A new push of Saharan dust is expected to spread across Costa Rica this week, bringing hazy skies, reduced visibility and poorer air quality, with Thursday and Friday forecast to be the most difficult days. Residents may notice a pale or milky appearance in the sky known as calima, caused by fine particles suspended in the atmosphere. The Saharan dust originated over North Africa and traveled thousands of kilometers across the Atlantic Ocean and Caribbean Sea before reaching Central America. The dry air associated with Saharan dust can also limit the development of rain clouds, allowing particles to remain suspended longer. Conditions are forecast to improve considerably over the weekend as the main concentration of dust moves away from Costa Rica.