We are starting to see the onset of an active period of tropical development in the eastern Pacific basin. Over the weekend of 18-19 July 2026, two separate systems were experiencing different stages of their life: Elida was dying out near the west coast of Mexico while Fausto was starting to consolidate into a tropical storm. The following satellite loops from GOES-18 (GOES West) show these systems. The first is the Band 2 visible product. Elida is in the western center of the animation while Fausto is in the south central part of the loop.

Here’s the same loop as before, but from the Band 13 infrared perspective. Here, it is clear that Fausto represents deeper convection was the infrared imagery shows much colder cloud tops for that storm than it does for Elida.

Polar-orbiting satellites around this time provide some additional perspective on these storms. First, let’s look at some scatterometer data to evaluate near-surface winds. Here’s a view from OSCAT3 of Elida on Sunday the 19th. OSCAT tends to have more uncertainty in the wind vector retrievals than ASCAT does, but makes up for it with a wider swath and fewer gaps between swaths. (ASCAT was particularly unlucky with both storms on the 19th). Here we see clear evidence of a focused area of circulation with winds in the center maxing out at around 30-40 kts.

Going further south to Fausto at roughly the same time in the 19th, we see a circulation that is not quite as refined as Elida. Winds are slower and the center of circulation isn’t as circular.

Elida has propagated to the north, into the cooler waters of the midlatitude eastern Pacific. Between the 19th and the 20th, it lost its tropical storm status and is now officially post-tropical. However, Fausto is continuing to intensify and model tracks show that it may impact Hawaii in the coming days, so we’ll look at it a bit more. Here’s a frame from the CIMSS D-MINT product from 1930 UTC on the 19th, approximately the same time as the animated loops above). D-MINT uses microwave and infrared observations to assess the intensity of tropical cyclones. The left three panels show three different microwave channels, and forecasters can use these to more easily identify the center of circulation when the infrared or visible images are cluttered with high-level cirrus shields. Here we see the circulation is likely centered around the lower-left hand corner of the microwave images. The rightmost panel depicts the mean surface wind of the system as estimated by the D-MINT algorithm, and in this case it is around 30 kts.

We can use satellites to gauge how much Fausto improved from Sunday the 19th into Monday the 20th. We’ll start by looking at more recent scatterometer observations. In the ~25 hours between the OSCAT plot shown above and the more recent one below, Fausto’s circulation tightened up immensely and became much more circular.

We also see the intensification in D-MINT. This prodcut relies on available microwave satellite observations and not all satellites contain the same set of channels, hence the difference in the images shown here. Regardless, the algorithm now projects a mean surface wind of 44 kts by 1524 UTC, about 20 hours later than the image above.

NOAA’s National Hurricane Center projects that Fausto will become a hurricane on the 20th. Model forecasts, including the GFS and Google’s DeepMind show Fausto continuing to the east-northeast, weaking to a tropical storm just before it passes to the north of Hawaii. However, the long-term forecasts also show additional Pacific tropical systems developing south of Mexico and continuing to the east, so eyes will be on the Pacific for some time to come.

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Tropical Depression Two developed in the northeastern Gulf of Mexico at 1500 UTC on 19 July 2026 — and 1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible images (above) showed the slow trend of organization during the day (there was a 49-minute gap in image coverage as Mesoscale Sectors were rearranged). GLM Flash Points highlighted intermittent lightning activity associated with areas of deep convection. Tropical Depression Two was moving very slowly through an environment of relatively low wind shear, and was traversing warm water.

Metop ASCAT surface scatterometer winds at 1424 UTC (below) were generally at or below 25 kts — and wind gusts from nearby buoys and ships were also 25 kts or less in the animation shown above.

The corresponding 1-minute GOES-19 Infrared Window images (below) indicated that the coldest cloud-top infrared brightness temperatures of convection were generally in the -65 to -70 C range.

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5-minute CONUS Sector GOES-18 (GOES-West) Visible and Infrared Window images (above) showed the rapid development of a relatively compact thunderstorm east-southeast of Salt Lake City on 18 July 2026.

The coldest thunderstorm cloud-top infrared brightness temperature was -48.76 C at 1741 UTC (above) — which represented an altitude just below the Most Unstable (MU) air parcel’s Equilibrium Level (EL), according to a plot of 1800 UTC rawinsonde data from Salt Lake City (below).

This thunderstorm produced GOES-18 GLM-detected lightning activity from 1726-1816 UTC (below) — beginning 5 minutes after the LightningCast probability first exceeded 75% (violet contours), and 10 minutes after the probability first exceeded 50% (green contours). The parallax-adjusted LightningCast product was used in this case, to portray the highest probability of lightning at the surface (instead of at the cloud top). Tragically, a hiker died after being struck by lightning near American Fork Twin Peaks (which is located about 4 miles southwest of Alta). (media report)

A time series of GOES-18 LightningCast probability and GLM flash counts in the vicinity of Heber City Municipal Airport (KHCR) — the closest airport to the fatal lightning event — is shown below. In addition, at 1756 UTC lightning in the distance was noted at Salt Lake City (KSLC) and Provo (KPVU).

The largest GOES-18 GLM Flash Point area in the vicinity of Alta was 228 km² at 1806 UTC (below). Note that the Flash Point appeared just south of the cluster of large Flash Extent Density pixels — this is because gridded GLM products (such as Flash Extent Density) are mapped to correspond to a mean cloud top height, in contrast to the Flash Points which are mapped to correspond to the surface location of the lightning.

