Satellite Liaison Blog

The period of 09/27/21 to 10/02/21 was very stormy stretching from the western Bering Sea to the British Columbia and Alaska panhandle regions. Three storm-force lows moved generally west to east with a final storm achieving hurricane force before making landfall just north of Sitka, Alaska. The AirMass RGB imagery from Himawari and GOES-17 along with scatterometer (ASCAT) data available from the Metop-A/B/C satellites provides forecasters at the NWS Ocean Prediction Center with some powerful tools to monitor and predict this series of high impact storms. This blog post will show some examples of imagery, surface maps, and ASCAT data used during this time.

A picture or in this case, an animation is worth a million words. There is so much happening in this animation above that it’s hard to explain any one feature without your eyes being drawn to another feature. There are two storm force lows, a couple gales, and a recurving typhoon. Can you tell which is which? I will break down what is happening here in the following images.

Now with the NWS/OPC surface analyses overlaid, you can tell where the surface low pressure systems, high pressure systems, and recurving typhoon (lower left) are located throughout the animation. For our first storm-force low of interest, I’ll show some AirMass RGB and ASCAT imagery along with surface maps to show the portion of the storm that is the strongest. For the AirMass RGB imagery, the red colors indicate descending dry air that is rich in ozone and potential vorticity. This means the brighter the red coloring, the stronger the warming (drying) in the 350 mb to 700 mb level and the more ozone and potential vorticity available to the storm system. The green coloring is higher moisture and typically, a warmer mid-troposphere, while the bluish, purple coloring is higher moisture, but cooler mid-troposphere.

As you see in the above images, the OPC surface map at 0000 UTC on 09/30/21 was very active with two storm-force lows, a developing storm force in the eastern Pacific, a couple gales, and a recurving typhoon near Japan. The strongest storm force is the one in the northern Bering Sea, west of Alaska with winds of 55-60 kt (65-70 mph) near the Siberian coast (white circle in ASCAT image) as a barrier jet forms as the air quickly converges into a meso- to micro-scale jet due to the strong storm circulation and terrain near the coast. This storm would fill and drop southeast rather fast (>30 kt/35 mph) and begin to merge with the developing gale (near the forecast 998 mb label) south of the Aleutians.

The two animations above show the next phase of this multi-day evolution ending with the strong hurricane-force low that moves towards the Alaska panhandle. Note how fast features are moving south of the Aleutian Islands into the Gulf of Alaska thanks to a strong upper-level jet. I’ll break down this series of storms below.

In this next set of images, another storm-force low is developing as it approaches Queen Charlotte Island, British Columbia, Canada at 0000 UTC on 09/30/21. At this time the storm is producing winds to 45 kt (50 mph), but strengthening rapidly. By 0600 UTC on 09/30/21, the storm achieves storm-force verified by excellent ASCAT coverage with winds 50-55 kt (60-65 mph) nearing the southern tip of Queen Charlotte Island and the Hecate Strait. The storm makes landfall the following hour and later dissipates over the mountains of British Columbia.

Although I won’t cover this next storm-force low beyond the ASCAT image above, winds did approach 45-50 kt (50-55 mph) near southwest Kodiak Island (white circle) which just meets the storm-force warning criteria. This low would eventually provide additional vorticity advection for the hurricane-force low farther south.

The above sequence of GOES-17 AirMass RGB imagery shows the evolution of the hurricane-force low that develops along an active baroclinic zone. These types of storm evolutions are called Shapiro-Keyser cyclogenesis and can lead to some of the strongest (wind perspective) extratropical cyclones.

Thanks to some very timely ASCAT-C overpasses, the hurricane-force low was verified with winds peaking around 75 kt (85 mph), which is very intense for a non-tropical cyclone.

The wind/wave analysis above shows significant wave heights associated with the hurricane-force approaching 41 ft! It is possible individual waves were significantly higher.

