Satellite Liaison Blog

The Decker Wildfire has been burning just a few miles south of Salida, CO in the far northern Sangre de Cristo wilderness since 8 September 2019. As of 13 October 2019, the fire had burned 8,118 acres and has prompted periodic evacuations and pre-evacuations. On 13 October 2019, the fire had broken containment during critical fire weather conditions. The intensification could be seen in GOES-East 3.9 um SWIR imagery via the flare up in brightness temperature south of Salida around 18Z (Fig 1).

The smoke plume was easily diagnosed in GOES-East visible imagery extending well east of the fire within strong westerly flow (Fig 2). A significant increase in smoke production was observed after 18Z, following the flare up seen in the SWIR imagery.

SNPP VIIRS True Color imagery with VIIRS Active Fires product overlaid during the early afternoon shows numerous thermal anomalies (~750 m spatial resolution) associated with the fire along with the extensive smoke plume (Fig 3).

The IMET tasked to the fire requested that WFO PUB request a mesoscale sector in support of the fire fighting activities. WFO PUB requested another mesoscale sector the following day (10/14) given continued critical fire weather conditions over the fire.

A photo taken around 2300 UTC from between Canon City and Pueblo shows the impressive smoke plume around sunset (Fig 4).

A S-NPP pass during the night of the 13th provided VIIRS Day Night Band imagery over Colorado with favorable illumination. The Decker Fire is readily apparent in the imagery as a cluster of bright light south of Salida in a region that would otherwise be dark.

Bill Line, NWS

An early season winter storm brought much colder temperatures and widespread snowfall to portions of the eastern Rockies and high plains October 9-10. Analysis of GOES-16 water vapor imagery shows key large scale features associated with the system as it digs south into the Great Basin and WY/CO (Figure 1) through 12Z. Overlaid on the animation are 700-300 mb GFS-derived Quasi-Geostrophic Omega, highlighting regions of greatest ascent and descent, correlating with what is observed in the imagery. The surface cold front is also seen pushing south through the high plains.

Now analyzing GOES-16 IR imagery over the same period and zooming in, the southward progression of the cold front is easily diagnosed in the imagery, including the banking of cold air up against the Colorado front range and Sangre de Cristo Mountains. An overlay of a surface wind analysis confirms the progression of the front. 60 mph winds were measured behind the front across southern Colorado.

Behind the front in northern Colorado during the evening of the 9th, thunderstorms managed to develop, producing heavy graupel and small hail. GLM Flash Extent Density from GOES-16 showed a lightning jump during the development of the strongest storm, which produced up to 3/4″ hail.

The Suomi NPP VIIRS Day Night Band (DNB) Near Constant Contrast (NCC) product provided high resolution “visible” imagery during the night as the front pushed south and low clouds expanded across the plains, thanks to illumination from the moon.

The storm system resulted in widespread snowfall amounts of up to around 5 inches over the portions of the Colorado I-25 corridor and eastern plains. The Day Cloud Phase Distinction RGB can be utilized during winter weather events to diagnose developing bands of snow or track ongoing snow bands during (especially in poor radar coverage areas). Using this event over southeast Colorado as an example, shades of cyan colored clouds (water clouds) transitioning to bright green represent increase of ice in the cloud top and a potential snow producing cloud/band (Fig 5). Multiple snow bands developed in the vicinity of Pueblo and areas south, expanding east through the afternoon in the presence of strong upper forcing and low-level easterly/northeasterly upslope flow.

Overlaying base radar reflectivity, one can see the snow bands as observed in radar imagery match up well with our analysis of the bands in RGB imagery (Fig 6).

NOAA-20 VIIRS DNB NCC imagery from the next evening provided an early view of snow cover over eastern Colorado from the previous day’s storm (Fig 7). Widespread snow cover is observed along the I-25 Corridor from Colorado Springs to Fort Collins, and much of the plains to the east. Further south, snow cover resulting from the banded snowfall is diagnosed near and south of Pueblo. Low clouds are masked with the GOES fog difference (blue).

Bill Line, NWS

NWS forecasters have the ability to make modifications to the three RGB components (Red, Green, Blue) in AWIPS. These modifications can be made easily by right-clicking (and hold) on the loaded RGB in the product legend, and selecting the “Composite Options” (Fig 1). Slider bars and numerical values for the max and min values, along with the Gamma, for each of the Red, Green, and Blue composition of the RGB will appear. The forecaster can adjust the numbers using the sliders or by editing the numbers, which will adjust the appearance of the RGB on the fly. It is recommended these adjustments be made on the fly as opposed to saving a procedure as desired thresholds will change depending on the time of day, season, and situation. The goal of the adjustments is to enhance the usefulness of the RGB by drawing out relevant features in certain situations.

