PyroCb in Idaho

A small pyroCb cloud developed from the Pioneer Fire in Idaho during the evening hours on 19 August 2016, which difted quickly to the southwest; GOES-15 (GOES-West) 0.63 µm Visible and 3.9 µm Shortwave Infrared images (below) showed the fire hot spot (red pixels on the 3.9 µm images) and the pyroCb plume in the visible. Since the pyroCb occurred near sunset there is not a lot of visible imagery to show the southwestward  progression of the pyroCb cloud (which would have placed the cloud between the 415-320 mb or 7.3-9.1 km altitude, according to winds from the Boise ID sounding).

GOES-15 0.63 µm visible channel (left) and 3.9 µm shortwave IR channel images (right) (click to play animation)

GOES-15 0.63 µm visible channel (left) and 3.9 µm shortwave IR channel images (right) (click to play animation)

Since GOES-15 has a lower Infrared channel resolution (4 km), the pyroCb cloud-top IR brightness temperatures appeared warmer than the -40º C threshold for classification as a pyroCb. However, a 1-km resolution NOAA-18 image at 1:11 UTC on 19 August (below; courtesy of René Servranckx) showed the coldest cloud-top IR brightness temperature of the pyroCb to be -49.1º C (yellow color enhancement), or between 10.8-11.5 km according to the Boise sounding data.

NOAA-18 AVHRR 0.64 µm visible (top left), 3.7 µm shortwave IR (top right), 10.8 µm IR window (bottom left) and false-color RGB composite image (bottom right).

NOAA-18 AVHRR 0.64 µm visible (top left), 3.7 µm shortwave IR (top right), 10.8 µm IR window (bottom left) and false-color RGB composite image (bottom right).

In addition, AVHRR 12 µm imagery shows the pyroCb reaching -52º C (yellow color enhancement).

AVHRR 12.0 µm IR image

AVHRR 12.0 µm IR image

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