Although not available in real-time for forecasters, the above SAR image shows some incredible detail in the winds field associated with the hurricane-force low as it approached Sitka, Alaska during the early morning hours of 10/02/21. Note the strong wind gradient to the northwest of Queen Charlotte Island which depicts the powerful cold front. This was associated with a squall line that produced some rare lightning strikes and wind gusts of around 95 kt (109 mph) at the Ketchikan Airport in the southern Alaska panhandle. Please see the NWS Juneau twitter feed for more information. Meanwhile, multiple wind gusts of 70-90 mph were reported along the coast, while the hurricane-force sustained winds slowly diminished as the storm filled and approached land.

This opening act to the fall/winter baroclinic season in the North Pacific was very impressive and with a Sea Surface Temperature Anomaly map that looks this warm and a strong temperature anomaly gradient across the North Pacific, I expect we will be seeing a plethora of storm and hurricane-force lows in the coming weeks. In the meantime, it has quieted down, though I assume it’s very temporary.

Thank you for reading!

The active wildfire season over the western US this summer has resulted in periodic days of smokey skies downstream. Forecasters are concerned with the detection of smoke since it has impacts on local air quality and visibility, and is the source of public inquiries. During the daytime, smoke is easily diagnosed by forecasters using GOES and VIIRS visible, near-IR and multispectral products, such as Geocolor. At night and in the absence of these channels/products, smoke is much more difficult to discern using IR-only-based products save for the most dense of smoke plumes. For example, ABI IRW imagery from the evening of 19 Sep 2021 is shown in Fig 1. Signs of smoke are not readily apparent.

A nighttime smoke detection option available to forecasters in AWIPS is the VIIRS Day Night Band (DNB) Near Constant Contrast (NCC) product. Available from both SNPP and NOAA-20, this product is available 2-4 times per night over a given location across the CONUS due to overlapping swaths. During the early morning, pre-dawn hours of 19 Sep 2021, forecasters at NWS Bismark, ND were analyzing the NCC imagery. They noted in surface obs slightly reduced visibility at locations within the CWA (8 SM in southwest ND), and highlighted in an AFD update: “VIIRS Near Constant Contrast satellite product at 08Z shows areas of smoke across eastern Wyoming and Montana, pushing into western North Dakota.” Figure 2 captures the 08Z NCC product at hand.

An animation of the three overnight VIIRS passes captures the evolution of smoke across the region (Fig 3). The smoke becomes less apparent later in the evening with shifting viewing angle, but can still be tracked with careful analysis. During the 1.5 hour period, the smoke is observed shifting north and east across the BIS CWA.

BIS went on to mention: “HRRR Smoke guidance indicates smoke moving eastward alongside the thermal ridge.” The VIIRS NCC provides a check on HRRR smoke model analyses and forecasts overnight (Fig 4). Combined, the forecaster could make a assessment on where smoke was at present, and where its influence would be during the day.

This case provides a great example of a forecaster leveraging the VIIRS NCC product to diagnose smoke coverage across the region overnight, confirm the likely source of reduced visibility, and provide a check on model smoke output.

Bill Line, NESDIS and CIRA

Severe thunderstorms developed along a cold front across the Upper Midwest and Canada during the afternoon of 16 Sep 2021. During the early afternoon, NWS/MPX (Twin Cities/Chanhassen, MN) forecasters were monitoring various GOES-East products to assess convective potential. From the MPX AFD: “Regional radar and enhanced satellite imagery is showing convection developing along the international border in northwest Minnesota. RGB enhanced satellite does show more glaciated clouds across northern Minnesota with only water clouds across the central part of the state.” Given the analysis, while convection was developing further north, there was still quite some time before it would get started in central Minnesota, but clear skies would allow for instability to increase ahead of the front. Figure 1 depicts the Day Cloud Phase Distinction RGB being discussed up to the point of AFD publication.

