A strong cold front (surface analyses) was moving eastward from the southern Plains toward the lower Mississippi Valley on 15 April 2023 — GOES-16 (GOES-East) Total Precipitable Water and Lifted Index / Convective Available Potential Energy Derived Stability Indices (above) revealed a broad corridor of moisture and instability ahead of the cold front.

1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images centered over southwestern Missouri (above) included time-matched (+/- 3 minutes) plots of SPC Storm Reports — which showed thunderstorms that produced hail as large as 4.00 inches in diameter and wind gusts as high as 97 mph in Missouri.

The corresponding 1-minute GOES-16 “Clean” Infrared Window (10.3 µm) images with plots of time-matched SPC Storm Reports (below) indicated that some of the thunderstorm overshooting tops exhibited infrared brightness temperatures in the -65 to -70ºC range (darker red to black enhancement).

As the thunderstorms moved farther northeast, one tornado produced EF1/EF2 damage in Missouri — with another cluster of weak tornadoes in general vicinity of St Louis. 1-minute GOES-16 Visible and Infrared images centered over St Louis are shown below.

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2.5-minute rapid scan (Target Sector) JMA Himawari-9 “Red” Visible and “Clean” Infrared Window images (above) showed Category 4 Cyclone Ilsa as it approached the northwest coast of Australia, eventually making landfall near Port Hedland (station identifier YPPD) just after 1500 UTC on 13 April 2023. Overshooting tops within the eyewall region occasionally exhibited infrared brightness temperatures of -90ºC or colder (shades of yellow embedded within darker purple areas).

A Suomi-NPP ATMS Microwave (183 GHz) image from the CIMSS Tropical Cyclones site (below) displayed a closed eyewall structure at 0543 UTC, with a spiral band extending southward.

A RCM-3 SAR image at 1030 UTC (source) is shown below; the peak SAR-derived radial velocity was 144.36 knots within the northeast quadrant of Ilsa.

Himawari-9 Infrared (11.2 µm) images (below) included an overlay of deep-layer wind shear at 1200 UTC — which showed that Ilsa was moving through an environment of low shear (as it traversed warm Sea Suface Temperatures).

A GMI Microwave image at 1821 UTC (above) and a DMSP-18 SSMIS Microwave image at 2006 UTC (below) revealed that Ilsa’s closed eyewall remained intact for several hours after the storm had moved inland, while maintaining Category 4 intensity (as of 1800 UTC).

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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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