Satellite Liaison Blog

***NOAA-21 VIIRS Data are Preliminary and Non-Operational***

The JPSS-2 polar-orbiting weather satellite launched from Vandenberg Space Force Base on 10 Nov 2022, becoming NOAA-21 upon reaching orbit. NOAA-21 joined NOAA-20 and S-NPP as the third JPSS series satellites, all flying with similar instruments. The Visible Infrared Imaging Radiometer Suite (VIIRS) provides global imagery at visible and infrared wavelengths at 375-m (I-bands) and 750-m (M-bands) resolution. The first science data from VIIRS were available on Dec 5, some of which were shared in this NESDIS article, consisting of visible and near-infrared bands. From this imagery, stunning 750 m True Color imagery were available, such as that in Figure 1.

Shortly after the VIIRS cryoradiator doors opened on 8 Feb 2023, science data from the infrared bands and Day Night Band became available, such as that in Fig 2 and 3, and in a NESDIS article.

The VIIRS Imagery EDR Science team has been evaluating the imagery quality, finding the imagery to be of impressive quality with very little deficiencies. After a presentation and review on Feb 23, VIIRS EDR Imagery was declared Beta Mature effective 1845 UTC 10 Feb 2023. Some examples of the remarkable NOAA-21 VIIRS EDR Imagery are shown below, including comparisons with that from S-NPP and NOAA-20.

Currently, NOAA-20 is followed by NOAA-21 by a quarter orbit (~25-min) which is followed by S-NPP by a quarter orbit (25-min), allowing for three VIIRS scans within a ~50-min period. Three-image sequences from the three instruments allow for short animations of a given phenomena, and also for one to compare the quality of the imagery, including imagery artifacts and geolocation errors.

The following 750-m resolution True Color Imagery comparison from 9 Feb 2023 over Florida and surrounding waters really exemplifies the stunning imagery available from VIIRS, including varying vegetation and ocean color, as well as the movement of clouds (Fig 4). Notice the general appearance of the imagery appears identical between the three sensors, with no shift in landmass.

The next image sequence, in animation form, looks at 375-m Band I1 Visible imagery over Puerto Rico (Fig 5). Once again, the land mass remains stationary, indicating that the geolocation is quite good across the three instruments. The three VIIRS provides an improved analysis of evolving features, with 25-mintues between scans vs the 50-min interval with two VIIRS.

Another NOAA-20/NOAA-21/S-NPP 3 VIIRS animation captures ice movement in the Alaska Region overnight in 750-m LWIR Band M15 (Fig 6).

Of course all 22 NOAA-21 VIIRS bands are investigated over a variety of scenes. For example in Fig 7, a region over Antarctica and adjacent waters is shown for all VIIRS bands

A similar animation comparing all 22 bands from NOAA-21 VIIRS is shared from over Tropical Cyclone Freddy on 13 Feb 2023 (Fig 8).

The 742-m Day Night Band/Near Constant Contrast product is one of the 22 Imagery products evaluated. The product is compared with that from NOAA-20 and S-NPP in Fig 9 from the same granules as in Fig 6. Again, the ice motion is apparent, in addition to lights associated with the Prudhoe Bay Oil Field. Aside from some more apparent striping which should be rectified with future calibration updates, the imagery looks great.

Various popular (among operational users) RGBs, which leverage the VIIRS bands, are viewed as well. Sometimes, band combinations can make certain imagery artifacts more apparent than when viewing the single band alone. Below are examples of the NOAA-21 Nighttime Microphysics RGB over Alaska (Fig 10), The Snowmelt RGB over the Northern US plains and adjacent Canada (Fig 11), True Color Imagery with Single Band M13 over Chile (Fig 12), and Day Fire RGB also over Chile (Fig 13)

Finally, NOAA-21 VIIRS Imagery captured the evolution of Tropical Cyclone Freddy from near Australia on Feb 10 all the way through Madagascar on Feb 23. The following animation leverages composites of the M15 IR band to show the 12-hourly evolution through the period.

The Provisional Maturity Review for NOAA-21 VIIRS Imagery will take place several weeks from this post.

Bill Line, NESDIS/STAR, Curtis Seaman, CIRA

GOES-18 became the operational GOES-West satellite at 1800 UTC on 4 Jan 2023 from the 137.0W position. The accompanying press release for the move can be found here. GOES-17, currently at 137.3W, will begin its drift to the 104.7W storage position on 10 Jan 2023, where it will serve as the on-orbit spare for both GOES-East and GOES-West.

Online, GOES-18 imagery can be viewed on the STAR Image Viewer, as well as on CIRA Slider. NWS AWIPS users will have noticed the uninterrupted change from GOES-17 to GOES-18 after 1800 UTC.

Loading PACUS Sector GOES-West ch08 water vapor imagery in AWIPS over the EPAC cyclone, one observes the change in imagery appearance from 1756 UTC (GOES-17) to 1801 UTC (GOES-18), becoming slightly “cleaner/smoother” (Fig 1). Of course, users are well aware of the particular improvement of imagery going from GOES-17 to GOES-18 during the GOES-17 “warm periods“, which resulted in significant degradation of the GOES-17 imagery. See past examples of transition from G17 to G18 into interleave periods.

