Satellite Liaison Blog

You may have noticed a change to the GOES-R RGBs in AWIPS since the May/June 2018 RPM update. A new and improved method for calculating the RGBs was implemented. One of the most notable benefits of this change is that users can now control the ranges of the three RGB components based on the physical units (reflectance, brightness temperature), instead of the 0-255 color range as was the case before (Fig 1). Similarly, when sampling the RGB in AWIPS, users now see the physical units for each of the three RGB components (Fig 1). The new method for computing RGBs may also lead to improved performance on AWIPS workstations. Finally, minor projection issues are resolved with the new method.

Figure 2: 5 August 2018 GOES-16 Day Cloud Phase Distinction RGB, point sampling readout, and Composite Options. Full res

Users are reminded that the default RGB ranges were chosen for a reason, and altering them will change the interpretation of the RGB, potentially negatively.

Below is an example of how a user may alter an RGB (Fig 2 and 3). The “simple” Day Cloud Phase Distinction RGB is great for differentiating various cloud types and clouds from snow from bare land, during the day. In this RGB, however, the green component (0.64 um) becomes saturated fairly quickly (reflectance >78%). So, for example, forecasters cannot interrogate  features atop deep moist convection using this RGB that are otherwise apparent in visible imagery (texture, overshooting tops, etc) . This isn’t necessarily one of the purposes of this RGB, but a forecaster may want to expand it’s capabilities regardless. With the new design, a user can simply load the composite options for the RGB, and adjust the max for the green component up to, say, around 100%.

Figure 2: 5 August 2018 GOES-16 Day Cloud Phase Distinction RGB and point sampling readout. Full res

Figure 3: 5 August 2018 GOES-16 modified Day Cloud Phase Distinction RGB and point sampling readout. Full res

This change allows for details in the visible channel to be apparent in this RGB. However, users must keep in mind the green influence will be less for all features in the RGB. Low water clouds will appear closer to blue than blue/green, and snow will be a darker shade of green. Highly reflective cold cloud tops (deep convection) may appear more red than yellow.

Bill Line, NWS

Severe storms produced large hail (including significant) and tornados across Wyoming and Colorado on 29 July 2018. Strong northwest flow over a moist airmass led to very favorable shear and instability across the region, and a SPC Enhanced Risk for severe was in place. GOES-16 1-min imagery was available to support NWS forecasters during the event. Storms early on produced overshooting tops and above anvil cirrus plumes, a signature indicative of severe and significant severe potential. The plumes appear as smooth cirrus cloud features emanating from the overshooting top and downstream over the storm anvil. Cumulus clouds are also analyzed being drawn into the southern regions of the storms, indicative of strong inflow winds.

Figure 1: 29 July 2018 GOES-16 1-min VIS. Full res

A little later over east-central Colorado, a severe storm developed that produced a measured wind gust of 83 mph, along with hail at least 2.75″ in diameter (baseball). GOES-16 1-min imagery of this storm showed a large and persistent overshooting top and an above anvil cirrus plume (VIS, Fig 2). The corresponding 1-min IRW imagery (Fig 3) shows a large overshooting top (round region of coldest pixels) along with a relatively cooler area immediately downstream of the overshooting top (completing the thermal couplet) and a relatively cool region extending downstream above the anvil (above anvil cirrus plume). Overlaying a semi-transparent IRW on the VIS, we get the sandwich image combination (Fig 4). Radar imagery of the storm showed reflectivity over 80 dBz along with significant beam attenuation, indicating a lot of hail (Fig 5).

Figure 2: 29 July 2018 GOES-16 1-min VIS. Full res

Figure 3: 29 July 2018 GOES-16 1-min IRW. Full res

Figure 4: 29 July 2018 GOES-16 1-min IRW. Full res

Figure 5: 29 July 2018 KPUX 0.5 degree radar reflectivity. Full res

Bill Line, NWS

A cluster of thunderstorms made a long trek south through the southeast Colorado plains Thursday night into early Friday morning. The storms produced heavy rainfall and gusty winds, including a 45 knot measured gust at La Junta. Additionally, the storm produced frequent lightning as evidenced by GOES-16 GLM and NLDN CG data. To the west of the storm, low clouds developed along the I-25 corridor in the anomalously moist atmosphere. Low ceilings brought IFR conditions to KCOS and MVFR to KPUB.

Cloud top brightness temperature trends from ABI IR and GLM total lightning trends were analyzed through the night in order to monitor the health of the storm cluster. Given the 45 knot wind report and constant cold IR temperatures and total lightning, SPS’s were issued for the duration of the storm. The 4-panel animation shows several long flashes extending into the anvil stratiform region of the system, from which several CGs were measured by NLDN.

