April is one of Rabat's finest months. Daytime highs settle around 21°C, the gardens are lush, the storks are busy on the Chellah ruins, and the Atlantic light is clear and generous. Rain becomes occasional rather than frequent, evenings are pleasantly mild, and the whole capital is comfortable to explore from morning to dusk. For sightseeing — the Oudayas, the Hassan Tower, the medina and the riverfront — there are few better windows.
The mild maritime climate makes April ideal for combining the capital with a wider northern itinerary. Casablanca is an easy hour away by train, while the Roman city of Volubilis and the grand gate of Bab Mansour at Meknes are rewarding day trips in warm, settled spring weather. In Rabat itself, the gardens of the Oudayas and the Andalusian quarter are at their most colourful, and the long walk down the medina to the sea is a pleasure.
Crowds and prices begin to build with the spring travel season, but Rabat stays calmer than Morocco's headline cities, so it remains relaxed and good value by comparison. The combination of warm, bright days, green gardens and reliably mild weather makes April a near-ideal month for a first, full-featured visit to Morocco's elegant, unhurried capital.