Satellite Liaison Blog

Widespread gusty winds and blowing dust developed across portions of Nevada during the late afternoon/evening of 28 June 2020 in association with a potent upper low and related cold front. GOES-West upper level water vapor imagery with RAP 500 mb analysis contoured depicts the evolution of the compact upper low sagging southeast across the Pacific Northwest, forcing frontal boundaries south across Nevada (Fig 1).

At 2212 UTC, the NWS Reno, NV AFD included the following text: “The winds are kicking up dust off the Carson Sink in eastern Churchill County as evidenced by the GOES-17 dust satellite imagery. While cloud cover is blocking the evidence of dust from the playa farther north, dust can be seen coming off the Black Rock/Smoke Creek deserts from the Fox Mountain ALERT cam. So far evidence of major reductions in visibility are scant given the lack of visibility sensors in the dust plume areas.”

Both GOES-East and GOES-West captured the development and evolution of blowing dust plumes and wildfire hot spots across Nevada during the day. First analyzing 0.64 um VIS, blowing dust is most apparent extending south out from under the broad cloud shield over central Nevada (Fig 2 and 3). Another source of obvious blowing dust develops slightly further south near the southwest NV/CA border. Finally, a smoke plume becomes apparent in southern Nevada toward the end of the period. Blowing dust and smoke is most obvious in the VIS near sunset and in the GOES-East imagery where/when forward scattering becomes greatest. Similar to the 6/25 event, it is important for forecasters in the western 1/3 of the US to keep in mind they have two sources for 5-min imagery (GOES East and West), and the ideal source may vary from event to event.

10.3 minus 12.3 um Split Window Difference imagery with a linear gray colorscale and IRW overlay for coldest BTs (clouds) captured the blowing dust as the darkest grays to black in the scene (Fig 4 and 5). Additional plumes become more easily detectable than in the VIS alone, including in far southern Nevada near the beginning of the period, and smaller more subtle plumes in far east-central Nevada and southwest Utah during the middle of the period.

10.3 minus 11.2 um Split IRW Difference imagery captured the blowing dust similarly to the SWD using similar color tables (Fig 6 and 7).

Given the dry and windy conditions, conditions were ripe for the development of wildfires as well. Viewing 3.9 um imagery during the same period, several wildfire hot spots appear during the day as relatively dark gray flickering pixels (Fig 8 and 9). This linear grayscale colortable applied to 3.9 um imagery remains the authors recommended method for wildfire hot spot detection. The range is set as -40C (white) to 110C (black). Hot Spots appear as relatively dark gray and flickering pixels, and is consistent across all seasons and locations.

One can combine the SWD, IRW, and SWIR channels to create an RGB that combines dust plume detection with wildfire hot spot detection (Fig 10 and 11). In this RGB, dust plumes are vivid green, wildfires are red, bare ground is shades of dark red/green/cyan (depending on sfc temp), thick clouds are vivd blue to cyan, thin cirrus clouds are very dark blue to black, low stratus clouds are a medium green, and bodies of water are a dull cyan. Dense smoke plumes may also appear as dark green-to-cyan. In the RGB animation, the dust plumes contrast well against the background surface and above clouds. The primary dust plumes referenced earlier are obvious, with the additional smaller plumes very apparent as well. Wildfire hot spots, small and large, also pop against the bright background. Cloud classification also remains possible.

Features identified in the Dust Fire RGB are noted in Fig 12.

NOAA-20 and SNPP passes provided high resolution VIIRS imagery over the location of blowing dust and wildfires during the early afternoon. The same Dust Fire RGB is applied to the VIIRS imagery, which allows for a more detailed (spatially) look at the blowing dust underneath the clouds and it’s evolution over the 42 minute period, as well as developing active wildfires to the southeast (Fig 13 and 14).

Finally, 1-minute GOES-West satellite imagery was available over the region courtesy of SPC for: “SPC Critical Fire Weather in CA/NV/UT/AZ” (Fig 15).

The “Dust Fire RGB” is available in AWIPS upon request (contact bill.line).

