Satellite Liaison Blog

Severe thunderstorms developing off of a E NM/W TX dryline produced hail to the size of baseballs (2.75″) and a few tornados during the afternoon/evening of 17 May 2021. GOES-East Split Window Difference (SWD) – IR Imagery Combo captured the evolution of the dryline early on in the day prior to the development of cumulus clouds and eventual deep convection. The 10.3 – 12.3 SWD with gray scale color table, discussed in previous blog posts, highlights the sharp boundary from drier lower atmosphere (darker gray) to greater moisture (lighter gray). By overlaying cold 10.3 um BTs, we add information where SWD provides little (thick clouds) and can analyze thunderstorm development in the context of the moisture boundaries. In this case, the combo shows convective initiation along a dryline spanning from E NM south through W Texas, and into Mexico. Please note, when using the SWD to track LL moisture, a positive lapse rate is required (temperature decreasing with height). Finally, the SWD also captures blowing dust within the stronger southwesterly flow in the southwest portion of the scene (darkest gray; negative values of 10.3 – 12.3 um SWD). NWS convective warning polygons are also shown in many of these examples. Of note, the NWS Midland, TX office was handicapped in that the WSR-88D was down due to a failed power supply for much of the day, so they had an exceptional reliance on other distant radars and satellite imagery for this event.

Corresponding visible satellite imagery from GOES-East captures the evolution of the atmosphere from clear sky to cumulus clouds to deep convective initiation.

Comparing the SWD and VIS, we see that by late morning, pieces of the dryline, including dryline bulges, can be diagnosed in the SWD, even before cu start to develop along the boundary.

Later in time, visible imagery shows cu developing along and ahead of the dryline as diagnosed in in the SWD, including early deep convective development ahead of the dryline bulges.

Focusing in on the region and overlaying surface obs, we get an idea of how the SWD provides greater spatial and temporal detail as a supplement to the coarser surface observations in tracking the evolution of the dryline. Note the higher dew points east of the dryline, and rapid cooling of dew points as the dryline crosses the obs.

One-minute imagery from GOES-East was available to forecasters over the region. At NWS Midland, TX, the forecaster working the mesoscale desk utilized the Day Cloud Phase Distinction RGB leading up to convective initiation to monitor for relevant mesoscale signatures and for early signs of glaciation. The dryline bulge noted above can also be inferred in this imagery as the region of cu-free airmass southwest of Midland pushing northeast. This feature was noted by forecasters as a potential area of CI (specifically, N/NE of the bulge) given favorable low level moisture convergence and backing of surface flow. Forecasters also noted, from the early imagery, boundaries and HCRs over the northeastern part of the CWA, which indicated to them the amount of low level shear and potential helicity storms could ingest. Based on trends in this RGB, the forecaster notified warning staff when towers were starting to glaciate. In the GOES-East 1-min Day Cloud Phase Distinction RGB animation below, towering cu and glaciation becomes obvious just south and south-southwest of Midland toward the end of the animation, ahead of the dryline bulge.

Convective initiation continued over the following hour, as was apparent in the same RGB imagery, ahead of the dryline bulge southwest of Midland. Also included in the next animation is GOES-East GLM Minimum Flash Area (MFA), which was also being viewed by NWS/MAF during this event. Although lightning activity was relatively low with these storms, the early flashes were quite small, indicating to the forecasters of continued storm intensification. Additionally, the presence of lightning prompted the issuance of an Airport Weather Warning for Midland International Air and Space Port (within 10 nm of storm).

As storms matured, forecasters continued to view GLM products (FED and MFA), as well as ProbSevere, to aid in situational awareness regarding updraft trends and identifying storms with greater severe potential. Forecasters also noted the presence of above anvil cirrus plumes (AACPs) with the strongest storms. The 4-panel below includes (cw starting with top left panel): VIS, DCPD RGB, VIS+GLM FED, VIS+GLM MFA, and warning polygons on all panels.

