Dense Fog — San Juan River Basin, Colorado

2025-04-20 · San Juan River Basin, Colorado

Event narrative

Dense fog that produced visibility of 1/4 mile or less at the KDRO ASOS was observed, via satellite, to extend into the adjacent Colorado Forecast Zone 023. The nearest surface observation points in this zone, including the KPSO AWOS, were well north of the patch of dense fog, which had remained in the river basin close to the New Mexico border. However, with the visibilities produced in the adjacent zone, it is highly likely that these conditions extended, at least locally, into this zone as well. No reports of injuries, damages, or fatalities were received related to this event.

Wider weather episode

A wet spring storm had moved through western Colorado in the days before this event, bringing mountain snow, as well as mixed rain and snow in the lower elevation valleys. Particularly, in the southern Colorado valleys, rain and snow allowed for increased surface moisture to become trapped. As skies cleared and temperatures cooled, this trapped moisture condensed, becoming patchy dense fog across the southwestern Colorado valleys.

Source: NOAA Storm Events Database, event_id 1257254. Narrative written by the NWS forecast office that issued the report.