Mid-September brought a period of active Fire Weather, resulting in several large wildfires and widespread smoke, to Pacific Northwest US. GOES and VIIRS Imagery provided stunning and operationally useful information about the environment and fires and smoke.
A GOES-West animation captures the ignition (or re-ignition) of wildfire hot spots coinciding with the development of dry air across the northwest US (Fig 1). The animation includes GOES-West Water Vapor Imagery (gray) with the derived TPW as an overlay (colors) and derived product wildfire hot spots (yellow pixels). As the dry air expands from the 7th to the 10th, numerous hot spots, including several large ones, appear. From the 10th to the 12th, moisture increases from the south and the west in association with a tropical cyclone (Kay) and a mid-altitude cyclone, respectively, helping to calm the fire activity.
Zooming out and focusing just on only GOES-West water vapor imagery, in the early part of the loop, we diagnose fairly strong northwest flow in the upper levels along with periodic disturbances across the Pacific Northwest (Fig 2). During the second half of the loop, increasing moisture and cloudiness are observed to develop across the region in associated with Kay from the south and the mid-latitude storm from the west.
Three of the significant wildfires during the period will be discussed below, using a GOES-West “Geocolor-Fire” procedure in AWIPS. The imagery display used to depict each wildfire includes a base of Geocolor in order to highlight the wildfire smoke plume and surrounding clouds and vegetation, with an overlay of ch07, ch06, and ch05, in order to show details of the wildfire hot spot. The swir/nir overlay are included as varying degrees of transparency and colors with final colors ranging from red to yellow to white for “lesser” to “greater” wildfire intensities (similar to with the Fire Temperature RGB). While this procedure is great for communicating/depicting a given wildfire and tracking smoke coverage, it should not be used for new fire hotspot detection since relatively “cool” hot spots will be missed. It is recommended to stick to basic ch07 single band imagery for that task.
On the 8th, the Mosquito Fire located between Sacramento and Lake Tahoe experienced a period of rapid growth and smoke output. The fire, which began on Sep 6, grew from under 7000 acres on the morning of Sep 8 to 29,000 acres in the afternoon of the 9th. The fire had grown to 46,000 acres by Sep 12. The Geocolor-Fire procedure captures the large and intense heat signature, along with the dense smoke plume as it races east over lake Tahoe (Fig 3). Additionally, periods of pyrocumulus clouds are observed over the fire. One-minute temporal resolution allows one to observe the hot spot and smoke plume evolve in ~real-time and with smooth animations, as opposed to waiting for relatively choppy animations with longer timesteps.
Forecasters and satellite analysts are aware that smoke is particularly difficult to detect at night in satellite imagery given the absence of reflectance channels, and weak to no signal in infrared channels. Therefore, although currently only available over any given location of the CONUS 2-4 times per evening within a timespan of 55 min – 3.5 hours, VIIRS Day Night Band Near Constant Contrast Imagery is a valuable operational tool for detecting and tracking wildfire smoke at night.
For the Mosquito Fire, overnight, smoke is observed maintaining a presence from Modesto north to Sacramento, and east over Lake Tahoe and Reno. This knowledge can be useful for aviation forecasts, temperature forecasts, and general communication to the public. The light emitted from the wildfire itself can also be observed in the imagery, providing more information on which parts of the fire are more or less active. In this case, the wildfire is located just left of center in the image, just south of I-80, and appears as a “v-shape”.
On Sep 9, the Cedar Creek Fire in Oregon, which began on Aug 1, grew from 33,100 acres in the morning to 51,800 acres the morning of the 10th. The fire had grown to 86,000 acres by Sep 11 PM. Geocolor-Fire imagery shows an intense hot spot and smoke plume already by sunrise, with smoke streaming over Eugene, OR all day. (Fig 5)
Overnight VIIRS NCC product shows the densest portion of the smoke plume shifting north north of Eugene and toward Portland. The wildfire is the bright area in the lower right part of the image, and is burning strongest on the western front, with continued slightly weaker burning to the east.
Finally, The Bolt Creek fire east of Seattle initiated early in the morning on Sep 10, and grew to 7,600 acres by the early afternoon of the 11th. Geocolor-Fire Imagery captures some of this rapid growth during the day of the 10th, along with a growing smoke plume as it drifted west over northern parts of Seattle (Fig 7). Occasionally “bursts” in updraft activity over the fire sent smoke slightly higher in the atmosphere and subsequently to the east as it tapped into the westerly flow aloft.
The VIIRS NCC during the following evening captures widespread smoke across the area along with increasing cloud cover. Focusing in on the wildfire located in the center of the image, a relatively dense plume of smoke is diagnosed streaming north over the northern Seattle suburbs. A relatively bright ring of light marks the outer perimeter of much of the fire.
Bill Line, NESDIS/STAR
Satellite Liaison Blog 