Satellite Liaison Blog

An isolated severe thunderstorm developed at the intersection of a dry line and warm front in northeast Texas during the late afternoon and evening of 08 April 2021.

GOES-East split window difference imagery captured the eastward progression of the dry line during the day (west-to-east rapid transition from low values/dark gray to higher values/light gray), filling in the temporal/spatial gaps between sfc obs. The severe thunderstorm developed just ahead of the dry line where it interacted with the warm front. An overlay of cold IRW BT’s adds information about cloud top features not apparent in the SWD.

Day Cloud Phase distinction RGB imagery at 1-min intervals could be used to gain confidence when and where convective initiation was become most probable. The following six figures include 30 minute periods of 1-min DCPD RGB imagery ending at key points (Fig 2a-e).

The first period shows a transition of the cu fiend in the southwest part of the scene near KBWD, setting it apart from the rest of the scene. Individual cu begin to transition from cyan to green (slight vertical growth and glaciation), and exhibit vertical growth and clumping. From across the full scene, this area appears most favorable for future CI.

The “green-up” and clumping trend continues during the next 30 minute period ending 30 minutes later, but with enhanced growth and a brighter green (more glaciation) for one such cu ESE of KBWD.

Ending 18 minutes later, the aforementioned cu initiates but develops an orphan anvil. Although failed initiation, it represents increasing potential for imminent CI.

Ten minutes later, a cu cloud further to the northwest transitions cyan to green and bright green, representing additional glaciation and vertical growth.

Eighteen minutes later, this area of cu continues to grow, becomes red/orange (continued glaciation and cooling of cloud top), and eventually produces lightning (GLM FED).

The full evolution from both the DCPD RGB and VIS is shown in Fig 3 and 4. While one can analyze cu trends in the VIS such as clumping, vertical growth, orphan anvils, additional phenomena such as glaciation and cooling are easily diagnosed in the RGB as well.

One-min feature-following VIS-IR Sandwich imagery during the day characterizes the cloud top trends of the supercell. Of note is the large and persistent overshooting top (OT) and downstream cold region (thermal couplet), and a long-lived above anvil cirrus plume extended downstream from the OT (Fig 5). Additionally, rapid expansion of the anvil is observed.

A longer, 5-min, VIS-IR animation extending into the evening includes NWS warning polygons and local storm reports (LSRs; Fig 6). The thunderstorm had numerous reports of large hail associated with it (up to baseball size), along with damaging wind gusts.

Finally, an animation of GLM Flash Extent Density shows the rapid uptick in lightning activity during the middle of the storm life cycle, followed by a downtick in activity prior to weakening and decay of the storm.

Bill Line, NESDIS and CIRA

Strong winds gusting over 45 knots and dry surface conditions led to yet another southern plains blowing dust event on 6 April 2021. This time, the main source point of blowing dust was the dry San Luis Valley (SLV) of southern Colorado, and later, the eastern Colorado plains.

Forecasters at NWS Pueblo anticipated the potential for blowing dust early in the day, and had issued a High Wind Warning for the SLV with mention of Blowing Dust reducing visibility. As such, forecasters were monitoring the “Dust RGB” imagery, in addition to webcams, throughout the day. By early afternoon, widespread and dense blowing dust had developed in the northern portion of the San Luis Valley. Per the NWS, the satellite data gave them the nudge to call ALS patrol and find out what was going on up there. Nearby webcams were also utilized to confirm reduced visibilities. Based on information from satellite, webcams, and law enforcement, a Dust Storm Warning followed by a longer duration Blowing Dust Warning, was issued for much of the northern San Luis Valley (Fig 1).

A forecaster working the event went on to mention that the satellite was most valuable for observing lofted dust near the source region, where visibility was most significantly reduced and the scene clear of cloud cover. Satellite became less useful later in the event as the dust was lofted higher and become more diffuse, and as high clouds obscured the scene.

Other imagery from GOES-East and available in AWIPS that captured the blowing dust quite well during the day include a VIS-SWD sandwich procedure (Fig 2). This procedure highlights likely blowing dust as yellow (negative values of SWD), in order to attract the users attention from the otherwise gray scene.

