Lower-tropospheric vortex north of Hawai’i

December 2nd, 2021 |

GOES-17 “Red” Visible (0.64 µm) images, with and without plots of Derived Motion Winds [click to play animated GIF | MP4]

GOES-17 (GOES-West) “Red” Visible (0.64 µm) images, with and without plots of Visible Derived Motion Winds (above) showed a lower-tropospheric vortex propagating west-northwestward to the north of Hawai’i on 02 December 2021. There were no ship or buoy reports in the vicinity of the vortex, but Derived Motion Wind speeds were 20-25 knots or less during this time period.

Convergence near the center of the vortex was aiding in the development of some shallow convection — and GOES-17 Day Cloud Phase Distinction RGB images (below) indicated that the tops of many cloud features comprising the vortex were glaciating (exhibiting shades of green to yellow),

GOES-17 Day Cloud Phase Distinction RGB images [click to play animated GIF | MP4]

Quiz Time: What county in the USA has all boundaries visible from satellite?

December 2nd, 2021 |
MODIS-derived BRDF from 1 December 2021 (Click to enlarge)

MODIS-derived (from Terra and Aqua satellites) Bidirectional Reflectance Distribution Function (BRDF), above, (as noted in this blog post), shows the (meager) snow distribution as of early December. How many counties (or parishes) in the United States (out of more than 3000!) are clearly delineated in Satellite Imagery such as what is shown above? Counties that are primarily islands (or peninsulas) — Dare County in North Carolina, for example — show up well (False Color image shown here, in an image taken from VIIRS Today), but the inland borders do not.

For a county to be recognizable from Space, its landcover must differ significantly from adjacent counties. In the zooming-in animation below (from RealEarth, click the image to zoom in), users will note that Menominee County in northeast Wisconsin becomes apparent. Menominee County is almost entirely forest (unlike its neighbors) and as such has a much different signal in the (for example) 0.87 µm channel on VIIRS (or 0.86 µm on GOES-16). When it is zoomed in, the outlines of the County are obvious.

MODIS-derived BRDF from 1 December 2021 at various zoom levels (Click to animate)

The county also shows up well in the VIIRS True Color/False Color toggle below, from 30 November. The southern edge of the snow at that time was just southeast of Menominee County, and the land-use change across the county border is apparent. Snow in the county (cyan in the False Color enhancement) is difficult to view from the imagery — because of the pine forests!

VIIRS True-Color and False-Color imagery over northeastern WI, 1838 UTC on 30 November 2021 (Click to enlarge)

Menominee County has been on this blog before! In 2007, a tornado tracked through Menominee County and left a visible scar in satellite imagery (link). Eight years later (link), the scar was still apparent! November 6 2021 was a clear day over the upper Midwest. Suomi-NPP True Color imagery, below (link to original large image), still shows vestiges of the scar!

Suomi NPP True-Color imagery, 6 November 2021. The outline of Menominee County is apparent, as is the southwest-to-northeast tornado scar