1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Infrared images (above) showed thunderstorms that produced very heavy rainfall — with 4 sites reporting over 11 inches across parts of the Milwaukee metro area (text list | radar-estimated rainfall) during the 12-hour period from early in the evening on 09 August into the early morning hours on 10 August 2025. The development of new storms west of the Milwaukee area (after 0300 UTC) then trained eastward across areas affected by previous convection, further enhancing rainfall totals and leading to significant flash flooding. GLM Flash Points revealed that abundant lightning activity was associated with these thunderstorms — and some thunderstorm overshooting tops exhibited infrared brightness temperatures as cold as -77ºC (denoted by shades of white embedded within dark black regions).

At Milwaukee International Airport, the 24-hour rainfall total of 5.74″ (on 09 August) and the 48-hour rainfall total of 6.91″ (from 09-10 August) were both the second-highest on record for that location. 1-hour precipitation amounts at METAR sites across the metro area were as high as 2.02″ at Milwaukee International Airport KMKE at 0600 UTC (below) — most of Milwaukee County was under a Flash Flood Warning at the time. Other notable 1-hour precipitation amounts included 1.68″ at Milwaukee Timmerman Airport KMWC (at 0800 UTC), 0.97″ at KMKE (at 0400 UTC) and 0.93″ at Waukesha County Airport KUES (at 0300 UTC). These rainfall rates were high enough to occasionally reduce the surface visibility to 1 mile or less at KMKE, KMWC and KUES.

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A plot of rawinsonde data from Davenport, Iowa at 0000 UTC on 10 August (above) revealed a Total Precipitable Water value of 1.90″ — which was above the 90th percentile for all 10 August / 0000 UTC soundings at that site (below). The presence of such a moist atmosphere was a key ingredient contributing to the heavy rainfall across southern Wisconsin. Furthermore, according to the rawinsonde data plot, the coldest cloud-top infrared brightness temperatures seen in 1-minute GOES-19 imagery (-77ºC) represented a significant overshoot of the Most Unstable (MU) air parcel’s Equilibrium Level (EL).

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In addition to the aforementioned heavy rainfall, during the afternoon hours on 09 August (around 2100 UTC, or 4 PM local time) two hikers were injured by a lightning strike near the Ice Age Trail in Palmyra, with one requiring hospitalization (media report). GOES-19 Visible and Infrared images that included contours of LightningCast Probability (below) indicated that lightning probabilities rapidly increased across that general area, reaching 90-100% over Palmyra about an hour before the lightning strike incident. There were also distinct clusters of GLM Flash Points in the vicinity of Palmyra around and shortly after 2100 UTC.

A time series of GOES-19 LightningCast Probability and GOES-19 GLM-detected lightning at and within 5-10 miles of the closest airport to Palmyra (Waukesha County Airport KUES) also displayed the rapid increase in LightningCast Probability, which began around 1930 UTC (below).

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Elevated smoke levels have been present in the upper Midwestern United States for well over a week, but recent synoptic-scale pattern shifts have started to bring in clearer (albeit warmer and more humid) air from the south. The following animation shows GOES-19-observed aerosol optical depth (AOD) for 1400 UTC (9:00 AM local time) for each day between 25 July and 8 August 2025. Even as far back as the beginning of this loop, Wisconsin, Michigan, and the western Great Lakes are shown to have very high levels of smoke.

The smoke has not disappeared from the midlatitudes of the northern hemisphere; it has simply propagated out to sea. The same aerosol optical depth product (this time viewing a larger portion of the GOES-19 disk) shows that very high levels of aerosol remain. While the air over the midwestern United States is in better shape, the same cannot be said for the northeastern United States and the maritime provinces of Canada. (Note: the high AOD in the lower right hand corner, behind the SSEC logo, is Saharan dust that has blown off into the Atlantic.)

The poor air quality observed by satellite can be verified by looking at a contemporaneous map of in situ air quality observations. The following image depicts PM2.5 s observed by the global network of in situ PurpleAir sensors. While not a governmental network, PurpleAir has the advantage of transcending national borders. There is clearly a strong relationship between the satellite-identified regions of high AOD and surface-based data.

This change in air quality was largely driven by shifts in the synoptic scale flow. Consider the two 500 mb charts displayed side by side. The one on the left is from 1200 UTC on 2 August 2025 while the right is from the same time but on 8 August 2025. For the earlier map, when air quality was at its worst for the Midwest, a high amplitude ridge was present over the western United States and the prairies of Canada. Temperatures were cool and dew points were lower than typical for early August, but the air was originating from the Canadian wildfires and advecting smoke into the central United States. Contrast that with the later map. A ridge is now present over the upper midwest, bring with it heat and humidity, but also air from smoke-free regions.

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5-minute PACUS 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 the Bronco Fire in southeast Arizona produced a pyrocumulonimbus (pyroCb) cloud as it was experiencing very active to extreme fire behavior on 07 August 2025. The pyroCb cloud 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 — beginning at 2156 UTC on 07 August.

Note that smoke drifting north-northeastward from the Bronco Fire eventually reduced the surface visibility to 4 miles at Show Low (METAR identifier KSOW) by 0100 UTC on 08 August (below).

The hazy signature of northward-drifting smoke was apparent in GOES-18 True Color RGB images from the CSPP GeoSphere site (below).

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The coldest pyroCb cloud-top IRBT was -51.59ºC at 0016 UTC on 08 August (above). On a plot of rawinsonde data from Tucson, Arizona (below) the air temperature of -51.59ºC occurred at an altitude around 11.3 km — not far below the Most Unstable (MU) air parcel’s Maximum Parcel Level (MPL) of 11.6 km.

The Bronco Fire burned very hot, intermittently exhibiting 3.9 µm infrared brightness temperatures as high as 137.88ºC — which is the saturation temperature of the GOES-18 ABI Band 7 detectors — from 2111 UTC on 07 August to 0016 UTC on 08 August (below).

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Clean Infrared Window (10.3 µm) images (above) showed a cluster of thunderstorms that eventually congealed into a large Mesoscale Convective System, producing a tornado, hail as large as 2.75″ in diameter and wind gusts as high as 99 mph (SPC Storm Reports) across parts of eastern South Dakota on 05 August 2025. Frequent pulses of overshooting tops were apparent with these thunderstorms.

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