The SAR wind analysis above shows curious banded wind features over central Lake Huron. The bands have a vertical separation of around 10 km and exist just south of essentially calm winds (magenta in the enhancement used). Peak winds within the bands 8-10 m/s, and the (weaker) winds in between the peaks are 4-6 m/s. Because this blogger can’t quite figure out why they’re there, the ‘What the Heck is this?’ category is being used. The region of light winds is between a cold front to the north, and high pressure to the south (1500 UTC surface analysis). The slider below compares the wind field to the 3.9 µm brightness temperature field (Note that only values between 0 and 6^o C are shown). There is an obvious relationship between brightness temperatures between the very light winds between northern lower Michigan and Manitoulin Island — the lake surface has brightness temperatures between 2.2^o and 2.8^o C where winds are lighter vs. 3^o – 3.9^o C where stronger winds exist to the south; however, the banded wind features do not appear to have an appreciable effect on the underlying lake surface temperatures.

The 1200 UTC sounding from Detroit, from the Wyoming Sounding site, shows stable air below 800 mb. The airmass will be chilled from beneath when it moves over the Lake, too, so a strong surface inversion likely exists as well.

The toggle below compares derived winds and Normalized Radar Cross Section (NRCS) fields at 1144 UTC from RCM-2 observations.

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Added: 17 April 2023: This website shows SAR data over Lake Huron only (other individual Great Lakes views are available here). Included at the Lake Huron website is a netcdf file that combines both scenes on this day over Lake Huron, shown below in a slider with the GOES-16 Low-Level water vapor imagery (that is, Band 10 at 7.34 µm). There are features in the ABI imagery that overlap the wind features. (Click here to see a toggle). Note that the color enhancement bounds have been altered slightly from the default (-109 to 55 ^oC) to -107 to 58 ^oC to make the bands more obvious.

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The animation of GOES-16 Band 10 imagery from 1101 – 1201 UTC (i.e. bracketing the SAR observations), below, shows that the bands persist, at least for this hour, and perhaps the wind features extend inland over lower Michigan; at least, the features in the Band 10 imagery show up there!

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The computed weighting function for the Detroit sounding at 1200 UTC on 13 April 2023, below, (from the CIMSS Weighting Function site) shows results for the three ABI infrared Water Vapor channels (Bands 8, 9 and 10 at 6.19, 6.95 and 7.34 µm, respectively). Much of the energy sensed by the ABI at 7.34 µm originates from a layer between 600 and 700 mb.

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Sentinel-1A orbits have a repeat cycle of 12 days, and the second observation in April over Samoan waters occurred on 13 April, as shown above (there were SAR winds created in this domain on 1 April as well, here, on a similar weak-wind day). Diagnosed winds are uniformly light (3-7 knots) in the absence of strong convection. The atmosphere is very moist, as shown in the MIMIC Total Precipitable Water animation (below) from 0000-0900 UTC on 13 April. Note that the region of strongest winds in the image above, to the west of Upolu and near the western edge of the domain, is likely an artifact from reflection of the SAR signal off of ice from the deep convective cloud at the western edge of the SAR domain. This toggle of winds and Normalized Radar Cross Section (NRCS) data shows the characteristic feathery structure in NRCS fields that arise when cloud ice is present.

Sentinel-1A will overfly Samoa again around 0552 UTC on 25 April.

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Clear skies over the upper Midwest allowed all 3 JPSS Satellites — Suomi NPP, NOAA-20 and NOAA-21 — to obtain excellent views of the Great Lakes on 11 April 2023. The Great Lakes are largely ice-free (with the exception of a few bays in northern Green Bay, over northern Lake Superior, and over northern Lake Huron). (Here are two images from 7 March for comparison). The CIMSS Direct Broadcast site includes imagery for each of the five Great Lakes (here’s Lake Erie, for example, from NOAA-20 at 1846 UTC on 11 April, via this direct link to this directory, valid for about a week); the animation below shows Suomi NPP, NOAA-20 and NOAA-21 images of the Great Lakes from the CIMSS Direct Broadcast website (link) with 5 images between 1705 and 1911 UTC. Multiple JPSS Satellites means that time animations are easily created.

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VIIRS imagery is also available at the VIIRS Today Site and at the CIMSS VIIRS Imagery Viewer. True-Color imagery is also available via an LDM feed from CIMSS.

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GOES-16 (GOES-East) Shortwave Infrared (3.9 µm), Fire Temperature RGB, and Fire Power / Fire Temperature derived products (above) showed thermal signatures from a recycling plant fire in Richmond, Indiana on 11 April 2023. The Fire Power and Fire Temperature derived products are components of the GOES Fire Detection and Characterization Algorithm (FDCA).

GOES-16 True Color RGB images from the CSPP GeoSphere site (above) provided a good portrayal of the contrast between the dark black smoke plume and the surrounding bare ground — which was also evident in True Color RGB images from GOES-18 (GOES-West), in spite of the rather large viewing angle from that satellite (below).

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