The discussion continues: “In addition to the RGB images, the satellite derived stability indices does show an enhanced area of both higher K-Indices, and CAPE values over west central Minnesota this afternoon. … once the cold front
arrives later this afternoon/early evening along this enhanced area of greater instability and moisture, convection should develop.” The discussion is captured in Figure 2 and 3. CAPE values are increasing and arrive at levels sufficient for severe convection, while K-index values allude to scattered-to-numerous thunderstorm coverage. The analysis is a great example of utilizing various satellite tools to assess the current convective environment and produce a short-term forecast based on current trends.

Shortly thereafter (at 2047 UTC), a NWS/SPC mesoscale discussion was issued for much of Minnesota ahead of the CF, with a 80% chance of watch issuance. The MD mentions: “Visible satellite imagery further indicates inhibition has rapidly eroded as CU field across the area has become more agitated with vertical development over the past hour or so. While CAMs guidance suggest convective initiation may not occur until closer to 00z, observational trends suggest storms could develop sooner.” The visible imagery discussed is shown in Figure 4 ending just after the issuance of the MD, with corresponding Day Cloud Phase Distinction RGB imagery in Figure 5. Both capture the vertical cu development in north-central MPX and southwest DLH, with the RGB also revealing the glaciation of cumulus clouds (cyan changing to bright green/yellow). Convection would initiate over the next hour (first GLM flash at 2153 UTC), and mature over the following hour (first warning, TOR, at 2245 UTC). This is a great example of a forecaster relying on observational trends in decision-making and as a check on model guidance. In this case, storms did indeed develop sooner than was suggested in CAM guidance, per the forecaster’s discussion.

Convention would continue to grow upscale thereafter, with numerous severe thunderstorm and tornado warnings issued across MPX’s area (Fig 6). These storms produced large hail (to 2.5″ in diameter) and strong/damaging winds. The 1-min visible imagery near sunset reveals cloud texture well with increased shadowing, allowing one to easily diagnose features such as OTs and AACPs associated with individual updrafts.

A longer VIS animation with GOES CAPE and surface obs overlay shows convective evolution along/ahead of the cold front and within the CAPE max (Fig 7).

Severe convection also developed north of the border in southwest Ontario. These storms were moving quick, with Env Canada warnings listing storm motion at around 60 mph! The GOES-East 1-min mesoscale sector included this area, with visible imagery and AWIPS tools confirming the fast storm movement (Fig 8).

A storm relative animation of the 1-min VIS+IR sandwich better characterizes the large overshooting top and downstream warm anomaly with this storm. The animation also reveals the influence of the storm on the surrounding environment, particularly the appearance of low stratus bending toward the storm updraft in the inflow region of the system.

Bill Line, NESDIS and CIRA

Hurricane Ida made landfall along the Louisiana coast on 29 August 2021 as a category 4 Hurricane packing sustained wind speeds of 150 mph. Numerous wind gusts over 60 mph were measured at the surface onshore, including a few measured gusts over 100 mph. There were numerous reports of flash flooding, with a large swath of 6+” rainfall falling in the <24-hr period (Fig 1). There was also significant storm surge along the coast. This post will share select NOAA satellite imagery capturing Hurricane Ida. All imagery was created in AWIPS (unless otherwise noted).

GOES-East mesoscale sector (1-min) imagery was available for Ida throughout its evolution. The center of circulation (eye) cleared out quickly during a 2.5-hour period on the 28th, shown here in 1-min VIS (Fig 2). The health of the eye and surrounding thunderstorm activity can be studied in detail with the 1-min, 500 m resolution imagery.

At sunrise on the 29th, GOES-East 1-min VIS revealed the mature eye of the now major hurricane as it approached the Louisiana coast. Smaller scale circulations (mesovorticies) can be diagnosed in the 1-min VIS within the eye of the hurricane from sunrise on the 29th through landfall (Fig 3). The sun angle at sunrise allows the opportunity to investigate eyewall thunderstorm activity in better detail given the shadowing, as well as abundant gravity wave activity atop the clouds emanating away from the eye.

