January is Casablanca's wettest, greyest month, but it is never cold by Moroccan standards: daytime highs hover around 17°C, kept mild by the Atlantic, while evenings turn cool and damp. The city is at its quietest — a working business capital rather than a tourist crush — so the headline sight, the colossal Hassan II Mosque on the seafront, can be toured in calm, and the Art Deco boulevards of the centre-ville explored without crowds.
This is a month for the indoor, cultural side of Casablanca. The mosque's guided interior tour, the Villa des Arts, the morning fish market and the cafés of the old Habous quarter all reward a rainy afternoon. Showers tend to arrive in blustery bands off the ocean rather than settling in all day, so dry windows for a seafront walk along the Corniche usually open up. Pack a proper waterproof and you will rarely be caught out.
For travellers framing Casablanca as a business-plus-culture stop — a day or two bookending an imperial-cities or coastal trip — January works well and cheaply. Rabat is an easy hour up the coast for a contrasting day, and the city's hotels sit at their winter lows. Just plan around the weather: keep sightseeing flexible and treat the bright spells between fronts as your cue to head outdoors.