Satellite Liaison Blog

Gusty winds, low relative humidity, and dry fuels resulted in high fire danger across parts of Colorado in mid-November, 2021. These conditions allowed for the growth of the Kruger Rock Fire near Estes Park, CO on 16 Nov 2021.

GOES-East shortwave IR imagery, however, did not detect the wildfire hot spot during the morning and afternoon, despite the fire quickly growing to over 75 acres. However, when one viewed the GOES-West shortwave IR imagery, the hot spot was easily diagnosed from initiation through the afternoon. An animation comparing SWIR imagery from GOES-East and GOES-West is shown in Figure 1.

The explanation for this appears to be a couple of factors. The most significant factor was a persistent and optically thick mountain wave cloud, oriented above a point just east of the fire, blocking the heat signal to GOES-East, but not to GOES-West. Note that at 105W, this location is in the middle (longitude) of the two GOES satellite (137.2W and 75.2W), meaning pixel sizes are similar. Another 2-panel GOES-East/West comparison is shown in Figure 2, but this time comparing Natural Fire Color RGB Imagery, which shows the hot spot and cloud cover in the same image. GOES-West has an unobstructed view of the fire, while a cloud appears to mask the view from GOES-East. A similar case of a mountain wave cloud blocking a wildfire hot spot signature occured last eyar with the Cameron Peak Fire.

Another factor that may have weakened the SWIR hot spot signal from GOES-East compared to GOES-West was that the wildfire was burning on a west facing slope. Therefore, while the GOES-West satellite had a direct and unobstructed view of the heat signature, the GOES-East satellite view of the heat signature may have been partially degraded due to terrain blocking. Figure 3 shows the satellite comparison again, but a little later in the afternoon as the primary wave cloud shifted to the east. The hot spot signature becomes apparent in the GOES-East imagery, but not to the degree that it was earlier from GOES-West. Note, during the same time period, additional clouds developing from the west begin to obstruct the view of the hot spot from GOES-West. Not a clear comparison, unfortunately, so the influence of terrain is not straightforward with this case.

VIIRS passes during the early afternoon provided yet another view that captured the wildfire hot spot signal during the early afternoon. The VIIRS SWIR imagery is available at 375 m resolution from the I bands (compared to 2 km at nadir from ABI), and is a component of the Natural Fire Color RGB (Fig 4). Parallax causing shifting of clouds also plays a role here, from scan to scan, depending on where the viewing target lies within the VIIRS swath. Terrain correction allows the hot spot to remain at the same location from scan to scan. The ~1850 UTC scan captured the fire heat signature beneath the cloud, albeit under what appeared to be a relatively transparent one. Subsequent scans detected the hot spot from the clear sky.

The example underscores the importance of forecasters viewing imagery from both GOES-East and GOES-West when possible in such situations. Timely VIIRS imagery can also be useful in determining the exact location of the hot spot consistently from scan to scan and in more detail, and when viewing among clouds and on terrain.

Bill Line, NESDIS and CIRA

GOES Imagery has long been a valuable tool for fog detection and tracking, both during the day and night. With GOES ABI, forecasters are able analyse low clouds and fog in even better detail, spatial and temporally. Further, the additional spectral bands allow for more insight into the features through the generation of multispectral products such as RGBs.

NWS Bismark, ND forecasters leveraged GOES-East ABI Imagery in tandem with area webcams and surface obs to analyze fog evolution prior to and after sunrise on 09 Nov 2021, informing their forecast decision-making. While GOES imagery provides a great look at the spatial extent of low clouds and fog and their evolution with time, the webcams and surface obs allow the user to determine actual surface conditions associated with the satellite cloud feature. At 1213 UTC, the forecaster issued an update to the Area Forecast Discussion that read: “GOES Nighttime Microphysics shows extent of fog in southwest North Dakota, possibly nudging into the south central this morning. Based on cameras and coverage depicted on satellite imagery, coverage is somewhat patchy, but has lowered visibility at Hettinger down to 1/4 mile. An SPS was issued to address fog this morning for this area. Fog will gradually dissipate mid-morning as boundary layer mixing increases after sunrise.”

The Nighttime Microphysics RGB imagery that goes with the above discussion captures the low clouds and fog as a light orange/light brown/yellow color, compared to the pink clear-sky land background, blue/magenta bodies of water, and red (thick) to black (thin) high clouds (Figure 1). The imagery shows the development and northward surge of low clouds and fog from beneath exiting upper level cloud cover over a 5-hour period ending just prior to sunrise. The webcams (and METARs) confirmed conditions beneath the suspected low clouds, per the discussion.

Forecasters continued to analyze satellite imagery and webcams after sunrise to inform their decision-making, as the low clouds and fog hung around. At 1505 UTC, Forecasters wrote: “Latest satellite and webcams indicate fog over the southwest and south central is beginning to dissipate. We did extend the areas of fog farther east and extend the SPS for fog through 16 UTC. Otherwise no changes to the current forecast.” During the daytime, multispectral products such as the Day Cloud Phase Distinction (Fig 2) and Day Snow Fog (Fig 3) RGBs may be utilized, in addition to visible imagery (Fig 4). In the three hour period following sunrise, these animations show the fog and low clouds dissipating through the morning hours, with surface conditions confirmed by webcams and METARs.