During a similar time period, a zoomed out view of GOES-East Natural Color Imagery characterizes the size of the storm with respect to the 1000 km x 1000 km mesoscale sector. GOES-East GLM Flash Points are overlaid (Fig 4).

A longer, 2-min resolution animation of visible imagery captures the period of Ida evolution from sunrise around 1217 UTC to to landfall at 1655 UTC (Fig 5).

GOES-East 2-min VIS+IR sandwich imagery combines the high detail of the VIS with the qualitative (brightness temperature) information of the IR into a single image during the period following landfall (Fig 6).

The full daytime evolution of the Ida is shown in 5-min CONUS VIS imagery in the following feature relative animation (Fig 7). The eye of the storm maintains itself well inland, possibly due in part to the marshlands along/near the coast.

An animation of VIS during the day and IR during the night with GLM flash points presents the evolution of Tornado (red), Severe Thunderstorm (yellow), Extreme Wind (magenta), Marine (cyan) and Flash Flood (green) Warnings with respect to the path of the hurricane and lightning progression (Fig 8).

The full evolution of Ida from just prior to becoming a hurricane to just after being downgraded to a tropical storm is shown in 30-min Geocolor+GLM Imagery (Fig 9) and VIS+IR sandwich daytime imagery transitioning to IR at night (Fig 10).

S-NPP and NOAA-20 VIIRS instruments also captured detailed views of Ida. The Day Night Band Near Constant Contrast product provided a detailed (750 m) “visible” imagery at night (Fig 11; expand Aug 28, 29, 30).

A VIIRS pass shortly after landfall on the 30th depicted the detailed IR structure of the storm (Fig 12).

Hurricane Ida made landfall in Louisiana on the 16-year university of Hurricane Katrina. A comparison between GOES-12 imagery of Katrina and GOES-16 imagery of Ida can be found on the STAR website, courtesy of Matthew Jochum, STAR.

GOES-17 (GOES-West) full disk imagery also captured Hurricane Ida with 10-min resolution (Fig 13 and 14). The high viewing angle provides an alternative perspective of the storm compared to that from GOES-East and VIIRS, specifically additional texture detail within the eye and surrounding convection. Full resolution GOES-17 iamgery created in McIDAS.

Ida Remnants continued north across the eastern United States through the early week. On 01 Sep, the storm brought an abundance of moisture to the northeast, resulting in heavy rain and widespread flash flooding, in addition to severe thunderstorms and tornados. A long animation of GOES-East IR and GLM flash points with NWS warning polygons overlaid captures the evolution of the storm through the northeast on the 1st and associated NWS warnings (Fig 15).

Focusing on the New York City area, GOES-East IR imagery reveals Ida associated thunderstorms that resulted in considerable flash flooding. Persistent cold and cooling cloud tops (< -70C) and overshooting tops can be diagnosed in the imagery over the region during the 4-hour period.

GOES-East hourly upper-level water vapor imagery shows the evolution of Ida from landfall on the 29th through exit of the northeast US on the 2nd (Figure 17). The imagery shows the increase in deep moisture across the eastern US during the period, and interaction of Ida with a shortwave trough and increasing mid-upper-level flow as the storm progressed north. Dry/descending air is diagnosed expanding across the eastern US in the wake of Ida.

ill Line, NESDIS and CIRA

There have been numerous large wildfires across the western US in recent years. After the fire reaches 100% containment, the danger is not over. The wildfire completely changes the hydrology of the landscape due to loss of groundcover and altered soil chemistry resulting in hydrophobicity (Fig 1). Therefore, flash flooding and debris flow are major concerns to life and property over, around, and downstream of burn scars in the years following a wildfire. The characteristics of the burn scar are monitored closely, and rainfall thresholds for the possible occurrence of flash flooding are established and modified over time. Given the considerable threat, forecasters in NWS offices must monitor shower and thunderstorm development closely around burn scars. Not only are they issuing Flash Flood products, but they are in constant contact with core partners regarding the latest developments with regard to the flash flood threat.

