A fast-moving thunderstorm complex raced across North Dakota and Minnesota in the late afternoon/evening/overnight on 20-21 June 2025, as shown above. GOES-19 band 13 (10.3 µm) imagery and derived stability (Lifted Index) show the development of notable instability with an alignment over North Dakota along the direction of convective movement. One very noteworthy aspect of the cold cloud-tops in GOES-19 is their very rapid movement across central North Dakota from about 0100-0500 UTC on 21 June. Mesoscale discussions from SPC on this complex are here, here, here, here, here, here, here, here, here and here (!! — there were a lot of them!). SPC Watch numbers 447, 448 and 449 covered this system.

This system caused numerous tornadoes and severe wind reports as shown below.

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Overlapping 1-minute Mesoscale Domain Sectors provided GOES-19 (GOES-East) imagery at 30-second intervals over much of the area affected by this severe convection; shown below is Infrared imagery of a large mesoscale convective system over western/central North Dakota and a pair of supercell thunderstorms in eastern North Dakota as they eventually merged and began to move eastward across northwestern Minnesota. Pulsing overshooting tops exhibited infrared brightness temperatures in the -75 to -79ºC range (brighter white pixels embedded within dark black areas) — which represented a significant overshoot of the Most Unstable (MU) air parcel’s Equilibrium Level (EL), according to rawinsonde data at Bismarck ND and Aberdeen SD.

The supercell thunderstorms that developed over eastern North Dakota produced several tornadoes, including an EF3-rated tornado near Enderlin shortly after 0400 UTC that was responsible for 3 fatalities (NWS Grand Forks damage survey) **NOTE: after further investigation, Enderlin tornado #1 was upgraded from an EF-3 to an EF-5; specific details are available here. This was the first EF5-rated tornado in the US since 20 May 2013 in Moore OK**. Hail as large as 3.00″ in diameter also was reported with these supercell thunderstorms. The highest wind gusts associated with this derecho event included 111 mph in eastern North Dakota and 106 mph in northwestern Minnesota.

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1-minute Mesoscale Domain Sector GOES-18 (GOES-West) “Clean” Infrared Window (10.3 µm) images and “Red” Visible (0.64 µm) images with an overlay of the FDCA Fire Mask derived product (above) showed that a wildfire southwest of Nenana, Alaska (METAR site PANN) produced two pyrocumulonimbus (pyroCb) clouds late in the day on 20 June 2025 . The pyroCb clouds exhibited cloud-top 10.3 µm infrared brightness temperatures (IRBTs) in the -40s C (denoted by shades of blue to cyan) — a necessary condition to be classified as a pyroCb — with the first pyroCb developing at 0027 UTC on 21 June, and the second pyroCb forming at 0226 UTC. These were the first confirmed pyroCbs in Alaska for the 2025 wildfire season.

Another wildfire just east of Healy Lake, Alaska later produced a larger pyroCb, developing at 0326 UTC (below).

The coldest cloud-top IRBT exhibited by the Healy Lake pyroCb was -57.12 C at 0607 UTC (below) — colder than the -43.66 C and -49.01 C IRBTs for the two pyroCbs produced by the wildfire southwest of Nenana.

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible and Infrared images (above) showed Hurricane Erick as it intensified from a Category 2 storm at 1800 UTC on 18 June to a Category 3 storm by 0000 UTC on 19 June 2025. The eye became a bit more defined during that time period — and convective bursts within the eyewall occasionally exhibited cloud-top infrared brightness temperatures of -80ºC or colder (violet pixels embedded within brighter white regions).

Erick was moving through an environment characterized by low values of deep-layer wind shear (below) — a factor that favored further intensification.

A DMSP-18 Microwave image at 2154 UTC on 18 June (below) displayed a large outer eyewall (and hints of a partial inner eyewall), suggesting that an eyewall replacement cycle might soon occur.

1-minute GOES-19 Infrared images (below) showed the period where Erick continued its rapid intensification, becoming a Category 4 storm just before 0600 UTC on 19 June. The hurricane weakened somewhat to Category 3 intensity shortly before making landfall in far western Oaxaca, Mexico around 1200 UTC on 19 June (and the eye became ill-defined closer to the time of landfall). Convective bursts west of the eyewall occasionally reached -90ºC (yellow pixels embedded within darker purple areas).

Deep-layer wind shear remained very low in the vicinity of Erick (below), maintaining a favorable environment for intensification — and the hurricane also traversed very warm Sea Surface Temperatures during its period of rapid intensification.

A DMSP-18 Microwave image at 1030 UTC on 19 June (below) suggested that landfall might have occurred a bit earlier than 1200 UTC.

Deep-later wind shear, DMSP and Sea Surface Temperature images were sourced from the CIMSS Tropical Cyclones site.

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The mp4 animation below (created using geo2grid from CSPP Geo) shows a broader-scale view of Erick during its intensification prior to landfall. Very cold cloud tops initially surround the strengthening center. Subsequently, an extensive region of even colder cloud tops develops well southwest of the storm center.

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5-minute CONUS Sector GOES-19 (GOES-East) Near-Infrared and Shortwave Infrared images (above) showed thermal signatures of an explosion of SpaceX Starship at the Starbase launch facility in South Texas that occurred at 0401 UTC on 19 June or 11:01 PM CDT on 18 June 2025 (NASASpaceflight.com article).

The resulting large fire was hot enough to be flagged as a Processed Fire by the GOES-19 Fire Detection and Characterization Algorithm (FDCA), with a Fire Power value of 46.85 MW at 0401 UTC (below).

The Next Generation Fire System (NGFS) also displayed GOES-19 Fire Detection polygons (below) — beginning at 0401 UTC, the time of the Starship explosion.

A cursor probe of a GOES-19 NGFS Fire Detection pixel at 0401 UTC is shown below.

In spite of its larger satellite viewing angle and less frequent 10-minute Full Disk scans over Texas, a distinct thermal signature (darker blue pixels) was still seen in a 0400 UTC GOES-18 (GOES-West) Microphysics RGB image (below). The 0400 UTC GOES-18 Full Disk scan was viewing southeastern Texas around 0402-0403 UTC. There were no Full Disk sector NGFS polygons plotted on the GOES-18 RGB images, due their processing being restricted to Alaska and western Canada (for now).

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