There are occasions where making these modifications will extend or improve the usefulness of the RGB, particularly for RGBs which utilize VIS or NIR channels, and therefore depend on sunlight. The Day Cloud Phase Distinction (DCPD) RGB is useful for tracking cumulus cloud evolution from early water cloud (cyan), to convective initiation and glaciation (bright green), to mature convection (yellow). Because this process often takes place midday during the summer, the relatively low max thresholds of the reflectance/albedo components (79% for the 0.64 um vis green component, 59% for the 1.61 um snow/ice band blue component), are often exceeded, causing those components to wash out and provide no texture detail. Therefore, it is beneficial to increase the thresholds for those VIS/NIR fields to ensure saturation of the field will not occur. The exact thresholds to set will depend on the situation, including time of day, time of year, location, etc. These changes should only take around 15 seconds to make, and may need to be updated periodically during the day as the sun angle changes. A video from the 2019 Satellite Applications Workshop exemplifies the process of making adjustments to the DCPD RGB is such a situation.

A convective initiation example from 9 August 2019 over Colorado compares the DCPD RGB before (Fig 2) and after (Fig 3) a change to the RGB recipe was made. The forecaster was monitoring the scene for signs of imminent convective initiation, and made the changes to the RGB on the fly. A comparison of the values for the default RGB and modified version, along with the corresponding imagery at 2014Z, is included in Figure 4.

It is also beneficial to modify the DCPD RGB during low light situations, just after sunrise and before sunset, in an effort to extend its usefulness. During these times of day, features will be more difficult to discern due to low albedo from the green (0.64 um) and blue (1.6 um) components relative to the ranges set in the RGB. Therefore, adjusting the upper threshold downward for both will make cloud features apparent slightly earlier in the morning and later in the evening. If doing this in the morning, the user will need to be sure to return thresholds upward as albedo increases.

A common situation where such low light adjustments are helpful is for low cloud monitoring around sunrise or sunset. For example, early morning low clouds in the San Luis Valley of CO/NM on 12 August 2019 were difficult to visualize in the RGB with default settings (Fig 5). Adjusting the upper bounds downward for the VIS and NIR components, the fog (aqua colors) becomes brighter and easier to diagnose (Fig 6). The adjustments and direct comparison are shown in Figure 7.

Alternatively during low light situations, the Gamma values for the reflectance components in an RGB can be lowered in an effort to put more weight on them. An example of valley fog over PA/NY compares decreasing the Max values with decreasing the Gamma values for the VIS (green) and NIR (blue) components in the DCPD RGB (Fig 8). Both adjustment strategies similarly make the fog more apparent when compared to the default settings. Some combination of Max/Gamma reduction would also work to draw out the low level cloud features.

The VIS/IR Sandwich RGB similarly benefits from adjustments during low-light situations. Lowering the max threshold and gamma for each of the three components equally results in a brighter picture with clearer detail in convective cloud tops. An example of the changes made for a likely severe storm in southern Colorado during the evening of 13 September 2019 is shown in Figure 9. Features such as cumulus clouds, overshooting tops, and above anvil cirrus plumes are more easily and quickly detected in the modified/brighter imagery.

Forecasters across the northern US plains have found utility in the Day Snow-Fog RGB for identifying and tracking areas of blowing snow. This RGB includes two VIS/NIR components, and therefore its use can be extended further into the morning and evening by making simple adjustments (Fig 10). Carl Jones (FGF) and Andrew Ansorge (DMX) discussed this task at the 2019 Satellite Applications Workshop, and specifically mention the value of making on-the-fly adjustments to the RGB in an effort to make features clearer during low light situations.

Alternatively, there are also situations where these modifications may change the meaning of the colors in the RGB, and could lead to misinterpretation of important features. Additionally, making adjustments to an RGB and then sharing it with others who are not aware of the specific adjustments and interpretation of the new scheme can be dangerous. Therefore, forecasters making adjustments should be sure to understand how their changes are influencing the meaning of the final RGB, and should probably not save and share modified AWIPS RGBs with others. Rather, the process or practice of modifying an RGB to help in specific situations should be shared.

Bill Line, NWS

An isolated and long-lived thunderstorm developed along the Raton Mesa during the late afternoon of 13 September 2019 in an environment characterized by weak forcing but favorable SBCAPE (~1500 j/kg) and EBSHEAR (~35 knots). While probability was low that a storm would develop, any storm that did develop had the potential to be strong to severe. Surface southerly to southeasterly upslope flow onto the Raton Mesa and low level convergence with the deepening surface lee trough would be the drivers for initiation. Early day HRRR runs hinted at the potential for very isolated storm development in this area as well.

Clear skies prior to cumulus cloud field development and deep convective initiation (CI) allowed for the analysis of the split window difference early in the day. There were no obvious signs of moisture pooling or boundaries in the area of future CI. However, upon crunching a linear grayscale colortable, a subtle moisture maximum corridor is apparent along the northern edge of the Raton Mesa between KTAD and K4V1, east of KVTP. This would imply relatively high amounts of low level moisture, maybe low-level moisture convergence/pooling, and an opportunity area for CI. Additionally, there appears to be a surge eastward out of La Veta Pass (KVTP) prior to CI, possibly enhancing low level moisture convergence up the northern portion of the Raton Mesa. These signs, along with what the HRRR had been showing, should give a forecaster increasing confidence that this particular area probably has the best chance for CI.