A GOES-West mesoscale sector was available over the region for fire weather, and provided an alternate perspective of the dust at high temporal resolution. The VIS-SWD sandwich procedure is shown for comparison to the GOES-East version.

The blowing dust continued east and into the evening. Additional blowing dust developed across the far eastern Colorado plains into the evening, prompting the issuance of additional Dust Storm Warnings and Advisories by PUB and GLD, and High Wind Warnings with mention of Blowing Dust. Dust RGB imagery captures the evolution of the Dust east into the evening, but increasing cloud cover late makes analysis of blowing dust difficult.

The Day/Night DEBRA-Dust algorithm, available on CIRA Slider or in AWIPS on request, tracks the dust into the night as cloud cover overtakes the scene.

As pointed at by NWS PUB, this event gives one a good idea of how the Great Sand Dunes became what they are, where they are!

Bill Line, NESDIS and CIRA, with input from NWS PUB

A mid-level trough traveling east across the northern US brought widespread strong winds and high fire danger to much of the central US on 29 Mar 2020. GOES-East water vapor imagery captures the feature, ahead of which dry and warm conditions had developed. The cold front forced south by the associated Canada/US border shortwave is also evident in the moisture imagery.

Given the expected conditions, the NWS Storm Prediction Center had issued a very large Critical Fire Weather area in their Fire Weather Outlook for the day. Widespread RH below 20% and wind gusts over 40 mph would develop within the critical fire weather area during the day.

Deep vertical mixing along with a tightening surface pressure gradient resulted in strong surface winds developing across the region. 12Z Soundings from Denver and Rapid City captured the very deep dry air ahead of the trough. SPC Sounding Climatology indicated these atmospheres very close to their record Daily Min for TPW, with 0.1″ each.

GOES-East shortwave IR imagery from the day and evening reveals the evolution of the cold front south across the plains, along with the development of wildfire hot spots (black pixels).

Focusing on South Dakota, Natural Color Fire RGB imagery from the day captures a few large wildfires and their associated smoke plumes, along with the push of cooler air.

A comparison between ABI and VIIRS Fire Temperature RGBs over the hot spots provides an example of the additional spatial detail VIIRS provides over ABI regarding ongoing burning area. A Sentinel-2 pass provided even better detail around 1751 UTC, with the 10 m true color imagery showing the burned area and smoke plumes associated with the Rapid City wildfire.

Given the strong winds, blowing dust was of concern as well. 10.3 – 12.3 um Split Window Difference imagery from the northern plains shows relatively dark gray steaks developing behind the cold front under otherwise clear skies. These are areas of blowing dust, where the SWD is relatively low, or near to below zero. Algorithms and displays with set SWD thresholds had a more difficult time capturing these plumes of blowing dust as the signal wasn’t particularly strong. Sometimes, the basic SWD with lienar grayscale colortable will be ideal for detecting blowing dust.

Combining the SWD with SWIR and IR, we have a product that can be utilized to diagnose the wildfire hot spots and blowing dust plumes together.

Another VIIRS-ABI example shows the utility of VIIRS imagery for improved assessment of blowing dust plumes, including their exact sources. A South Dakota plume is barely recognizable in the ABI Day Land Cloud Imagery, while the plume and source region are clear in the same imagery but from VIIRS. Sentinel imagery form 1 hour earlier also captured the dust plume and source with even greater detail.

A thicker region of blowing dust developed within the San Luis Valley, and east over the southeast Colorado plains. This time, we view a VIS-SWD sandwich product to diagnose the denser dust plume. Surface obs indicated widespread wind speeds over 40 knots.

Finally, a couple areas of blowing dust also developed across Utah and Nevada during the afternoon in association with a smaller shortwave embedded within the base of the broader trough.

Bill Line, NESDIS and CIRA

Strong southwesterly winds wrapping around the south/west portion of an upper low traversing the southern US plains resulted in the development of widespread blowing dust. Surface dew points within the dry southwesterly flow dropped into the single digits to below zero, while widespread wind gusts over 40 knots were also observed. Initially, blowing dust developed out of the Chihuahuan Desert of northern Mexico, and was drawn east and north across Texas throughout the day. Later, thunderstorms developing further north in east-central New Mexico sent an outflow boundary east into west Texas, along and behind which a very dense dust plume developed. This region of blowing dust, or haboob, reduced visibilities considerably along it’s path, resulting in the issuance of NWS Dust Storm Warnings. Fortunately, a GOES-East 1-min mesoscale sector was available over the region to aid in monitoring for wildfire hot spots, but also provided a unique view of the blowing dust plume. There were numerous photos and videos shared on social media captured visibilties well less than 1/4 mile within the blowing dust plume.

