Satellite Liaison Blog

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

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

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

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

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

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

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

Bill Line, NESDIS and CIRA; Curtis Seaman, CIRA

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

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

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

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

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

Bill Line, NESDIS and CIRA

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

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

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

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

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

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

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

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

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

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

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

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

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

Carl Jones
Meteorologist
NWS Grand Forks

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

Some images from within the dust plume:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

— NWS Pueblo (@NWSPueblo) January 15, 2021

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

— NWS Amarillo (@NWSAmarillo) January 15, 2021

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

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

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

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

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

A shortwave trough digging southeast across the eastern Rockies and into the high plains sent a cold front south across the region during the overnight hours early on 14 Jan. Evolution of the shortwave and associated cold front can be analyzed in GOES Water vapor imagery from the 13th through the 14th (Fig 1). An overlay of RAP 250 mb wind speed shows the development of a 150+ knot (red contour) jet in relation to the water vapor features. The jet becomes increasingly amplified as it digs south on the backside of the broader trough and as the western US ridge builds. Fast moving high clouds are observed in the location of the jet core, along with a temperature gradient (cold to warm poleward) across the jet. Finally, plentiful gravity waves are apparent, many in association with the high terrain, throughout the animation, representing areas of potential aircraft turbulence.

Winds behind the front increased during the morning of the 14th, resulting in areas of blowing dust. Viewing GOES-East visible and geocolor imagery alone, however, the lofted dust is difficult to discern (Fig 2 and 3).

Bringing in IR based products, split window difference in Fig 4 and Dust-Fire RGB in Fig 5, the lofted dust becomes more apparent across southeast CO and southwest Kansas into the OK/TX panhandles and eastern NM. Note, for the SWD product, the VIS-Square-Root color table was applied with a range of -1 to 12. This allows the lofted dust signature on the low end of the range to pop (dark gray to black), while ensuring high clouds on the upper end of the scale do not become washed out (light gray to white).

The GOES-East DEBRA-Dust product, shown here as a semi-transparent overlay on Geocolor, also captures portions, but not all, of the blowing dust in the area (Fig 6).

Finally, the (10-min) GOES-East Aerosol Detection – Dust derived product, available during the daytime, did a decent job at capturing much of the dust during this period, primarily with medium to low confidence (Fig 6a).

Turning our attention to GOES-West imagery, the lofted dust is significantly more apparent in the reflectance imagery/products; VIS in Fig 7 and Geocolor in Fig 8. The improved detection during the early daytime period by GOES-West vs GOES-East here is due to increased forward scattering given the position of the sensor (component west of location) relative to the sun (component east of location). Of note, the GOES-West CONUS sector does not extend east to this location. GOES-West full disk imagery (shown here) captures the event at 10-min resolution, but full resolution full disk imagery is not available to forecasters in NWS AWIPS. Therefore, forecasters would need to view the GOES-West products via other means (for example, CIRA Slider) in order to analyze the best high resolution view of the lofted dust during the morning. After midday, forecasters should transition to viewing GOES-East reflectance imagery for the ideal view of the lofted dust.

As pointed out by Tim Schmit (STAR/ASPB), the lofted dust was detectable in the 1.37 um “cirrus” band. Recall, this band is sensitive to absorption by moisture in the atmosphere, so to detect a near-surface/surface feature requires a dry atmosphere. Analyzing the imagery, the early day blowing dust discussed above was not apparent (Fig 9). However, a pocket of blowing dust becomes obvious by late morning traveling south across the middle of the domain. Comparing with surface observations, this area of blowing dust apparent in the 1.37 um imagery matches well with a minimum in surface dew point temperature (down to -2F!). The early day blowing dust occurred with dew points around 20F, confirming enough moisture was present in the atmosphere here to limit detection into the low-levels in the 1.37 um band.

The southward progression of the dry air pocket is also diagnosed in GOES-East TPW imagery (Fig 10).

Bill Line, NESDIS and CIRA

GOES-East Day-Snow-Fog RGB imagery played an important role in operational decision-making at NWS Norman, OK (OUN) when forecasting fog and low stratus progression on 03 Jan 2021. Making this situation particularly difficult was the presence of snow cover beneath the thin low cloud/fog deck, as cloud features could not be easily discerned in visible satellite imagery alone. From OUN, “Since the area of fog/stratus was so thin, you could see the snowpack through the deck, making it even more difficult to discern on visible satellite. The RGB allowed the liquid cloud to “pop out” so we could see the development and dissipation trends.”

