Wax paper sky: Wildfire smoke blots out sun and blue sky again

Chalk up another smoky sky day across Minnesota Friday.

The usually blue October sky above Minnesota is tinted white again. The smoke plume is emanating from wildfires in Wyoming, Colorado and California. You can see the smoky smudges drifting eastward on Friday GOES-16 visible satellite loop from the Rockies into the Upper Midwest.

Friday’s wildfire smoke map generated from U.S. Forest Service data shows thicker smoke plumes covering parts of the Upper Midwest. You can see the individual wildfire sources out west.

Trimming temperatures

The smoke over Minnesota Friday is thick enough to reflect some of the inbound solar radiation that would otherwise be used to heat the ground. The low October sun angle also makes this effect stronger than it would in mid-summer.

The result is that temperatures are likely several degrees cooler than forecast than they would be under a clear blue sky Friday.

Smoke reaching ground level?

Some of the smoke may be reaching ground level in southern Minnesota. Friday’s air quality report from the MPCA shows air quality reading into the moderate (51-100 ppm) range in the Twin Cities (60 ppm) and southern Minnesota. Marshall’s reading of 97 ppm is close to the “unhealthy for sensitive groups” category.

Air quality is expected to improve this weekend as frontal systems pass through Minnesota. Here are the latest air quality forecast details from the MPCA.

Thu, Oct 8, 2020:

Another wave of upper level smoke from wildfires in CO/WY as well as California is expected to transport over the state late this afternoon, but is expected to remain loft today. A sunny, pleasant day is otherwise expected.

A warm-up is expected tomorrow as southerly winds continue to pull in warm air from the south. High temperatures may reach the low 80s in the southwest corner of the state. A cold front will pass through the state late in the afternoon.

Some upper level smoke is expected to mix down to the surface along the cold front as it moves across the state. Therefore, Yellow (moderate) air quality is forecast for central and southern Minnesota. The warm, dry air will also favor ozone. In addition to the smoke, ozone may reach Yellow AQI category for the southern part of the state along with the Twin Cities.

Winds will remain from the north most of the day Saturday and temperatures will return to average. This will clear any lingering smoke and return air quality to the Green (good) category statewide. Winds will return from the south as the next weather system approaches on Sunday. Air quality should remain in the Green category Sunday.