Satellite imagery is a vital tool utilized by forecasters when monitoring convective development near burn scars. Considering many of the western fires occur in remote, high-terrain regions, radar coverage is often degraded or not available at all to forecasters (beam blockage, distance from radar), making satellite data even more important to forecasters during such burn scar flash flooding situations. One-minute imagery has particular value in these rapidly evolving situations, allowing forecasters to diagnose boundary interactions and convective trends as early as possible. The example in Figure 2 is from a 2018 Hayden Pass burn scar flash flood event in which 1-min GOES-East VIS was leveraged for tracking convective growth, minute-by-minute, under high level cloud debris near a burn scar in a radar poor region. Forecasters are strongly encouraged to request a mesoscale sector when showers and thunderstorms are forecast in the vicinity of burn scars.

Prior to the development of the first cloud, forecasters monitor water vapor imagery for deep moisture availability and for subtle shortwave troughs that may force downstream convective initiation. Using a 30 July 2021 BOU burn scar flash flood event as an example (East Troublesome and Cameron Peak burn areas), subtle shortwaves could be diagnosed pushing north along the western periphery of a broad central US Ridge and within a stream of enhanced southerly moisture feed (Fig 3). The shortwaves advanced north across CO and eventually into the N CO Rockies, aiding in afternoon/evening convective initiation along the far eastern portion of the moisture stream and within weak mid-upper level flow.

Satellite products, specifically the Day Cloud Phase Distinction (DCPD) RGB, have particular value in the pre-convective environment, when forecasters are using it to monitor cumulus cloud growth and signs for convective initiation. The DCPD RGB captures initial cumulus cloud development (aqua colors), their initial vertical growth and eventual glaciation (aqua > green), and finally convective initiation and rapid vertical growth (green > yellow). By observing the early signs of near-future convective initiation near a burn scar (prior to any radar echoes), forecasters can provide very early alerts to their core partners detailing their latest thoughts on flash flooding risks over the burn scars. Figure 4 from the BOU example shows DCPD RGB evolution prior to the first Flash Flood Warnings. Cu are observed developing along the high terrain through the morning including over the burn scars, with several areas of glaciation developing by 1731 UTC over/near the burn scars. This would be a decision point for forecasters to alert partners of the growing convective threat near the burn scars.

Playing the animation through the afternoon, areas of the cu field continued to glaciate, with heavier rain showers and thunderstorms eventually developing over the burn scars resulting in the issuance of Flash Flood Warnings (Fig 5).

Another DCPD RGB example comes from the Grizzly Creek Burn scar on 03 July 2021. Forecasters monitoring trends in the 1-min RGB imagery across the area acknowledged the increasing potential for near-future development just upstream of the burn scar by 1951 UTC (Fig 6). Initiation had occurred west and east of the burn scar, while more immature cu were beginning to develop just to the northwest (upstream) of the burn scar in an area of untapped instability. Based on the favorable environment, likely storm motion, and trends in satellite imagery, a Flash Flood Watch was issued for the burn area at 2004 UTC.

Glaciation would occur shortly thereafter, followed by the development of thunderstorms and their advancement over the burn scar, per the 1-min DCPD RGB imagery. A Flash Flood Warning was issued for the burn scar at 2104 UTC, primarily based on the development of a lofted thunderstorm core diagnosed in radar imagery. The end result was numerous debris flows over interstate 70 around 2130 UTC.

