1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and Low-level Water Vapor (7.3 µm) images (above) showed a mesoscale disturbance that was moving northward over the eastern Brooks Range in far northeastern Alaska on 17 April 2019. The curved configuration of the associated cloud structure suggested that a closed circulation center was present (or had just recently developed) — while surface analyses showed an area of low pressure much farther to the south along the Alaska/Yukon border, there were no features moving northward across the region shown in the GOES-17 imagery.

Light to moderate snow was reported at Arctic Village as this mesoscale disturbance moved over the area (below).

375-meter resolution Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2131 and 2313 UTC (below) provided a more detailed view of this feature, in which the clouds exhibited an appearance suggestive of embedded convection. Cloud-top infrared brightness temperatures were as cold as -50ºC just southwest of Arctic Village on the 2313 UTC image — this corresponded to an altitude of 8.5 km on the 00 UTC Fairbanks rawinsonde data.

13-km NAM model fields (below) showed no clear signature of either a closed circulation or a discrete vorticity center — so satellite imagery was depicting the presence of an important feature that was not captured by numerical models. While the 18 UTC model run did show an area of light precipitation moving northward toward the region, the 00 UTC model run scaled back the areal coverage of this precipitation.

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The subtle thermal anomaly (or “hot spot”) from the Notre Dame Cathedral Fire was evident in 4.8-km resolution (at satellite nadir) EUMETSAT Meteosat-11 Shortwave Infrared (3.92 µm) imagery (above) as a cluster of brighter yellow pixels just north of Paris Orly International Airport (LFPO) near the center of the images on 15 April 2019.

The fire reportedly began around 1650 UTC; the maximum 3.92 µm brightness temperature sensed by Meteosat-11 was 284.5 K (11.35ºC) on the 1745 UTC image, not long after the fire had spread to the large spire of the cathedral (Meteosat-11 was actually scanning the Paris area at 1756 UTC, since the Meteosat Second Generation satellites scan each Full Disk from south to north). Clouds approaching from the west began to mask the fire signature at 1930 UTC.

Even though high clouds had begun to move overhead, a thermal signature (darker black pixel) could still be seen in 1-km resolution Metop-A and Metop-C Shortwave Infrared (3.75 µm) images at 2009 and 2048 UTC (below, courtesy of William Straka, CIMSS). The maximum 3.75 µm brightness temperature detected by Metop was 291.1 K (18.0ºC).

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16-Panel GOES-17 Full-Disk Advanced Baseline Imager (ABI) Imagery, 0010 – 2340 UTC on 14 April 2019 (Click to play mp4 animation)

Solar illumination of the GOES-17 Advanced Baseline Imagery (ABI) was at a maximum on 14 April, so that the effects of the Loop Heat Pipe that is not operating at its designed capacity (and therefore cannot keep the ABI detectors as cold as preferred) were at their worst. (This image of the predicted Focal Plane Temperature from this blog post shows the mid-April peak to be warmest). The animation above shows that only Band 14 (11.2 µm) was able to send a useable signal during the entire night. The Band 14 data are biased, however. The image below compares GOES-16 and GOES-17 temperatures over a region on the Equator (here, from the GOES-17 perspective, and here, from the GOES-16 perspective, from this website) equidistant between the two sub-satellite points (75.2º W for GOES-East, 137.2º W for GOES-West).  GOES-17 slowly cools relative to GOES-16 (assumed to be ‘truth’) before undergoing a series of cold/warm/cold oscillations relative to GOES-16.   So while a useful signal is preserved, algorithms that rely on threshold temperatures, or brightness temperature difference fields (such as the 3.9 µm – 11.2 µm Brightness Temperature Difference), would likely produce unexpected results.

 

Loop Heat Pipe issues should slowly subside over the coming weeks.  ‘Predictive Calibration’ is likely to be in place by the time the (Northern Hemisphere) Autumnal Equinox arrives.  This will extend the useful signal for the ABI channels.  One might even conclude that this current episode will have the worst impact on useable imagery from the ABI.

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An outbreak of severe weather began in eastern Texas on the morning of 13 April 2019, where thunderstorms produced hail up to 3.0 inches in diameter, tornadoes and damaging winds (SPC storm reports). 1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images (above) showed the clusters of thunderstorms that developed as a surface low and associated frontal boundaries moved eastward (surface analyses). The corresponding GOES-16 “Clean” Infrared Window (10.3 µm) images (below) revealed numerous overshooting tops with infrared brightness temperatures as cold as -70 to -75ºC. In addition, the storm producing 3.0-inch hail and damaging winds at 1428 UTC exhibited an Above-Anvil Cirrus Plume (Visible/Infrared toggle).

A comparison of Terra MODIS Visible (0.65 µm) and Infrared Window (11.0 µm) images at 1650 UTC is shown below.

Later in the day, the thunderstorms continued to produce a variety of severe weather as they moved eastward across Louisiana and Mississippi, as shown by GOES-16 Visible and Infrared images (below).

After sunset, the thunderstorms continued to move eastward, spreading more serve weather across Mississippi into Alabama and far southern Tennessee (below).

VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP (below) provided additional views of the storms as they were moving across Mississippi and Alabama. Several bright lightning streaks were evident on the Day/Night Band images. Note: the NOAA-20 image (downloaded and processed from the Direct Broadcast ground station at CIMSS) is incorrectly labeled as Suomi NPP.

On a NOAA-20 VIIRS Day/Night Band (0.7 µm) image at 0825 UTC (below), an impressively-long (~400 mile) dark “post-saturation recovery streak” extended southeastward from where the detector sensed an area of very intense/bright lightning activity northeast of Mobile, Alabama.

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