![\"Meteosat-11](\"https:\/\/cimss.ssec.wisc.edu\/satellite-blog\/wp-content\/uploads\/sites\/5\/2018\/10\/181029_meteosat11_visible_shortwaveInfrared_infraredWindow_South_Africa_pyrocb_anim.gif\")
<\/a>Meteosat-11 Visible (0.8 \u00b5m, top),<\/em> Shortwave Infrared (3.92 \u00b5m, center)<\/em> and Longwave Infrared Window (10.8 \u00b5m, bottom)<\/em> images [click to play animation | MP4<\/strong><\/a>]<\/p><\/div>The Garden Route Fires had been burning since about 24 October 2018 near George along the southern coast of South Africa (media story<\/strong><\/a>). On 29 October, EUMETSAT<\/strong><\/a> Meteosat-11 High Resolution Visible (0.8 \u00b5m), Shortwave Infrared (3.92 \u00b5m) and Longwave Infrared Window (10.8 \u00b5m) images (above)<\/strong><\/em> showed an elongated west-to-east oriented thermal anomaly or fire “hot spot” (red pixels)<\/em> just northeast of George (station identifier FAGG)<\/em> on Shortwave Infrared imagery during the hours leading up to the formation of a pyrocumulonimbus<\/strong><\/a> (pyroCb) cloud around 1300 UTC. The pyroCb exhibited the characteristic warm<\/strong> (+10 to +15\u00baC, darker gray enhancement)<\/em> shortwave infrared cloud-top signature just off the coast at 1315 UTC<\/strong><\/a>, — this is due to enhanced solar reflection off ice crystals that are smaller<\/em> compared to those of conventional thunderstorm tops.<\/p>\n Zooming out a bit to follow the southeastward drift of the pyroCb cloud (below)<\/strong><\/em>, the coldest cloud-top 10.8 \u00b5m infrared brightness temperature (BT) was -61\u00baC (darker red enhancement)<\/em> at 1315 UTC — then the cloud tops remained in the -55 to -59\u00baC range (orange enhancement)<\/em> for the next 6 hours or so. Leveraging the large difference between cold 10.8 \u00b5m and warm 3.92 \u00b5m BTs, NRL<\/strong><\/a> calculates a pyroCb index, which classified this feature as an “intense pyroCb” (1315 UTC<\/strong><\/a> | animation<\/strong><\/a>). The coldest 10.8 \u00b5m cloud-top BT of -61\u00baC roughly corresponds to an altitude of 13.5 km based on 12 UTC rawinsonde data from Port Elizabeth (plot<\/strong><\/a> | list<\/strong><\/a>).<\/p>\n Meteosat-11 Shortwave Infrared (3.92 \u00b5m, left)<\/em> and Longwave Infrared Window (10.8 \u00b5m, right)<\/em> images [click to play animation | MP4<\/strong><\/a>]<\/p><\/div>Imagery from NOAA-19 at 1420 UTC (courtesy of\u00a0Ren\u00e9\u00a0Servranckx) also revealed the warm (dark gray)<\/em> Shortwave Infrared pyroCb signature, along with a minimum cloud-top infrared BT of -58.1\u00baC (below)<\/strong><\/em>.<\/p>\n NOAA-19 AVHRR imagery at 1420 UTC [click to enlarge]<\/p><\/div>A Suomi NPP VIIRS True Color Red-Green-Blue (RGB) image at 1230 UTC (below)<\/strong><\/em> was about a half hour before the formation of the pyroCb, but it did show a signature of smoke drifting southeastward off the coast.<\/p>\n Suomi NPP VIIRS True Color RGB image [click to enlarge]<\/p><\/div>On the following day (30 October), a NOAA-20 VIIRS True Color image (below)<\/strong><\/em> 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.<\/p>\n NOAA-20 VIIRS True Color RGB image [click to enlarge]<\/p><\/div>A time series of of surface observations from George (below)<\/strong><\/em> supported the idea of a cold frontal passage: ahead of the front, temperatures rapidly rose to 104\u00baF\/40\u00baC (with a dew point of 39\u00baF\/4\u00baC) on 28 October<\/strong><\/a> 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.<\/p>\n<\/a><\/a><\/a><\/a>