Similarly and as convection continues to grow, VIS+IR Sandwich imagery is utilized by forecasters to monitor for growing convective threats to burn scars. The imagery maintains the high detail from the VIS, which is important for diagnosing cumulus cloud and storm top trends and details. At the same time, the imagery incorporates quantitative information (IR Brightness temperatures) for forecasters to further assess trends in convective development and heavy rain rate potential. Cooling convective tops represent strengthening thunderstorms, while, just as important, warming tops (and losing texture) signal a weakening trend. The example in Figure 8 occurs during the same time period as that in Figure 5. Areas of rapid cooling and coldest convective cloud tops are easily found in the sandwich imagery, and correlate to greatest heavy rain potential (and FFWs when over burn scars).

Another important use of these GOES imagery products, particularly far from the satellite subpoint, is to track the movement of the thunderstorm updraft. Oftentimes, these summertime thunderstorms over the high terrain develop in areas of weak steering flow, with anvil motion deviating considerably from actual storm movement. Therefore, it is important for forecasters to analyze the movement of the updraft in satellite imagery if possible, as slow moving storms anchored to the terrain pose an elevated flash flood threat. Finally, one must account for parallax when considering the location of thunderstorms with respect to the burn scar.

Bill Line (NESDIS and CIRA)

Input from Klint Skelly (NWS/PUB), Paul Schlatter (NWS/BOU), Michael Charnick (NWS/CYS, previously NWS/GJT)

GOES-15 began planned supplemental operations on Aug 4 to provide additional Eastern Pacific tropical cyclone support due to the operational impacts from the GOES-17 ABI Loop Heat Pipe anomaly (details here) This support is planned to continue through Sep 3. Given the coverage over the western US, the GOES-15 Imager also captured the intense wildfire activity, which allowed for comparisons with the newer GOES-17 ABI. Example comparisons between the two Imagers remind us of some of the improvements we have in wildfire monitoring with the GOES-R era satellites.

Starting with the 3.9 um SWIR imagery, abundant wildfire hot spots are diagnosed from both satellites across northern California on 08 Aug 2021 (Fig 1). However, the smaller/cooler fires that appear as faint hot spots in the ABI imagery, are very difficult to impossible to discern in the GOES-15 Imagery due to the poorer spatial resolution. The difference in temporal cadences is obvious, with the routine 5-minute imagery of the ABI allowing for smoother animations, for the ability to detect fires earlier, and for easier tracking of fire evolution with time. The image navigation from ABI is significantly better than that of GOES-15 at this point, with no noticeable movement from image to image. Finally, the saturation temperature in the ABI SWIR channel is much higher than previously.

A similar comparison is made between the VIS channels in order to observe the smoke plumes (Fig 2). In addition to those points referenced previously, the higher spatial resolution in the VIS makes clearer the areas of smoke including their source points, smoke edges, and development of pyrocu.

The 5-min ABI imagery shown above is from the routinely available CONUS sector. Of course, forecasters can request 1-min mesoscale imagery whenever desired, allowing for wildfire hot spots and smoke plumes to be detected even earlier, and tracked in more detail (Fig 3).

Bill Line, NESDIS and CIRA

Starting the day of June 16, 2021, a plume of elevated smoke originating from the Robertson Draw fire in Montana began moving over the Dakotas. Day shift forecasters at the Grand Forks, ND, NWS office were briefed of this smoke moving towards their CWA, possibly impacting daytime temperatures and in turn, potential convection later in the afternoon along a cold fropa. With the expectation of smoke hindering the amount of insolation during peak heating hours, forecasters set out to track this smoke using GOES imagery, namely visible imagery from ABI’s channels 1 and 2, CIRA’s Geocolor RGB, as well as the GOES Aerosol Optical Depth product.

While plume guidance was available from the HRRR-smoke model, close observation of the elevated smoke using satellite imagery was performed to truly define the spatial bounds in an effort to set an observed trajectory. Given the expected absence of large changes within the mid level environment, a persistence forecast using the smoke’s observed trajectory was performed using the Distance Speed and Time of Arrival tools within AWIPS. Using both persistence trajectory forecast and model guidance, an assessment could be made to highlight the geographical areas that would most likely be under veil of elevated smoke during peak heating hours (roughly thought to be between 15 – 00 UTC during this time of year), thus indicating areas that have best chance of seeing some loss of insolation.

