A multi-panel display of 1-minute Mesoscale Domain Sector GOES-18 (GOES-West) ABI images (above) showed either a reflectance signature or a thermal signature of sunlight reflecting off the Topaz Solar Farms on 18 June 2026. A signature was evident in 13 of the 16 ABI spectral bands (no signature was evident in Water Vapor bands 08/09/10) — and due to a relatively dry atmosphere (Vandenberg CA rawinsondes), there was even a subtle signature in the near-infrared 1.38 µm “Cirrus” band 04 (1838 UTC images).

A closer view of the band 07 Shortwave Infrared imagery (below) displayed the large thermal signature — in fact, the 3.9 µm infrared brightness temperature peaked at 137.88ºC (which is the saturation temperature of GOES-18 band 07 detectors) from 1833 UTC to 1842 UTC. In the far eastern portion of the images, the thermal signature of a small wildfire was also apparent.

A closer view of band 02 Red Visible imagery (below) revealed the appearance of vertical striping that emanated northward and southward from the Topaz solar farms. These image artifacts were likely related to saturated ABI detector column amplifiers, due to an excess charge induced by intense sunlight reflection off the large solar panel arrays.

A larger-scale view of the Visible image at 1837 UTC (below) showed that these striping artifacts extended a considerable distance from the Topaz site.

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In the afternoon and evening of 17 June 2026, a series of tornadoes struck the states of Illinois and Indiana. As of the writing of this post (1600 UTC on 18 June) the SPC Storm Reports only indicate tornadoes in Illinois, but remotely-sensed observations indicate that the likelihood of a significant tornado in south-central Indiana was high. UPDATE 19 June: NWS Indianapolis Survey Crews have confirmed the presence of multiple tornadoes in Indiana. The tornado discussed at the end of this post was rated as an EF2. The NWS has a map of tornado paths on their site.

We’ll start, though, by looking at the larger scale setup for this event. Here’s the 1200 UTC 250 hPa chart courtesy of NOAA’s Storm Prediction Center. A quick glance shows an elongated jet streak extending from central British Columbia all the way to the Dakotas, with a small shortwave trough over Iowa. However, as we noted a few days ago, there’s a significant number of 1200 UTC radiosondes that aren’t being launched. It’s therefore reasonable to look to an alternate data source to confirm how well this analysis matches reality.

Fortunately, satellites can support such a sanity check. The water vapor channels are able to detect the motion of clear air. There are three such channels aboard the GOES Advanced Baseline Imager, and each is sensitive to water vapor in a different part of the atmosphere. Band 8 (6.19 microns) is in a portion of the electromagnetic spectrum where water vapor absorbs very strongly, therefore it is mostly sensing information near the top of the atmosphere. Let’s take a look at what that looked like around 1200 UTC. Here, we see that the general flow pattern identified by the 250 hPa chart in the western continental United States is correct, though there might be some hints of wiggles in the actual flow that don’t necessarily show up in the analyzed map.

It’s that shortwave over the upper Mississippi Valley that is of greatest interest to this particular case. This isn’t really an example of boundary-driven convection initiation as we see with fronts. Those boundaries were much to the west or north of where we saw convection initiate, and thus it’s the dynamical influence of the upper-level flow that really helped the storms to get going. Let”s take a look at the initiation, this time using the high resolution Band 2 visible imagery. This loop covers 1800 to 2100 UTC and shows a line of storms firing from north central Indiana to eastern Kansas. Embedded in the laerge cloud shield in the right side of the loop was an initial round of storms that largely brougt strong winds to the area. However, it is those storms firing up along the line that proved to be a more significant concern.

As this line moved to the south, it formed embedded tornadoes in west central Illinois. The tornadoes were reported between 2330 and 130 UTC. By 0200 UTC the storms were well into Indiana where they were continuing to cause destruction. Here is a view of the mesoscale sector 1 minute Band 13 Infrared channel. Note the presence of multiple overshooting tops in close proximity to each other in the center of the loop.

The Doppler radar at Indianapolis showed strong evidence of tornadic conditions. Here’s a loop of the storm relative velocity (left) and reflectivity (right) for south central Indiana from 0115 UTC to 0300 UTC. There is a tight couplet that moves due east across the center of the image just south of Martinsville and a broader and weaker center of circulation that propagates to the southeast across Bloomington.

