Himawari-8 “Clean” Infrared Window (10.4 µm) images (below) further revealed the 3 distinct pyroCb pulses — 2 originating from the southernmost fire located near 29.5ºS / 124.4ºE, and a smaller one originating from a fire located farther to the northwest. Cloud-top infrared brightness temperatures cooled to the -59 to -63ºC range for the pair of larger pyroCbs (which was close to the tropopause temperature of -64ºC on Perth soundings: plot | data) with temperatures reaching -51ºC with the smaller northernmost pyroCb. Also apparent was a surge of cooler air moving northeastward behind a surface trough, whose arrival appeared to coincide with the pyroCb formation. A time series of surface data from Forrest (YFRT) clearly showed the arrival of the cool, moist air behind the trough.As shown using RealEarth, an overpass of the Suomi NPP satellite provided a more detailed view of the first (and largest) pyroCb at 0537 UTC (above), with NOAA-20 capturing the second pyroCb cloud about an hour later at 0628 UTC (below). The coldest cloud-top infrared brightness temperature on the 0537 UTC Suomi NPP VIIRS image was -70ºC (darker black enhancement); in addition, there appeared to be an Above-Anvil Cirrus Plume associated with that pyroCb, extending southeastward from a subtle Enhanced-V signature at the upshear (northwestern) edge of the cloud (where the warmest temperature was -48ºC, green enhancement). On Himawari-8 Shortwave Infrared (3.9 µm) images (below), the pyroCb clouds exhibited a warmer (darker gray) appearance compared to adjacent conventional cumulonimbus clouds — this is due to the fact that ice crystals ejected into the pyroCb anvils are smaller (due to their shorter residence time within the intense updrafts above the fires), and these smaller ice crystals are more effective reflectors of incoming solar radiation. The large flare-up of red-enhanced land during the day is due to highly reflective soils of the Great Victoria Desert that quickly become very hot.
Zooming out a bit to follow the southeastward drift of the pyroCb cloud (below), the coldest cloud-top 10.8 µm infrared brightness temperature (BT) was -61ºC (darker red enhancement) at 1315 UTC — then the cloud tops remained in the -55 to -59ºC range (orange enhancement) for the next 6 hours or so. Leveraging the large difference between cold 10.8 µm and warm 3.92 µm BTs, NRL calculates a pyroCb index, which classified this feature as an “intense pyroCb” (1315 UTC | animation). The coldest 10.8 µm cloud-top BT of -61ºC roughly corresponds to an altitude of 13.5 km based on 12 UTC rawinsonde data from Port Elizabeth (plot | list).Imagery from NOAA-19 at 1420 UTC (courtesy of René Servranckx) also revealed the warm (dark gray) Shortwave Infrared pyroCb signature, along with a minimum cloud-top infrared BT of -58.1ºC (below). A Suomi NPP VIIRS True Color Red-Green-Blue (RGB) image att 1230 UTC (below) was about a half hour before the formation of the pyroCb, but it did show a signature of smoke drifting southeastward off the coast. On the following day (30 October), a NOAA-20 VIIRS True Color image (below) showed the classic comma cloud signature of a mid-latitude cyclone south of the coast, with the band of cold-frontal clouds extending northward across Lesotho. Note the thick plume of smoke spreading eastward within the strong post-frontal westerly winds. A time series of of surface observations from George (below) supported the idea of a cold frontal passage: ahead of the front, temperatures rapidly rose to 104ºF/40ºC (with a dew point of 39ºF/4ºC) on 28 October about 1.5 hours prior to the formation of the pyroCb — then strong westerly winds (gusting to 40 knots/21 mps) with rising pressures and falling temperatures followed on 30 October. The pyroCb research community believes that this is the first documented case of a pyroCb on the African continent.
— Active NorCal (@ActiveNorCal) September 6, 2018
A longer animation of GOES-16 “Red” Visible, Shortwave Infrared and “Clean” Infrared Window images displayed using McIDAS (below) showed that the first hot (red) Shortwave Infrared pixels appeared at 2027 UTC. The fire caused a 5-mile section of Interstate 5 to be closed. GOES-17 (positioned at 89.5º W longitude during its post-launch checkout phase) had a more direct view of the pyroCb than GOES-16 (positioned over the Atlantic Ocean at 75.2º W longitude) — and GOES-17 “Red” Visible, Shortwave Infrared and “Clean” Infrared Window images are shown below. Unfortunately the default GOES-17 Western US Mesoscale Domain Sector was shifted farther to the south on this day, so 1-minute imagery of the pyroCb event was not available.
* GOES-17 images shown here are preliminary and non-operational *
Another view using GOES-16 “Red” Visible, Shortwave Infrared, “Clean” Infrared Window (10.3 µm) and the Cloud Top Temperature product (below) showed the pyroCb cloud as it drifted rapidly northeast over Nevada and Oregon, along with a second (albeit smaller) pyroCb cloud which developed around 0130 UTC. One standard parameter used for defining a pyroCb cloud is a minimum cloud-top longwave infrared brightness temperature of -40ºC (ensuring complete glaciation) — and in this case with 1-minute imagery, the multi-spectral Cloud Top Temperature (CTT) product (FAQ) indicated that the pyroCb cloud reached the -40ºC threshold 19 minutes earlier than the 10.3 µm infrared imagery. From that point forward, the CTT product was consistently at least 5-10ºC colder than the 10.3 µm brightness temperature; the CTT product eventually displayed a minimum value of -53.9ºC over northeastern California. Even as the 10.3 µm brightness temperature began to rapidly warm after about 0100 UTC, the CTT product continued to display values in the -45 to -50ºC range (shades of green) which allowed for unambiguous tracking of the pyroCb.In the case of the second (smaller) pyroCb cloud that formed from the Carr Fire after 0130 UTC, the 10.3 µm brightness temperature failed to reach the -40ºC threshold, while the CTT product again displayed values in the -45 to -50ºC range. The coldest CTT value of -53.9ºC (seen with the initial pyroCb) roughly corresponded to an altitude of 12.5 km or 41,000 feet according to 00 UTC rawinsonde data from Reno, Nevada (below). Strong upper-tropospheric winds of 80-90 knots rapidly transported the pyroCb anvil northeastward.