Bill Line, NESDIS and CIRA

A series of potent mid-latitude cyclones brought an active period of weather to much of the US during the end of October. GOES Water Vapor imagery with GLM overlay captures the large scale features influencing the active period from the morning of Oct 24 through the morning of Oct 28 (Fig 1). The animation begins with the much discussed atmospheric river pushing across the west coast, characterized by relatively cool BTs in the water vapor imagery due to the presence of abundant atmospheric moisture and cloudiness.. The associated shortwave makes landfall on the US coast thereafter and advances across the southwest US, as drying/descending air coupled with cooling ascending air is diagnosed in the water vapor imagery with the amplifying trough. During the second half of the animation, this system continues east across the southern plains into the southeast, resulting in several rounds of severe weather. At the same time, another shortwave trough exits the midwest into the northeast, forcing the development of severe weather along its path. This system merges with another shortwave moving northeast along the east coast, developing into a strong nor’easter. The pulses of severe weather are apparent as increase in cloud cover (very cold BTs) and development of lightning (yellow-red overlay).

A GOES water vapor imagery analysis, typical of NWS forecasters, was presented by NWS AMA in their AM 26 Oct AFD ahead of expected severe weather forced by the approaching western US system: “The latest water vapor imagery reveals very dry subsiding air moving along the base of an upper level trough near the AZ/CA border. Lift associated with this system is now evident in east central AZ up across the Rocky Mountains. As this system advances east, strong jet level winds will move into the Panhandles, with some stacked jet alignment across the western zones this afternoon.”

A great water vapor analysis was presented by NWS ALY for the East Coast events during the morning of 26 Oct: “GOES 16 water vapor imagery shows the 3 upper-level features that will come together over the next several hours to produce a rapidly deepening coastal low. There is a southern stream shortwave off the East Coast, another shortwave currently over Virginia and North Carolina, and a remnant upper low over Michigan. What was initially the primary surface low weakened earlier tonight over Pennsylvania, and the new coastal low has developed in response to the southern stream disturbance off the Coast of the Carolinas and has already intensified to 995 mb. With this classic Miller Type B storm track, this coastal low is expected to continue to intensify as it moves northeastward during the day today.”

Focusing on 26 Oct, the western shortwave trough brought blowing dust and severe weather to the southern US plains. The split window difference (with IRW overlay for cold BTs), captured several plumes of blowing dust (low to neg SWD, or dark gray to black in this scale), including in southeast AZ, Chihuahuan Desert, and west Texas all within the strong/dry southwest flow (Fig 2). The SWD also reveals the presence of the dryline extending north across west TX through west Kansas (sudden transition from dark grey (dry) to light gray (moist), west to east). Convection initiates along this boundary toward the end of the animation.

Related to the blowing Dust, NWS EPZ wrote in their PM 26 Oct AFD: “Blowing dust still a concern, not many plumes visible from satellite though a few obs sites are reporting visby reductions. Willcox Playa [in southeast AZ] looks like it is starting to shed blowing dust off to the east across the Lordsburg area.”

The GOES TPW product also captures the deeper moisture gradient present along the N-S oriented dryline, along which convection subsequently develops (Fig 3).

Focusing on convective initiation along the dryline over the W OK/TX panhandle border, a 1-min GOES-East VIS/DCPD RGB side-by-side animation shows the value of the RGB (Fig 4). By 2222 UTC, the DCPD RGB begins to show glaciation within the cu field (transition from cyan to green to yellow), signification initiation is imminent. Meanwhile, in the VIS, one can diagnose vertical cloud growth and clumping of cu, but cannot classify glaciation. Note, the recipe for the DCPD RGB was modified slightly in this case, lowering the upper end of the VIS and Snow/Ice band components to account for the lower sun angle and resulting lower reflectance values.

Convection would go on to initiate, with the first lightning detected by GLM at 2248 UTC, and first convective warning at 2321 UTC (Fig 5).

An IR animation shows the evolution of convection, including severe storms, across Oklahoma through the evening (Fig 6). The GLM Flash points overlay (as opposed to the gridded overlay) allows one to view the IR image and GLM data within a single image without blocking the important cloud top information of the IR. The rapid dropoff of lightning activity toward the end of the animation is coincident with cloud top warming and weakening of the convective line.

The VIIRS DNB/NCC product captured active convection further south slightly after the animation above (Fig 7a and 7b). The two images provide a more detailed view of convection (visible imagery at night), and even captures a lightning flash, in the second image, associated with convection developing ahead of the main line in southern Texas.

Another line of severe storms developed across the southeast US on the 27th. GOES-East 1-min VIS and GLM flash points captured individual convective updrafts and potentially stronger storms embedded within the broader line of convection (Fig 8).

Bill Line, NESDIS and CIRA

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