Zooming out on the impressive cyclone approaching the west coast, and viewing a longer animation of GOES-West Airmass RGB imagery, we can again note the transition from GOES-17 to GOES-18 midway through the loop (Fig 2). Specifically, areas of horizontal striping from GOES-17 are not present from GOES-18.

Bill Line, NESDIS/STAR

A considerable winter storm system brought bitterly cold temperatures, strong winds, and snow to a broad swath of the US during the week leading up to Christmas 2022. A potent shortwave trough embedded in strong northwesterly flow dug southeast across the Rockies on 21-22 Dec, east through the central plains on 22 Dec, and lifted east/northeast toward the east coast on 22-23 Dec. Accompanying the shortwave trough was a sharp cold front that dropped surface temperatures dramatically along its path. For example, the temperature at DIA dropped 37F in 1 hour (42 to 5F)! The average daily temperature at DIA on the 22nd was -15F, which was the 2nd coldest day on record at DIA. Thanks to NWS Boulder for these statistics.

GOES-East water vapor imagery provided a great depiction of the shortwave traveling across the country (Fig 1). The shortwave, or local vorticity max, can be diagnosed in the imagery as an area of compact cyclonic flow in the moisture field and clouds, and tight couplet of drying/descent (warm BTs; upstream of trough axis) and moistening/ascent (cooler BTs; downstream of trough axis). Contours of 500 mb wind speed capture the strong jet that was associated with the trough, with a core of 120+ knot winds! Additionally, contours of surface temperature overlaid highlight the progression of the cold front in association with the trough, with freezing temps (darkest blue) clearing Texas. From NWS Marquette’s water vapor analysis later on the 22nd: “Increasingly negative-tilt mid-level trough now moving into the central CONUS as noted on the latest water vapor imagery and its associated 160+ kt upper-level jet rounding the base of the trough will cause rapid deepening of the storm system over the central Great Lakes over the next 24-48 hours.”

An alternative view of the trough is in the Airmass RGB, which includes the reddening signal of high PV/stratospheric air descending deep into the troposphere and where cyclogenesis is occurring, which is quantified by an overlay of 1.5 PVU pressure contours (Fig 2).

The progression of the front south across the central and southern high plains can be visualized in GOES-East IR imagery, leveraging a grayscale color map with max and min values selected to represent warmer BTs as dark gray and colder BTs as light gray (Fig 3). This can quickly and easily be done in AWIPS by modifying the colormap range. The surface obs provide the degree of temperature drop across the front, while the satellite imagery provides rapidly updating and spatially fluid information about the exact location of the front.

Focusing on the front progression across southern Colorado, and leveraging 2-min updating imagery, we see the front backing west across the plains and into the eastern mountains, and then slowly creeping into the mountain passes (Fig 4).

Further south across Texas during the day on the 22nd, we leverage a TrueColor/IR image combination to capture the cold air progression in the context of clouds and land features (Fig 5). The IR overlay is semitransparent, gray scale colormap, ranging from black on the warm side of the front to white on the cold side.

Strong winds blowing over fresh snowfall across the central and northern US plains resulted in widespread blowing snow, which was captured in satellite imagery given clear skies within the arctic airmass. Previous posts on this blog discuss blowing snow detection with ABI and VIIRS imagery (use the search box on the right). An experimental blowing snow RGB has been tweaked over time to provide a product that attempts to highlight regions of blowing snow, including blowing snow that has transitioned into HCRs, across a broad range of geography, seasons, and time of day. A zoomed out view of the RGB during the day shows how widespread the blowing snow was during the day (Fig 6). Important features include blowing snow (orange or bright pink), snow cover (darker red), bare ground (green), clouds (purple or blue). The RGB is fairly similar to the Day Snow Fog RGB, but more clearly reveals and isolates the blowing snow signature by leveraging the 500 m VIS and and focusing the recipe on lower-reflectance signatures, which adds more contrast to the image.

Zooming in on a couple of regions, we highlight areas of intense blowing snow, confirmed by surface observations, occurring over western Nebraska, western South Dakota, and eastern Nebraska into Iowa (Fig 7-9). Within these plumes of blowing snow, visibility was often reduced to below 1/2 mile.

In fact, the Omaha, NE NWS office leveraged the Day Snow Fog RGB for Blowing Snow detection during the event: “The clouds are pushing southeast of the area, but we are still seeing quite a bit of blowing snow on our GOES16 RGB Day Snow-Fog curve. And in open areas, visibilities are still being reduced to 1 to 3 miles, based on surface observations and DOT plow cams.” See below for a comparison between that, and the experimental Blowing Snow RGB.

A similar RGB can be created with VIIRS imagery at 375 m (Fig 10). Notice that the regions of blowing snow become brighter when positioned near the edge of the VIIRS swath.

Figure 10: 22 Dec 2022 VIIRS experimental Blowing Snow RGB.

