Pyrocumlonimbus cloud spawned by the Bringham Fire in Arizona

June 11th, 2020 |

GOES-17 “Red” Visible (0.64 µm, top), Shortwave Infrared (3.9 µm, center) and “Clean” Infrared Window (10.35 µm, bottom) images, with hourly plots of surface reports [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm, top), Shortwave Infrared (3.9 µm, center) and “Clean” Infrared Window (10.35 µm, bottom) images, with hourly plots of surface reports [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the formation of a pyrocumulonimbus (pyroCb) cloud that was spawned by the Bringham Fire in extreme eastern Arizona during the afternoon hours on 11 June 2020. To be classified as a pyroCb, the deep convective cloud must be generated by a large/hot fire, and eventually exhibit cloud-top 10.35 µm infrared brightness temperatures of -40ºC and colder — assuring the heterogeneous nucleation of all supercooled water droplets to form ice crystals. The pyroCb cloud then moved northeastward across far western New Mexico.

In Shortwave Infrared imagery, the fire’s thermal anomaly or “hot spot” was depicted by the cluster of red pixels — and the pyroCb cloud tops  appear warmer (darker gray) than those of nearby conventional thunderstorms, due to enhanced reflection of solar radiation off the smaller ice crystals found in the pyroCb anvil (reference).

The pyroCb exhibited minimum cloud-top 10.35 µm infrared brightness temperature in the -40 to -49ºC range (shades of blue) — according to rawinsonde data from Tucson, Arizona at 00 UTC on 12 June (below), this roughly corresponded to altitudes of 10-12 km.

Plot of rawinsonde data from Tucson, Arizona [click to enlarge]

Plot of rawinsonde data from Tucson, Arizona [click to enlarge]

Suomi NPP VIIRS True Color RGB image, with plots of VIIRS Fire Radiative Power [click to enlarge]

Suomi NPP VIIRS True Color RGB image, with plots of VIIRS Fire Radiative Power [click to enlarge]

A Suomi NPP VIIRS True Color Red-Green-Blue (RGB) image viewed using RealEarth (above) included plots of VIIRS Fire Radiative Power. The hazy signature of smoke drifting northward was apparent in the image. In fact, a plot of surface observation data at Springerville, Arizona (KJTC) (below) indicated that surface visibility was eventually reduced to 7 miles around 23 UTC as strong southerly winds advected smoke northward from the fire.

Plot of surface observation data at Springerville, Arizona [click to enlarge]

Plot of surface observation data at Springerville, Arizona [click to enlarge]

Leave a Reply