The forecaster on shift mentioned that the GOES-East RGB imagery influenced operational decision-making related to TAFs as well as the temperature forecast. Specifically, “Use of the Day Snow-Fog RGB was critical in my forecast for the KOKC TAF, along with hourly temperatures west of OKC. While we did have a TEMPO group of IFR conditions at KOKC for a couple of hours due to uncertainty and potential impact, the dense fog and stratus dissipated on the western and northern edge of the OKC runway complex. The high res models forecasted this area to persist through the afternoon across the OKC metro to the KOUN terminal area, but with the aid of the RGB trends, we were confident that it would not make it past the western parts of OKC.”

First, GOES-East 0.64 um imagery reveals, to an extent, low clouds evolving atop snow cover (Fig 1). Given the similar appearance between the low cloud cover and snow cover and semi-transparency of the cloud cover, the precise location and edges of the cloud cover is difficult to discern throughout the evolution.

Now viewing the Day-Snow Fog RGB, the low clouds pop as shades of light blue against the background of red (snow cover) and green (bare ground), allowing for it’s precise location to be more easily tracked in space and time (Fig 2).

Similarly, Day Cloud Phase Distinction RGB imagery can be utilized to discern low clouds (light blue) over snow cover (green) and bare ground (darker blue) with more clarity than VIS alone (Fig 3).

Bill Line (NESDIS and CIRA), Kevin Brown (NWS/OUN), Randy Bowers (NWS/OUN)

An active synoptic pattern brought a wide variety of weather to portions of the central US during the day on 23 Dec 2020. From GOES-East water vapor imagery, one can diagnose a series of guilty shortwave troughs: one lifting northeast across the midwest, and the other on its backside digging southeast into the southern high plains (Fig 1).

The western shortwave trough sent a cold front south down the central/southern high plains during the morning, with gusty northerly winds developing in its wake. Given the dry antecedent conditions, widespread blowing dust developed, first across southeast Colorado, and spreading south into western Kansas and the TX/OK Panhandles.

GOES-East 1-min imagery was available over the region, capturing the blowing dust evolution through the day. During the morning, the lofted dust was clearly evident in 1-min animations of both the Geocolor and DEBRA-Dust products (Fig 2 and 3).

A 2-min VIS feature-following zoom animation provides a unique perspective of dust plume relative evolution, including periodic cumulus cloud development atop the blowing dust (Fig 4).

Combining the Geocolor and DEBRA-Dust products for the duration of the daytime allows for the lofted dust to be highlighted within a more natural looking animation (Fig 5).

In the absence of DEBRA-Dust in AWIPS, a similar product can be made by combining geocolor (or single-band VIS) with the SWD as an overlay and applying a varying transparency color table around the values for lofted dust (Fig 5b).

Finally, the Dust-Fire RGB captured the dust (relatively bright green) well, along with a few wildfire hot spots (red) in its path (Fig 6). Clouds (and very cold land) appear as various shades of blue.

NWS Amarillo issued a great tweet highlighting the blowing dust in GOES-East Geocolor imagery:

Looking at a few areas of blowing dust in SW Kansas and the Oklahoma Panhandle. Some of this dust may continue to move south, but should stay aloft. #txwx #okwx #phwx pic.twitter.com/cRdZ8UOLjt

— NWS Amarillo (@NWSAmarillo) December 23, 2020

The blowing dust was captured in slightly higher detail in SNPP and NOAA-20 VIIRS geocolor imagery:

To the northeast, on the backside of the eastern shortwave, gusty north winds forced areas of blowing snow. The blowing snow can be diagnosed in an RGB similar to the Day-Snow Fog RGB, but replacing the 0.86 um band with the higher resolution 0.64 um band for the red component, and making other minor adjustments. This RGB is introduced for regions of blowing snow in South Dakota (Fig 7) and ND/MN/Canada (Fig 8). Kudos to Carl Jones (NWS Grand Forks, ND) for pointing out these areas of blowing snow.

Bill Line, NESDIS and CIRA

Widespread strong to severe thunderstorms developed across Argentina during the day on 18 December 2020. To capture the phenomena, a GOES-East meso-sector (-1) was positioned over the region, per a international request via the NESDIS Satellite Analysis Branch, which read, “Possible explosive cyclogenesis over central Argentina may bring heavy rains with possible severe thunderstorm and high surface winds”. GOES-East Full Disk water vapor imagery captured the evolution of a compact shortwave trough moving onshore in western South America and helping to spark widespread thunderstorm development (Fig 1).