Bill Line, CIRA and NESDIS

Thunderstorm outflow winds resulted in lofted blowing dust across west-central Nevada during the early evening hours of 25 June 2020. GOES-West Meso-1 was available over the region per a request from SPC for “SPC Elevated Fire Weather Risk in the Southwest and Marginal Severe Risk in WY”. NWS Reno, NV issued a Dust Storm Warning (polygon) at 0129 UTC for the blowing dust plume (Fig 1). They were able to confirm the blowing dust using satellite imagery, radar imagery, sfc obs, and local webcams/video. From an early evening AFD update: “Wind gusts 40-50 mph were widespread behind this outflow with satellite, observations and video showing blowing dust accompanying the outflow.”

***Dust Storm Warning*** Until 8:30 PM. Visibility dropping to less then 1/4 mile with strong winds in excess of 50 mph.

Dangerous life threatening travel along I-80 between Lovelock and Reno, Highway 50 and Highway 95 between Carson City and Fallon. #nvwx pic.twitter.com/Izame2ZPfQ

— NWS Reno (@NWSReno) June 26, 2020

The region of blowing dust can be diagnosed accelerating west away from the area of thunderstorms after 0030 UTC through sunset in GOES-West 1-min visible imagery (Fig 2). The Dust Storm Warning Polygon is included in the animation. Although the 0.5 km VIS provides a detailed view of the plume which is characterized by moderate reflectance values and laminar appearance, the signature is not obvious when viewing a broader area, and does not catch the eye.

The plume of blowing dust is similarly apparent in daytime geocolor/true color imagery (Fig 3).

Now viewing GOES-West 1-min SWD imagery, typically reliable for 24/7 lofted dust tracking, the region of blowing dust extending from the thunderstorm complex is even less apparent (Fig 4). The signature is very dark gray using this color table. The stripes/noise apparent in the imagery are associated with the G17 cooling issues.

If we combine multiple IR channels/differences into a single RGB, we have a method that allows the blowing dust to pop while also maintaining cloud classification (Fig 5). Dust appears as a bright cream or white, compared to the background bright blue bare ground, red/orange for cold/thick clouds, dark blue or black for cold thin clouds, and magenta for warm/low clouds. This RGB combines the SWD, IRWD, and IRW channel, and will capture dust day and night. The noise associated with G17 cooling issues are exaggerated in channel combinations. However, important signatures are still able to be diagnosed.

Taking a quick look at 5-min CONUS GOES-East VIS, the dust signature is not readily apparent (Fig 6). Given the viewing angle, much of the blowing dust is hidden by the thunderstorms to the east along with new cumulus cloud development. Forecasters within the western 1/3 of the US must always keep in mind the two GOES satellites available and how viewing angle may affect the appearance/detectability of a given feature in a given situation.

Bill Line, CIRA and NESDIS

An all encompassing Fire RGB allows a forecaster to monitor three important components to an ongoing wildfire in a single RGB: the wildfire hot spot, the smoke plume, and the burn scar. In order to do so, the RGB combines the 3.9 um shortwave IR channel for hot spot detection (red component), the 0.87 um component for land change (green component), and 0.64 um for smoke (blue component). This RGB is fairly similar to the “Day Land Cloud Fires RGB”, already in AWIPS, but allows for detection of smaller/cooler wildfires given the inclusion of 3.9 um vs 2.25 um, and easier detection of smoke plumes and burn scars given tweaked ranges. This RGB was first discussed here.

One-minute imagery from GOES-East was available over the southwest US on the 16th courtesy of WFO Tuscon with a reasoning of “Several IMETs deployed”. Viewing the Mangum fire in north-central Arizona during the afternoon of 6/16/2020 using the Fire RGB, the large hot spot is obvious as several red pixels (large red contribution with small green and blue; Fig 1). The thick smoke plume emanates from the hot spot to the northeast, and is characterized by medium cyan colors (similar green and blue contributions, small red). Finally, areas that had burned the previous days to the southwest of the hot spot are almost black with little contributions from all three components. Elsewhere, highly vegetated areas (such as the region around/in which the fire is burning) appear deep green, the Colorado River and other waterways are dark blue to almost black, while non-vegetated areas are dull green. The 4-panel in Fig 2 includes the RGB during the same period along with the three components.

