GOES-16 Mid-level Water Vapor (6.9 µm) and “Clean” Infrared Window (10.35 µm) images, with pilot reports of turbulence plotted in cyan/yellow [click to play animation | MP4]

GOES-16 (GOES-East) Mid-level Water Vapor (6.9 µm) and “Clean” Infrared Window (10.35 µm) images (above) revealed the formation of transverse banding along the eastern periphery of a decaying Mesoscale Convective System in the Upper Midwest during the morning hours on 07 August 2021. Transverse banding is a satellite signature that usually indicates an enhanced potential of turbulence (reference)— and there were indeed multiple reports of light-to-moderate turbulence within the 26-50,000 feet altitude range (cyan).

CIMSS Scientists have used machine-learning to create a predictive tool for moderate-or-greater (MOG) turbulence based in part on satellite imagery. The product for 1405 UTC on 7 August is shown below. A maximum is anchored on the MCS. This product is available online here. Training for this product is here.

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Synthetic Aperture Radar (SAR) winds are derived from a microwave signal pinged from a satellite; backscatter is converted into winds (given a background field that is typically from a numerical model). The wind structure here is suggestive of a bowing feature to a convective downdraft. How does it compare to radar or satellite imagery? GOES-16 Satellite imagery for the hour bracketing the imagery above is shown below. Convection (weak) is apparent moving east from the tip of Keewenaw peninsula.

What did radar imagery look like at this time? The imagery below, courtesy Nick Langlieb, the SOO at WFO Marquette, shows radar echoes (base reflectivity) at a different level than the Lake-surface values sampled by SAR, so a direct comparison is a challenge (click here to see Correlation Coefficient at the same time). It’s peculiar that no radar signal is apparent to match the strong SAR winds just offshore from the tip of the Keewenaw peninsula (between 88º and 87.5º W) — although there is a feature oriented north-south a small distance to the west of the peninsular tip; there seems to be a better (but not exact) match with the SAR winds near 87º W.

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Clear skies over the Great Lakes (except for Lake Superior) allowed for VIIRS data to record temperatures over the Great Lakes in the early morning of 5 August 2021. In situ data from moored buoys closely match ACSPO (Advanced Clear-Sky Processor for Oceans) values. Southwestern Lake Erie is warmest, with temperatures as warm as 78ºF (pink/white enhancement). Green Bay and Saginaw Bay are as warm as 75ºF. The analysis below (from this link at the Great Lakes Environmental Research Lab) also shows values largely in agreement with the above analysis.

AWIPS-ready files of these fields are available from the CIMSS LDM feed.

There plots of basin-wide average temperatures suggest that the Great Lakes (except for Lake Superior) are a bit cooler in early August of this year than they have been at this time in the recent past.

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The animation above shows NUCAPS sounding availability plots from sequential NOAA-20 overpasses on 5 August 2021. Stations that are north of about 39 N will occasionally see profiles from two sequential overpasses, as was the case above at Buffalo NY, and also Pittsburgh PA. A benefit of NUCAPS soundings is that they show up halfway between 0000 and 1200 UTC upper-air soundings. The animations below show 0000 UTC and 1200 UTC soundings from Buffalo (top) and Pittsburgh (bottom) with two soundings from NUCAPS from the closest point to the upper air launch.

When sequential overpasses happen, a forecaster can use information to tell how things are changing on 90-minute timescales. Even with only one profile, however, one can view changes between the synoptic upper-air soundings. It is worth mentioning a couple obvious differences between the two data sources: Radiosondes are sampling a line that moves up in the atmosphere over a period of time (up to two hours!); that line can extend over a significant horizontal distance; in contrast, NUCAPS observations are volumetric and instantaneous. NUCAPS profiles are very smooth compared to radiosondes, and extreme values, or very thin layers are unusual in NUCAPS profiles.

NUCAPS profiles are available at this OSPO site. Gridded NUCAPS fields are here.

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