Here’s a single time step from the radar loop, showing the storm relative velocity (left), correlation coefficient (center), and reflectivity (right). The ball of blue in the center panel, at the same location as a tight velocity couplet and very high reflectivity levels, likely represents debris in the air. The closer the correlation coefficient is to 1.0, the more spherical the scatterers. As this storm moved across the Morgan-Monroe State Forest, it likely kicked up a substantial amount of tree debris (which is clearly aspherical) causing it to appear this way on the radar.

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible and Infrared Window images (above) showed Potential Tropical Cyclone One as is intensified to form Tropical Storm Arthur as of 1500 UTC on 17 June 2026. Plots of surface winds at METAR sites revealed that strongest winds were occurring in the eastern semicircle of Arthur, with a peak wind gust of 57 kts (66 mph) at Galveston Airport (a wind gust to 81 mph was recorded at a maritime site east-southeast of Galveston). An isolated inland convective cell produced GLM-detected lightning activity northeast of the storm center from 1357-1428 UTC. The exposed low level circulation center of Arthur moved inland after 1500 UTC, and began to slowly migrate westward — then later re-formed to the northeast after 2100 UTC.

The bulk of Arthur’s deep convection remained offshore, south and southeast of the storm center — due to the deep-layer wind shear that was present across the area (below).

Sea Surface Temperatures (SSTs) across the northwestern Gulf of Mexico were around 28 C (below) — although a small area of nearshore water having a SST value of 29 C existed in the area where Arthur formed.

Wind shear and SST products were sourced from the CIMSS Tropical Cyclones site.

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The National Weather Service offices in much of the central and western continental United States have modified their radiosonde launch times. Instead of the standard synoptic times of 0000 and 1200 UTC, these offices have shifted that latter time to 1800 UTC. Since radiosondes are labor-intensive, this change to the middle of the day helps ensure that sufficient staffers are around to launch the balloon and maintain operational readiness. Here, courtesy of the NOAA Storm Prediction Center, is a slider juxtaposition of a map of the 1200 and 1800 UTC radiosonde launches showing how the majority of the missing 1200 UTC sites are instead showing up at 1800 UTC.

Of course, if you are used to looking for radiosondes at certain times, this shift might be disruptive to your workflow. Here’s a case where satellites can once again come to the rescue by helping to fill in those gaps. This blog has frequently talked about the advantages of the NUCAPS product, in which combined infrared and microwave sounders deliver vertical profiles of temperature and dew point from the polar orbiting NOAA-20 and NOAA-21 satellites. While they don’t give the same vertical resolution as the radiosondes, they make up for it in observational density. Here’s an animation of the distribution of NUCAPS profiles across North America from the NOAA LEO satellites. Remember, this can be used as a proxy radar: green is where both infrared and microwave satellite retrievals are available and thus are indicative of clear skies; yellow is where microwave is available but infrared isn’t, and thus shows where the skies are cloudy, and red is where neither infrared nor microwave are valid and thus shows where it is raining. This animation shows roughly 18 hours of NUCAPS availability over CONUS, from 0000 UTC on Sunday the 14th to 1800 UTC on the 15th.

Of course, the temporal gaps cannot be ignored. One thing to do is use the GOES Legacy Atmospheric Profile (LAP) products instead. These are not going to have the same vertical detail as the NUCAPS soundings because they don’t have the same information content. While there are many hundreds of channels from the infrared CrIS sounder, the GOES LAP product just uses the ABI channels. This results in a reduced ability to capture small-scale features compared to the hyperpsectral CrIS sounder. At the same time, there’s no microwave instrument in geostationary orbit. This means that GOES soundings can only happen in locations where skies are clear since clouds are opaque to infrared radiation and thus block all radiation originating from the surface. However, unlike NUCAPS, the GOES soundings have far greater temporal availability given their basis in geostationary observations.

A little over a year ago, we wrote a blog post discussing the LAP products, and we encourage you (and NWS users in particular) to check it out to see how to access these soundings and learn about their applications and limitations.

The next generation of US geostationary satellites, GeoXO, promises to unite the vertical resolution of the existing LEO satellites with the temporal resolution of geostationary orbit. The GeoXO Sounder (GXS) will provide hyperspectral observations from geostationary orbit, drastically improving both the temporal and spatial resolution of the sounding observations. Similar observations are already underway from EUMETSAT’s MTG-IRS and China’s GIIRS, and we can expect Japan’s Himawari-10 to be operational in the coming years as well. It is truly an exciting time for people, like your author, who are fans of hyperspectral thermodynamic profiling!

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