This was at 4:45PM taken in between Lamesa and Seminole, Texas. ⁦@TxStormChasers⁩ ⁦@rrobertswxlab⁩ ⁦@NWSMidland⁩ pic.twitter.com/oNTYdO7DrV

— Cam Wade (@gcwade) March 22, 2021

The Midland, TX NWS office noted the critical role satellite imagery and products played in operations during the event. In particular, Geocolor and DEBRA-Dust products were important in timing the outflow boundary and associated wind shift, denoted in imagery by the very thick dust plume, as it quickly approached a wildland fire west of Andrews, TX. Forecasters were able to communicate the precise timing of the outflow to local partners, resulting in fire crews moving off the southern periphery of the fire prior to the wind shift and dramatic drop in visibility, potentially saving lives and equipment. Thankfully, the wind shift took the fire south of town.

GOES-East Fire Temperature RGB Imagery within the 1-min sector highlighted the wildfire hot spot well as it developed amidst southwesterly flow ahead of the outflow boundary.

GOES-East DEBRA-Dust imagery within the 1-min sector, available on the CIRA SLIDER, highlighted the blowing dust as it developed behind the outflow boundary and approached the location of the wildfire.

Day Land Cloud RGB imagery within the 1-min sector, available in AWIPS, provided a detailed view of the very thick blowing dust plume as it developed behind the outflow boundary and advanced east through the evening (Fig 1). The animation captures the dust plume in the context of NWS Dust Storm Warnings and surface observations, which measured wind gusts over 40 knots and visiblities as low as 1/2 mile. The more transparent area of lofted dust (out of Mexico) is diagnosed ahead of the more dense dust plume that resides within the thunderstorm cold pool. The 1-min imagery allows for the exact position of the dense blowing dust and likely reduced visibility to be analyzed in real-time and between observations.

The CIRA Geocolor product was available within the 1-min sector and accessible through the CIRA Slider webpage (Fig 2). The dust plume is especially apparent in the GOES-East true color imagery closer to sunset with increased forward scattering toward the satellite sensor.

Given the dry and windy conditions, fire danger was high across the region, influencing the growth of several wildfires. One-min Natural Color Fire RGB imagery from GOES-East captured the dust plume, clouds, and wildfire hot spots (red) and smoke plumes in a single product (Fig 3). Of note is the large hot spot WNW of Midland, TX, discussed in an earlier paragraph.

The lofted dust from both Mexico and NM/TX continued east and then north around the low during the evening, and was still detectable early the next morning. A VIS-IR-Split Window Difference procedure captured the evolution of the dust during the day and evening (Fig 4). The procedure relies on the 10.3-12.3 um Split Window Difference for detecting lofted dust, and overlays it as a semitransparent shade of yellow for negative values (dust signal).

Other procedures and products capture the blowing dust day/night, including the Dust-Fire RGB (Fig 5; which also shows the wildfire hot spots), and the CIRA Debra-Dust product (Fig 6; can be accessed on CIRA Slider).

Impacted NWS offices shared various imagery products of the blowing dust, shown below.

500pm NIce satellite image of difference between an Haboob and our large scale wind/dust event. Haboob is much smaller scale but usually denser dust. #txwx #nmwx pic.twitter.com/AMTaFfLDL4

— NWS El Paso (@NWSElPaso) March 22, 2021

This satellite loop from https://t.co/LdSlQVUAo5 shows the current state of weather across W. TX. The haboob is moving into the Big Country, and a front is moving in behind it that has dropped temps into the 40s & lower 50s. #lubwx #txwx pic.twitter.com/pdoVRALTFM

— NWS Lubbock (@NWSLubbock) March 23, 2021

Very strong winds 60+ mph are causing a dust storm from SE New Mexico into the northern and western Permian Basin (Yellow on satellite). Visibilities will drop to as low as 1/4 mile or less. Please avoid travel if possible. #nmwx #txwx pic.twitter.com/hLpe2IanXI

