Tropical Storm Marco over the northwest Caribbean Sea, shown above in a toggle of GOES-16 ABI Clean window imagery (10.3 µm) and a NUCAPS diagnosis of 850-500mb lapse rates, is over very warm waters and in a region of favorably low diagnosed vertical wind shear. (Wind shear is from this website, (direct link to shear); the product is described here)  An inhibiting feature in strengthening, as noted in the National Hurricane Center discussion, is stable air.

NOAA-20 overflew Marco shortly before 0700 UTC on 22 August, and NUCAPS soundings derived from CrIS and ATMS data on NOAA-20 showed the stable mid-tropospheric air surrounding the storm. The 850-500 mb lapse rates were around 5.5 C/km. (Gridded NUCAPS data can also be viewed here) Individual soundings over western Cuba and just off the northwest tip of the Yucatan peninsula also show the relatively stable air. (Click here to see the Lapse Rate Analysis overlain with NUCAPS Sounding Availability points from the AWIPS display)

Marco’s future path is forecast to move over very warm waters that are shown in the ACSPO analysis of SSTs, below, from Suomi-NPP VIIRS data.  Consult the National Hurricane Center for the latest on this storm that will likely affect the Texas/Louisiana Gulf Coasts.

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A comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Near-Infrared (1.61 µm and 2.25 µm) images along with the VIIRS Active Fires product (above) showed nighttime visible reflectance and thermal signatures of the numerous wildfires that were burning across Northern California at 1001 UTC or 3:01am PDT on 20 August 2020. A closer view is available here.

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) Fire Temperature Red-Green-Blue (RGB) and “Red” Visible (0.64 µm) images (below) displayed the thermal signatures and smoke plumes associated with the Northern California fires.

GOES-17 True Color RGB images created using Geo2Grid (below) provided a closer view of the dense residual smoke and new smoke plumes across Northern California.

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 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) displayed the well-defined eye of Category 4 Hurricane Genevieve in the East Pacific Ocean (off the west coast of Mexico) on 18 August 2020. Genevieve underwent a period of rapid intensification during the pre-dawn hours that day (ADT plot).

A GOES-16 Visible image at 1617 UTC (below) includes plots of Metop-A ASCAT scatterometer surface winds — the highest wind was 69 knots just northeast of the storm center.

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GOES-16 (GOES-East) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed 2 pulses of pyro-convection emanating from the Williams Fork Fire that was burning between between Kremmling (K20V) and Berthoud Pass (K0CO) in Colorado on 14 August 2020. The cloud of the second pulse, originating around 2300 UTC, exhibited infrared brightness temperatures of -40ºC and colder  (shades of blue in the 10.35 µm images) — assuring the heterogeneous nucleation of all supercooled water droplets to form ice crystals, and thereby meeting the criteria of a pyrocumulonimbus (pyroCb). The pyroCb then drifted east-southeastward across Colorado.

The coldest pyroCb infrared brightness temperature was -46ºC, which corresponded to an altitude near 11 km according to rawinsonde data from Denver (below).

===== 15 August Update =====

On the following day, 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) Visible, Shortwave Infrared and Infrared images (above) showed another pyroCb that developed around 2240 UTC. This pyroCb moved southeastward, exhibiting cloud-top infrared brightness temperatures as cold as -55ºC — which, according to rawinsonde data from Denver (below) represented an altitude near 12 km.

Farther to the west, the Loyalton Fire was burning in northern California, near the border with Nevada. 1-minute Mesoscale Domain Sector GOES-17 (GOES-West) Visible, Shortwave Infrared, Infrared Window and Fire Temperature Red-Green-Blue (RGB) images (below) showed that this fire produced a pyroCb cloud around 2100 UTC, which then drifted northeastward across the California/Nevada border.

This event exhibited extreme fire behavior, producing fire whirls and prompting NWS Reno to issue a Tornado Warning for the source region of the pyroCb at 2135 UTC. The cloud-top infrared brightness temperatures of the pyroCb were around -55ºC; rawinsonde data from Reno (below) indicated that this corresponded to an altitude near 12 km.

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