GOES-East 1-min VIS-IR Sandwich Combo imagery captures the first three hours of development of a supercell thunderstorm off of the southern dryline bulge. Of note is the rapid anvil expansion, obvious and large OT that develops, along with an associated Above Anvil Cirrus Plume, indicative of a particularly strong updraft and severe threat. The storm produced very large hail during this time period.

Later, GOES-East 1-min VIS shows the thunderstorm during the period of tornado development. The increased shadowing toward sunset allows texture in the storm top, including features such as the OTs and AACPs, to become even more obvious.

Bill Line, NESDIS and CIRA and Brian Curran, NWS Midland, TX

Widespread severe weather brought large hail, damaging winds, and tornados to two areas of the central US on 27 April 2021: Eastern Colorado and central Texas. Given the expected weather, two GOES-East mesoscale sectors were positioned over the region, with a slight N-S overlap in the middle. A simple AWIPS procedure allows one to view the two mesoscale sectors as a single product instead of two separate (overlaying) products, allowing one to view 30-sec imagery where the sectors overlap (Fig 1). If interested, feel free to reach out!

Within the southern mesoscale sector (on the edge of the overlap), a strong and long-lived thunderstorm traveling ENE across north central Texas produced hail larger than baseball size (3″ reported), along with a tornado. GOES-East 1-min VIS-IR Sandwich imagery centered over the storm revealed a large and relatively cold overshooting top and a long-lived above-anvil cirrus plume representing an exceptionally strong/consistent updraft and severe potential (Fig 2). Further, the exposed updraft and inflow region on the south side of the storm allows one to diagnose a cyclonic rotation in the updraft (mesocyclone), along with inflow feeder clouds (another severe indicator). This storm-relative example allows the user to more easily diagnose and follow storm features.

The storms in eastern Colorado were located within the mesoscale sector overlapping area, allowing for 30-second imagery. A thunderstorm developing just east of Colorado Springs produced accumulating hail. Thirty-second vis-ir sandwich imagery revealed features rising and rotating around the exposed southern portion of the updraft (Fig 3). By including the semi-transparent IR overlay for cold BTs, we can more easily focus on the warmer (non-colored) features outside of the anvil top.

Further east and a little later, a thunderstorm produced a tornado near the intersection of 3 county warning areas (BOU, PUB, GLD). This storm was warned on by all three WFO’s simultaneously! Additionally, the warnings issued by PUB were the 2nd and 4th smallest tornado warnings issued by PUB since 2007 (SBW era). This storm was also captured by the GOES-East 30-second imagery (Fig 4). Once again, the exposed updraft and high temporal spatial resolution imagery allows one to diagnose a rotating updraft.

There were several storms that produced accumulating hail across Colorado during the afternoon. These hail swaths were captured in GOES-East imagery as well (Fig 5). The Day Cloud Phase Distinction RGB highlights the hail swaths quite well (as green, similar to snow cover) compared to visible imagery alone (hail swaths and cloud both highly reflective). Dashed green lines highlight the southeast border of hail swaths. Kudos to Jorel Torres (CIRA) for pointing these out.

GOES-East 30-sec adjusted Day Cloud Phase Distinction RGB imagery focused on the El Paso County storms highlights the cloud detail in the thunderstorms as well as the hail swaths at moments between cloud cover (Fig 6). Hail swaths can be found just east of Peyton and east of Yoder.

The hail swaths could also be diagnosed in the high resolution VIIRS imagery, in both the Day Cloud Phase Distinction RGB (green), and snowmelt RGB (dark blue; Fig 7).

A video montage shows the impressive El Paso County hail swath:

Hail along Judge Orr Rd and North Ellicott Hwy in El Paso County. Courtesy of 11 Breaking Weather Chaser @NorthernChase #cowx pic.twitter.com/yZeJR9BlqD

— Brian Bledsoe (@BrianBledsoe) April 27, 2021

Bill Line, NESDIS and CIRA

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