A fast-moving shortwave trough brought a quick shot of wintry precip to parts of the Upper Midwest during the early part of 15 Jan. With an associated surface low pressure departing into the Ohio Valley, and high pressure building in from the west, northwest winds gusting to around 30 mph developed across the region.
The gusty northwest winds lofted snow off of the ground, causing areas of blowing snow and leading to reduced visiblities under otherwise clear skies across southern Minnesota and northern Iowa during the afternoon and early evening of 15 Jan. Bands reminiscent of cloud streets associated with the areas of blowing snow could be diagnosed in GOES-16 imagery. First analyzing the 0.64 um VIS, the bands of lofted snow area not obvious, but shadowing, especially later in the day, and the high (500 m) resolution of the band allowed for detection of the features (Fig 1).
The 1.6 um “snow/ice” band has been shown to effectively highlight areas of lofted snow (blowing snow) from the clear sky. The reflectance of the lofted tiny ice particles is typically between that of snow/ice on the surface (lower reflectance) and low liquid clouds (higher reflectance). Therefore, the lofted ice (over snow) can be more easily identified in the 1.6 m band vs the 0.64 um band, despite having a lower (1 km) spatial resolution.
Combining the aforementioned two bands with the 10.3 um IR window band in the Day Cloud Phase Distinction RGB, we get an even better picture of the blowing snow. The lofted ice is identified as a dull cyan above the surface snow (green) and adjacent to the low liquid water clouds (bright blue).
The Day-Snow-Fog RGB, which also includes the 1.6 um band (along with 0.87 um and 3.9 – 10.3 um difference), has been discussed as an effective means of identifying and tracking blowing snow. The contribution from 1.6 um band is the main driver behind the detection, with slight contribution from the other two components. For blowing snow detection, we replace the 0.87 um component with the higher resolution 0.64 um visible channel in order to capture finer details in the blowing snow bands.
Slight modifications were made to the RGBs in order to better highlight the feature of interest. The recipes used in this post are shown in figure 5.
Finally, a SNPP overpass during the early afternoon allowed for high resolution VIIRS imagery of the blowing snow bands to be collected. The 375 m 1.61 um band (I3) provided a great depiction of the blowing snow “streets” across the region.
Bill Line, NESDIS/CIRA