During winter, a fine carpet of mustard blossoms overtakes Napa Valley vineyards. The mustard blooms in the winter, from about January to March. (Amanda McClements/For The Washington Post)

In California’s Napa Valley, winter is a season that really cuts the mustard

Convertible or no convertible? That was the critical question.

I was booking a rental car for a January trip to California’s Napa Valley, while simultaneously checking the wine country weather online. Something I’d been doing for days. As if I could affect climate change by hitting “refresh.”

The forecast called for highs in the measly low 50s with a likelihood of rain. No convertible.

Where to go and what to know in Napa.

Time to revise my wine country daydream. In my mind, the scene played out like one of those teeth-whitening commercials — convertible top down, wind-whipped hair, warm rays of golden sun bouncing off lush vineyard leaves. I laugh, step on the gas and flash a gleaming white smile (commercial smiles are impervious to repeated tastes of jammy zinfandels!) as I ride off into the vine-covered hills.

I’d actually lived that fantasy — and driven that convertible — a few times. My first trip to the region about six years ago was during the climatic perfection that is October. I fell in love, hard. Autumn in the Napa Valley casts a strong spell, with its amber-hued vineyards, 80-degree days and cool nights warmed by ubiquitous fireplaces.

Since then, I’ve made an almost yearly pilgrimage to eat, drink and soak in the scenery — always in the glorious warmth of fall. So when a business trip called my husband to San Francisco in mid-January last year, and he asked whether I’d like to tack on a few days at our favorite spot in the region, my first reaction was “Of course!” My second was “Brr.”

To my East Coast brain, January means barren landscapes with nary a touch of life, save for prickly, persistent evergreens. There would be good wine, no doubt, but visions of leafless, dormant vines, gray skies and that infamous bone-chilling California fog clouded my excitement.

Then I arrived and met the mustard.

After pointing our non-convertible north out of San Francisco, over a mist-shrouded Golden Gate Bridge and into wine country, we cruised up Napa’s well-trod Route 29 and ran into a most welcome and breathtaking sight: The valley floor was blanketed in a vibrant carpet of bright yellow mustard flowers.

Despite many visits, I was ignorant to the winter phenomenon known as mustard season in the Napa Valley. As locals tell the story, Spanish friars who established missions up and down the state in the 1700s sprinkled mustard seeds as they went, leaving a canary-colored path in their wake. Better than bread crumbs, I suppose?

Thanks to winter rains, the hearty wild mustard starts populating the valley floor with blossoms in January and blooms until about March, when many winemakers plow it back into the soil, where it adds nitrogen.

The showy display can stop cars in their tracks. Literally.

Rounding a bend in the road, we avoided a near pileup as cars swerved onto the shoulder to ogle a particularly stunning vineyard teeming with mustard. We hopped out to join a handful of tourists wading through the knee-high blooms for photo ops.

The winter sun hung low in the sky, casting dramatic rays on the field. Gnarled black vines stretched up from the sea of yellow like witches’ hands. A professional photographer, set up deep in the flowers, snapped away at a family kneeling in the buttery glow.

So I’d clearly been wrong about that whole “barren” thing. As my pre-trip anxieties melted away like the snow that almost never falls here, other off-season perks became apparent.

The vibe in the tasting rooms we visited — from Carneros’s Cuvaison to notable sparkling wine producer Schramsberg — was downright serene, a stark contrast to fall’s harried grape harvest season.

“Once the wine’s in and fermenting, it’s the quietest time of the year, so the winemakers are relatively cool, calm and collected,” said Clay Gregory, president and chief executive of the Napa Valley Destination Council. “So it’s a great time to get more personal attention from winemakers and winery owners.”

Mustard aside, the marketing minds at the council have started pushing another moniker to drum up tourism in the slow months: “Cabernet Season.” The bold flavors of Napa’s flagship wine, cabernet sauvignon, are perfect for cold nights, Gregory explained. “And it’s a lot better than calling it winter.”

To seek out tastes of those signature cabs, we ensconced ourselves in one of the comfortable cottages at the Carneros Inn, well positioned between the bases of the Sonoma and Napa valleys.

Once the site of a trailer park and RV storage, the 27-acre resort now comprises neat rows of cottages and homes, several restaurants, a gourmet market, a spa and — my favorite — a hilltop pool where horses from the neighboring farm saunter up to the fence in hopes of scoring an apple handout from the orchard.

Our cottage’s spacious private patio, lined with a corrugated metal fence and scrubby rosemary bushes, was outfitted with heaters, a gas fireplace and a clawfoot tub, turning January’s chill into a treat.

As we set out the next morning for our first wine-tasting appointment, thick fog hung oppressively overhead. But there was the cheerful mustard to the rescue, tenaciously glowing in the midday gloom.

At Spring Mountain Vineyard, the manicured hillside backdrop for the 1980s soap opera “Falcon Crest,” we splurged on a bottle of the lush 2005 Elivette, a blend of cabernet sauvignon, cabernet franc, petit verdot and merlot.

From there, we continued up the mountain, where nubbly green moss coated the blackened branches of damp trees. Somewhere along the ascent to 2,000 feet, we burst through the blanket of fog, leaving behind what looked like an ocean of undulating clouds concealing the valley below.

Perched on the sun-drenched mountaintop at Pride Mountain Vineyards, whose property is bisected by the Napa-Sonoma county line, it seemed that the season had changed on us. Then came a winter reminder: The case of wine we ordered wouldn’t ship until the low temperatures back in Washington stayed above 45, we were informed. That could be several months, I fretted, pining for the black cherry-nosed cab they’d boxed up for us.

We ran into a few other winter snags. I was eager to try the Napa restaurant Oenotri, a hot Italian newcomer since my last trip, but it was closed for a winter break. A few other well-known eateries were also taking seasonal timeouts.

But we had no problem scoring a table at the buzzing Rotisserie and Wine, then a month-old Tyler Florence restaurant on downtown Napa’s revitalized riverfront. The menu’s South-by-way-of-wine-country slant meant a dinner of deviled eggs topped with crisp chicken skin and hot sauce, and duck confit with waffles.

On our last day, the gloom was back as we pulled into Francis Ford Coppola’s Rubicon Estate (recently renamed Inglenook). From the parking lot, we waded through a milky fog so thick it would have provided perfect cover for Kurtz’s lair in “Apocalypse Now.” Inside, Coppola’s collection of vintage zoetropes and cinema memorabilia distracted us from the main wine attractions.

For a final stop, we hit an old favorite, Frank Family Vineyards, where the tasting notes for the 2008 Reserve Zinfandel called out wintry imagery — minced meat tarts and roasted hazelnuts. I quizzed the woman doling out splashes about living through wine country winters. “Even when it’s dark and gray, it’s not gross,” she said. “It’s never not nice.”

Even if you’re not riding in a convertible.

Where to go and what to know in Nappa.

McClements is a Washington-based writer and creator of the food and dining site Metrocurean.