Advanced Scatterometry (ASCAT) plots derived from MetopB and MetopC, above, shows a pulse of winds associated with a Gulf of Tehuantepec wind event. Gales are widespread, and winds up to 45 knots are plotted. When Tehuano Gap Winds occur in clear skies (as in this example), the effect on the sea state can become apparent in visible imagery. On 9/10 April, high clouds masked the view of the ocean as shown in the animation of CSPP Geosphere true color imagery on 9 April 2025, below. You can see, however, the rapid motion of the clouds over the narrow Isthmus of Tehuantepec and the dissipation of those clouds in their descent towards the ocean.

The strong winds forced the development of large waves, as shown below in the plot of Significant Wave Heights.

Scatterometry plots and altimetric wave heights are available at this website. These are derived from microwave observations that are not affected by the widespread clouds.

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GOES-18 True Color imagery during the day on 7 April, above, shows the development of a standing wave downwind of the elevated topography on the Aleutian peninsula between King Salmon and Perryville. (Note also the faint signal of volcanic ash as discussed here) What atmospheric conditions support the development of these clouds? Soundings from King Salmon AK at 1200 UTC/7 April and 0000 UTC/8 April, below, taken from the University of Wyoming Sounding site, show very strong northerly winds at low-levels and near dry-adiabatic conditions at 1200 UTC. At 0000 UTC, the low-level winds are relaxing but the steep low-level lapse rate persists. By 0000 UTC, Aleutians are starting to be affected by a system dropping down from the north as evidenced by changes in the cloudiness in the animation shown above. The inversion is between 850 and 900 mb, around 1000 m above Sea Level. Only a few peaks in this area of the Aleutians reach above 1 km (link).

Day Cloud Phase Distinction imagery during the day on 7 April, below, suggests that the standing wave cloud is glaciated.

Mid-level Water Vapor infrared imagery (6.95 µm), below, also shows the development of the standing waves. Surface observations show very strong northerly winds off the Bering Sea.

The toggle below between VIIRS and GOES-18 ABI visible (0.64 µm) imagery highlights the importance of VIIRS data at high latitudes. There is a significant parallax shift in the GOES-18 imagery such that the standing wave is shown to be over the mountains, rather than displaced to the south as in the VIIRS imagery (and, likely, in reality). VIIRS data also allows the use to see the shadow of the higher clouds on the terrain below; the oblique view from GOES-18 misses that feature.

The animation below compares zoomed-in VIIRS imagery from Visible (I01, 0.64 µm), shortwave infrared (I04, 3.87 µm) and longwave infrared (I05, 11.45 µm) channels. Solar reflectance of 3.74 µm energy means the clouds and surface are warm — but note how the shadow of the clouds — where little solar reflection occurs — are relatively cold!

VIIRS data can be used to create Day Cloud Phase Distinction RGBs, as shown in the animation below (courtesy Carl Dierking, GINA), and the multiple JPSS Satellites (Suomi NPP, NOAA-20 and NOAA-21) means excellent temporal resolution.

JPSS Satellites carry infrared and microwave sounders, and data from those sounders are used to create vertical profiles of moisture and temperature, i.e., NUCAPS soundings. The animation below shows three soundings near the standing wave. There is a strong inversion upstream of the standing wave cloud, and the inversion is not so pronounced downstream of the cloud. The boundary layer in all three soundings is dry adiabatic.

My thanks to Aaron Jacobs, WFO Juneau and Carl Dierking, GINA, for alerting me to this interesting case, and supplying imagery and suggestions. Aaron also forwarded along the following screen captures of FAA Webcams at Chignik Bay and Perryville shown below.

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Heavy rains during the first week of April have led to significant flooding along the Ohio (and other) Rivers. The slider above compares True-Color imagery from CSPP Geosphere on 24 March — long before the rains — and on the morning of 7 April 2025 — during the floods. The expansion of the Ohio River, a sinuous brown in the image, is apparent, as is the general greening up of the background as Spring progresses. (Click here for an annotated image from 7 April that includes local geography, and here for the same annotation from 24 March).

Cloud cover after a rain event can make flood detection from satellites a challenge. SAR data can be used to detect floods underneath clouds (or at night) and imagery is available at this RealEarth-powered website. RadarSat imagery from late on 6 April 2025, below, shows the extent of the flooding over southern Illinois and southwestern Indiana. Regions where SAR data suggests flooding is occurring are shown in red.

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Clear Skies over the Ohio River valley on 8 April allowed for excellent coverage from a multitude of satellites that can assess the horizontal extent of flooding. For example, False-color imagery from Sentinel-2 (at this link), toggled below with a ‘before’ image from 22 March 2025, shows the obvious increase in flood waters.

Sentinel-2A horizontal coverage doesn’t cover the entire flooded region — but clear skies on 8 April allowed the VIIRS flood product to create information over the Ohio River Valley and mid-Mississippi River Valley, as shown in the image below (taken from this website).

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Added, 11 April 2025, below: The CIMSS Flood Product (1-day VIIRS Composites, source) during the 4 mostly clear days from 7-10 April 2025 is shown below. Memphis is at the southern edge of the image, where the Mississippi takes a long and lazy southerly to westerly curve. Some of the flooded tributaries of the Mississippi in western Tennessee show decreasing flood waters over these 4 days.

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1-minute Mesoscale Domain Sector GOES-18 (GOES-West) nighttime Dust RGB + daytime True Color RGB images created using Geo2Grid (above) revealed a plume of resuspended volcanic ash (shades of pink/magenta at night, hazy shades of tan during the day) from the 1912 Novarupta-Katmai eruption in Alaska — which was being transported offshore across the Shelikof Strait toward Kodiak Island on 07 April 2025. In the absence of snow cover, surface volcanic ash within the Valley Of Ten Thousand Smokes was being lofted by strong northwesterly winds that were being channeled through the valley. An advisory issued by the Anchorage Volcanic Ash Advisory Center (text | graphic) indicated that the resuspended ash layer extended to maximum altitude of 6000 ft.

In an animation of 1-minute GOES-18 Visible images (below) it is interesting to note that Buoy 46077 in the Shelikof Strait was situated within an eddy of relatively light and variable winds — and there appeared to be minimal amounts of resuspended ash that had become entrained within that eddy.

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