The AWIPS menu entry for this “Fire RGB” is available upon request.

VIIRS DNB NCC imagery captured the light from the wildfire during the overnight hours early on the 16th in three passes (two from SNPP, one from NOAA-20; Fig 3). The active areas of the wildfire are obvious as a ring of light around previous burned area. The most active region of the wildfire, on the northern front, is also diagnosed from the imagery. Finally, a relatively dim glow adjacent to the wildfire is suspected to be scattering of light off of the smoke/haze. Changing position of the wildfire and suspected haze glow is due to parallax given different viewing angles with each of the three frames.

The HRRR-Smoke model, which utilizes information from polar-orbiting satellites (VIIRS, MODIS), provides a prediction as to how smoke will evolve from the fire in the near future. In this case, the model (early morning cycle) accurately predicted smoke associated with the Mangum fire to spread northeast across southeast Utah, northwest Colorado, and into southern Wyoming by the evening (Fig 4). This information can be used by local officials to anticipate smoke reports from the public, and associate them with a particular fire upstream.

Bill Line, NESDIS and CIRA

A potent shortwave trough ejecting east into the central/southern plains resulted in strong surface winds and widespread blowing dust across portions of Texas and Oklahoma on 09 June 2020. GOES-East upper level water vapor imagery showed the progression of the shortwave and wrapping of dry/descending air around it’s southern and eastern peripheries (Fig 1).

NWS Norman, OK (OUN) monitored the development of blowing dust using satellite imagery and surface obs starting early in the morning on the 9th. From the OUN 1419 UTC AFD update: “Updated the forecast through tonight to add blowing dust to the weather component and lowered temperatures for this afternoon” and Aviation update: “Updated most TAFs to include blowing dust that will result in restricted visibilities and even some cigs. MVFR conditions appear likely especially for brief period across western Oklahoma.”

There are various satellite tools available to forecasters in AWIPS to observe the evolution of dust. During this event, OUN forecasters mentioned their use of IR imagery prior to sunrise and 0.64 um visible imagery after sunrise to track the evolution of the dust plume into western Oklahoma. They also noted value in using the Dust RGB, Ash RGB, and Geocolor products during the event.

During the previous late evening and early morning prior to sunrise, 10.3 um IR imagery captured the progression of the cold front south and east across the southern High Plains (Fig 2). Surface observations along the way reported the dramatic wind shift and increase to northwesterly, along with visibility reductions (due to blowing dust). The GOES imagery filled the spatiotemporal gap between those surface observations.

While IR imagery alone provides a good view of the cold air surge, it doesn’t differentiate areas of lofted dust. As has been shown numerous times on this blog, the 10.3 – 12.3 um split window difference (SWD) is efficient at detecting areas of lofted dust and areas of thick blowing dust (see here). This is primarily due to the sensitivity of the 10.3 um channel to absorption by lofted dust particles. The SWD (with IRW overlay for cold brightness temperatures [clouds]) is effective at highlighting lofted dust during the night, in addition to day. In this case, the lofted dust shows up well throughout the nighttime period as near-to-below zero values, or moving plumes of relatively dark gray (Fig 3). RGBs that include the SWD (Dust, Ash) are also effective at highlighting lofted dust at night, and are shown later in this post.

One-minute imagery was available over the region starting during the morning of the 9th from both GOES-East (Fig 4) and GOES-West (Fig 5) satellites. Comparing 0.64 um visible imagery from both perspectives, it is obvious that the GOES-West perspective provides better detection of blowing dust during this time period, due to forward scattering of the airborne particles. The high temporal coverage allows for real-time awareness regarding blowing dust location. The simple grayscale colortable is modified to focus on the lower end of the scale, better highlighting the lofted dust. This can easily be done in AWIPS by adjusting the max value downward in the “change colormap” option.

Now viewing visible imagery during the full day from each satellite, at peak sun angle, detection is degraded from both satellites given a lack of forward scattering into the satellite sensor (Figs 6 and 7). For this location, GOES-West provides superior aerosol detection in the morning, while GOES-East is best during the evening, due to forward scattering.