Figure 1: 27 July 2018 GOES-16 FED (TL), AFA (TR), TOE (BR), and KPUX base reflectivity and NLDN CGs (BL). Full res

As the storm advanced south, low clouds spread west to the I-25 corridor. The Nighttime Microphyics RGB was utilized to track the progression of the low clouds and amend/update TAFs. The image combination below shows the nighttime microphysics RGB with IR brightness temperatures overlaid (gray-scale) for the coldest temperatures. GLM Flash Extent Density is also overlaid.  In the RGB, recall that during the warm season, the ~aqua colors represent warm liquid water clouds, the ~tan colors are cooler water clouds, and the red colors are cold ice clouds (overlaid with IR in the animation below).

Figure 2: 27 July 2018 GOES-16 5-min Nighttime Microphysics RGB (color underlay) with IR brightness temperatures overlaid (grayscale) and GLM Flash Extent Density overlaid. Full res

Bill Line, NWS

A long-lived, prolific above anvil cirrus plume (AACP) generating storm produced large hail and heavy rainfall as it tracked southeast along the Sangre de Cristo mountains in south-central Colorado on Tuesday. The largest hail report from the storm was 1.75″, 12 miles south of Westcliffe. The storm tracked over two burn scars, leading to flash flooding. The AACP signature indicates a particularly strong updraft and increased likelihood of a severe storm.

Figure 1: 25 July 2018 GOES-16 5-min visible satellite imagery. Severe thunderstorm (yellow) and flash flood (green) warnings and storm reports also included. Burn scars outlined in red. Full res

Bill Line, NWS

Severe thunderstorms developed across central Iowa during the afternoon of 19 July 2018, producing multiple tornados. Fortunately, 1-minute imagery from GOES-16 was available over the region to aid forecasters during the event.

GOES-16 derived motion winds in the area of tornadic development indicated enhanced low-level and deep layer shear just prior to initiation. With surface winds of 12 knots from 160 degrees and GOES-16 DMWs indicating ~1 km winds of 16-20 knots from around 220 degrees, 0-1 km shear was around 16 knots, which is favorable for supercell tornados (Fig 1). DMWs around 6 km were 40-50 knots from 275 degrees, which yields a 0-6 km shear vector of around 49 knots, favorable for supercell development. Figure 2 combines the mesoscale and CONUS winds to show the abundance of winds vertically and horizontally that can be available from GOES-16. Numbers from the nearby DMX VAD wind profiles are similar.

Figure 1: 19 July 2018 GOES-16 VIS, Derived Motion Winds, and surface METARs. Full res

Figure 2: 19 July 2018 GOES-16 5-min VIS and Derived Motion Winds (CONUS and Mesoscale), and METARs and surface obs. Full res

GOES-16 CAPE showed convection develop on the western edge of a CAPE max. As has been found in previous experiments, although CAPE derived from GOES may often be lower than other sources, the gradients in the moisture/instability fields are captured well.

Figure 3: 19 July 2018 GOES-16 5-min VIS and CAPE, LSR’s. Full res

NUCAPS profiles from Suomi-NPP were available ahead of the line of the line of storms around the time of initiation (Figure 4). Considering central Iowa does not have a balloon launch, temperature and moisture profiles from polar orbiting satellites have exceptional value. The surface conditions of the profiles need to be modified to match nearby obs. After doing so, the profiles near Des Moines indicated around 2,000 j/kg of MLCAPE and up to 4,000 j/kg of SBCAPE, supportive of strong updrafts (Figure 5). Further, the mid/upper levels of the profiles were dry above moist low levels, indicating favorable convective instability.

Figure 4: 1927 UTC 19 July 2018 GOES-16 VIS, Suomi-NPP NUCAPS sounding availability, METARs. Full res

Figure 5: 1927 UTC 19 July 2018 Suomi NPP NUCAPS sounding immediately ESE of Des Moines, IA. Surface modified to match nearby METARs. Full res

GOES-16 1-min imagery revealed progressively enhanced cumulus development and clumping northwest of Des Moines between 1800 UTC and 1900 UTC. Initiation took place shortly thereafter, confirmed by the first GLM total lightning detections at 1926 UTC (Figure 6). The first tornado was reported around 1950 UTC, just as GLM FED values began to rapidly increase. A max of 3 flashes/5-min was detected at 1940 UTC, and a max of 23 flashes/5-min was detected at 1950 UTC. At 2000 UTC, a max of 100 flashes/5-min was detected with this storm as it continued to produce a tornado. The updraft weakened briefly thereafter, before strengthening again from 64 flashes/5-min at 2037 UTC to 142 flashes/5-min at 2112 UTC when 1.5″ hail was reported.