GOES-16 “Red” Visible (0.64 µm, left) and Shortwave Infrared (3.9 µm, right) images, with hourly plots of surface reports [click to play animation | MP4]
GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (above) showed the smoke and pyrocumulus clouds as well as the thermal anomaly or “hot spot” (red pixels) associated with the Cranston Fire — located in the center of the images — which started southwest of Palm Springs, California (KPSP) around 1852 UTC or 11:52 am PDT on 25 July 2018. The large areas of red seen on the Shortwave Infrared images early in the animation were signatures of very hot sandy soil surfaces of the southern California deserts. Note the very warm airt temperatures seen across the region; Palm Springs had an afternoon high of 116ºF, and Thermal KTRM had a high of 119ºF.
A slightly different view — with the fire located in the lower left corner, southwest of KPSP — using GOES-16 “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.3 µm) images (below) revealed that the fire actually produced 3 distinct pulses of pyroCumulonimbus (pyroCb) cloud, where the 10.3 µm cloud-top infrared brightness temperature reached or exceeded the -40ºC threshold (lime green enhancement). Three specific times that these separate pyroCb clouds were evident were 2102 UTC, 2147 UTC and 2312 UTC.
GOES-16 “Red” Visible (0.64 µm, left), Shortwave Infrared (3.9 µm, center) and “Clean” Infrared Window (10.3 µm, right) images, with 4-letter airport identifiers plotted in yellow [click to play animation | MP4]
Another view of the pyroCb pulses was provided by a 4-panel view of GOES-16 “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm), “Clean” Infrared Window (10.3 µm) and Cloud Top Phase (below). The coldest 10.3 µm cloud-top infrared brightness temperatures were -55ºC as the primary pyroCb anvil drifted northeastward toward the California/Nevada border.
GOES-16 “Red” Visible (0.64 µm, top left), Shortwave Infrared (3.9 µm, top right), “Clean” Infrared Window (10.3 µm, bottom left) and Cloud Top Phase (bottom right) images [click to play animation | MP4]
There was also substantial lightning observed with these pyroCb clouds:
Loop of fire temperature RGB showing #CranstonFire in Southern California yesterday. Total lightning also overlaid showing pyrocumulus generated dry lightning. Areas of glint also seen towards end of the loop from solar farms reflecting light directly into the #GOESEast ABI pic.twitter.com/9wsBBeJsAu
— William Churchill (@kudrios) July 26, 2018
Below is a timelapse video of the first 8 hours of the fire, which shows the pyroCb evolution at the end.
===== 26 July Update =====
GOES-16 “Red” Visible (0.64 µm, top left), Shortwave Infrared (3.9 µm, top right), “Clean” Infrared Window (10.3 µm, bottom left) and Fire Temperature (bottom right) images [click to play animation | MP4]
Another pyroCb was produced by the Cranston Fire on 26 July, as shown by GOES-16 “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm), “Clean” Infrared Window (10.3 µm) and Fire Temperature images (above). Similar to the previous day, there appeared to be 2 pulses of pyroCb formation — with cloud-top infrared brightness temperatures cooling to -44ºC. Pyrocumulus from the smaller Ribbon Fire (just southeast of the Cranston Fire) could also be seen.
* GOES-17 images shown here are preliminary and non-operational *
The Ferguson Fire in central California produced a pyrocumulonimbus (pyroCb) cloud during the afternoon hours on 15 July 2018. GOES-16 (GOES-East) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed that the high-altitude portion of the pyroCb cloud then drifted northeastward toward the California/Nevada border, where cloud-top infrared brightness temperatures cooled to near -55ºC (orange enhancement) as it crossed the border around 0005 UTC on 16 July.
A comparison of Visible images from GOES-15 (0.63 µm), GOES-17 (0.64 µm) and GOES-16 (0.64 µm) is shown below — with the imagery displayed in the native projection of each satellite. Images from GOES-16/17 are at 5-minute intervals, while images from GOES-15 are every 5-15 minutes depending on the operational scan schedule of that GOES-West satellite. GOES-17 was at its post-launch checkout position of 89.5ºW longitude, so it offered a more direct view of the pyroCb cloud.A toggle between NOAA-19 Visible (0.63 µm), Shortwave Infrared (3.7 µm) and Infrared Window (10.8 µm) images (below) showed the pyroCb cloud southwest of the California/Nevada border (between Bridgeport KBAN and Mammoth KMMH) at 2327 UTC. In spite of a minimum cloud-top 10.8 µm infrared brightness temperature of -59ºC (red enhancement), note the darker (warmer) appearance of the cloud on the 3.7 µm image — this is due to reflection of solar radiation off the smaller ice particles of the pyroCb anvil. The -59ºC temperature roughly corresponded to an altitude of 13 km or 42.6 kft on the 00 UTC Reno, Nevada rawinsonde report (plot | data) A time lapse of the pyroCb was created by Sierra Fire Watch (below).