— NWS Midland (@NWSMidland) March 22, 2021

Using our Dust RGB composite on GOES satellite, you can see those dark pink, almost red areas indicating thick blowing dust moving into Rotan and Sweetwater. Visibilities in this area have been reported as low as 150-250 yds. Avoid driving in these areas if you can! #txwx #sjtwx pic.twitter.com/phfWn3ga1F

— NWS San Angelo (@NWSSanAngelo) March 23, 2021

Procedures and products shown in these blog posts can be requested by NWS users.

Bill Line, NESDIS and CIRA

Input from NWS Midland, TX

A strong upper low digging into the southwest US forced the development of strong southwesterly winds and very dry conditions at the surface out of Mexico into New Mexico and western Texas. Winds gusted over 60 knots across the region, and dew point temperatures fell to below zero degrees F. The gusty southwesterly winds lofted a significant amount of dust out of northern Chihuahua, Mexico which quickly advanced to the northeast into New Mexico and Texas. Additionally, dust was observed emanating from White Sands in southeast New Mexico. The blowing dust resulted in a widespread drop in visibilities to below 1 mile, including reduction to below 1/4 mile at times. Given the conditions, Blowing Dust Advisories and Blowing Dust Warnings were issued by the National Weather Service.

A VIS-SWD Sandwich combo captures the evolution of the dense and wide dust plume quite well during the daytime (Fig 1). The procedure uses a VIS underlay, and semitransparent yellow 10.3 – 12.3 um Split Window Difference overlay for values less than zero. This procedure can easily be created in AWIPS (or delivered upon request) using already available data. Surface observations are included in the animation, showing the exceptional wind gusts, bone dry dew points, and reduced visibilities.

A similar animation uses products derived outside of AWIPS to capture the dust evolution. The CIRA Geocolor product provides a colored image of the scene, while the semi-transparent DEBRA-Dust overlay captures the dust as yellow through a dedicated dust detection algorithm (Fig 2). Both products are available on CIRA Slider, as well as via delivery of additional data to AWIPS.

The Dust continued to advance north and east during the overnight hours, wrapping around the eastern side of the upper low. An animation similar to Fig 1, but transitioning to IR at night, continues to capture the dust plume through the evening hours as yellow (Fig 3). By the next morning at the end of the animation, a faint dust signature is still apparent over the low clouds in Kansas.

The DEBRA-Dust product similarly continues to capture the blowing dust signature through the evening and into the next day (Fig 4).

RGBs utilizing the SWD are valuable tools for tracking lofted dust day/night, in addition to cloud classification and other applications. Additionally, weak dust signals can be captured in carefully crafted RGBs that are missed in products that include strict thresholds. An experimental Dust-Fire RGB highlights dust (day/night) as a relatively bright cyan to bright green (thick dust plume), as well as wildfire hot spots as bright red, high/opaque clouds as darker green, cirrus as dark blue or black, and low clouds as gray (Fig 5).

VIIRS I-band imagery during the early afternoon provided a very high resolution (375 m) view of the dust plume. The higher resolution imagery provides more insight into the blowing dust, allowing forecasters to more easily and more precisely identify the onset of blowing dust, dust plume edges, relatively dense portions of a dust plume, and location of dust origination. Compared in Figure 6 are the 375 m Day Land Cloud RGB from VIIRS (left), and 1 km GOES-East ABI Day Land Cloud RGB (right; at nadir, so lower resolution at this location so far from nadir).

Bill Line, NESDIS and CIRA

Forecasters at NWS Amarillo, TX utilized GOES-East shortwave IR satellite imagery to alert partners of a newly developed wildfire in the Oklahoma Panhandle during the afternoon of 04 March 2021. Mesoscale 1-min imagery was available over the region, and was utilized by forecasters to monitor for wildfire hot spots. In fact, due to periodic cloud cover across the scene, the mesoscale 1-min imagery helped in detecting the hotspot (with confidence) roughly 9-minutes ahead of what was possible in the CONUS 5-min imagery. Given the periodic cloud cover, the 1-min imagery helped to capture the “in-between” moments that the 5-min imagery missed. The utilization of the hot spot notification tool with the GOES-East 1-min mesoscale imagery allowed forecasters to relay information on the location of the wildfire and current conditions in a quick and easy manner.