A long duration (5-min-updating) IR-Window animation of the full mesoscale sector captures the evolution of the thunderstorms from the early day into the early nighttime (Fig 2). Not only are widespread thunderstorms detected, but an outflow boundary/cold front is analyzed racing north in the wake of the thunderstorms, adjacent to the high terrain, over the northwest portion of the sector (diagnosed as a sharp transition to relatively light gray, or cool, brightness temperatures).

First focusing on convective initiation for some of the most impressive, in appearance, thunderstorms, the Day Cloud Phase Distinction RGB, (at 1-min resolution) captured the trend from growing cu field (cyan clouds), to glaciation (cyan => green), to failed updraft attempts and orphan anvils (red/yellow) (Fig 2).

Playing the full animation, successful convective initiation is observed shortly thereafter (Fig 3). Note, the RGB shown was modified from the default recipe, which quickly reaches the max threshold for the reflectance components during the summer. In this example, the green (0.64 um) component max was raised to 105%, while the blue (1.61 um) component max was raised to 65%. After making the adjustment, cloud top texture becomes apparent.

Following initiation, thunderstorms quickly matured and developed impressive storm top signatures, including rapidly expanding anvil, abundant texture, overshooting tops, and long-lived above anvil cirrus plumes, per 1-min VIS (Fig 4). In this example, a color table focusing on higher reflectance was utilized in order to best capture the storm top detail.

Over the same region and time period, a 1-min VIS-IR sandwich overlay provides more insight about the storm top features by adding brightness temperature information (Fig 5).

Now turning attention to activity near the outflow/cold front progression and lofted dust was apparent along and behind the boundary per 0.64 um VIS (Fig 6) and daytime Geocolor imagery (Fig 7). The DEBRA Dust product highlighted regions of most likely dust (Fig 8). The blowing dust along and behind the boundary apparent in the imagery acts as a fluid tracer of the dense air as it flows within the valley and interacts with higher terrain. Video of the blowing dust was captured from the region (see here and here).

A Dust-Fire RGB not only shows the blowing dust (bright green), but also indicates wildfire hot spots (isolated pixels of bright red) in the scene (Fig 9). A large hot spot is detected in the southeast portion of the scene early in the period, while two smaller hot spots are found in the left center portion of the scene ahead of the cold front and blowing dust. Deep convection appears as blue, drier boundary layer as medium green, and a relatively moist boundary layer as medium-dark red.

Finally, a longer VIS-IR transition animation captures the full evolution of the boundary and related blowing dust into the evening (Fig 10).

Bill Line, NESDIS and CIRA

A mid-December winter storm brought significant snowfall to the northeast US, including totals over 40″ (Fig 1)!

GOES-East Water Vapor imagery from Sunday evening through Thursday morning captured the evolution of the shortwave trough, a key ingredient to the major winter storm, across the nation (Fig 2). An overlay of RAP analysis fields helps one to correlate the synoptic scale features apparent in the water vapor imagery with those in the upper level analysis. For example, the sharp temperature gradient on the southern periphery of the wave (cold on south side, warm on north side) represents the location of upper level jet winds. Additionally, the shortwave is easily identified given the cyclonic circulation apparent in animations, but also via the couplet of warm/dry descending air and cool/moist ascending air

A IR-VIS/IR Sandwich transition procedure from GOES-East shows the evolution of the system along the east cost during the evening of the 16th into the morning of the 17th, with the surface low circulation becoming exposed during the daytime (Fig 3). The overlay of RAP analysis MSLP adds quantitative information about surface pressure trends and .

GLM imagery captured a few instances of lightning within areas of ongoing snow (thundersnow) during the overnight hours, including in W PA and SE PA early in the evening/animation, and then in NH by early morning and late in the loop. Abundant lightning was detected with thunderstorms off the coast along the front (Fig 4).

