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). 1-minute GOES-18 Infrared imagery with overlays of GLM Flash Points and the Total Precipitable Water 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 (a Flash Flood Warning was issued at 0154 UTC on 05 May). The development of rain showers and thunderstorms was enhanced by the presence of a surface trough / stationary front in the vicinity of the Samoan islands (surface analysis: 0000 UTC).

The coldest cloud-top infrared brightness temperature exhibited by storms in the vicinity of Tutuila was -78.14ºC (above) — which was 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 fact, according to the climatology of TPW for all 0000 UTC soundings at Pago Pago (below), the TPW value of 2.81″ at 0000 UTC on 05 May 2026 was significantly higher than the previous maximum value for that time/date (2.63″).

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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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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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One of the defining characteristics of spring in the upper midwest is a land surface that warms up much more quickly than the many lakes do. There’s a couple of reasons for this: water itself has a higher heat capacity than soil does, sun penetrates into the lakes somewhat which distributes the energy over a greater depth than is possible in land, and currents (especially in the Great Lakes) can mix cold water to the surface. This combines to create a large amount of thermal inertia and thus the lakes are slow to warm in the spring and summer compared to the surrounding land. (The opposite happens in the fall and early winter, and is a primary contributor to lake effect snow).

It doesn’t take a Great Lake to have an impact on local weather. We can see this happen even with more modestly sized lakes, and an excellent example was seen on 1 May 2026. Here is an animation from the GOES West (GOES-19) Band 2 visible imagery, depciting clouds over northern Minnesota and Wisconsin. Recall, Band 2 is the highest resolution band and is the best tool for identifying the size and extent of individual cumulus clouds during the day. Based on the direction that the clouds are moving, it’s clear that winds are from the north-northwest. However, as the clouds move over the lakes, they vanish. While it’s most apparent south of Lake Superior, many of the less pronounced lakes in Minnesota are also contributing to this downstream clearing. Even the small lakes in the southwest corner of the loop show this imapct.

So what’s going on here? In short, the colder lakes are killing the surface fluxes that contribute to buoyancy and vertical cloud development. We’ve frequently discussed lake breezes in various blog posts over the years, and while those circulations are driven by a similar difference in the land and water temperatures, that’s not quite explaining what’s happening here. If this were a lake breeze, we’d see the clearing happening on all sizes of the lake, not just the sides downstream of the prevailing synoptic flow.

CIMSS’s Community Satellite Processing Package for Geostationary Data (CSPP Geo) applies processing to geostationary satellite observations to create Level 2 products. One of these products is the land surface temperature, derived from the GOES-19 Advanced Baseline Imager (ABI) infrared channels. We can use that to see just how much of a surface temperature difference is present between the lakes and the land. While it’s only possible to measure the surface temperature in clear sky conditions, the areas downwind of the lakes offer plenty of opportunity to make those measurements in a cloud-free environment. This movie shows the CSPP Level 2 land surface temperature product as displayed on the CSPP Geosphere site. Note how the lakes are a deeper blue than the surrounding land, indicating that they’re colder.

But how much colder are they? Sure, we can eyeball the temperature differences. But, crucially, CSPP also offers data readouts. All you have to do is load up a product and mouse over it, and a box will pop up telling you what the value is at that point. Here’s an animation of the CSPP-observed surface temperature for a point both over and downwind of Mille Lacs Lake in central Minnesota. This animation alternates between the two sites every five seconds, and the target point is just to the northwest of the upper left corner of the readout box. Note how over this short distance the temperature changes by 8 degrees C, or over 14 degrees F. Since cumulus clouds are driven by positively buoyant surface parcels ascending from warm surfaces, as the buoyant plumes move over the cold water, the low-level air parcels are no longer warmer than the air above them and so they stop ascending, killing the clouds.

Earlier we said that this was not a lake breeze case because the reduction in cloudiness doesn’t appear anywhere but the downstream sides of the lakes. However, that doesn’t appear to the case on the western point of Lake Superior as clearing can be seen both north and south of the lake. However, as the blog has discussed before, Duluth is an unusual place. There’s over 800 feet of elevation difference between the lake surface and the airport up on the bluffs just five miles away. That results in cold air being trapped in the Superior basin and whatever lake breeze is being created by the temperature difference finds it challenging to deeply penetrate inland to the north due to the sharp elevation difference. Here’s the Band 13 (10 micron) infrared window view focusing on greater Duluth, with surface observations overlaid on top. Note the 6 degree air temperature difference between the lake and Duluth International Airport and the lack of surface winds coming from the lake, which seems to indicate that at best the lake breeze and the larger synoptic flow have battled to a stalemate. That convergence may also explain the band of enhanced convection paralleling Superior’s north shore.The northeasterly flow at Sky Harbor in the lake basin and Superior-Bong airport may also indicate a weak lake breeze funneled up the St. Louis River valley.

The meteorological impacts of the lakes on convective growth are small, but they are noticeable. On other days in which the larger-scale atmospheric instability is greater, we may see upscaling and precipitation in other regions but a lack of convection and precipitation in the downstream locations.

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