Multiple PyroCb’s in northwestern Canada

åAfter several days of wildfire activity over parts of northern British Columbia (BC), northern Alberta (AB), and the Northwest Territories (NWT) of Canada (which produced a great deal of smoke, but no pyroCb activity), the conditions of the synoptic-scale environment became more favorable on 14 July 2014, allowing multiple pyroCb events (at least five?) to occur across that particular area. Very warm air was brought far northward — surface air temperatures as warm as 93º F or 33.9º C were seen in the Great Slave Lake region — ahead of a cold frontal boundary that was moving slowly eastward and southeastward across the region (surface analysis maps).

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

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

A comparison of GOES-15 (GOES-West) 1-km resolution 0.63 µm visible channel and 4-km resolution 3.9 µm shortwave IR channel images (above; click image to play animation) showed the widespread fire hot spots (dark black to red shortwave IR pixels) and the pyroCb clouds that developed in association with some of the larger fires.

The corresponding GOES-15 4-km resolution 10.7 µm IR channel images (below; click image to play animation; also available as a MP4 movie file) revealed that there were a few pyroCb clouds associated with the larger fires over northern BC, northern AB, and the NWT which began to exhibit cloud-top IR brightness temperature values of -40º C and colder (bright green color enhancement), indicating complete glaciation of the convective cloud top.

GOES-15 10.7 µm IR channel images (click to play animation)

GOES-15 10.7 µm IR channel images (click to play animation)

A higher spatial resolution view was provided by Suomi NPP VIIRS 375-meter (projected onto  a 1-km AWIPS grid) 0.64 µm visible channel, 3.74 µm shortwave IR, and 11.45 µm IR channel images at 21:10 UTC (below). The 4-letter identifier for regional upper air reporting sites are labeled in cyan.

Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images

On the corresponding VIIRS Red/Green/Blue (RGB) true-color image from the SSEC RealEarth web map server (below), the dense wildfire smoke was easy to identify due its gray appearance (in contrast to the brighter white clouds).

Suomi NPP VIIRS true-color Red/Green/Blue image

Suomi NPP VIIRS true-color Red/Green/Blue image

For 3 of the larger of the BC, AB, and NWT fires, NOAA ARL HYSPLIT model 180-hour forward air parcel trajectories (below) suggested a variety of long-range smoke transport pathways. The altitudes selected for the trajectories (8, 9, and 10 km) bracketed the approximate altitude of the -40º C level on the Fort Smith NWT (CYSM) and Fort Nelson, BC (CYYE) 12 UTC rawinsonde data.

HYSPLIT forward trajectories from BC pyroCb

HYSPLIT forward trajectories from BC pyroCb

HYSPLIT forward trajectories from AB pyroCb

HYSPLIT forward trajectories from AB pyroCb

HYSPLIT forward trajectories originating from NWT pyroCb

On the following morning of 15 July, Suomi NPP VIIRS visible and IR images (below) showed a large remnant pyroCb cloud that had drifted to the east of Great Slave Lake. The coldest VIIRS IR brightness temperature was -56º C, which was close to the tropopause temperature on the 12 UTC  Fort Smith (CYSM) sounding.

Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11.45 µm IR channel images

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