Figure 6: 19 July 2018 GOES-16 1-min VIS, GLM FED 5-min accumulation, LSR’s. Full res

Further south, severe thunderstorms produced widespread damaging winds, including a reportedly fatal storm that capsized boats on Table Rock Lake. GOES-16 1-min visible imagery showed rapid updraft growth with this storm through old anvil clouds up to the tropopause, quickly producing overshooting tops and an above anvil cirrus plume, the latter of which is a sign of a particularity strong storm.

Figure 7: 19 July 2018 GOES-16 1-min VIS over southern MO. Full res

Bill Line, NWS

GOES-16 GLM data was utilized to help monitor storm activity near the site of the El Paso County Fair during the week of July 14 – July 21. The fair takes place in Calhan, which is in northeast El Paso County. During the late afternoon of July 17, a cluster of thunderstorms approached the fair grounds from the west. Given the potential for rain, breezy winds, and lightning (confirmed in GLM with CG’s confirmed by NLDN), EL Paso County Sheriff’s office was notified at around 2345 UTC. Figure 1 shows a 1-hour long loop updating every 1-minute, while Figure 2 is the same animation but with the break points discussed in the rest of this post.

Figure 1: 17 July 2018 clockwise from upper right: GLM Flash Extent Density (FED), GLM Average Flash Area (AFA), GLM Total Optical Energy (TOE), ABI VIS, KPUX 0.5 degree radar reflectivity, NLDN CG’s. GLM data is 5-min accumulation updating every 1-minute. Full res

By 0000 UTC (the middle of the loop), 0.5 degree radar reflectivity showed the eastern edge of a cell moving into Calhan, with NLDN confirming cloud to ground lightning strikes. However, GLM FED indicated lightning activity still well to the west of town. This discrepancy is due to parallax effect inherent in the GLM data. The GLM data in AWIPS is formatted to the 2 km ABI fixed grid, so is influenced by the same parallax effect. In Colorado from GOES-East, lightning objects will appear slightly to the north and west of where it actually is occurring over the surface. Users will need to get used to the degree of the effect in their CWA, and use radar, NLDN, etc to confirm where that lightning is actually occurring.

By 0029 UTC (the end of the loop), radar and NLDN data would indicate Calhan in a gap of thunderstorm activity. However, GLM shows mainly long flashes continuing to extend over and around Calhan, implying a continued lightning threat away from the updraft cores and over the fair grounds.

Figure 2: 17 July 2018 annotated clockwise from upper right: GLM Flash Extent Density (FED), GLM Average Flash Area (AFA), GLM Total Optical Energy (TOE), ABI VIS, KPUX 0.5 degree radar reflectivity, NLDN CG’s. GLM data is 5-min accumulation updating every 1-minute. Full res

The Total Optical Energy Product was not found to provide any additional value over FED and AFA in this case.

Bill Line, NWS

The last couple of weeks have featured a few news stories on all the African dust in the Atlantic, some of which made it as far west as Houston and even Oklahoma City!  Is it normal to see this much dust in the Atlantic?  Yes!  In the central U.S.?  Well, maybe that part is a bit unusual.

It just so happens that we are running a Saharan Air Layer (SAL) Evaluation that started on 06/17/18 and will run until 09/30/18.  The participants include the National Hurricane Center, Weather Prediction Center, Melbourne, Ruskin, Miami, Key West, San Juan forecast offices, and the Caribbean Institute for Meteorology and Hydrology in Barbados.  The concept is to test the utility of many different dust or moisture products as it relates to the SAL events with subtopics focusing on convection, air quality, visibility, and lightning.  By running an evaluation in this way (weather event focused), we hope to get valuable feedback from forecasters on which products perform well and which ones may need some work.  We will also be comparing dropwindsondes during special Hurricane Research Division (HRD) flights to the NOAA Unique Combined Atmospheric Profiles (NUCAPS) to increase confidence in the soundings over the tropical Atlantic.

I have included two animations of the SAL outbreaks from 07/05/18 – 07/11/18.  You may also notice Hurricane Beryl and Hurricane Chris forming on the edge of the larger outbreak that follows Beryl.  This dust was pulled rather far north and got wrapped up in the circulation of Chris, leading to an increase in lightning (not shown, yet).  Meanwhile, Beryl formed quickly, then dissipated quickly, but that appeared to be more due to the shear (very strong easterlies at low-levels), which caused decoupling from the convection.

GOES-16 Dust RGB showing a couple SAL outbreaks stretching across the tropical Atlantic. (Click here to open in a different window)

GOES-16 SAL Split-Window for a different prospective on the SAL outbreaks.  (Click here to open in a different window)

Stay tuned for more updates on the SAL evaluation and a look at some of the products that are being evaluated in operations.

Thanks for reading!