On 28 November 2025, large regions of standing waves were present throughout the eastern seaboard. When air flows across mountainous regions it gets forced upward by orographic lift. The air cools as it rises due to adiabatic expansion. If the environment is largely stable, the upward motion is inhibited as the ascending air parcels find themselves too warm for the environment and so the air starts to sink. As it sinks, it warms due to adiabatic compression and eventually starts rising. This process can repeat itself many times as the air races hundreds of kilometers downstream of the initial range. While most commonly associated with the Rocky Mountains, they can occur over other, shorter landforms like the Appalachians. If the air is sufficiently moist, this can manifest itself as a series of parallel cloud bands, as can be seen in the GOES-19 True Color view. Note the ridged clouds that are particularly noticeable in Pennsylvania and Virginia. At the tops of these waves, when the air is at its coldest, condensation occurs. At the bottom, the cloud droplets evaporate as the air is warmed, leading to clear skies in between the ridges.

However, what if there’s not enough moisture for condensation to happen? Can these waves still be seen? If you’re looking using a water vapor channel, then the answer is yes. Look at the following animation of the 7.34 micron (low level water vapor) band from GOES-19. Note now in eastern Virginia and North Carolina, even though skies are clear the same wave pattern is visible. There’s even a particularly interesting feature in central Virginia where eastward-moving flow is creating its own waves that are intersecting with the westward flow over the Appalachian Mountains which is creating wave interference.

These events matter because these mountain waves are a significant cause of clear air turbulence (CAT). Turbulence associated with convection is easier for aircraft pilots and flight planners to identify and avoid since it is found in the vicinity of deep, moist convection. CAT, on the other hand, is not visible to the naked eye at standard visible wavelengths, but water vapor imagery can help pilots avoid these situations.

It’s important to note that the Channel 10 (7.34 micron) channel shown above is largely sensitive to low level water vapor. The waves depicted here are unlikely to disturb aviation too much as they are occurring at a level where most planes are just passing through on their way up to cruising altitudes or down to airports. However, these waves are still visible on the upper level water vapor channel, Channel 6 (6.19 microns).

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A EUMETSAT Meteosat-10 False Color RGB product from the NOAA/CIMSS Volcanic Cloud Monitoring site (above) showed the signature of a large volcanic cloud following the explosive eruption of Hayli Gubbi in Ethiopia, which began around 0830 UTC on 23 November 2025. Since this False Color RGB product uses the 8.7 µm spectral band (which is sensitive to SO₂ absorption) in its green component, shades of green exhibited by much of the larger eastward-moving cloud indicated a mixture of volcanic ash and SO₂ — while the shades of pink exhibited by the smaller northwest-moving cloud indicated that it was composed primarily of ash.

Sentinel-5P #TROPOMI measurements at ~11:00 UTC show most of the SO? emissions from #HayliGubbi spreading east in the upper troposphere. Plume contains ~44 kilotons of SO? (~0.04 Tg).

— Prof. Simon Carn (@simoncarn.bsky.social) 2025-11-23T17:53:45.223Z

A radiometrically retrieved Meteosat-10 Volcanic Ash Height product (below) indicated that maximum ash heights associated with the larger eastward-moving cloud were in the 18-20 km range — while the smaller northwest-moving cloud had ash heights generally in the 3-5 km range.

A Volcanic Ash Height product derived using higher-spatial-resolution VIIRS data from NOAA-21, Suomi-NPP and NOAA-20 (below) indicated that maximum ash heights of the larger cloud were in the 16-18 km range — which were closer to the height values listed in volcanic ash advisories (FL450 = 13.7 km; FL500 = 15.2 km) from the Toulouse VAAC.

A Meteosat-10 Ash Loading derived product (below) indicated that loading was quite high within the larger eastward-moving cloud, and generally low to moderate within the smaller northwest-moving cloud.

A Meteosat-10 Ash Effective Radius product (below) depicted the presence of larger ash particles within the higher-altitude cloud, in contrast to smaller ash particles within the lower-altitude cloud.

A toggle between Low-level (700-850 hPa) and High-level (200-700 hPa) Deep Layer Mean Wind or “Environmental Steering Product” (source) at 0900 UTC on 23 November (below) showed lower-tropospheric southeasterly winds and upper-tropospheric westerly winds that were responsible for the transport of the 2 different volcanic clouds.

===== 24 November Update =====

10-minute Full Disk scan JMA Himawari-8 Air Mass RGB images created using Geo2Grid (above) showed a signature of the SO₂-rich volcanic cloud as it emerged from over the northern Arabian Sea and moved northeast across parts of Pakistan, India, Nepal and finally the Tibet region of southwestern China on 24 November (2130 UTC Toulouse VAAC final advisory). Since the red component of the Air Mass RGB uses the 7.3 µm spectral band — which is also sensitive to SO₂ absorption — the Hayli Gubbi volcanic cloud appeared as brighter shades of magenta.