A timeline comparing the 1-min mesoscale imagery (top row) with 5-min CONUS imagery (bottom row) is shown in Figure 1. Increase the Zoom in your browser for better view of the slide show. Alternatively, larger versions of the individual components of the slide show can be accessed: Period 1, Period 2, Period 3, Period 4, Period 5, Period 6. The wildfire hotspot appears as relatively dark pixels, just northwest of Guymon, OK.

An animation shares similar information in Figure 2.

Individual animations are shown for the 1-min meso imagery (Fig 3) and 5-min CONUS imagery (Fig 4). The hotspot is easily diagnosed in the 1-min imagery, despite the cloud cover, as an apparent flickering of dark pixels. In the 5-min imagery, however, there are 2 images that provide a glimpse of the hotspot, with only one showing an obvious signal.

This is a great operational example showing the value of 1-min satellite imagery (compared to 5-min) for wildfire hot spot monitoring. The availability of 1-min imagery allowed for roughly 9-minutes of lead time (over 5-min imagery) for the confident detection of a wildfire hot spot and notification of its presence to core partners.

Kaitlin Rutt, NWS AMA; Bill Line, NESDIS and CIRA

A EUMETSAT blog post discusses in detail the winter weather that impacted the southern US in mid-Feb 2021. Specifically, it highlights satellite tools for differentiating snow cover vs ice cover.

Satellite channels in the Near-Infrared can be used to differentiate ice cover vs snow cover since ice absorbs more strongly than snow at these wavelengths. This difference in absorption is apparent in the ABI 1.6 μm band and the lower resolution 2.25 μm band. Similarly, snowpack characteristics can be gleaned from analysis of the near-IR bands. Fresh, clean snow will reflect more energy compared to old, melting, dirty snow.

The VIIRS 1.24 μm band is even more sensitive to absorption differences among snowpack characteristics and between snow and ice. A VIIRS “Snowmelt RGB”, developed by Curtis Seaman at CIRA, combines the 1.6 μm (red), 1.24 μm (green), and 0.64 μm (blue) bands from VIIRS to capture the varying characteristics of snow cover, and snow vs ice cover. From the Mid-Feb event, and specifically the significant 17 Feb snow/ice storm, the zone of ice cover (relatively dark blue) that fell along the southern extent of the winter storm can easily be differentiated from the snow cover (relatively light blue) to the north in the VIIRS Snowmelt RGB (Fig 1). Also note the cloud development over the areas where rain/freezing rain fell vs snow covered grounds (see EUMETSAT blog post for more details on this).

In the absence of the 1.24 μm band on ABI, a similar (experimental) GOES Snowmelt RGB can be created using the 1.6 μm, 2.25 μm, and 0.64 μm bands (Fig 2). A west-east oriented corridor of snow fell across the already snow covered upper Midwest on 27 Feb. As clouds cleared during the day on 28 Feb, the relatively light blue of the newer snow corridor contrasts with the darker blue (lower reflectance in near-IR) of the older snow to the north in Minnesota and south in Iowa.

Comparing with VIIRS Snowmelt RGB with a mostly cloud free scene on 01 Mar, we see that both products capture the differing snowpacks, with the VIIRS product showing even greater contrast between new and old snow, and in higher spatial resolution (Fig 3). Note another band of (light) snow fell overnight on the 28th, and can be observed in the imagery extending from North Dakota, southeast across central Minnesota into southeast Minnesota.

If we loop through a period from the 28th through the 2nd of March using both the VIIRS snowmelt and ABI Snowmelt RGBs (Figs 4 and 5), we can see that the snowpack gradually gets darker as the snow melts and absorption in the near-IR increases.

Figure 6 compares three near-IR bands from VIIRS, VIS, and the Snowbelt RGB for the Midwest scene on 01 March. Note the difference in reflectance between the new snow and old snow becomes greater from 2.25 um and 1.61 um to 1.24 μm. The difference in snowpacks is unrecognizable in the VIS alone. The RGB allows one to differentiate the fresh snowpack from the older snowpack as well as other features such as bare ground, open waters, and clouds.