The Geocolor product also highlights the blowing dust, but suffers from similar deficiencies as the visible channels (Fig 8). IR bands and band combinations can then be used to improve detection.

After sunrise, the SWD-IR combo continues to prove effective in detecting the blowing dust plumes consistently throughout the whole day (Fig 9). After the initial dust plume from southeast Colorado into Oklahoma, several areas of blowing dust develop over west Texas, and later out of the OK/TX Panhandles.

Corresponding 10.3 – 11.2 um imagery captures the plumes with similar or even more pronounced negative values (11.2 um less sensitive to moisture absorption than 12.3 um), but since the clear sky areas have very small differences, contrast from plume to no plume areas is less than in the SWD imagery (Fig 10).

The Dust RGB (Fig 11) and the Ash RGB (Fig 12) contain the same ingredients (channels and channel differences), but with different thresholds. Both include the SWD, which significantly influences the dust detection. These RGBs can be used for cloud classification at the same time as dust/ash detection.

However, slight modifications to the RGB recipe(s), particularly the SWD component, can further highlight the presence of lofted dust (magenta) using the same ingredients. In this case, the only changes were to modify the ranges of the RED component to Max=0.5 and Min=-6.0, and modify the Gamma for the RED and GREEN components to 2.50. These changes take seconds to make, and can be done on the fly during an event (see tutorial here).

Wildfires also developed within the dry and windy environment during the afternoon of the 9th. The smoke and wildfires are not readily apparent in the IR detection methods used for blowing dust. However, this would be useful considering wildfires and associated smoke often develop in the same environment as blowing dust. A daytime dust/fire RGB captures the blowing dust (green), wildfire hotspots (red), and thick smoke (dark cyan emanating from hotspot) plumes (Fig 14).

Finally, during the overnight hours of the 9th, NOAA-20 and SNPP VIIRS Day Night Band Near Constant Contrast Imagery captured the blowing dust expanding across the Panhandles (Fig 15 and 16).

Bill Line (NESDIS and CIRA) and OUN forecasters

Landspout tornados and severe thunderstorms impacted southeast Colorado and southwest Kansas during the afternoon of 21 May 2020 (spc reports). GOES-East satellite imagery was used by NWS PUB forecasters to analyze the cumulus cloud field leading up to convective initiation, and gauge convective evolution as storms matured.

Analyzing 1-min visible imagery during the two hours between 1859 and 2059 UTC, the cu field across southeast Colorado from just north of Holly to Campo became increasingly agitated, with the greatest clumping and vertical growth occurring between Lamar and Holly (Fig 1). These cumulus cloud trends were signs of imminent convective initiation. Additionally, forecasters diagnosed significant low-level cyclonic vorticty given the evolution and character of the broad cu field in the imagery across southeast Colorado into southwest Kansas. Finally, the movement of cu clouds to the west with towering cu tops and orphan anvils drifting to the east highlighted the presence of substantial low-mid-level shear.

The insight gleaned from satellite imagery along with additional knowledge about the environment gave forecasters confidence that a landspout tornado threat existed with any storm that might develop in the area, in addition to the large hail threat. The trends in satellite imagery also helped forecasters to message this risk to core partners and the public. Two tweets were sent during this period, highlighting the threat for strong to severe thunderstorms (Fig 2), and landspout tornados (Fig 3).

We'll give this visible satellite view a 9/10. Also… it shows low level cyclonic rotation in the congested cumulus fields. A few strong to severe storms are possible over the southeastern plains over the next few hours. #COwx #Colorado pic.twitter.com/sp2q7DwhX3

— NWS Pueblo (@NWSPueblo) May 21, 2020

There is a landspout risk over the southeastern plains over the next few hours. These are very hard to see with radar, so if you see any spin-ups, report it to us! We'll monitor using the #pubspotter hashtag. #COwx #Colorado

— NWS Pueblo (@NWSPueblo) May 21, 2020

Visible imagery during the following two hours (2059 – 2258 UTC) showed continued upscale growth of cumulus clouds across the region, including convective initiation and eventual development of strong-severe thunderstorms (Fig 4). Multiple instances of landspout tornados were confirmed during this period near the CO/KS border in association with the growing cumulus clouds.

