During a period when American Samoa had been under a Flash Flood Watch, the Weather Service Office at Pago Pago requested that a GOES-18 (GOES-West) Mesoscale Domain Sector be positioned over the region (due to their lack of radar, satellite imagery can be a critical tool for monitoring the development of deep convection). 1-minute GOES-18 Infrared imagery with overlays of GLM Flash Points and the Total Precipitable Water (TPW) derived product (above) showed clusters of deep convection with intermittent lightning activity that moved across the main island of Tutuila (located just south of where the imagery is centered) as well as the smaller Manu’a Islands (~65 miles to the east) during a 15-hour period on 04-05 May 2026. At the Pago Pago METAR site on Tutuila, most of their calendar day 24-hour precipitation for 04 May (2.21 inches) occurred during the period shown in the GOES-18 animation above — and a Flash Flood Warning was issued at 0154 UTC on 05 May.

The coldest cloud-top infrared brightness temperature exhibited by storms in the vicinity of Tutuila was -78.14ºC (above) — which was at an altitude near the Most Unstable (MU) air parcel’s Equilibrium Level (EL), according to rawinsonde data from Pago Pago (below). That sounding also depicted an atmosphere which was very moist and unstable, with parameters that were favorable for the further development of deep convection. In addition, rain shower and thunderstorm activity was enhanced by the presence of a surface trough / stationary front in the vicinity of the Samoan Islands (05 May surface analyses: 0000 UTC | 0600 UTC | 1230 UTC).

It is noteworthy that according to the climatology of TPW for all 0000 UTC soundings at Pago Pago (below), the TPW value of 2.81 inches sampled at 0000 UTC on 05 May 2026 was significantly higher than the previous maximum value on record for that particular time/date (2.63 inches).

The MIMIC Total Precipitable Water product (below) showed the band of high moisture that was moving southeast across the Samoan Islands during this flash flooding event.

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Version 1 of the NOAA/CIMSS LightningCast model uses GOES-R ABI images to predict the probability of lightning in the next 60 minutes at any given location. It is being transitioned to NOAA/NESDIS operations. LightningCast v2 has been developed and is being evaluated at NOAA’s Hazardous Weather Testbed. Version 2 incorporates MRMS Reflectivity at -10^oC, which is a well-known product used to help determine the ice content in convection. We’ve found that version 2 improves short-term lightning predictions across the contiguous U.S. (CONUS), with a very small reduction in performance in regions outside CONUS. Here are some examples.

Dallas / Forth Worth Metro

On April 29, the Dallas / Fort Worth metro region was socked in with dense mid- and high-level cloud cover. There was very little contrast or texture in the cloud tops in the ABI imagery. Thus, LightningCast v1 had low probabilities until convective cloud features began to poke up from the thick cloud canopy and the cloud-top brightness temperature began to cool. However, LightningCast v2 had moderate-to-high probabilities much sooner, owing to the Reflectivity -10^oC predictor.

In two convective areas southwest of Forth Worth and over Fort Worth proper, LightningCast v2 provided 17 minutes and 5 minutes of additional lead time to the first flashes detected by GLM, respectively, compared to version 1. When plotted as a line graph over TCU’s Amon G. Carter Stadium, the version 2 probability shows a clear uptick 5 minutes before version 1. Later, version 2 remains higher than version 1 during another burst of lightning.

Pennsylvania

Meanwhile, Pennsylvania was also socked in with dense cloud cover on the same day. Some shallow convection remained hidden to version 1, whereas version 2 had higher probabilities over the electrified region. While this was a difficult case due to the marginal nature of the convection, version 2 still provided more reliable guidance.

Mississippi Valley

In the central Mississippi Valley, LightningCast version 2 correctly had higher probabilities in southern Illinois, western Kentucky, eastern Kansas, and eastern Arkansas compared to version 1. It correctly had lower probabilities in western Indiana, as well. All are areas of adequate radar coverage.

We’ve demonstrated that the radar predictor adds a lot of value over CONUS, while the model has in general learned to rely on satellite inputs where radar coverage is absent. Version 2 isn’t better in every instance, but overall, it provides superior guidance.

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) GeoColor RGB images (above) showed areas of blowing dust — lofted by strong southwest winds (with gusts in the 30-40 mph range) blowing across recently-plowed agricultural fields — that were being transported northeastward from central Illinois to northern Indiana on 04 May 2026.

A Blowing Dust Advisory had been issued for the entire region earlier in the day — and three Dust Storm Warnings were later issued for parts of central Illinois (below) as the plumes of blowing dust began to increase during the afternoon hours. Blowing dust reduced the surface visibility to 1.75 miles at Danville (KDNV), 5 miles at Rantoul (KTIP) and 7 miles at Kankakee (KIKK).

1-minute GOES-19 True Color RGB and Dust RGB images created using Geo2Grid (below) provided a comparison of the two RGB combinations — plumes of blowing dust were first apparent in the Dust RGB images (shades of magenta), but then the airborne dust began to exhibit a better signature in True Color RGB images (hazy shades of tan) later in the day as forward scattering increased from the GOES-19 satellite perspective.

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5-minute CONUS Sector GOES-19 (GOES-East) Visible and Infrared images (above) showed a couplet of thunderstorm cells that moved toward the South Texas coast during the afternoon hours on 01 May 2026 — which produced hail, an EF1-rated tornado and damaging wind gusts as high as 119 mph (SPC Storm Reports | NWS Corpus Christi damage survey).

GOES-19 Infrared images (below) showed 3 METAR sites (Victoria KVCT,  Port Lavaca KPKV and Palacios KPSX ) that were directly affected by these thunderstorm cells — and depicted the rapid cooling followed by the warming of cloud-top infrared brightness temperatures over the course of about 1 hour.

 

The coldest cloud-top infrared brightness temperature exhibited by the northernmost storm was -80.53ºC at 1931 UTC (above) — which represented a ~2.5 km overshoot of the Most Unstable (MU) air parcel’s Equilibrium Level (EL) to near the Maximum Parcel Level (MPL), according to a plot of rawinsonde data from Corpus Christi at 1800 UTC (below).

GOES-19 Water Vapor images (below) revealed rather dry middle-tropospheric air (shades of yellow to orange) just west of the severe thunderstorms.

As the dry middle-tropospheric air moved eastward in the wake of the severe thunderstorms, the DCAPE at Corpus Christi increased from 866 J/kg at 1800 UTC to 1047 J/kg six hours later at 0000 UTC (below) — indicative of an increasing tendency for the downward transport of strong winds aloft toward the surface.

Today's damage survey from Coleto Creek Rsvr southeast to Placedo and Point Comfort showed a 40 mile long swath of destructive straight-line winds of up to 120 mph as well as an EF-1 tornado southwest of Guadalupe by Jared and York Road. Read more here: https://t.co/KQAv2AuDn1 pic.twitter.com/lqjLj1sTjl

— NWS Corpus Christi (@NWSCorpus) May 3, 2026

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