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Snow squalls across the Upper Midwest

By Scott Bachmeier •

GOES-16

GOES-16 “Red” Visible (0.64 µm), “Clean” Infrared Window (10.35 µm) and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

The NWS Aberdeen forecast office issued a Snow Squall Warning on the morning of 09 April 2020 — and a sequence of GOES-16 (GOES-East) “Red” Visible (0.64 µm), “Clean” Infrared Window (10.35 µm) and Day Cloud Phase Distinction Red-Green-Blue (RGB) images (above) showed the southeastward movement of numerous convective cloud features responsible for the snow squalls. Cloud elements whose tops were glaciating exhibited shades of green in the RGB images; however, most cloud-top infrared brightness temperatures were generally rather warm (therefore lacking a color enhancement). No signatures of lightning were seen in GLM Flash Extent Density data with this shallow, low-topped convection. Of particular interest was the ~20 mile wide northwest-to-southeast oriented swath of fresh snowfall produced by these snow squalls, which passed through Aberdeen (KABR) and could be seen through gaps in the clouds on Visible (shades of white) and RGB images (shades of green); Aberdeen received 0.3 inch of snowfall.

Farther to the south and east, NWS Sioux Falls also issued a Snow Squall Warning — similar signatures of convective elements were seen in the GOES-16 imagery (below), including the glaciation of some of the cloud tops. Snowfall amounts were generally light (around 0.1 inch), but surface visibility was reduced to zero in some of the snow squalls.

GOES-16 "Red Visible (0.64 µm), "Clean" Infrared Window (10.35 µm) and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm), “Clean” Infrared Window (10.35 µm) and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

In addition, NWS Duluth issued a Snow Squall Warning; the corresponding GOES-16 imagery is shown below. Snowfall reports included 1.4 inches at Duluth (accumulating within 30 minutes) and 2.5 inches at Butternut, Wisconsin.

GOES-16 "Red Visible (0.64 µm), "Clean" Infrared Window (10.35 µm) and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm), “Clean” Infrared Window (10.35 µm) and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

It should be noted that these were the first Snow Squall Warnings issued by each of the 3 NWS forecast offices.



Important aspects of the boundary layer across the Upper Midwest were revealed by plots of rawinsonde data from Aberdeen, South Dakota and International Falls, Minnesota (below) — steep low-level lapse rates (surface – 3 km values of 7ºC per km) with ample moisture, and strong winds. The upper portion of the shallow convective layers were within the important -12 to -18ºC dendritic growth zone.

Plots of 12 UTC rawinsonde data from Aberdeen, South Dakota and International Falls, Minnesota [click to enlarge]

Plots of 12 UTC rawinsonde data from Aberdeen, South Dakota and International Falls, Minnesota [click to enlarge]

A time-lapse video of snow squalls that moved through Madison, Wisconsin can be seen here.

Categories: GOES-16, Red-Green-Blue (RGB) images, Winter weather