In addition to the landspout threat, forecasters were motioning the development of severe thunderstorms. As convection continued to grow upscale and mature from Springfield to north of Holly/Lamar, forecasters paid close attention to IR-Window imagery (Fig 5). The IR imagery showed where the most rapid convective initiation was occurring, and was used to help forecasters determine which cell(s) would become most dominant. The most impressive and persistent cold cloud top temperatures and overshooting top developed within the broader region of convection with a storm between Lamar and Holly. This storm also quickly produced an above anvil cirrus plume, indicating a particularly strong updraft and severe potential. Severe thunderstorm and tornado warnings were issued with this region of development, which produced confirmed tornados and baseball sized hail.

Combining the VIS and IR into a sandwich image combo reveals the development of a dominant cell quite well with this case through the blending of texture and brightness temperature information (Fig 6). Details of the overshooting top and above anvil cirrus plume become obvious.

Viewing an animation covering the full duration of this event, the evolution of the cu field in the context of RAP analyzed sfc vorticty and 0-3 km MLCAPE (good fields for assessing landspout potential) is observed (Fig 7). The large values of sfc vorticty from the model generally agree with what is implied from the satellite imagery. Values of 0-3 km MLCAPE increased over and east of Campo during the afternoon. The region of overlap between the two fields near the CO/KS border is where landspout tornados were observed.

Bill Line (NESDIS and CIRA) and Klint Skelly (NWS PUB)

Very dry and breezy conditions developed across southeast Colorado during the afternoon of 20 May 2020 ahead of a broad western US upper trough and behind a surface dryline. With deep vertical mixing occurring behind the dryline, RH values fell to around 10 %, and winds gusted 30-40 knots. A wildland grass fire initiated north of Kim, CO during the early afternoon.

A GOES-East 1-min meso sector was available over a region including the wildfire during the day in support of convective warning operations (Fig 1). A watchful eye would notice the flickering of a faint hot spot below thin cirrus clouds by around 1945 UTC. With 5x more images , a forecaster can be more confident in wildfire detection earlier when using 1-min imagery over 5-min imagery. A simple gray-scale color table applied to ABI single-band 3.9 um imagery has proven to be a very reliable method for detecting wildfire starts, especially when 1-min imagery is available.

Later, as the fire continued to grow, an impressive smoke plume developed. The 1-min visible imagery shows the rapid growth of the plume, and even development of pyrocumulus adjacent to a colder cloud shield. IRW brightness temperatures associated with the pyrocu reached -20C shortly after 0100 UTC.

A long animation of the wildfire combines visible, SWIR and IRW imagery along with RAP surface analysis RH and wind gust fields for the duration of the event. The animation shows the fire initiating as wind gust speeds increase over 30 knots and RH values drop below 15%. The fire continues to burn hot well after sunset, before decreasing in intensity as wind speeds died down and RH values rose.

A 4-panel image of the wildfire and smoke plume during the early evening provides a variety of unique RGB displays for tracking the hot spot and associated smoke plume in unison. At this time, the hot spot was quite expansive, and pyrocumulus developing within the smoke plume.

S-NPP and NOAA-20 VIIRS imagery also captured the wildfire during it’s early stages, and during the evening. The same gray scale color table is used for each VIIRS/ABI image pair.

The 375 m I-4 band (3.74 um) imagery captured the wildfire earlier than was possible in the 2-km ABI imagery, and pinpointed it to a smaller region (a single dark pixel at 1915 UTC; Fig 5). At 2000 UTC, the fire had spread to a few pixels, but was still quite faint in the ABI imagery. However, as was shown, the animations of 1-min ABI imagery (not possible with VIIRS) allowed for confident detection of a hot spot by this point. By 2051 UTC, the wildfire hot spot was obvious in both VIIRS and ABI, but with VIIRS narrowing down the location to a much smaller area.

During the evening, both instruments continue to detect heat associated with the wildfire/burned area, with VIIRS pinpointing the burn region more precisely (Fig 6).

