PyroCb in Colorado

On 10 July 2016 a pyroCb formed in association with the Hayden Pass fire in central Colorado. Both GOES-15 (GOES-West) and GOES-13 (GOES-East) detected the smoke plume and pyroCb cloud, as well as the fire hot spot. The pyroCb (38.3 N 105.8 W) occurred at around 22:30 UTC. Starting at 20:00 UTC on 10 July, the animations below show visible (.63 μm) in the top panels, shortwave IR (3.9 μm) in the middle, and IR Window (10.7 µm) in the bottom panels (click images to play animation). In the shortwave IR images the red pixels indicate very hot IR brightness temperatures exhibited by the fire source region.

GOES-15 (GOES-West) visible (top), shortwave IR (middle), and IR Window (bottom) images [click to play animation]

GOES-15 (GOES-West) visible (top), shortwave IR (middle), and IR Window (bottom) images [click to play animation]

GOES-13 (GOES-East) visible (top), shortwave IR (middle), and IR Window (bottom) images [click to play animation]

GOES-13 (GOES-East) visible (top), shortwave IR (middle), and IR Window (bottom) images [click to play animation]

Usually such pyroCb clouds are detectable by GOES satellites, with the criteria that they exhibit an IR Window (10.7 µm) cloud-top brightness temperature of -40º C or colder. However, in this case the 4-km GOES IR resolution was not sufficient to detect a brightness temperature colder than -20ºC. To classify this as a true pyroCb, 1-km resolution POES imagery was used. The NOAA-18 4-panel image below (courtesy of Rene Servanckx) shows a pyroCb cloud-top IR brightness temperature of -44.6ºC at 00:35 UTC on 11 July, which is indicated by a green color enhancement on the bottom left panel.

POES 1-km resolution images (upper left: 0.64 µm visible;upper right: 3.8 µm shortwave IR; lower left: 10.8 µm IR window; lower right: false-color RGB composite)

POES 1-km resolution images (upper left: 0.64 µm visible;upper right: 3.8 µm shortwave IR; lower left: 10.8 µm IR window; lower right: false-color RGB composite)

As the fire continued to burn into the subsequent nighttime hours, a comparison of Suomi NPP VIIRS shortwave infrared (3.74 µm) and Day/Night Band (0.7 µm) images at 08:59 UTC or 2:29 am local time on 11 July (below) showed the large hot spot (black to yellow to red color enhancement) as well as the bright glow of the large Hayden Pass fire (located in the lower center portion of the images); in addition, similar signatures of smaller fires burning northwest of Boulder (station identifier KBJC) and near/along the Colorado/Wyoming border could be seen.

Suomi NPP VIIRS shortwave infrared (3.74 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

Suomi NPP VIIRS shortwave infrared (3.74 µm) and Day/Night Band (0.7 µm) images [click to enlarge]

OMPS Aerosol Index images below (courtesy of Colin Seftor) show the transport of smoke on 11 July. The maximum AI index was found to be 4.3 at 45.4 N 98.9 W (over northern South Dakota) around 18:48 UTC (center image). This is far northeast of the original Colorado pyroCb.

OMPS Aerosol Index image on 11 July

OMPS Aerosol Index image on 11 July

Due to a favorable sun/satellite forward scattering geometry, the east-northeastward transport of the smoke pall from the 10 July flare-up of the Hayden Pass fire was also evident on the following morning (11 July) GOES-15 visible images (below), with the hazy signature of smoke aloft drifting over parts of Kansas, Nebraska and South Dakota.

GOES-15 visible (0.63 um) images [click to play animation]

GOES-15 visible (0.63 um) images [click to play animation]

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