Now a few zoomed in looks at the VIIRS RGB over Nebraska, South Dakota, and Iowa. In particular, notice individual plumes of blowing snow are more well defined and can be diagnosed little better, and shadows cast by the plumes are also more apparent. Below are a couple of regional comparisons between ABI and VIIRS of the RGB (Fig 11 and 12).

The method above, of course, leverages VIS, NIR, and LWIR channels. At night, however, we must rely on IR imagery to isolate the feature. A method that seems to work fairly well (though not as effective as the daytime technique) is the single band IR imagery with a grayscale colormap and range focused around that of the surface (Fig 13). Again, these tweaks to the colormap range are simple to make in AWIPS from event to event. The plumes of blowing snow, developed into HCRs, exhibit a few degree cooler BT compared to the clear/background surface. In the animation, the region of blowing snow appears more uniform in Iowa, organizing into the HCRs over Illinois and eastward.

Widespread Blowing snow continued into the day on the 23rd from the upper Midwest southeast across the Ohio River Valley region within a broad region of surface winds gusting over 40 mph.

Numerous NWS offices leveraged satellite imagery to detect and track the plumes of blowing snow. See a few examples below, with AFD snippets and accompanying Blowing Snow RGB imagery over the region.

Aberdeen, SD: “Blowing snow RGB sat pix indicate that blsn is gradually ending over the James valley, and has pretty much ended over the Missouri valley. Will maintain the blizzard warning after 00Z for the Coteau and wc MN, since winds will continue to howl over the area well into the evening. However, will allow the warning to expire for the James valley come 6pm CST.”

Davenport, IA: “Looking out the window, the peak gusts are containing instantaneous white outs, while the steady condition is above that level. The worst conditions are visible on satellite, with convect roll streamers of blowing snow showing up, again, mainly over the central and northern CWA.”

Grand Forks, ND: “Satellite observations indicate a few prominent blowing snow plumes (horizontal convective rolls) creating significant travel difficulties and whiteout conditions. These plumes are located as follows:…”

and:

“A few other areas of blowing snow plumes do exist in the region, however are not substantial from satellite observations. This doesn’t mean there isn’t visibility issues outside the above listed areas, just that they aren’t strong enough to register a signal on satellite. Observations outside of these plumes appear to indicate areas of blowing snow still existing, with visibility between 1 and 5 miles at times. Within the aforementioned stronger blowing snow plumes, blizzard conditions will continue through the rest of the afternoon until sundown.”

Bill Line, NESDIS/STAR

A Kona low brought a series of strong thunderstorms to the Hawaii Islands lasting from late on the 17th to late on the 19th. The storms resulted in the issuance of severe thunderstorm watches and warnings, flash flood advisories and warnings, and special marine warnings. Thunderstorms produced gusty winds, small hail, and heavy rainfall, and caused many to lose power.

Water Vapor imagery with NWP 500 mb height and wind speed overlaid showed the evolution of the robust mid-latitude cyclone as it dipped southeast from well north of the islands, and associated thunderstorms developed and moved west to east across the state. The Jet as analyzed in the model data is appropriately located over a region of fast moving clouds/moisture features and a sharp T gradient as observed in water vapor imagery. From NWS HFO early on the 18th: “Satellite imagery shows an impressive mid-latitude cyclone deepening over the Central Pacific Basin as digs southward toward the islands.” and in the afternoon of the 18th: “On satellite, we can already see the deep trough quickly approaching the state with a line of thunderstorms developing ahead of the front.”

One can leverage the Airmass RGB imagery to diagnose areas of descending stable stratospheric (high PV) air into the troposphere, which appear as red in the RGB. Overlaying isobars of the 1.5 PVU surface provides a quantitative proxy for the dynamic troposphere location, or where stratospheric air is dipping into the troposphere (high pressure areas). The high pressure PVU areas of the NWP field match up well with the satellite observations, and indicate a region favorable for cyclogenesis.

An animation of VIS/IR sandwich (day) and IR (night) imagery focused on the islands captures the evolution of thunderstorms during the two day period, with NWS Warning polygons overlaid. The procedure allows one to monitor convective cloud top trends (BTs, features such as OTs and AACPs, texture) seamless during the day and night, while also observing lightning trends with the unobtrusive GLM flash points. From NWS HFO early on the 19th: “This mornings radar and satellite imagery shows scattered thunderstorms all across the state with the main impacts being damaging winds in excess of 60 mph.” And after the storms had passed late later on the 19th: “The vigorous cold front has finally moved east of the Big Island this evening as satellite imagery shows a line of strong thunderstorms moving eastward away from the Big Island.”

Hawaii is in the southwest corner of the PACUS sector, allowing for routine 5-min imagery to be collected. The Honolulu NWS forecast office requested GOES-West (1-min) mesoscale sector imagery during the event, allowing for storms to be analyzed in tremendous detail with little latency. Figure 4 provides 1-min sandwich imagery of thunderstorms crossing the big island late in the day on the 19th, which resulted in the issuance of two severe thunderstorm warnings. The imagery showed very active storm tops, including OTs and rapidly cooling BTs, and lightning activity as thunderstorms made landfall from the west.

Bill Line, NESDIS/STAR