A heavy sandstorm blanketed Saudi Arabia’s capital on Thursday, reducing visibility at times to less than a meter. Riyadh residents saw their city once again enveloped by dust as authorities put out safety messages to the inhabitants of the country’s largest population center. The Ministry of Health advised residents to take safety measures when heading outdoors. “It is important to wear a protective medical mask when leaving the house since the dust will agitate the respiratory system,” posted the Ministry in an Arabic tweet on its Riyadh account. The capital isn’t a stranger to sandstorms with occurrences this year in August, March and February.