Long-range transport of California wildfire smoke across the Upper Midwest

August 24th, 2020 |

GOES-16 True Color RGB images [click to play animation | MP4]

GOES-16 True Color RGB images [click to play animation | MP4]

GOES-16 (GOES-East) True Color Red-Green-Blue (RGB) images created using Geo2Grid (above) revealed the hazy signature of dense smoke aloft moving eastward across much of the Upper Midwest on 24 August 2020 — smoke that had been transported from large wildfires burning in California.

Images of 532 nm and 1064 nm lidar attenuated backscatter collected and processed by the University of Wisconsin Lidar Group at Madison from 00 UTC on 24 August to 00 UTC on 25 August (below) indicated that this smoke existed within altitudes between 2 km and 6 km.

532 nm and 1064 nm lidar attenuated backscatter during 24 August at Madison, Wisconsin [click to enlarge]

532 nm and 1064 nm lidar attenuated backscatter over Madison, Wisconsin [click to enlarge]

CIMSS Natural Color RGB images with plots of Pilot Reports are shown below. While this “simple” RGB does not depict the haziness of the smoke as well as the True Color RGB images above — which are corrected for the effect of Raleigh scattering — s subtle smoke signature was still apparent. Not many of the available Pilot Reports (PIREPs) explicitly mentioned any effects of the smoke, but one 1955 UTC PIREP indicated a reduction to Marginal Visual Flight Rules (MVFR, visibility of 3-5 miles) at at altitude of 11,500 feet (3.5 km).

CIMSS Natural Color RGB images, with plots of Pilot Reports [click to play animation | MP4]

CIMSS Natural Color RGB images, with plots of Pilot Reports [click to play animation | MP4]

Tropical Storm Laura south of Cuba

August 24th, 2020 |

GOES-16 4-panel display over Tropical Storm Laura, 0946 to 1621 UTC On 24 August 2020 (Click to animate); Upper Left: Band 13 “Clean Window” infrared (10.3 µm); Upper Right, Band 10 Low-level Water vapor infrared (7.3 µm); Lower Left: Band 2 Red Visible (0.64 µm); Lower Right, Day Convection RGB overlain with 5-minute aggregate GLM Flash Extent Density

Tropical Storm Laura’s path near/over the Greater Antilles has affected her strength, and the relative lack of organization means that night-time satellite identification of the center is a challenge. Consider the animation above. Northerly shear (analysis from this site) has shifted the coldest cloud tops to the south of the circulation center and with the 5-minute routine CONUS imagery, it is difficult to discern a surface circulation along the south coast of Cuba, where it was moving.  (A cluster of convection does appear there, although it is initially dwarfed in size by the convection to the south, south of 20 Latitude)

Visible imagery that becomes available at sunrise does show the center. The center gains prominence in the infrared as well as the convection to the south weakens. Note that the center can be discerned within the 1-minute shortwave infrared (3.9 µm) imagery from GOES-16 Mesoscale Sector 1: this link shows data from 0702 to 0803 UTC.  In the greyscale enhancement used in the linked-to animation, coldest cloud tops appear black and speckled because of a lack of precision at very cold temperatures in the 3.9 µm channel).

Sometimes, Day Night Band imagery from VIIRS can be useful in identifying tropical cyclone centers at night (see these 2016 examples with Matthew and Karl, for example). On the morning of 24 August, however, reflected moonlight was nil (Moonset over Cuba today was around 0500 UTC); in addition, the NOAA-20 overpass had Laura near the edge of the scan. Adaptive DNB imagery from Suomi NPP (just after 0700 UTC) and NOAA-20 (just before 0800 UTC), from the Direct Broadcast site at AOML in Miami, do show low clouds just south of Cuba, near the Jardines de la Reina, but it is a challenge to identify a surface circulation from this DNB imagery.

Suomi-NPP and NOAA-20 VIIRS Day Night Band Imagery at 0701 and 0752 UTC on 24 August 2020 (Click to enlarge)

Interests in Cuba and along the Gulf Coast of the United States should monitor closely the progress of Laura. Refer to the National Hurricane Center website for the latest forecasts.

Marco is sheared apart in the northern Gulf of Mexico

August 24th, 2020 |

GOES-16 Low-level Water Vapor Infrared imagery (7.34 µm), half-hourly from 0116 thorugh 1316 UTC, 24 August 2020, overlain with GOES-16 derived motion wind vectors at 250-350 mb (red) and Surface-900 mb (blue) (Click to animate)

Tropical system Marco (formerly a category 1 Hurricane) was weakened by shear overnight and early morning on 24 August (as forecast).  The half-hourly animation above, of GOES-16 Band 10, i.e., infrared “low-level” water vapor (7.3 µm), overlain with derived motion winds at upper (red) and lower (blue) levels (Click here to see only the water vapor animation;  here is the shear analysis from the SSEC Tropical website; Note in the animation how the number of low-level vectors increases greatly at the end of the animation as visible imagery becomes available at sunrise.  Also:  the shear in the eastern part of the domain, over the Florida Straits, suggests a favorable environment for Tropical Cyclone Laura, approaching western Cuba from the east) shows the effect of shearing.

Low level easterlies and upper-level southwesterlies mean that the vertical structure of the storm was interrupted:  the low-level circulation decoupled from the upper-level.   That is, the low-level circulation moved to the west as the mid- and upper-level parts of the storm moved north and east.  Result:  By sunrise, visible imagery (0.64 µm) showed the low-level swirl of the elongating near-surface circulation southeast of the mouth of the Mississippi River, and south and west of the main convection over and offshore of the northwest Florida panhandle.

GOES-16 Visible Imagery (0.64 µm) from Mesoscale Sector 2, 1129-1328 UTC 24 August 2020 (Click to enlarge)

For more information on Tropical Storm Marco, refer to the pages of the National Hurricane Center.