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Long-duration offshore transport of glacial silt from the Copper River Delta in southern Alaska

By Scott Bachmeier •

10-minute GOES-18 daytime True Color RGB and Nighttime Microphysics RGB images, from 2000 UTC on 11 December to 0000 UTC on 24 December [click to play MP4 animation]

10-minute Full Disk scan GOES-18 (GOES-West) daytime True Color RGB and Nighttime Microphysics RGB images — created using Geo2Grid (above) — showed the offshore transport of glacial silt from the Copper River Delta in Southcentral Alaska from 11-23 December 2025. Even though cloud cover occasionally obscured the signature of this plume of airborne glacial silt, its southward transport over the northern Gulf of Alaska was occurring during the entire 13-day period.

Focusing on one particular day (18 December), a GOES-18 Near-Infrared image at 2100 UTC (below) included plots of Metop-C ASCAT surface scatterometer winds — which showed wind speeds of 35-37 kts immediately offshore of the Copper River Delta (which is located just east of Cordova, PACV). Farther inland and to the northwest, note the peak wind gust of 53 kts at Valdez (PAVW) as gap winds were being channeled down Valdez Glacier.

GOES-18 Near-Infrared “Vegetation” (0.87 µm) image at 2100 UTC on 18 December, with plots of Metop-C ASCAT wind barbs (yellow) just offshore of the Copper River Delta [click to enlarge]

Metop-B Ultra High Resolution (UHR) ASCAT winds (below) displayed the narrow plume of higher wind speeds (shades of red) that arced southward then southeastward after emerging from the Copper River Delta.

Ultra High Resolution (UHR) Metop-B ASCAT winds at 1912 UTC on 18 December [click to enlarge]

RCM-2 Synthetic Aperture Radar (SAR) winds at 1558 UTC (below) also highlighted the plume of stronger winds (shades of yellow to red) emerging from the Copper River Delta.

RCM-2 Synthetic Aperture Radar (SAR) image at 1558 UTC on 18 December [click to enlarge]

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Alaska surface analyses every 6 hours, from 0000 UTC on 11 December to 0000 UTC on 24 December [click to play animated GIF]

Surface analyses during the 11-23 December period (above) depicted the strong coastal pressure gradient (closely-spaced isobars) between a cold inland area of high pressure and migratory areas of low pressure over the northern Gulf of Alaska. This strong pressure gradient forced gap winds to accelerate down the Copper River Valley (topography) and emerge from the coast.

The effect of the persistent inland area of high pressure was seen in a map of surface air temperature departure (below) — which ranged from -15 to -21ºF along the coast near the Copper River Delta (medium shade of blue) to -27ºF and colder (magenta) near the Alaska/Yukon border. On 22 December, minimum temperatures were quite cold across Alaska and Yukon (and included a low of -62ºF at Chicken).

Surface air temperature departure from normal, from 11-23 December (courtesy Brian Brettschneider, NWS Alaska Region) [click to enlarge]

Categories: Geo2Grid, GOES-18, Metop, Red-Green-Blue (RGB) images, SAR, Satellite winds