Bill Line, NESDIS and CIRA; Curtis Seaman, CIRA

A very shallow cold airmass had established itself across much of the high plains by the day on 9 Feb 2021. Analyzing the 12z Denver sounding, a strong temperature inversion is observed with a surface temperature of around -12C below a max temp of around 3C (Fig 1) less than 1 km AGL.

Viewing GOES-East Day Cloud Phase Distinction RGB imagery, the low clouds (light blue) trace the lowest elevation areas in the eastern valleys, representing areas of cool/saturated air below the inversion (Fig 2). Flurries were observed under these very shallow clouds. The higher elevation areas are cloud free as they lie within the warmer/drier air in the warm nose of the inversion.

A comparison between the cloud features in the imagery and the underlying topography is shown in Figure 3.

Within the river valleys and under the low clouds, temperatures were generally in the teens by the afternoon (Fig 4). In the clear sky, higher elevation areas of eastern Colorado, temperatures had risen into the 40s. Similarly warm temperatures were observed in the high mountain valleys to the west.

Other factors were influencing surface temperatures along the front range during the day. For example, at Cheyenne, a period of breezy westerly winds (subsidence) during the late morning quickly and briefly boosted temperatures into the mid 40s, which quickly moderated back into the upper 30s after a southerly wind shift (Fig 5 and 6).

Bill Line, NESDIS and CIRA

While there are many, many, many examples of RGB’s excelling at diagnosing the early stages of convection during the daytime, there seems to be a lack of examples showcasing similar RGB use during the nighttime. This is likely due to the absence of solar reflectance, particularly in the near-infrared. Reflectance within this wavelength spectrum aids in monitoring the stages of early convective growth through easy detection of cloud top glaciation. Such reflectance gives RGB’s like the Day Cloud Phase Distinction its superiority in monitoring the convective lifecycle. But is there an RGB that can perform a similar application without solar reflectance, i.e. at night? This post will attempt to shed light [get it?] on how the Nighttime Microphysics RGB can be utilized in anticipating convective initiation.

On the night of August 18, 2020, forecasters at the National Weather Service in Grand Forks monitored the potential for overnight thunderstorm development, but were unsure if forcing would be sufficient enough to overcome strong capping over the area. There was anticipation of a low level jet to develop somewhere over eastern North Dakota into northwest Minnesota serving as a potential spark to ignite convection through the capping inversion. While questions remained on where exactly this would happen, focus was given to the mesoanalyst role to monitor for this potential.

At around 12:30 am CDT, the Nighttime Microphysics RGB easily picked up on low level stratus developing northeastward over the northern Red River Valley in far northwest Minnesota. This stratus stood out from other nearby clouds with its telltale pale cyan color compared to higher level dark blue and red cousins to the east and south.

The pale cyan color is a result of increased values within the green gun, the Night Fog difference product (10.3 – 3.9 um), as well as a slight dimming in the blue gun, the longwave infrared band (LIR; 10.3 um), while no information was added from the red gun, the Split Window Difference (SWD; 10.3-12.3 um). These were all signs of low level stratus, mainly through the increased values within the Night Fog product indicative of clouds made of up water droplets. While it drew the attention of the forecasters, questions still remained: Does this low stratus represent the seeds to convection? Or is this simply a benign cloud feature?

Over the next hour, characteristics of this cloud feature changed. The low stratus changed from its uniform pale cyan color and ameba-like structure, growing dark red specks that slowly veered and expanded east-southeast.

The change in color is a result of increased values in the red gun (SWD), sharply decreasing values in the green gun (Night Fog product), and further decreasing values in the blue gun (LIR). This indicated parts of the stratus cloud were starting to glaciate as suggested by the sharp decrease in values from the Night Fog product, continued cooling in the LIR, and increasing difference between the “clean” and “dirty” LIR channels (SWD).

The awareness and knowledge of the subtle change in cloud characteristics as illustrated by the Nighttime Microphysics RGB was crucial in realizing the stratus cloud was continuing to grow one or more updrafts that were beginning to glaciate. This is analogous to the Day Cloud Phase Distinction RGB revealing glaciation of water comprised cumulus, a threshold designating convective initiation.