Bill Line (NESDIS and CIRA) and Mike Umscheid (NWS DDC)

Two rounds of severe convection developed over the Texas Panhandle during the afternoon and then evening of 07 May 2020. Storms developed amid increasing forcing associated The Amarillo NWS forecast office (AMA) utilized GOES-East imagery to track development.

GOES-East water vapor imagery highlighted a well-defined upper low digging southeast into the central US plains, with periodic and much more subtle perturbations in the W/NW flow to it’s south (Fig 1). Large scale forcing associated with these features aided convective development along surface/low-level boundaries.

The first round of severe storms developed over the southeastern portion of the Texas Panhandle along a dryline during the afternoon. Leading up to convective initiation, the AMA forecasters monitored the 1-min Day Cloud Phase Distinction RGB imagery for signs of imminent convective initiation (Fig 2). By 2055 UTC, it was apparent from the imagery that convective initiation was most most likely in the near-term over the southeast portion of the panhandle along the AMA/LUB county warning area (CWA) border. The cumulus cloud field was well established and maturing, cloud color was transitioning from cyan to green (glaciation), and orphan anvils were generated (failed initiation attempts). Shortly thereafter, deep convection initiated successfully just south of the CWA border in LUB’s area.

Forecasters from AMA noted the value of 1-min VIS/IR sandwich combo imagery as the convective scenario evolved (Fig 3). Of note early on was a new, stronger updraft developing ahead of the original updraft, quickly producing an above anvil cirrus plume. By 2216 UTC, a new updraft developed ahead of the main storm per cooling of cloud tops and increased cloud texture. This area of convection developed within the AMA CWA and forced the issuance of a severe thunderstorm warning. A storm split was apparent in the imagery a little later, by 2230 UTC, with continued cooling of cloud tops on the northeast cell (left split) and development of an OT. The right split accelerated to the southeast and maintained a large OT and prolific AACP. Forecasters noted the early signs of new updraft development and storm split were apparent in the 1-min satellite imagery just prior to radar.

An uninterrupted loop overlays MRMS MESH on the sandwich imagery, revealing the long hail swath associated with the main cell and right split, and apparent hail development from the forward convection in the southeast corner of AMA CWA, and eventually with the left split (Fig 4).

Later on that evening, additional convection developed across SW KS and the OK/TX Panhandles along a cold front within increasing large scale forcing for ascent ahead of the aforementioned shortwave. AMA forecasters noted the value of the 10.3 um IR window channel at night for analyzing this second round of convection (Fig 5). The imagery was utilized to identify the main updrafts of the stronger cores aloft given the appearance of overshooting tops, and to infer which updrafts were more likely to sustain themselves given cloud top IR temperature trends.

An animation of grayscale IRW and GOES-derived CAPE for the full-duration of the event shows a corridor of increasing instability ahead of the dryline during the afternoon, along/within which the initial round of convection developed and evolved. Instability remained high to the north ahead of the pressing cold front, with the second round of convection developing along the northwest CAPE gradient (cold front) as analyzed in the satellite product.

This blog post from CIMSS highlights the value of NUCAPS products from this event.

Bill Line (NESDIS and CIRA) and Kaitlin Rutt (NWS AMA)

Strong winds on the western portion of a deep surface low in association with an exiting shortwave trough resulted in lofted/blowing dust from the IA/NE/MO/KS Missouri River Valley (MRV) southeast across central Missouri. This is a favorable region for winds to go unimpeded, and the lofted dust is likely due in part to sedimentation/silt left behind from the big spring flooding of 2019. Further, it is still early in the planting season, so fields are susceptible to having dirt erosion. Local media shared photos of blowing dust across I-29, which runs along the eastern side of the MRV (Fig 1).

Blowing dust may be an issue on some highways this afternoon! Gusts to 55mph kicking up dirt from fields and creating limited visibility. This is from I-29 near mile marker 24 in Iowa. @NWSOmaha @WOWT6News pic.twitter.com/g0UMYY4qmQ

— David Koeller (@dkoellerwx) May 5, 2020

The Omaha NWS office noted the blowing dust on social media in the nighttime microphysics RGB (Fig 2). This RGB is effective in detecting lofted dust due primarily to the inclusion of the 12.3-10.3 um split window difference (SWD), which has been shown to be an effective ABI channel combination for dust detection (see previous blog post).

