Portugal has fairly mild winters by European standards. That said, it can get very wet and chilly, with bracing winds along the coast that make it feel much colder.
In the north of the country around Porto and the Douro wine country, expect average daily temperatures of around 52°F (11°C) and highs of 57°F (14°C) when the sun is shining. Average daytime temperatures in Lisbon are a shade warmer, hovering around the 55°F (13°C) mark, while the Algarve is warmer still, averaging 61°F (16°C). January sees around nine days of rainfall on average.
Crowds & Costs
After the Christmas and New Year festivities have fizzled out, Portugal falls into something of a winter slumber. Locals are also more relaxed at this time of year, so you may well see a more authentic side to the country.
It's a quiet time to visit but in many ways that's a bonus - the otherwise crowded big-hitters and Unesco World Heritage sites in Lisbon and Porto receive just a trickle of the usual visitors. It's a great opportunity to avoid the heat and squeeze in some days exploring galleries, museums, cafes and patisseries in the cities. Opening hours, however, may be restricted, and some sights only open for the summer season (roughly April through October).
On the plus side, you'll be able to take advantage of low-season deals and often significantly cheaper flights and room rates.
Where to Go
You'll want to pack a few layers, a light coat, waterproof and an umbrella at the very least when you're out and about in the cities. January is a wonderfully peaceful time to explore the capital, Lisbon, with its castle-topped historic center on the River Tagus.
Though a tad cooler and wetter, Porto is another terrific choice, with a maze of medieval alleys to wander, beautiful baroque churches to discover and an exciting food and drink scene. Don't limit your travels here, however: medieval Coimbra in central Portugal, home to the country's oldest university (founded in 1290), is a delight, as are walled towns like Évora in the south-central Alentejo region.
It's worth bearing in mind that many of the beach resorts in the south (the Algarve) and on the western Atlantic coast close entirely because of the weather. You might be able to secure a room, but don't expect a great deal else to be open.
What to Do
Rain doesn't necessarily put a dampener on a visit to Lisbon in January: there are plenty of excellent museums and art galleries to browse, and cafe-patisseries where you can happily while away the hours. You'll also sidestep the crowds at much-loved sights like the Unesco-listed Monastery of Jerónimos, which gets swamped in summer.
Riverside Porto has its own charm, and January is ideal for taking a food-focused spin of the city and hooking onto guided tours and tastings in its world-famous port wine lodges, without having to jostle with the crowds. Coimbra still has a buzz thanks to a lively student population, with bars, cafes and fado (traditional folk song) clubs tucked away in the labyrinthine alleys of its hilltop historic center.
Mild temperatures still mean a visit to the Algarve in January can have its own appeal. Come here for coastal hiking and back-country exploring in the white-washed towns that pepper the hilly interior instead of beach days.
You might not necessarily associate Portugal with snow, but there is moderate skiing in the mountainous Serra da Estrela, just east of Coimbra, when the flakes fall.
O Dia de Reis The Christmas fun is wrapped up for another year with Three Kings' Day (Epiphany) on January 6th, with family celebrations across the country. Children leave their shoes out for the Three Kings on January 5th, and in return, their shoes are filled with sweets and cakes. Patisseries sell the traditional bolo rei, a ring-shaped cake stuffed with candied fruit and nuts and dusted with icing sugar (traditionally, it also contained a baked fava bean for luck). Janeiras or Cantares de Reis go from door to door singing songs about the birth of Christ, and are offered sweets and wine.
Festa das Chouriças Grills are fired up in the small, prettily whitewashed hamlet of Querença in the Algarve for a festival devoted to smoked pork sausages. On the third weekend in January, locals celebrate their farming traditions, calling on São Luís (St Louis) to protect their pigs and livestock in return for an offering of chouriça. The day features parades, tastings and a sausage auction.
Festa das Fogaceiras Held each year on January 20th in the historic town of Santa Maria da Feira in northern Portugal, this religious festival traces its origins to the 16th century. Legend has it that São Sebastião (St Sebastian) saved the town from the plague when he was made offerings of fogaça (a sweet bread made from wheat, cinnamon and lemon zest). Today, girls in white dresses with bright sashes parade through the streets bearing the castle-shaped loaves (each with two paper flags) on their heads.