This is the fifth known U.S. lightning fatality of 2026 and the first in Utah since August 2024. 13 hikers have been killed by lightning since 2006. Know the forecast before your hike and head to a safe place when you see building clouds or hear thunder!kutv.com/news/local/h…

— National Lightning Safety Council (@lightningsafety.bsky.social) 2026-07-19T02:37:05.509Z

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The dominant weather story across much of the central United States remains the continuing impact of the Minnesota and Ontario wildfires on the air quality in the upper Midwest. You can see just how impactful the smoke was by looking at this slider of two images from the Blog’s home office on the campus of the University of Wisconsin-Madison. These two iamges were taken 24 hours apart, with the one on the left showing Madison’s isthmus and downtown on the hot and humid morning of Wednesday 15 July, while the one on the right shows the smoke-filled skies of 16 July. Watch as the prominent State Capitol, just 1.1 miles (1.9 km) away, disappears under the cloak of smoke.

Here’s a map of PM2.5 from Airnow.gov valid for 1900 UTC (2 PM CDT) on 16 July 2026. Hazardous air levels stretch all the way from north central Minnesota all the way to central Pennsylvania. The challenge of monitoring this outbreak of hazardous air was complicated by the fact that the day before, GOES-19 experienced an anomaly and was unable to transit observations until the early afternoon of the next day. In this post, we’ll explore a few of the alternatives for keeping track of what the air was doing until the workhorse geostationary platform could be returned to service.

Here in the Blog’s Headquarters City of Madison, the air quality degraded in the hours after sunset. While it’s easy to follow smoke during the day using satellites, tracking smoke at night can be challenging because the smoke particles are generally not significant sources of infrared radiation. However, there are other tools at our disposal that can be used to monitor this situation. Among the most important tools are ground-based air quality networks, such as those operated by the EPA or PurpleAir. Here’s a time series of a PurpleAir sensor in downtown Madison showing an initial increase in particulate matter around 10:00 PM CDT (0300 UTC) where the Air Quality Index (AQI) plateaued close to 200, then another increase around 4:30 AM (0930 UTC) to truly astonishingly high levels.

We can actually see the atmospheric current that brought the flow in. Here’s a loop from the Milwaukee/Sullivan NEXRAD radar showing the inland penetration of a lake breeze well into central Wisconsin. That lake breeze brought some relief from the humid conditions that had been dominating Madison’s weather for the previous few days, but it also cleared out air that originated from the south and instead replaced it with smokey air from the north. It’s also interesting to see how the lake breeze impacted the propagation of the radar beams. Lake breezes create shallow inversions as the cool air undercuts and lifts warm air. In this case, we see that shortly after the lake breeze front passed over the radar, the ground clutter increased significantly. This is because the lake breeze passage fostered an inversion over southeastern Wisconsin, refracting the radar beams in unexpected ways and fostering anomalous propagation.

The lake breeze can also be tracked with surface weather sensors. The Reliable Automated Instrumentation Network (RAIN) suite of sensors on the rooftop of Blog HQ provide a multiyear archive of weather conditions on the scale of a minute. Here’s a meteogram of 24 hours of conditions on 15-16 July. The arrival of the lake breeze can be seen right at 0300 UTC (10:00 PM CDT) with the rapid drop in temperature, increase in wind speed, and sharp change in wind direction from northwest to east.

The same cameras that we looked at above can also be used in the overnight hours. Here’s a movie between 8:00 PM and midnight CDT that shows the arrival of the smoke. See how the clouds disappear and the lights on the far shore of the lake vanish as the smoke arrives. While not appearing as dramatic as it would if the

The Space Science and Engineering Center (SSEC) is, along with NOAA, a parent of CIMSS. Researchers at SSEC are renowned experts in instrument design and deployment, and one of the highlights of SSEC’s work is the High Spectral Resolution Lidar, a laser-based instrument designed specifically to look at how aerosols like smoke are distributed through the atmosphere. This is a time-height cross section of aerosol backscatter running from 0000 to 0600 UTC (7:00 PM to 1:00 AM). We can see the smoke as the bright layer that first appears right after 0300 UTC (10:00 PM) and is about 1 km thick.

All of these things: the radar-indicated lake breeze front, the surface weather conditions, the HSRL cross sections, and the visible camera movie; all of these show significant events that are coincident with the sharp increase in AQI measured by the surface station.

The polar orbiting satellites operated by NOAA’s Joint Polar Satellite System (JPSS) also provide some unique perspectives on the event that we can’t get from geostationary view. This VIIRS true color image from NOAA-20 at 1756 UTC (12:56 PM CDT) perfectly encapsulates how widespread the smoke is. Nearly the entire states of Wisconsin and Michigan are severely affected, with additional impacts stretching from the Red River Valley to the Acela Corridor.

The VIIRS true color product has a spatial resolution of 750 m, which is slightly better than the 1 km resolution of its GOES counterpart. However, the practical resolution is a bit better because the GOES resolution is defined at the equator and it degrades the further poleward you go. By contrast, the VIIRS resolution doesn’t have a latitudinal dependence. That enables us to zoom in a little more than we might for a geostationary product. When we do, we see yet another interesting phenomenon.

Do you see how the cumulus clouds are almost exclusively outside the smoke, while the smokey regions are otherwise generally cloud free? This is likely because the smoke is attenuating enough of the incoming solar radiation to prevent surface-based convection from starting. When we talk about “fair weather cumulus,” we should make sure that the definition of “fair weather” includes no smoke.

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