See the light pink streak just right of center? That's some blowing dust causing issues along I-29 where Iowa, Nebraska and Kansas meet.

Darker pink represents actual clouds. #IAwx #NEwx #MOwx pic.twitter.com/4d6XWB2TQJ

— NWS Omaha (@NWSOmaha) May 5, 2020

Given the conditions, the NWS in Omaha issued a Special Weather Statement for “reduced visibility due to blowing dust” along I-29, and the NWS in Pleasant Hill mentioned, “reductions in visibility as a result of the blowing dust” in their Wind Advisory.

The SWD-IR combo procedure perhaps provides the best depiction from ABI of the blowing dust across the region for the duration of the event (Fig 3). The blowing dust appears as very dark gray to black (very low positive or negative difference values), while most clouds will appear as colors with the inclusion of cold brightness temperatures from the IR window channel. Small cumulus clouds will be lighter gray) The lofted dust is diagnosed to initiate near northwest Missouri in the presence of a tight surface pressure gradient and 40+ knot wind gusts. The lofted dust is carried southeast over I-29 and into central Missouri as it wraps around the southwest and southern portion of the surface low. The animation, lasting 10 hours, depicts the long duration of this event.

The blowing dust can also be diagnosed in the 500 m 0.64 um VIS channel. The color table used is modified to highlight lofted material (Fig 4). The blowing dust becomes most apparent near sunset, when forward scattering of dust particles toward the satellite is heightened.

Finally, a modified Dust RGB provides a great depiction of the blowing dust, while capturing cloud details as well (Fig 5). In this example, the dust appears as deep magenta, low/cumulus clouds dark blue, stratus or mid-level clouds as red, and cirrus clouds as black. The RGB recipe is shown in Fig 6.

SNPP and NOAA-20 consecutive overpasses provided higher resolution (750 m vs 2 km for GOES) VIIRS M-band SWD imagery near the beginning of the event, allowing for slightly more details (spatially) to be gleaned from the lofted dust. (Fig 7).

Bill Line (NESDIS and CIRA) and Andrew Ansorge (NWS DMX)

Severe thunderstorms developed across the southern plains on 4/22/2020 in association with a shortwave trough traveling east across the TX PH, OK, and N TX. GOES-East water vapor imagery shows the evolution of the large scale feature and associated thunderstorm development, with RAP analyses quantifying the wave and it’s influence on the surface pressure and surface/mid-level wind fields (Fig 1). The vorticity max becomes increasingly well-defined as it accelerates east across OK, with associated dry descending air through west Texas and moist ascending air over east TX/OK into the southeast US. Additional imagery from some of the notable thunderstorms will be highlighted in this blog post.

Thunderstorms were ongoing across the northern half of OK and initiating across the southern half of Oklahoma during sunrise on the 22nd. Analyzing GOES-East 1-min visible imagery, shadows associated with the low sun angle provided excellent detail about storm initiation and storm top features such as overshooting tops (OTs), above anvil cirrus plumes (AACPs) and anvil gravity waves (Fig 2).

During the early-mid afternoon hours on the 22nd, additional convection developed across southern Oklahoma near the interface of a dryline/cold front/warm front surface triple point. A GOES-East 1-min VIS-IR sandwich combo allows for a more detailed analysis of the thunderstorms than a either single channel alone (Fig 3). This sandwich combo was created using a VIS linear color scale with a semi-transparent IR overlay, and can be found on the STOR VLAB page. The procedure maintains details from the VIS while also including quantitative information from the IR that can be visualized and sampled. Features such as OTs and AACPs, as well as cooling/warning trends, are easily diagnosed in the imagery. Numerous NWS severe thunderstorm and tornado warnings were issued with these storms, and are shown in the animation. Note, while the base of the storms fall within the polygons, the storm tops are oriented north of the polygons due to parallax. These storms did produce tornados, severe hail, and severe wind gusts.

