Check the calima forecast before locking in January or February dates
Saharan dust intrusions peak in these two months and can haze the sky at lower elevations, even when Roque de los Muchachos itself, well above the dust layer, stays clear. If your trip has any flexibility, track current dust events before you commit to a Garafía house over an observatory day trip; a hazy week at the coast doesn't always mean a wasted week at altitude.