5-minute CONUS Sector GOES-18 (GOES-West) daytime True Color RGB and Nighttime Microphysics RGB images spanning the 7-day period from 31 July to 06 August 2026 (above) showed numerous dense smoke plumes emanating from active wildfires, along with widespread residual smoke from previous days of wildfire activity across much of the Pacific Northwest. At night, thermal anomalies associated with active wildfires (clusters of purple pixels) were evident. Note that a few of the larger and more dense smoke plumes exhibited shades of magenta after sunset — an indication that some blowing dust was intermingled with the smoke, which had been lofted by the strong surface winds that were a factor in rapid wildfire growth (the Red component of the Nighttime Microphysics RGB is this Split Window Difference).

Much of the Northwest US had been experiencing Moderate to Exceptional Drought during that particular week (below).

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5-minute CONUS Sector GOES-19 (GOES-East) Nighttime Microphysics RGB + daytime True Color RGB images from the CSPP GeoSphere site (above) showed the formation of nocturnal river valley fog over parts of the Mississippi River and a few of its tributaries in Wisconsin, Minnesota, Iowa and Illinois on 03 August 2026. The river valley fog then dissipated within a few hours after sunrise. Light winds and cloud-free conditions within a surface ridge of high pressure over the region allowed for ample radiational cooling that led to the fog formation,

GOES-19 Night Fog brightness temperature difference (BTD) + daytime Visible images (below) included hourly plots of Ceiling and Visibility — at some sites in the Wisconsin River valley, the visibility dropped to 1/4 mile (or even to zero) at times.

A NOAA-21 VIIRS Day/Night Band image at 0833 UTC (3:33 AM Central Time) revealed a faint signature of the river valley fog (below), as illuminated by the Moon (which was in the Waning Gibbous phase, at 75% of Full).

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1-minute Mesoscale Domain Sector GOES-18 (GOES-West) Visible images with an overlay of the Fire Mask derived product (above) showed the Old Trails Fire (initially named the Euclid Fire) as it started around 1907 UTC on 01 August 2026 — then grew rapidly as strong SW winds (with gusts as high as 40 knots) caused the wildfire to quickly expand into northwestern portions of the Spokane, Washington area (forcing numerous evacuations). SPC had highlighted much of eastern Washington as having an Extreme Fire Risk on that day — and NWS Spokane issued its first-ever Particularly Dangerous Situation (PDS) Red Flag Warning for the area.

1-minute GOES-18 GeoColor RGB images with an overlay of Next Generation Fire System (NGFS) Fire Detection polygons (below) provided a better view of the thermal structure/intensity of wildfires in the Spokane area.

1-minute GOES-18 True Color RGB images from the CSPP GeoSphere site (below) displayed a larger-scale view of the smoke plumes produced by the Spokane area wildfires. A few intermittent pulses of brighter-white pyrocumulus clouds were seen immediately downwind of the Old Trails Fire.

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According to the Tokyo VAAC, Sheveluch (located on Russia’s Kamchatka Peninsula) erupted around 0508 UTC (text | image) on 31 July 2026. A signature of the resulting volcanic cloud became apparent in 10-minute Full Disk scan GOES-18 (GOES-West) Ash RGB images (above) and Dust RGB images (below), created using Geo2Grid. Brighter shades of yellow in both RGB image types were indicative of a mixture of ash and SO₂ within the volcanic cloud. The volcanic cloud signature eventually became lost within a band of meteorological clouds associated with a cold front south of the Aleutian Islands.

GOES-18 Split Cloud Top Phase images (below) included plots of Pilot Reports (PIREPs) and Volcanic Ash Advisory/Forecast polygons issued by the Anchorage VAAC. The 8.4 µm spectral band is sensitive to SO₂ absorption which led to positive values (brighter green to yellow to red) in the imagery.

As the volcanic cloud advanced farther eastward across the Bering Sea, advisory responsibility was transferred from the Tokyo VAAC to the Anchorage VAAC, beginning at 1500 UTC on 31 July (below). The leading, faster-moving portion of the volcanic cloud had a maximum altitude of FL340 (34000 feet) — while the trailing, slower-moving portion had a maximum altitude of FL250 (25000 feet).

Wile many aircraft were flying above the FL340 (34000 feet) maximum altitude of the leading portion of the volcanic cloud, there were some pilot reports of Volcanic Ash (VA) clouds either in the distance or below the altitude of the aircraft (below).

The final Anchorage VAAC advisory for this event was issued at 1209 UTC on 01 August (below), as the volcanic cloud was approaching the Washington VAAC area of responsibility.

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