So we proved that the Nighttime Microphysics RGB can be used to assess convective initiation, but we already have other satellite tools to do this for us, particularly the 10.3 um LIR channel. This single LIR band has a long standing legacy as a useful tool in monitoring convective activity at night. But can this application of the Nighttime Microphysics RGB provide additional lead time towards convective initiation compared to monitoring cloud top temperatures on the 10.3 um LIR channel?

The animation above is a time matched side by side comparison of the Nighttime Microphysics RGB and LIR band. In this case, the easily definable signal of stratus becoming glaciated within the RGB gave around 30 minutes to 1 hour of additional lead time in raising awareness toward potential convective initiation compared to typical LIR if using -24 C as a threshold (standard color curve for LIR in AWIPS turns blue at -24 C). This additional lead time allowed forecasters to feel better prepared in messaging and internal warning operations (better preparation =  less surprises and more confidence in warning/no-warning designation).

While the Nighttime Microphysics RGB can provide crucial information of pre-CI development, it lacks valuable cloud top information after CI, an area where LIR still reigns supreme. So why not have both?

The animation above takes the best of both products by overlaying an adjusted LIR color table on top of the Nighttime Microphysics RGB. Simply make values lower than -24 C transparent within the LIR color table and keep it above RGB in the hierarchy of display within AWIPS. The LIR’s bright colors of ongoing convection probably stands out the most displaying details like a sprawling anvil, overshooting top, and warm trench indicative of an above anvil cirrus plume. But the RGB’s input in this same image can help focus attention west and north of ongoing convection. Notice the tight packs of small , discrete but glaciating cells as shown by a reddening color? This should raise awareness towards the potential of additional convection soon to initiate.

This Nighttime Microphysics RGB – LIR “sandwich” yields information that is helpful in both the pre-CI and post-CI environment. The remainder of the loop showed that many cells matured into robust convection. And while not all of these glaciating cells went on to become mature storms (notice the orphan anvils?), it still signaled the potential of additional development outside of ongoing convection. This knowledge directly led to refined messaging of severe threats for targeted locations, bridging the gap between outlook and warning phases.

For those wondering what hazards this event brought: hail. Numerous reports of large hail up to the size of golf balls fell during the early morning hours of August 19, 2020, within the central Red River Valley into northwest Minnesota. More environmental information can be found via SPC’s Event Archive.

Carl Jones
Meteorologist
NWS Grand Forks

Strong northerly winds on the backside of a broad central US low pressure system resulted in widespread dense blowing dust across the southern high plains on 15 Jan 2021. Wind gusts of 45-65 knots initiated blowing dust across eastern Colorado during the mid-late morning, which expanded south-southeast into southwest Kansas and the OK/TX panhandles by late morning into the early afternoon. The blowing dust resulted in widespread and prolonged visibility reductions to less than 2 miles, with temporary reductions to near-zero captured on video. These reduced visibilities prompted the issuance of multiple NWS Dust Storm and Blowing Dust warnings, as well as road closures.

Some images from within the dust plume:

#kswx chiseling. Doesn't seem to be helping any. Please stop blowing! pic.twitter.com/ZIA7FF4RL6

— A.J. Crotinger (@ajcrotinger) January 15, 2021

Hwy 40, 287 and I-70 are all closed. Do not travel if you are near these areas. #trafficalert #weatheralert pic.twitter.com/zV5bVBtdgu

— CSP La Junta&Lamar (@CSP_LaJunta) January 15, 2021

A GOES-East 1-min mesoscale sector was available over the region of blowing dust, thanks to a request the previous evening by NWS Norman for Fire Weather. The initiation of blowing dust in the morning across southeast Colorado is observed and tracked efficiently by GOES-East 1-min VIS-SWD combo, a procedure which can be created in AWIPS (Fig 1). The combo uses a semi-transparent SWD overlay with a range centered around that of the dust signal, allowing areas of potential dust to “pop”. The animation depicts the issuance of Dust Storm Warnings in relation to the dust evolution.

According to a NWS Pueblo forecaster, the GOES imagery aided in determining where and where not significant blowing dust was occurring, and was used in combination with surface obs and webcams to issue the warning. See text below for one of the warnings issued by NWS Pueblo (Fig 2).