===== 26 November Update =====

The leading edge of the SO₂-rich Hayli Gubbi volcanic cloud (brighter shades of magenta) eventually began to appear along the western limb of GOES-18 (GOES-West) Air Mass RGB images on 26 November (above), as the volcanic cloud started to move eastward across the North Pacific Ocean (east of Japan).

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The residents of American Samoa found themselves in the early morning hours of 20 November 2025, as strong maritime convection moved into the region. There is no radar in the area, so satellite observations are critical for operational awareness and nowcasting. The Band 13 infrared view on GOES-18 showed a large array of vigorous convective storms stretching east-west across the near-equatorial Pacific.

While this product gives a solid qualitative view of where deep, moist convection is taking place, additional products can also further inform as to the intensity of the storms. One of these is the Day Convection RGB. The recipe for this product is designed to show red when clouds are high and green where cloud droplets are large. The combination of high clouds and large droplets is found in deep convective plumes, while the combination of red and green produces yellow. The following animation shows that relationship in action. You might note that this loop spans the sunrise. Since the product relies heavily on near-infrared and visible reflectance, it can only be used during the day. The lack of yellow at the start of the loop does not mean that there is no deep convection. Instead, it just means that the 3.9 minus 10.3 micron brightness temperature difference which comprises the green channel of this image in very small at night (unless something is on fire).

With no radar, satellites have to step in and help fill the gap. The GREMLIN product is a machine-learning retrieval of rainfall from satellite brightness temperature observations, designed to mimic the radars that forecasters find so familiar. The following loop is from GREMLIN as displayed on AWIPS for roughtly the same time as the previous animations. Note the pulses of yellow over and around the island of Tutuilia, corresponding with rain rates of 40 mm/hr (more than 1.5 inches per hour).

Satellites can also help judge the convective instability of the atmosphere. NUCAPS-retrieved thermodynamic profiles from polar-orbiting hyperspectral infrared and microwave sounding instruments provide valuable information about the atmosphere’s thermodynamic state. Since NUCAPS retrieves dozens of profiles simultaneously, it’s possible to analyze the profiles like a three-dimensional cube, taking horizontal slices and seeing how key parameters change horizontally as well as vertically. The next image shows the 850-500 mb lapse rate over the central Pacific as calculated by NUCAPS and displayed in AWIPS. The NUCAPS availability parameter is plotted on top as an array of red, blue, or green dots. The values in the middle of the convection are untrustworthy as neither the infrared nor the microwave sounders can penetrate the convective cores. Still, the reliable locations show lapse rates approaching 6 C/km. In the tropics, the moist adiabatic lapse rate is less than it is in the tropics as more latent heat lease means a slower lapse rate. Therefore, the observed lapse rates can still indicate instability

Clicking on any of the dots in AWIPS brings up the sounding and its associated stability indices. For one green dot near Pago Pago, American Samoa, the environment is clearly moderately unstable with CAPEs in the mid-to-upper 1000s and effectively no CIN to restrain convection.

This just continues a trend of record-setting precipitation in American Samoa, which has previously been discussed on the blog. The chart below shows the accumulated precipitation for so far in 2025 (blue), the wettest year before now (2020, magenta), and normal (brown). Already in 2025, the total rainfall has exceeded every single year save one despite still having a month to go.

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10-minute Full Disk scan GOES-19 (GOES-East) Water Vapor images centered over the southern Great Lakes (above) included contours of Moderate Or Greater (MOG) Turbulence Probability (yellow contour = 40%) and Pilot Reports of Turbulence on 20 November 2025. The yellow 40% MOG contour progressed eastward across the southern Great Lakes and toward the Northeast US during the day — note the appearance of one report of Extreme Turbulence over the southwest portion of Lower Michigan around 1500 UTC.

Products from the Aviation Weather Center allowed cursor samples of two closely-spaced Pilot Reports of Extreme Turbulence — apparently from the same aircraft, as it was flying southeast (below).

The second encounter of Extreme Turbulence occurred at 1505 UTC, causing minor injuries (below).

A toggle between the 1501 UTC GOES-19 Water Vapor image and a 3-hour NAM40 model forecast of 250 hPa winds valid at 1500 UTC (below) indicated that the initial 1450 UTC Pilot Report of Extreme Turbulence (red symbol) occurred in an area of strong speed shear just north of the axis of a 150-knot jet streak (shades of orange). There was also the characteristic dry/moist gradient in Water Vapor imagery along the axis of the upper-tropospheric jet streak.

An animation of 5-minute CONUS Sector GOES-19 Water Vapor images with Pilot Reports of Turbulence is shown below.

Thanks to Rick DiMaio for alerting us to this case!

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