Further south in east Texas, a long-lived severe thunderstorm produced a track of tornado and severe hail/wind reports. This storm had an impressive appearance in GOES-East imagery, with persistent and large OTs, long-lived AACPs, and very cold tops (<-80C at times). A simple procedure in AWIPS combines the aforementioned VIS-IR sandwich combo with IR imagery to allow for a smooth transition between the two products (make the low end of the VIS transparent). A 2-hour animation of GOES-East 1-min imagery centered over the the storm using this procedure is shown in Figure 4.

A longer, 5-min animation shows the full 10-hr duration of the storm, and instead uses the “Daylight Transition” image combination feature available in AWIPS (Fig 5). Feature-following zoom is also used to provide a storm relative view of convective evolution.

Finally, a similar animation but highlighting GLM Flash Extent Density is available in Figure 6. The storm consistently produces an abundance of total lightning, with periodic lightning jumps/dips throughout the evolution.

Bill Line, NESDIS/CIRA

During the evening of April 21, 2020, several supercells developed in the Texas Panhandle into western Oklahoma producing hail resulting in numerous reports. Not only was the size of hail large, the amount of hail that fell was significant as noted by reports of accumulated hail of several inches deep. As storms snailed away from their deposited hail swaths, GOES-16 was there to view these swaths. This post will showcase how forecasters can view freshly deposited hail swaths using multispectral imagery at night.

Figure 1 depicts the Nighttime Microphysics RGB with the “clean” longwave infrared band (Band 13, 10.3 um) overlaid while making any temperatures warmer than -25 C transparent. This allows for cloud layer and phase information to be provided within the Nighttime Microphysics RGB while also monitoring very cold cloud top temperatures associated with severe storms as well as overshooting tops denoting an updraft penetrating into the tropopause. As the convective clouds and overshooting tops pull away from the border of the Texas Panhandle and western Oklahoma, notice one to three subtle, magenta-colored lines oriented northwest to southeast as skies clear (see annotated images here and here). These lines correlate well with highest reflectivities that had passed over previously in time as well as with storm reports of hail. These lines are a result of altered environmental and ground temperatures (in this case cooling) from the copious amounts of hail left behind their parent storms.

While the default composition ranges of the Nighttime Microphysics RGB within AWIPS-2 allow for just subtle signatures within the imagery, there is room for adjustment to enhance this signal. A good place to start is by looking at a 4 panel display of the RGB (Figure 2) being discussed and each of the its components set to a black to white scale with the RGB’s default ranges.

Sample the signal in question within each of the RGB’s components and adjust the range within the components until there is good contrast between the signal and background. Once the component’s ranges are adjusted to your liking, adjust them within the RGB itself. In this case, there was room for improvement mainly within the red component (the Split Window Difference, 10.3-12.3 um) and the blue component (“Clean” IR, Band 13, 10.3 um). However when adjusting the red component, the RGB itself became too saturated in red coloring. Therefore we can tone down the saturation of red by lowering the red component’s gamma. Figure 3 is what the new composition looks like now (click here for actual recipe values).

Do you think the hail swaths show up better in the adjustments as shown in Figure 4? Making an adjustment on the fly works in this case, but might not for all cases. Thus adjustments to RGBs are advised to only be made on a case by case basis, especially with those having a large dependency on infrared temperatures. It is also worth noting that this approach of using multispectral satellite imagery to observe accumulated hail swaths is dependent on cloud-free skies as well as enough hail to actually make an alteration to the ambient environmental and ground temperatures.

So how does this apply to IDSS? Well besides increasing overall situational awareness, noting hail swaths in near real time lends confidence in derived products like MRMS MESH tracks through observations. This could also allow forecasters to help core partners like DOT maintenance crews target areas for hail removal should they request it. Additionally, this could also provide an opportunity for target LSR intel gathering, or even safety messaging as accumulated hail can produce hazardous travel conditions through slick roadways and reduced visibility should hail fog form (which by the way is also detectable in this approach through the use of the 3.9-10.3 um “Fog/Low Stratus” Brightness Temperature Difference as the Nighttime Microphysics RGB’s green component).

Carl Jones
Meteorologist
NWS Grand Forks