West Fork fire complex: pyrocumulonimbus penetration of existing cumulonimbus clouds

GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images (click image to play animation)

GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images (click image to play animation)

McIDAS images of 1-km resolution GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel data (above; click image to play animation) showed a pyrocumulonimbus (pyroCb) cloud from the West Fork fire complex rapidly penetrating the tops of surrounding orographically-induced cumulonimbus (Cb) clouds, beginning around 20:10 UTC or 2:10 PM local time on 28 June 2013. This pyroCb cloud was located just northwest of Wold Creek Pass (station identifier KCPW). The GOES-13 satellite had been placed into Rapid Scan Operations, providing twice as many images during this short time period compared to GOES-15.

A timely overpass of the Suomi NPP satellite allowed a comparison of AWIPS images of 1-km resolution VIIRS 0.64 µm visible, 1.61 µm near-IR, 3.74 µm shortwave IR, and 11.45 µm longwave IR channel data at 20:17 UTC (below). Some important observations include: (1) as seen on the GOES visible imagery, the penetrating pyroCb cloud had a darker gray appearance compared to the adjacent brighter white Cb cloud tops; (2) a number of negative and positive cloud-to-ground lightning strikes were associated with the adjacent Cb clouds; (3) the pyroCb cloud appeared much warmer (darker) than the surrounding convective clouds, due to solar reflection off of much smaller cloud particles — the warmest 3.74 µm IR brightness temperature was +31º C; (4) the pyroCb cloud exhibited much colder 11.45 µm IR brightness temperatures than the surrounding Cb clouds, with a minimum of -71º C.

Suomi NPP VIIRS 0.64 µm visible, 1.61 µm near-IR, 3.74 µm shortwave IR, and 11.45 µm longwave IR channel images

Suomi NPP VIIRS 0.64 µm visible, 1.61 µm near-IR, 3.74 µm shortwave IR, and 11.45 µm longwave IR channel images

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