Satellite Liaison Blog

An abundance of strong thunderstorms developed across portions of the US High Plains on 18 May 2018, producing severe criteria hail, winds, and a few tornados. 1-min satellite imagery from GOES-16 was available over the region for this event per a request by the Storm Prediction Center. Notable during this event was the abundance of satellite cloud top signatures apparent with the storms during the early evening. The VIS+IR Sandwich image combo highlights these features quite well. This image combo is created using the 0.64 um VIS as an underlay, and 10.3 um IR as an overlay. The 0.5 km VIS captures the detail in the imagery, while the IR captures the quantitative brightness temperature information. The IR overlay is fully transparent below a certain threshold to allow for detailed analysis of cumulus clouds pre-CI using the VIS alone. The coldest brightness temperatures, which are associated with the cloud tops, are made semi-transparent (40%). Cloud top features apparent in this animation are overshooting tops (cooler temperature, increased texture, shadow), above anvil cirrus plumes (warm anomoly downstream of overshooting top, relatively smooth), and gravity waves (ripples) emanating from the updrafts. The rapid anvil expansion with these storms is also indicative of strong updrafts. The persistence of these features indicates long-lived strong updrafts.

Figure 1: 18 May 2018 GOES-16 1-min VIS+IR Sandwich image combo. Full res

Bill Line, NWS

A Supercell thunderstorm brought accumulating hail to east-central Colorado on 14 May, just east of I-25 and north of Castle Rock. The hail on the ground was observed by GOES-16 products. The 0.5 km, 0.64 um VIS revealed the hail swath quite well as the storm advanced east (Fig 1). The Day Cloud Phase Distinction RGB, which utilizes the 0.64 um channel (green) in addition to the 1.6 um NIR channel (blue) and 10.3 um IRW channel (red), made the hail swath even more apparent (Fig 2). The ice is highly reflective in the VIS and lowly reflective in the 1.6 um channel, like the thunderstorm clouds. However, unlike the clouds, the hail swath is warm because it is being sensed at the surface. The result is a hail swath (dark green) that contrasts nicely with the surrounding clouds (yellows, reds).

Figure 1: 14 May 2018 GOES-16 5-min 0.64 um VIS. Hail swath is apparent north of Castle Rock. Full res

Figure 2: 14 May 2018 GOES-16 5-min Day Cloud Phase Distinction RGB. Hail swath is apparent north of Castle Rock (green). Full res

Bill Line, NWS

Winds gusting out of the north at over 40 mph spread across the southeast Colorado plains during the morning and early afternoon of 26 April 2017. Given the strong winds, dust was picked up from two separate areas as detected by the GOES-16 10.3 – 12.3 split window difference (Figure 1). Lofted dust detection using GOES-16 has been described in previous blog posts.  Using the GOES-16 imagery and burn scar maps, it was quickly determined that the blowing dust was emanating from two very recent burn scars: the 117 fire in southern El Paso County and the Badger Hole fire in eastern Baca County. In this example, the dust signal in the imagery was subtle, but the moving pixels of relatively darker gray, combined with the location relative to the burn scars and confirmation via a webcam, gave us confidence that we were seeing blowing dust. The linear gray color scale was adjusted to make the dust areas more obvious. The dust was not easily apparent in visible imagery or radar imagery (KPUX radar was not available).

Figure 2: 26 April 2018 GOES-16 5-min 10.3 – 12.3 um split window difference imagery (gray scale) and IR window channel imagery for cold clouds (color). Yellow circles surround the regions of blowing dust, captured in the imagery as moving pixels of dark gray. The two recent burn scars are outlined in red. Full res

Given what was observed in GOES-16 imagery and confirmed in webcams, areas of blowing dust was added to the forecast grids (Figure 2) through the morning into the early afternoon, when wind speeds would begin to subside. The GOES-16 imagery was used to outline the narrow regions where blowing dust was occurring and would likely continue to occur. The AFD was also updated to read: “GOES-16 split-window difference imagery and webcams indicate blowing dust emanating off of the recent 117 Fire burn scar in southern El Paso County and Badger Hole Fire burn scar in eastern Baca county. Winds out of the north are gusting over 40 mph in these areas, carrying dust well south, reducing visibility and air quality in areas. Have added blowing dust to the grids through the early afternoon, after which wind speeds will begin to decrease.”

Figure 2: 1600 UTC 26 April 2018 PotBlowingDust grid (left) and Weather grid (right). BD = Blowing Dust. Red outlines are burn scar areas. Blowing dust regions were outlined with reference to GOES-16 split window difference imagery. Full res

If someone in eastern Baca County were to check their forecast during this period, it would look like that in Figure 3.

Figure 3: NWS website screen capture for 3 NE Walsh, CO in eastern Baca County. Full res

Bill Line, NWS

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

A potent mid-level trough advanced east through the four corners and Rocky Mountain region during the day 17 April 2018. Strong southwest winds mixing down to the surface along with very low RH and dry fuels led to extreme fire danger across a large portion of the southern US Plains, including southeast Colorado (Fig 1). Wind gusts in excess of 60 mph were measured across the region within a High Wind Warning, including 68 mph at KCOS and 67 mph at KPUB. GOES-16 provided forecasters in the region with detailed views of developing wildfires and blowing dust. 1-min imagery was available in support of this event.

