstairs, Monroe and Turner take a break, joke around, and confess to wedding jitters.

Turner says she’s happy that Rosalee gets to wear a glamorous, strapless white wedding gown, as opposed to the heirloom garment the character was supposed to wear. That particular costume was a bit, well, frumpy.

“I would say ‘frumpy’ is a kind word,” Mitchell chimes in.

"We went properly bridal shopping in downtown Portland," Turner says, to find the dress. After a quick consult with one of the wardrobe crew, Turner says the dress came from AniA Collection.

The wedding is “a big deal,” Turner says, “so I thought more of a show-stopper dress was appropriate,” especially now that Rosalee has fallen in love, and is embracing more of her feminine side.

As for how Monroe is feeling about getting married, Mitchell says, “It’s just ‘Pinch me, is this real?’ That’s the basic thing.” Monroe –- a Blutbad, or werewolf-like Wesen –- has evolved since “Grimm” began.

Monroe has “gone from being a horologist hermit” who only left his clock-making to go outside to get his mail, “to someone who’s crime-fighting with a Grimm, and falling in love with another species.” That would be a Fuchsbau, Rosalee’s fox-like alter ego.

Outside, enjoying the sun during the break, Russell Hornsby is trying not to give away too much about what happens in the "Grimm" finale. He will reveal that his character, Hank, Nick's partner on the Portland Police force, walks the bride down the aisle.

"I am indeed honored," says Hornsby. He also hints that Adalind (Claire Coffee), the Wesen Hexenbiest, may be up to witchy mischief in the season finale, and that there may be more surprises ahead for Sgt. Wu (Reggie Lee), the Portland Police officer who has seen things he can't explain.

As “Grimm” wraps up its third season, a fourth season has been ordered, which means Hornsby will be spending even more time in Portland.

“I actually feel like my life is here now,” he says. “I’ve gotten a lot more involved in the community.” He’s also heard from real members of the Portland Police force, including one cop who said he wouldn’t be surprised if there were real Wesen here in Portland.

Just as the cameras are ready to roll, a smoke alarm inside the house starts blaring. Everyone takes a break, and Giuntoli and Tulloch pull up a chair on the log house’s front porch.

With the alarm loudly beeping in the background, Giuntoli says that Monroe and Rosalee’s wedding puts Nick is in a delicate position.

“Nick is trying to be a friend to people, and it’s probably making their lives worse,” Giuntoli says, adding that Nick “feels like a burden to a lot of his people.”

As real police show up to deal with the smoke alarm, Tulloch says the drama for her character –- who already suffered from a curse that made her forget Nick and become erotically obsessed with Nick's boss, Captain Renard (Sasha Roiz) –- may not be over.

“Everybody always asks me what’s going on with the love triangle with Renard,” Tulloch says. “And what I always say is, you undoubtedly have not seen the end of it.”

Finally, the smoke alarm is silenced, and it’s back inside to film. But Tulloch is already looking forward to what’s next.

“The show has gotten better from season to season,” she says. “So if the past is any indication, Season 4 is going to be even better.”

-- Kristi Turnquist

Do you have questions, rants or raves about Season 3 of "Grimm"? Join Kristi Turnquist this Thursday for a special all-"Grimm" TV Talk Live, our weekly live chat here at Oregonlive.com/tv, every Thursday at noon.