Convergence along the leading edge of this surge is apparent in radar imagery progressing toward the moisture maximum just prior to CI.

GOES-16 5-min Sandwich RGB imagery provided some helpful insight during the evolution of this event. During the early stages, clumping cu were becoming more apparent northwest of KTAD after 20Z, with an orphan anvil developing around 21Z off of the easternmost towering cu (fig 3). This feature indicates a failed convective initiation attempt and that a capping inversion is still present but may be on the verge of breaking. Convection successfully initiated from the same area shortly thereafter.

After convective initiation, the IR component to the sandwich appears and rapid cooling is apparent. Pretty soon after CI, an overshooting top is diagnosed, and an associated above anvil cirrus plume shortly thereafter. It appears as though plume generation likely began between 2220Z and 2230Z, at least 15 minutes prior to Maximum Estimated Size of Hail (MESH) first exceeding 1″. One-minute imagery would have made detection and tracking of this feature easier. Figure 4 zooms in on the area of interest and ends on a time when both the OT and plume are obvious in the sandwich imagery.

GOES-16 sandwich RGB imagery for the full duration of the storm through sunset and with no annotations is included in Figure 5. The storm remained over rural areas so warnings were not verified. MESH algorithm indicated hail larger than 1″ in diameter for much of the time between 2245Z and 0055Z, with a peak over 2″ around 0030Z (end of the animation).

Bill Line, NWS

Tropical Cyclone Dorian become a hurricane on 28 August 2019. By the early morning of the 29th, the Dorian remained a category 1 hurricane as it advanced to the northwest, north of Puerto Rico.

GOES-East IR imagery and Sea Surface Temperature derived product with NHC forecast track overlay show the hurricane expected to continue through very warm waters as it approaches the Florida East Coast (Fig 1). Temperatures are between 29C and 30C along the track, or around 85F.

A 1-min mesoscale sector from GOES-East was available over the system. The high resolution imagery aids forecasters in identifying the center of circulation, as well as in tracking thunderstorm activity. Visible imagery with a semi-transparent GLM Flash Extent Density overlay at sunrise on the 29th clearly showed the center of circulation, with areas of thunderstorms, some strong, embedded in the outer bands (Fig 2).

Zoom in view on center of circulation at sunrise Fig 3).

The strong thunderstorm just northeast of the center of circulation exhibited high flash rates (see Fig 2) as well as persistent overshooting tops and even an above anvil cirrus plume, much like we see with strong thunderstorms over the CONUS (Fig 4).

Bill Line, NWS

Thunderstorms developed along a SW-NE oriented boundary draped across north-central Oklahoma during the early evening hours of 26 Aug 2019. The storms quickly grew upscale into a Mesoscale Convective System (MCS), and tracked south through central Oklahoma during the night, producing strong/damaging wind gusts and large hail.

One-minute visible imagery from GOES-East clearly shows convergence along a boundary, development of towering cu along the boundary, and eventual convective initiation (Fig 1), all in real-time. Storms quickly reached the equilibrium level and developed overshooting tops (OTs) and above anvil cirrus plumes, indicating particularly robust updrafts. Given the time of day around sunset, the shadows cast on the anvil provide additional insight into the vertical extent of the OTs.

GOES-East IR imagery showed rapid cooling of cloud tops as well as the development of overshooting tops (Fig 2). One method for viewing GOES imagery and GLM fields together in one display is to create a GLM contour color table. Since GLM fields are not gridded data in AWIPS, one cannot easily change it to a contoured field. However, the user can create a color table that implements contours at chosen thresholds instead of a constant fill. This display allows one to view VIS or colored IR imagery and GLM FED data in one display, not needing to make the GLM field semi-transparent. The GLM color table in this example includes three thresholds: 1 Flash/5-min (blue), 25 Flashes/5-min (Cyan), 100 Flashes/5-min (Yellow). For the most part, these solid color contours stand out and do not interfere with the IR colors.

Bill Line, NWS

Very deep convection developed over the western Mexico near the Gulf of California during the late afternoon hours of 20 August 2019, lasting into the early evening. This area of convection produced overshooting tops with IR brightness temperatures less than -90C (Fig 1)!

Analyzing a nearby sounding, these storms developed in an extremely moist environment (TPW=2.49″), very strong instability (MLCAPE = 4660 j/kg) and a very high equilibrium level (around 16.5 km). Based on the sounding, the -90C observed IR brightness temperatures likely put the OTs over 17.5 km above the surface!

Corresponding visible imagery of one of the storms is equally impressive. The final frame shows an OT penetrating deep across the equilibrium level casting an obvious shadow on the anvil (Fig 3).

Finally, a VIS/IR comparison of a -90C OT (FIg 4).

Bill Line, NWS