1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Infrared images (above) included plots of 1-minute GLM Flash Points (which are parallax-corrected to correspond to their surface locations) — and showed an increase in thunderstorm coverage and lightning activity across southeastern Wisconsin late in the day on 15 April 2026.

Unfortunately, one lightning-related fatality occurred south of Pewaukee, Wisconsin around 0043 UTC or 7:43 PM Central Time (Local Storm Report). A cursor sample of a GLM Flash Point just southeast of Pewaukee (below) revealed a rather large flash area of 1114 km² at 0041 UTC (7:41 PM Central Time).

1-minute GOES-19 Infrared images with contours of ProbSevere LightningCast probability (below) indicated that the LightningCast probability over Pewaukee was consistently at or above 90% beginning at 0015 UTC.

A plot of LightningCast Probability and GOES-19 GLM Flash Count (below) revealed that the LightningCast Probability was 73% or higher during the 30-minute period preceding a marked increase in GLM Flash Count in the vicinity of Waukesha County Airport (KUES, which is located about 3 miles south of Pewaukee).

This is the first lightning fatality of 2026. Details are scarce right now.The safest place to be during a thunderstorm is in a substantial building with electrical and plumbing in the walls. Fully enclosed metal vehicles also provide protection.When thunder roars, go indoors!

— National Lightning Safety Council (@lightningsafety.bsky.social) 2026-04-16T13:25:15.423Z

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible images (above) included time-matched (+/- 3 minutes) plots of SPC Storm Reports — which showed the tornadoes, large hail (up to 4.00″ in diameter) and damaging winds (as high as 88 mph) that occurred across much of southern Wisconsin (along with adjacent parts of far northeast Iowa and far southeast Minnesota) on 14 April 2026. Numerous overshooting tops were seen in the Visible images.

The corresponding 1-minute GOES-19 Infrared images (below) revealed pronounced enhanced-V cloud-top signatures with several of the severe thunderstorms.

The coldest cloud-top infrared brightness temperatures exhibited by pulses of overshooting tops were -78ºC (brighter white pixels embedded within dark black areas) — which corresponded to a significant (~2 km) overshoot of the Most Unstable (MU) air parcel’s Equilibrium Level (EL), according to plots of rawinsonde data from Davenport, Iowa (below). CAPE values of 4000-4300 J/kg indicated that significant instability was present south of a frontal boundary which was draped across Iowa, Wisconsin and lower Michigan.

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2.5-minute Target Sector JMA Himawari-9 AHI Visible images (above) showed Super Typhoon Sinlaku as its eye approached Saipan (station identifier PGSN) in the Mariana Islands on 13-14 April 2026. Mesovrticies were evident within the eye. After reaching its peak intensity on 12 April (blog post 1 | blog  post 2), Sinlaku was in the process of a gradual weakening trend, decreasing from Category 5 intensity to Category 4 intensity by 0000 UTC on 14 April (JTWC discussion).

A longer animation of Himawari-9 Infrared images (below) showed Sinlaku making landfall on the islands of Saipan and Tinian, as a Category 4 storm around 1432 UTC on 14 April.

Microwave imagery (source) from ATMS (below) displayed the large outer eyewall ring that remained after Sinlaku had undergone a recent eyewall replacement cycle. The islands of Saipan and Tinian were located within this large eyewall.

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2.5-minute Target Sector JMA Himawari-9 AHI Infrared images (above) showed Super Typhoon Sinlaku as it rapidly intensified to a 160-knot Category 5 storm (ADT | SATCON) by 1800 UTC on 12 April 2026, southeast of Saipan (station identifier PGSN) in the Mariana Islands. Cloud-top infrared brightness temperatures began to gradually warm once Sinlaku reached peak intensity.

A nocturnal NOAA-20 VIIRS Day/Night Band image (below) provided a stunning example of mesospheric airglow waves that were propagating radially outward from Sinlaku.

Microwave images from DMSP-18 and ATMS (below) did display evidence of dry air becoming entrained into the circulation of Sinlaku, which was beginning to surround the well-defined eye and eyewall..

Sinlaku was moving through an environment characterized by fairly low values of deep-layer wind shear (below) — one factor which favored the rapid intensification of this tropical cyclone.

Sinlaku was also traversing warm water, as seen in relatively high values of Sea Surface Temperature and Ocean Heat Content (below).

Himawari-9 Infrared images with plots of Mesoscale Atmospheric Motion Vectors or AMVs (below) highlighted areas of high-altitude radial outflow — which enhanced upper-level divergence and promoted the maintenance of convective updrafts.

Microwave, Wind Shear, Sea Surface Temperature, Ocean Heat Content, Mesoscale AMVs, ADT and SATCON images/plots were sourced from the CIMSS Tropical Cyclones site.

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