Figure 1: SPC Day 1 Fire Weather Outlook valid 17 April 2018.

Blowing dust originating from the Great Sand Dunes in the eastern San Luis Valley in southern Colorado was clearly apparent in 0.64 km 500 m visible imagery after 1400 UTC (Fig 2). The dust can be seen quickly spreading to the northeast over parts of Pueblo and Colorado Springs and eventually all the way to northeast Colorado within the strong southwest flow. The blowing dust prompted the issuance of a rare Dust Storm Warning by NWS Pueblo. Additionally, smoke plumes from developing wildfires are apparent, including a large fire in the southeast corner of the state.

Figure 2: 17 April 2018 GOES-16 5-min 0.64 um visible imagery. Full res

The 10.3 – 12.3 um “Split Window” difference depicts blowing dust particularly well given the increased sensitivity of the 10.3 um channel to absorption by airborne silicates. In the Figure 3, blowing dust (negative values in this difference product) is visualized by very dark gray to tan colors. This difference is utilized in RGBs to aid in dust identification.

Figure 3: 17 April 2018 GOES-16 5-min 10.3 – 12.3 um split window difference. Full res

NWS forecasters monitored for wildfire hot spots utilizing the rapid updating 3.9 um channel imagery. The 3.9 um channel is the most effective GOES-16 band for detecting wildfire hots pots. Multiple grass fires erupted across southeast Colorado  during the day, prompting evacuations in some instances. Figure 4 depicts the evolution of the wildfires during the afternoon and early evening, with dark gray to yellow pixels indicating progressively hotter hot spots.

Figure 4: 17 April 2018 GOES-16 5-min 3.9 um shortwave IR imagery. Full res

Bill Line, NWS

An impressive mid-level trough advanced across the central Great Plains on 13 April 2018 bringing a variety of weather to the region. Some of the weather hazards included blizzard conditions, blowing dust, extreme fire weather conditions, and severe thunderstorms, including an SPC Moderate Risk for severe in Arkansas. GOES-16 1-min mesoscale sectors were available to forecasters in the area during this event.

The 5-min animation in Figure 1 combines multiple GOES-16 channels into one to capture the myriad of hazards. The gray scale underlay is the 10.3 – 12.3 um split window difference (SWD). The negative difference values, or brown colors, represent lofted dust across parts of Mexico, southern New Mexico, and west Texas. The color areas overlaying the SWD is cold values of the 10.3 um IR channel. Apparent are clouds associated with snow across Colorado and northward, and severe thunderstorms to the east. Finally, the small yellow areas are hot 3.9 um pixels, capturing the wildfires across western Oklahoma.

Figure 1: 13 April 2018 GOES-16 5-min SWD, 10.3 um IRW, 3.9 um SWIR. See text for details. Full res

Focusing in on the severe thunderstorms in eastern Oklahoma and northwest Texas, there was an abundance of GOES-16 Derived Motion Winds, including at the mid-levels, available over central Oklahoma prior to convective initiation (Fig. 2). Previous blog posts have discussed the utility of the derived motion winds for assessing the shear environment. Of course, favorable deep layer shear is a necessary ingredient for the development and maintenance of supercell thunderstorms.

Figure 2: 13 April 2018 GOES-16 CONUS (5-min) VIS and Mesoscale (5-min) Derived Motion Winds. Full res

Sampling the GOES-16 winds and nearby surface obs, one can compute 0-456 mb bulk layer shear of 40 knots (Figure 3), adequate for the development of Supercell Thunderstorms and severe weather.

Figure 3: 13 April 2018 GOES-16 CONUS (5-min) VIS and Mesoscale (5-min) Derived Motion Winds and sample readout. Full res

Bill Line, NWS

Extreme fire weather conditions developed across portions of CO/KS/NM/TX/OK on 12 April 2018 as winds increased and RH values decreased over dry fuels ahead of a trough digging into the four corners region. SPC highlighted a large area of extreme fire weather conditions in their fire weather outlook, along with an even broader critical area (Fig 1). Given the threat, both GOES-16 1-min meso sectors were requested and granted. SPC extreme fire weather outlook is priority number 6 for mesoscale sector requests in the case of multiple requests.

Figure 1: 12 April 2018 SPC Day 1 Fire Weather Outlook. Full res

Some of the largest and most threatening wildfires developed across western Oklahoma during the afternoon. GOES-16 1-min visible imagery captured the impressive smoke plumes under an otherwise clear sky (Fig 2), while the 3.9 um channel depicted the hot spots (Fig 3). The 1-min imagery allows for the detection of wildfires early in their development. This  capability is being used in some NWS offices to alert fire weather partners to new fire starts, sometimes prior to 911 calls.

Figure 2: 12 April 2018 GOES-16 1-min visible satellite imagery. Full res

Figure 3: 12 April 2018 GOES-16 1-min 3.9 um shortwave IR imagery. Dark gray/black to yellow are progressively hotter fires. Full res

Pyro-cumulus clouds were observed in the 1-min VIS with one of the Oklahoma fires a little later in the early evening hours (Fig 4).

Figure 4: 12 April 2018 GOES-16 1-min VIS of smoke plume over W Oklahoma. Full res

Bill Line, NWS