Panning out and observing the daytime evolution using GOES-East Geocolor, we see the location of the blowing dust in relation to the larger cyclone centered over Missouri/Illinois (Fig 3). The dust, in this case, is easy to diagnose in Geocolor, especially later in the day as forward scattering increases for GOES-East. Note, GOES-West provided slightly better detection of the dust in the reflectance bands and products during the morning (more forward scattering), but was only available at 10-min resolution, vs 5-min and 1-min from GOES-East.

The DEBRA-Dust product, available on the CIRA Slider, can similarly be used in combination with Geocolor imagery to highlight areas of blowing dust. With this event, the algorithm performed very well in capturing the blowing dust with no apparent false alarm, from both GOES-East (Fig 4a) and GOES-West (Fig 4b).

Given the strong dust signal, the Dust RGB also captured the dust signal quite well as red (Fig 5).

Finally, blowing dust was easily detectable in the Dust-Fire RGB (relatively bright green), along with periodic wildfire hot spots (red pixels) within and near the dust (Fig 6). This RGB is a useful situational awareness tool for tracking both the evolution of blowing dust and new wildfire starts, phenomena which occur under similar environmental conditions.

The NWS Aviation Weather Center issued multiple IFR SIGMETS due to the blowing dust, utilizing satellite imagery and surface obs (Fig 7). An AWC forecaster noted their increasing use of the Dust RGB in operations, and that it was utilized today to assist in product issuance.

VIIRS imagery provided a high resolution view of of the dust plume during the early afternoon. The Day Land Cloud RGB, created using the 1.6 um, 0.86 um, and 0.64 um I band channels for the RGB components, respectively, provides us with a 375 m RGB effective at highlighting lofted dust and distinguishing it from other features (Fig 8a and 8b). Blowing dust appears as relatively bright brown to tan, while liquid cloud tops are white/gray, ice cloud tops are cyan, and snow cover an even brighter cyan.

Even higher resolution imagery, 10 m true color, from Sentinel-2 was available over the blowing dust during the late morning when the event was well underway (Fig 9a and 9b). The zoomed in view captures areas of both transparent and opaque dust advancing across HWY 50 between Lamar and Holly in southeast Colorado.

NWS offices experiencing the blowing dust were active on social media sharing GOES imagery of the event as part of their Decision Support Services.

A dust storm warning remains in effect until 115 pm MST (Jan 15, 2021) across the southeast plains of CO. Gusty north winds in excess of 60 mph continues to create poor visibilities in blowing dust emanating across the plains, as the CIRA DEBRA sat product (yellow) shows. #cowx pic.twitter.com/cABbpoI4Ci

— NWS Pueblo (@NWSPueblo) January 15, 2021

Main dust plume moving south now approaching I-40 in Carson and Gray counties. Visibilities will reduce to less than 4 miles at leading edge of plume w/further deteriorating conditions possible if dust plumes fills in more to the south w/dangerous driving conditions #phwx #TXwx pic.twitter.com/JmuwvuwL0S

— NWS Amarillo (@NWSAmarillo) January 15, 2021

Blowing dust is once again a concern across far southwest and west central Kansas as wind gusts picked back up during the mid-morning hours. Expect wind gusts 55 to 70 mph through early afternoon. Blowing dust will reduce visibility, locally, to less than a mile. #kswx pic.twitter.com/FimlTAuCNW

— NWS Dodge City (@NWSDodgeCity) January 15, 2021

To close, the full daytime evolution of the blowing dust viewed in the GOES-East 5-min Geocolor/SWD image combo, with Dust Storm Warning polygons overlaid (Fig 10).

The blowing dust would continue to travel southeast through the night, reaching the Gulf of Mexico by the next morning. GOES-East IR-based multispectral products were effective in continuing to track the lofted dust through the evening. Shown is a modified version of the Dust RGB, with lofted dust appearing as a dark blue relative to surrounding areas (Fig 11). The CIRA geocolor product is appended to the start and end of the loop to capture the daytime reflectance view of the dust on either end.

Bill Line, NESDIS and CIRA, Steve Hodanish (NWS PUB), Declan Cannon (NWS AWC)