Armed with the knowledge of Channel 1’s superior aerosol detection, forecasters looked at this imagery to start the process of the smoke’s aerial extent and tracking. However, default colormap ranges within AWIPS made boundary definition of the smoke somewhat difficult during the low light hours of the morning, with little contrast between smoke and clear sky. Luckily, some minor colormap manipulation helped draw out the feature of interest, i.e. the area of smoke. The default minimum/maximum colormap ranges of 0-130 were edited to 10-30. Figure 1 shows the comparison between the default AWIPS range versus the constrained colormap range. While the edited range overexposed clouds within the area of smoke as well as underexposed land features, this was tolerable as it better revealed the spatial bounds of the smoke, from which trajectory analysis could made.

Figure 2 compares Channel 1 (0.47 um ‘blue’ visible band) to Channel 2 (0.64 um ‘red’ visible band), both of which have their colormap ranges edited to 10-30 and 5-30, respectively. Notice Channel 1’s superior ability to reveal the smoke compared to Channel 2. This is due to Channel 1’s sensitivity near the 0.47 um wavelength which can detect scattered solar radiation by atmospheric constituents better than Channel 2’s near 0.64 um wavelength, especially by larger aerosol particulates like dust, smoke, and pollutants. And perhaps the muted detail from land surface features (again, from Channel 1’s increased sensitivity to scattered radiation) as well as lower spatial resolution within Channel 1 compared to Channel 2 helps draw out the overall feature of interest, i.e. smoke.

The area of smoke was just within viewing range of GOES-East’s Aerosol Optical Depth product (AOD), too. This product helped increase confidence of the smoke’s extent near the leading and trailing edges, especially further into the day as the visual enhancement of the smoke due to additional scattering lessened with a decreasing solar zenith angle. Figure 3 shows the Aerosol Optical Depth product overlaid on top of range edited Channel 1. Confidence was placed in the presence of smoke for values of AOD generally larger than ~0.2-0.4 (blue-cyan colored). Note the masked data within AOD as flagged by things like clouds and GOES-East’s local zenith angle greater than 60 degrees, as well as others. Even portions of the smoke itself was masked by the product algorithm’s quality flags, however it was assumed smoke was still present between the edges of higher AOD as confirmed by Channel 1 imagery.

While colormap range manipulation during times of low solar light has shown operational relevance, it may be worth mentioning how changing the colormap’s grayscale may affect appearance of the smoke within visible imagery. The “ease” of feature identification can depend upon the observer, and is where subjective analysis of imagery can vary from person to person. Figure 4 displays a four panel animation of Channel 1 with four different colormap configurations: left panels = square root grayscale, right panels = linear grayscale, top panels = AWIPS default 0-130 ranges, bottom panels = range edited 10-30. Which colormap configuration can you most easily track the smoke? Does time of day influence your ability to observe the spatial bounds of smoke between the different colormaps? How about the ranges?

The CIRA Geocolor RGB also helped reveal the area of smoke in addition to differentiating smoke from clouds, as shown in Figure 5.

Ultimately, smoke and clouds did effect temperatures within portions of the Red River Valley into northwest Minnesota by limiting the amount of heating during this day, although it is hard to tell which may have had more of an impact, further compounded upon forecast accuracy of a changing lower level thermodynamic environment associated with thermal ridging and moisture advection ahead of a cold front. Nevertheless, here is an example showing Fargo only topping out at 88 F, whereas the interquartile and deterministic NBM forecasts were all higher. This also likely played a role in lessening convective potential along a cold fropa that afternoon making for a more effective capping inversion. The lack of insolation had a role in the removal of a marginal risk within an update to the Day 1 convective outlook collaborated between FGF and SPC.

Carl Jones (NWS Grand Forks) and Bill Line (NESDIS and CIRA)

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