The large (40,000 acre or 63 square mile)  “Esperanza wildfire” started during the early morning hours on 26 October 2006 in a portion of the San Bernardino National Forest near Banning, California (west of Palm Springs); this fire quickly burned out of control, and was responsible for the deaths of 5 firefighters. Santa Ana winds across the region were creating favorable conditions for rapid fire growth (the dew point at nearby Palm Springs dropped from 55ËšF at 19 UTC on 25 October to -1ËšF at 07 UTC on 26 October). GOES-11 3.9µm IR imagery (QuickTime animation, above) showed very hot brightness temperatures (yellow to red enhancement) in the vicinity of this large fire — hot fire pixels were first evident at 08:15 UTC (01:15 AM local time), and image pixel values reached the saturation temperature of the GOES-11 3.9µm detectors (337.2ËšK / 64ËšC / 147ËšF) as early as 12:45 UTC (5:45 AM local time). The Wildfire ABBA product (GOES-11 | GOES-12) also indicated saturated fire pixels (yellow) in that area (20:45 UTC WF_ABBA image).

GOES-11 visible channel imagery (QuickTime animation, below) showed a very large smoke plume from this fire, which was dispersed in different directions due to directional wind shear between the surface and the 500 hPa level (~18,000 feet in altitude). MODIS imagery of the fire from 26 October is posted on the UMBC Air Quality Smog Blog, while the IDEA Aerosol Optical Depth product from the following day shows continued smoke transport out across the adjacent Pacific Ocean.

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The AWIPS image of MODIS 11.0µm-3.7µm “fog/stratus product” (above) reveals several long plumes embedded within the extensive stratus cloud deck (yellow to red enhancement) that covered much of northern and central Minnesota during the pre-dawn hours on 19 October. These plumes likely originated at large coal-fired power plants (or paper mills?) located across that region — emissions from these industrial sources may have acted as cloud condensation nuclei, causing a higher concentration of smaller supercooled cloud droplets downwind of the plants.

The MODIS Cloud Phase product (below, lower left panel) showed that this stratus deck was primarily a water-phase cloud (blue enhancement); MODIS 11.0µm IR window channel brightness temperatures were generally around -14 C across that region, indicating that the stratus cloud was composed of supercooled water droplets. Note that these power plant plumes were not evident on the 4 km resolution GOES fog/stratus product (below, upper right panel). The GOES sounder Cloud Top Height values were around 11-12 kft over the area.

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A large Mesoscale Convective System formed over the Gulf of Mexico (just off the Texas coast) on 15 October, and this convection exhibited some very cold cloud top temperatures on AWIPS images of IR window channel data (above) — IR brightness temperatures were as cold as -91 C (-132 F) on the 1-km resolution 11.0 µm MODIS IR channel, and as cold as -87 C (-125 F) on the 4-km resolution GOES IR channel. Such cold cloud top temperatures are common in a tropical atmosphere, where the tropopause pressures are usually lower and the tropopause temperatures colder than atmospheres at mid-latitudes; the rawinsonde reports from Brownsville, Texas indicated a tropopause near the 100 mb level, with a nearly moist adiabatic lapse rate that is also typical of tropical air masses.

GOES sounder total precipitable water values were also quite high across the Caribbean and Gulf of Mexico, with PW exceeding 60 mm (2.4 inches) at some locations (below). This feed of tropical moisture helped to fuel severe convection on the following day which produced a few tornadoes along the Gulf Coast, along with record daily rainfall amounts at Houston, Texas (5.17 inches) and Galveston, Texas (3.91 inches) which caused fatal flash flooding to occur.

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GOES-12 6.5 µm water vapor channel imagery (QuickTime animation, above) revealed a series of vortices migrating southward along the western periphery of the large cold-core polar vortex that was centered over  southern Ontario on 13 September. Instability-like fragmentation of a potential vorticity (PV) strip along a stratospheric intrusion can lead to the development of this type of isolated subvortex structure (see Wirth et al, 1997). Within these mesoscale vortices, the tropopause was likely displaced downward several kilometers as vertical winds induced by local stratospheric intrusions brought drier air into the upper troposphere. AWIPS imagery of GOES sounder total column ozone (QuickTime animation, below) showed elevated ozone values (350-375 Dobson Units, green enhancement) co-located with the dry vortex signatures — elevated ozone is another signature of stratospheric air. Note that these vortices were forming in cloud-free air (GOES-12 4 panel image).

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