A shortwave trough brought strong, deep westerly winds to northern Colorado and an afternoon cold front on 14 October 2020. Analysis of GOES-East water vapor imagery reveals the shortwave dropping south through MT/WY and then east into the plains (Fig 1). The gusty winds and low RH along with continued dry fuels meant conditions were favorable for the rapid growth and spread of the Cameron Peak Wildfire, which had been burning for months in the mountains just west of Fort Collins.
The dangerous fire weather conditions did indeed cause the wildfire to grow considerably during the day, becoming the largest wildfire in Colorado recorded history at over 164,000 acres by early on the 15th, from 135,000 acres early on the 14th. The growth can be visualized in the fire information maps from Inciweb (Fig 2a). Evacuation zones expanded east to just west of Horsetooth Reservoir (Fig 2b).
Both GOES-East and GOES-West satellite imagery captured the evolution of the wildfire hot spot and smoke plume throughout the day. Given the satellite viewing angles and resulting forward scattering, GOES-West VIS provided a clearer view of the smoke plume during the morning, with GOES-East VIS the better option during the afternoon (Fig 3). Given the thick plume, both sensors provided adequate detection.
Focusing on GOES-East, 1-min imagery was available over the wildfire during the day. Early morning Natural Color Fire RGB imagery revealed a lenticular cloud stationary over the fire location around sunrise, dissipating into the morning and revealing the large hot spot (Fig 4).
The Natural Color Fire RGB imagery allows one to characterize various aspects of the wildfire given the three components: hot spot (SWIR), smoke plume (VIS), and burn scar (Veggie). While a similar RGB (Day Land Cloud Fires) is available in AWIPS, this particular RGB, which better detects hot spots, is not (though it can be requested). An example scene from this wildfire is annotated in Fig 5.
Later in the day, the wildfire broke containment and spread rapidly to the east. This expansion is shown in a 2.5 hour period of GOES-East 1-min imagery in the Natural Color Fire RGB (Fig 6).
The full daytime evolution of the wildfire in the Natural Color Fire RGB is shown in Figure 7. A similar animation is shown for the Fire Temperature RGB, which can be used to diagnose relative “hot” areas within the broader hot spot of a mature wildfire (Fig 8).
The smoke was present at the surface across Fort Collins from the morning through the early afternoon. However, a surface backdoor cold front pushed west into the I-25 corridor by mid-afternoon, clearing the near-surface smoke and dramatically improving air quality. The smoke plume remained aloft, however, as was shown in Fig 9, confirming the low-level nature of the cold front. IR-Window imagery with a grayscale color table captures the southwest evolution of the cold front and it’s minimal influence on the smoke plume aloft as observed by from satellite.
NOAA-20 VIIRS True Color Imagery and Active Fires Product around 2000 UTC (tail end of rapid spread east) provided a detailed view of both the smoke plume as well as the active fire burn area (Fig 10).
The natural color fire RGB can also be applied to VIIRS imagery (Fig 11). By using I-band imagery, the product becomes much more detailed given the 375 m spatial resolution. In this case, there were three VIIRS images available within a ~1.5 hour period from SNPP and NOAA-20, allowing for an analysis of the fire growth during that period. Note missing hot spot data within the larger hot spot due to band I4 (swir) pixel saturation. Land surface features such as wildfires are much easier to analyze in time in VIIRS imagery since the implementation of Terrain Correction for VIIRS EDR’s.
That evening, NOAA-20 VIIRS Day Night Band captured the glow associated with the Cameron Peak Fire, in addition to that from nearby city lights (Fig 13).
Some photography of the fire smoke plume from Oct 14 follows:
Bill Line, NESDIS/CIRA
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