A quick note on monitoring wildfire hot spots overnight. Wildfire hot spots observed in GOES-16 imagery will typically cool overnight due to a combination of poor fire weather conditions causing a decrease in fire activity, and cooling/loss of solar reflectance of the non-fire portion of the pixel causing an overall cooler pixel. Hot spots associated with active wildfires, however, will still typically be detectable in the 3.9 um shortwave IR channel though dimmer. Due to static thresholds required for RGB products in AWIPS, cool hot spots are not detectable in the current AWIPS Fire Temperature RGB. Therefore, hot spots that were previously active and detected in the RGB during the day may not be apparent in the RGB at night despite still being detectable in the raw 3.9 um imagery. This is reason for utilizing the raw imagery (3.9 um, 2.2 and 1.6 also if very hot fire) at night over the RGB. It is important for forecasters to be able to continue to monitor the evolution of wildfire hot spots overnight whenever possible. See two examples from southern Colorado during the overnight hours of 17/18 April.
The 117 Fire burned a large area of southern El Paso County during the day, continuing into the evening with 0% containment. Despite cooling significantly, the hot spot was still obvious through the night in 3.9 um imagery. The hot spot was not detectable in the Fire Temperature RGB except for a very brief period when a portion of the fire heated up.
Figure 1: 18 April 2018 GOES-16 5-min 3.9 um shortwave IR (top) and Fire Temperature RGB (bottom) over the 117 Fire in El Paso County, southeast Colorado. Darker (colored) pixels on left (right) represent the wildfire hot spot.
The Badger Hole Fire in eastern Baca County grew large quickly during the afternoon. Cooling overnight, the fire was still detectable in the 3.9 um channel, but not in the RGB.
Figure 2: 18 April 2018 GOES-16 5-min 3.9 um shortwave IR (top) and Fire Temperature RGB (bottom) over Badger Hole Fire in Baca County, southeast Colorado. Darker (colored) pixels on left (right) represent the wildfire hot spot.
Bill Line, NWS