As noted here, the ftp site that holds imagery from the CIMSS/SSEC Direct Broadcast site (link) includes daytime True-Color imagery (spectacular imagery!) derived from the NOAA-20 and Suomi-NPP VIIRS instrument. Daily sectorized views of each of the Great Lakes are created, and these can be strung together, as in this web post, to show the changes around the Great Lakes during the month of December. The animation above shows the changes over Lake Superior during December. (Click here to view an mp4 animation rather than the very large animated gif).

The toggle below compares the view over/around Lake Superior on 1 and 31 December 2020. The increase in snowcover is apparent. Ice does not appear widespread on Lake Superior however.  The 31 December 2020 Lake Ice Analysis (image available here) from the Great Lakes Environmental Research Lab (GLERL) (source, from here), shows little ice.  The MIRS Lake Ice Concentration (shown at bottom, available via an LDM feed from CIMSS), similarly shows little ice in the Lakes.

Animations similar to Lake Superior’s can be accessed in this webpost as mp4s: (Lake Michigan, Lake Huron, Lake Erie, Lake Ontario) or as animated gifs (Lake Michigan, Lake Huron, Lake Erie, Lake Ontario).

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GOES-17 (GOES-West) Air Mass RGB and Mid-level Water Vapor (6.9 µm) images (above) showed an anomalously-deep Hurricane Force low pressure system as it approached the western Aleutian Islands and moved into the Bering Sea on 31 December 2020 (surface analyses). The peak wind gust at Shemya (PASY) was 72 knots (83 mph) at 09 UTC.

A closer view using a GOES-17 Water Vapor image at 0910 UTC (below) included plots of Metop ASCAT surface scatterometer winds — the highest ASCAT wind speeds were 66 knots north of the storm center, and 78 knots south of the storm center.

A toggle between Suomi NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images (below) showed the cloud circulation associated with the low at 1457 UTC — ample illumination from a Full Moon provided a superb visible image at night.

In another comparison of Suomi NPP VIIRS Infrared Window and Day/Night Band images about 10 hours later at 0053 UTC on 01 January (below), note the ship report approximately 300 miles west-northwest of Shemya: 50 knot winds, with blowing spray (which is plotted with the symbol normally used to indicate blowing sand).

Model fields indicated that the height of the Dynamic Tropopause — taken to be the pressure of the PV1.5 surface — descended to the 600 hPa pressure level as the storm moved across the Shemya area (below).

Of particular significance was the fact that a new low pressure record for the State of Alaska was set when Shemya dropped to 924.8 hPa at 2159 UTC (below).

A new Alaska land-based low pressure record has been set! Shemya, AK dropped to 924.8mb at 2159Z (1259 AKST) today. The previous accepted record was from a ship in Dutch Harbor at 925mb in 1977. Pressure is now slowly rising at Shemya. #akwx #hurricaneforce pic.twitter.com/1yiYOPvsTr

— NWS Anchorage (@NWSAnchorage) December 31, 2020

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1-minute Mesoscale Domain Sector GOES-17 (GOES-West) Night Fog brightness temperature difference (BTD) and “Red” Visible (0.64 µm) images (above) showed the nighttime and daytime signature of a fog/stratus layer that had persisted throughout much of the Snake River Basin in southern Idaho on 29 December 2020. Some sites along the Interstate 84 corridor were reporting freezing fog — and the surface visibility was restricted to less than 1/4 mile at times in Boise (KBOI).

During the preceding nighttime hours, the extent of fog/stratus cloud within the Basin was well-illuminated by a nearly-full Moon (which was in the Waxing Gibbous phase, at 99% of Full) as seen in a Suomi NPP VIIRS image at 0856 UTC (below).

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GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) revealed the formation of a mesovortex in northern Lake Superior on 28 December 2020. Mid-lake convergence — as depicted by RAP40 model surface winds — contributed to the development of this feature.

ASCAT surface scatterometer winds from Metop-A at 1537 UTC (below) provided a good view of the cyclonic flow of the mesovortex in its early stages, before it became organized enough to become obvious on satellite imagery.

A toggle between ASCAT winds from Metop-A and Metop-B (source) is shown below.

VIIRS True Color and False Color RGB images from Suomi NPP and NOAA-20 (below) showed a higher resolution view of the mesovortex; the shades of cyan in the False Color images suggested that the tops of some of the cloud bands were becoming glaciated.

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False color images from VIIRS as shown above combine bands M11, I2 and I1: 2.25 µm, 0.865 µm and 0.64 µm. Inclusion of the near-IR channel at 2.25 µm causes a color change – less red (blue and green make cyan) – in regions where ice crystals exist, because ice crystals absorb, rather than reflect, solar energy at that wavelength. A similar occurrence happens at 1.61 µm wavelengths.

Accordingly, the Day Cloud Phase Distinction RGB, shown below, highlights ice crystals in clouds (they are yellow or orange because there is less green in the RGB where ice crystals are present;  before sunrise, and after sunset, the RGB is only red:  green and blue contributions depend on solar reflectance). Solar reflectance is small at all wavelengths at this time of year over Lake Superior, but a definite color difference in the clouds of the vortex is apparent. Snow showers/squalls are more likely where the Day Cloud Phase Distinction RGB suggests ice crystals in the clouds, as shown in this blog post (and this one!).

Mesoscale vortices over warm lakes owe their existence to sensible and latent heat fluxes from the (relatively) warm water into the colder atmosphere aloft. (Click here for a presentation of such an event over southern Lake Michigan). When the vortex moved over Ontario and lost the lake fluxes, it dissipated. Visible imagery from the morning of 29 December 2020, below, showed no circulation.

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