5-minute CONUS Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed narrow tendrils of river valley fog — along a portion of the Mississippi River and a few of its tributaries in Wisconsin, Minnesota and Iowa — which dissipated after sunrise on 05 May 2024.

In southwest Wisconsin, the GOES-16 Marginal Visual Flight Rules (MVFR) Fog Probability derived product (above) correctly displayed an area of increased MVFR Probabillty just north of KCMY-KVOK beginning at 0801 UTC — and at 0901 UTC the visibility at the METAR site located within that region of higher probability dropped to 1/4 mile with fog. At 1101 UTC, surface reports at 2 sites in southwest Wisconsin reported Freezing Fog, with visibility as low as Zero to 1/4 mile. While the MVFR product did display low to medium probability values for some of the more pronounced areas of river valley fog, many of the fog features were too narrow to be resolved by the 2-km resolution Infrared data from GOES.

The GOES-16 Low Cloud Thickness derived product (below) indicated that most of the fog and low stratus across the region was only 500-800 ft thick — with some of the more pronounced areas of river valley fog exhibiting values of 1000-1200 ft.

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EUMETSAT Meteosat-9 Infrared Window (10.8 µm) images (above) showed Cyclone Hidaya as it intensified from a Tropical Storm (at 1200 UTC on 02 May) to Category 1 Hurricane intensity at 0000 UTC on 03 May 2024 (advisory | discussion). JTWC later noted that Hidaya had become the most intense tropical cyclone on record for this region, peaking at 80 kt (discussion).

A DMSP-18 SSMIS Microwave (85 GHz) image at 0024 UTC on 03 May, from the CIMSS Tropical Cyclones site (below) revealed a well-defined eye and surrounding eyewall structure.

Cyclone Hidaya had been moving across warm water and through an environment of fairly low deep-layer wind shear (below), two factors which were favorable for intensification.

An overpass of RCM-3 provided Synthetic Aperture Radar (SAR) imagery (source) at 1531 UTC on 02 May (below) — the maximum sensed wind speed was 74.94 kt in the SE quadrant of the eyewall.

However, an overpass of RCM-3 at 1539 UTC on 03 May (below) sensed a maximum velocity of 92.29 kt in the NE quadrant.

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Although Hidaya weakened to Tropical Storm intensity at 0000 UTC on 04 May (track), Meteosat-9 Infrared images (above) showed that a few brief convective bursts occurred as the tropical cyclone was approaching the coast of Tanzania. Hidaya made landfall by about 0300 UTC on 04 May (near Mafia Island), while still at Tropical Storm intensity.

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Overlapping 1-minute Mesoscale Domain Sectors provided 30-second interval GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) — which showed thunderstorms that produced tornadoes, large hail (up to 4.4 inches in diameter) and damaging winds (SPC Storm Reports) across western Oklahoma on 30 April 2024. Pulses of overshooting tops and evidence of Above-Anvil Cirrus Plumes (reference | VISIT training | blog posts) were apparent in the Visible imagery.

A longer animation of 30-second GOES-16 “Clean” Infrared Window (10.3 µm) images (below) extended a few hours past sunset. The coldest overshooting top infrared brightness temperatures were in the -75 to -78ºC range (brighter shades of white).

Small Radiance Anomaly along the Focal Plane Array

An anomaly that’s immediately obvious is a “flicker” between Infrared images from the 2 Mesoscale Sectors (which was also evident in full bit depth AWIPS imagery). This oscillation is also seen in a McIDAS-X “radiance” animation of alternating Meso Sectors — where radiance values of 120 to 10 are mapped to brightness values from 0 to 255. This anomaly was due to combining 1-minute images from the upper portion of Meso 1 with 1-minute images from the lower portion of Meso 2 (figure) to create 30-second imagery; as the GOES ABI scans each Mesoscale Sector, a swath-to-swath discontinuity is mainly caused by the difference in detector response at the ends of the focal plane array (FPA) — depending on the location in the ABI field of regard (thanks to Tim Schmit, NOAA/NESDIS for tracking down the explanation for this image anomaly, which came from F. Yu, GOES Calibration Working Group). In general, the magnitude of these differences are less than 0.1 K @300 K (although for an extremely cold scene, the brightness temperature difference may be larger than 1 K). These difference values are within the ABI design specification.
Note that brightness temperature discontinuities can sometimes be seen between ABI horizontal scan swaths, if the scene is very cold. One such ABI Band 13 example was seen with Hurricane Zeta (from this blog post). In addition, here’s an example from Zeta showing a scan swath discontinuity from 3 GOES-16 sectors (Full Disk, CONUS and Mesoscale).

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Farther to the north, 30-second GOES-16 Visible images centered over southern Kansas (below) also displayed pulses of overshooting tops and signatures of Above-Anvil Cirrus Plumes.

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12 days after its powerful eruption on 17 April, 10-minute JMA Himawari-9 AHI Infrared Window (10.4 µm) images (above) showed another explosive eruption of Mount Ruang in Indonesia on 29 April 2024. The coldest cloud-top infrared brightness temperatures reached -90ºC (internal yellow pixels) at 1850 UTC, shortly after eruption onset. Note that the volcanic umbrella cloud exhibited concentric cloud-top gravity waves from about 1900-2100 UTC. At the surface, volcanic ash (VA) was reported at Menado (station identifier WAMM: text | plot) beginning at 0000 UTC on 30 April, which restricted the visibility to 3-4 miles.

The volcanic umbrella cloud-top gravity waves were more apparent in higher-resolution Himawari-9 Red Visible (0.64 µm) images (below).

A toggle between Himawari-9 Visible and Infrared images at 2150 UTC on 29 April (below) showed that the primary volcanic plume (which reached heights above that of the broader umbrella cloud) exhibited warmer infrared brightness temperatures — indicating that it had penetrated the local tropopause and extended into the lower stratosphere.

A plot of rawinsonde data from Menado, Indonesia at 0000 UTC on 30 April is shown below.

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Himawari-9 imagery below compares a zoomed-out version of upper-level water vapor (Band 8, 6.25 µm) and the window channel (Band 13, 10.4 µm) that is also shown above. The zoomed-out version reveals some similarities is size in the evolution of the eruption cloud to that of surrounding tropical convection occurring at the same time. The Band 13 imagery does show that the eruptive cloud penetrates higher into the atmosphere than typical tropical convection (as discussed above).

Himawari-9 SO₂ RGB imagery (created using Geo2Grid), below, certainly distinguishes between the eruptive cloud of Ruang (whose edges become tinged in shades of orange to pink, suggesting a mixture of SO₂ and Ash), and the developing cumulonimbus to the northwest.

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