london sky london turn unusual shade yellow monday storm ophelia bring dust sahara smoke wild fire southern europe filter certain wavelengths sunlight downgrade hurricane overnight ophelia cause two deaths ireland monday bad storm half century wind moderate british capital yellow sky surprise londoners many post picture social media ophelia come azores storm pick saharan dust north africa pick dust wild fire spain portugal spokeswoman britain meet office say yellowish hue dust high atmosphere blue element sunlight scatter dust red element get sun appear red get sort yellowish tinge say london sky turn yellow storm blow saharan dust spanish smoke