During the day of the 17th, numerous interesting features could be diagnosed in the GOES-East Day Cloud Phase Distinction RGB imagery (Fig 5). Surface features in clear sky areas include melting snow in Maryland, snow cover extent, and snow cover over forested areas vs that over non-forested areas. As for cloud features, low clouds and fog (liquid clouds), including over snow, can be differentiated from high/glaciated clouds and potential areas of snowfall. The precise location of the surface low can be tracked, along with nearby and abundant gravity waves which can imply turbulence. Further, individual/narrow snow bands are diagnosed across E NY, CT, RI, and MA.

A comparison for one time period between the DCPD RGB and MRMS composite reflectivity demonstrates the ability of the RGB to capture individual snow bands, which can be especially valuable as a compliment and in the absence of radar (Fig 6).

GOES-East 1-min mesoscale sectors were centered over the storm system during it’s evolution. One-minute visible imagery provided a detailed (spatially and temporally) view of the surface low circulation and adjacent cloud top gravity waves as it moved offshore (Fig 7).

Bill Line, NESDIS and CIRA

A series of shortwave troughs brought strong winds and a pair of widespread blowing dust events to E NM and W TX on Dec 13 and Dec 15, 2020. The first event saw the lofted dust begin in E NM, and expanding east into W TX during the day in response to a compact and quick moving shortwave trough digging across the region per 6.2 um water vapor imagery (Fig 1). Imagery for the Dec 13 case comes from the CIRA Slider, while Dec 15 imagery comes from AWIPS and CIRA Slider.

The blowing dust was captured well in GOES Geocolor imagery, and as has been discussed in previous blog posts, diagnosis in the western US is better in GOES-West imagery during the early day, and GOES-East imagery during the late day (Fig 2-3).

A product not discussed much on this blog, but is available on the CIRA Slider, and upon request, in NWS offices AWIPS, is the DEBRA Dust product from CIRA (Fig 4). The product is effective in drawing attention to regions of potential blowing dust, prompting further interrogation.

The next blowing dust event occurred, primarily across W TX, after another shortwave and associated jet streak tracked across the area, captured again in WV imagery and also analyzed in RAP 500 mb height field and 250 mb wind field (Fig 5). Dry descending air is observed and an intensifying 120+ knot jet max analyzed across W TX during the time of strong surface winds and blowing dust.

The following GOES-East imagery has been discussed in numerous dust posts on this blog, and includes Geocolor (Fig 6), DEBRA Dust (Fig 7), SWD-IR Combo (Fig 8), and Dust-Fire RGB (Fig 9). Each of these displays has proven effective in reliable blowing dust detection. While Geocolor provides high resolution daytime detection option and DEBRA-Dust a high resolution day/night option (but with some false alarm), SWD-IR combo and Dust-Fire RGB (which incorporates the SWD), provide day/night dust detection (at slightly lower spatial resolution), along with cloud classification. The Dust-Fire RGB has the added benefit of incorporating wildfire hot spot detection, which often develop during such high wind events. This particular SWD-IR procedure includes the SWD as the gray scale bottom layer, Clear Sky Mask as the middle layer, and cold IR BTs as the color top layer, in order to isolate the blowing dust feature (darkest gray) from clouds, while also including cloud temperature information. All methods require the forecaster to do some degree of analysis and interpretation in order to make a determination on whether the feature is dust.

Exemplifying the multiple dust detection methods available to and used by operational forecasters, NWS offices across the region shared various imagery on social media during the events:

12/13: This satellite image from late Sunday afternoon shows an area of blowing dust moving out of the Trans-Pecos into the Rio Grande plains. The dust shows up as a brown haze extending from Sanderson to Langtry to Del Rio. As of 5 PM, the visibility in Del Rio was 4 miles. pic.twitter.com/FACW3bswZd

— NWS Austin/San Antonio (@NWSSanAntonio) December 13, 2020

Satellite imagery from the last couple of hours highlights several interesting features. 1) The upper low that passed through last night with breezy winds is now spinning over OK/KS. 2) Blowing dust has been kicked up in Midland. 3) Fresh snow on the Rockies. #nmwx #txwx pic.twitter.com/eS0nukYzph

— NWS El Paso (@NWSElPaso) December 15, 2020

Blowing dust is affect parts of the area today. The thickest dust is the dark gray/black feature moving southeast within the white line near Sterling City, San Angelo. Folks from Eldorado to Menard to Brady can expect to see some of this dust in the next hour or two. #txwx #sjtwx pic.twitter.com/L1JD5mtV4I

— NWS San Angelo (@NWSSanAngelo) December 15, 2020

Bill Line, NESDIS and CIRA