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

A very broad upper trough slowly traversed the Contiguous United States during the week of 12 Dec 2022, resulting in considerable and widespread winter weather impacts for the northern half of the United States, and severe weather impacts for the south. Satellite imagery captured various unique aspects of the storm system.

First, a hourly water vapor animation with RAP 500 mb height and wind speed captures the evolution of the broad storm system through the week (Fig 1). In the imagery, one can diagnose the significant shortwave troughs, deformation zones, jet streaks, and moisture features associated with the trough that would come and go throughout the week.

A similar but more qualitative animation of All-Layer Precipitable Water (ALPW) product, derived from vertical sounding measurements form polar sensors, shows us how moisture evolves throughout the atmosphere as the upper low deepens (Fig 1b). Early on, for example, low-level moisture originates from the GoM, while mid-upper level moisture comes from the East Pacific. Deep moisture came together over the central/northern US to result in heavy snowfall.

From late on the 12th through the afternoon of the 13th, one can leverage water vapor imagery to diagnose lee cyclogenesis along the eastern part of the broader trough in eastern Colorado, and combine RAP MSLP to see deepening low pressure ahead of the strengthening shortwave, and the storm system becoming vertically stacked as it enters mature stages and occludes over Nebraska (Fig 2). From the imagery alone, one can diagnose moisture wrapping around the circulation, and widespread cloud cover developing from southeast Texas north to the ND/MN/Canadian border, southwest across Wyoming and Colorado. A GLM FED overlay captures the development of thunderstorms during the overnight hours from central Texas through Oklahoma into Kansas. The following animation also includes a SWD overlay, to highlight blowing dust (coming out of the Chihuahua desert late on the 12th) as brown.

Taking a closer look at the blowing dust on the 12th, we leverage an experimental “Color Vision Deficiency” (CVD) Dust RGB in order to highlight the dust feature better than is done in the traditional Dust RGB, particularly for Color Blind folks (Fig 3). In this RGB, blowing dust shows up as bright green to yellow against the blue clear sky background. As with the Dust RGB, cloud microphysics properties can be gleaned as well.

Focusing on the overnight thunderstorms, numerous reports of severe hail and wind, plus a few tornados, were reported across Oklahoma and Texas, including many reports in the Dallas/Fort Worth area. Another water vapor animation overlays RAP 500 mb 60 knot wind speed (yellow), 850 mb 40 knot wind speed (blue), and 300K Isentropic surface 310K equivalent potential temperature (green; Fig 4). The animation allows one to view the thunderstorm development in relation to relevant environmental fields. Specifically, storms develop where the strong low level jet developed beneath the midlevel jet, within a surge of increasing low-mid-level moisture.

The deepening cyclone from the 12th to the 13th, specifically cloud evolution, can also be visualized in day/night transition RGB imagery (starting as the DCPD RGB during the day on the 12th, transitioning to the NightMicro RGB at night, and back to the DCPD RGB during the day on the 13th; Fig 5). The RGB imagery makes it simple to connect cloud features between the two RGBs, and to differentiate low clouds from upper clouds across the scene day/night, and to identify development of convection across a boundary interaction during the night in west Texas and later across central Oklahoma and north Texas. Other interesting features observed in the NightMicro RGB imagery overnight include the recent rainfall signature left behind thunderstorms in west Texas, the emergence of low clouds from beneath upper clouds as the low levels become saturated near the low pressure center in eastern Colorado, and the widespread low clouds ahead of the front marking an abundance of low level moisture. One may also notice the difference in appearance of low clouds ahead of and behind the front due to differing airmass, and therefore, different contributions from the 10.3 um IR “blue” component (less blue in cold environment behind front).

Focusing in on the severe thunderstorms that developed across the DFW area during the morning of the 13th, 1-min feature following VIS/IR sandwich imagery reveals rapid cloud top cooling of new storms, numerous OTs, and persistently cold cloud tops with great texture, all signs of strong updraft and strong-severe storm potential (Fig 6).

Skipping ahead to the evening of the 13th through much of the 14th, widespread heavy and blowing snow continued across the northern US plains, and the severe thunderstorm threat shifted east to the southern MS Valley area. A water vapor animation with 300K isentropic surface equivalent potential temperature contours (color) and pressure contours(white) help one to visualize the surge of ascending moisture northward along the MS River ahead of the upper low, and then cyclonically around the low over the northern plains (Fig 7).

VIIRS Day Night Band Near Constant Contrast Imagery overnight early on the 14th provided detailed “visible-like” imagery of thunderstorms over Louisiana and Mississippi (Fig 8). The gray/color colormap allows one to view clouds in grayscale, and bright lights associated with cities and lightning flashes (of which there are a few) in color.

Thunderstorms continued east during the day and into the evening, producing several strong tornados and severe wind gusts. One such storm produced a tornado in the New Orleans area. GOES-East 1-min VIS/IR sandwich imagery captured the details of the storm, which exhibited rapid cooling to very cold BTs and a OT with above anvil cirrus plume, indicated a particularly strong and dangerous storm had developed (Fig 9). Cloud tops warmed, and texture was lost, as the storm moved east of New Orleans, indicating a weakening of the updraft.

Further west, strong northerly winds developing on the backside of the surface low had resulted in blowing dust across far east-central CO and southwest Kansas. True Color imagery from Geocolor captures the blowing dust well, particularly from GOES-East as the sun sets to the west, and forward scatting increases to the sensor (Figure 10).

Now on the 15th as the system continued to slowly shift east, taking a broader look at the north-central part of the US, the DCPD RGB with RAP MSLP contours shows the massive circulation centered over Minnesota during the day, with widespread low clouds (light cyan) under, south and east of the low center, higher level clouds (red) and implied greater mid-upper level moisture wrapping around the northern and western parts of the low, where heavier precipitation (snowfall) would be occurring (Fig 11). Further west, where dry northwesterly flow had developed, clearing revealed the fresh snowpack (green). The tight pressure gradient and surface obs capture the widespread gusty conditions that had developed around the low, especially west.

The strong winds on the backside of the low resulted in widespread blowing snow, reducing visibility to less than a 1/2 mile in many areas. Where skies were clear, the blowing snow could be diagnosed in the experimental GOES-East blowing snow RGB (Fig 12). In the following animation, the subtle signal of blowing snow appears as a slightly lighter shade of red against the red, snow-covered background, and amongst the bright blue and gray color of liquid clouds, and even fainter red of upper/ice clouds. Bare ground is bright green. Blowing snow may also be present under the bright blue/gray HCR clouds, where plumes of blowing snow evolve into. An experienced user of this RGB could diagnose widespread blowing snow from Lusk, WY southeast through Alliance toward North Platte and Imperial in Nebraska. In the following animation, blowing snow is most apparent over and around Alliance, NE. Blowing snow resulted in car accidents and the closure of I-80W in Big Springs, NE, very near the northeast corner of CO.

The plumes of blowing snow were captured in even greater detail by VIIRS, in its version of the experimental blowing snow RGB (Fig 13).

Looking back to the warm side of the system, a 3-day animation from GOES-East shows the evolution of strong-severe thunderstorms during the period, transitioning between IR imagery at night and VIS/IR sandwich imagery during the day (Fig 15).

A NOAA 72-hr snowfall analysis ending the evening of the 15th shows a widespread region of 8+” of snow had fallen across the northern US (Fig 16).

On the 15th, the northeast was also impacted by winter weather associated with the system, including freezing rain from western Virginia north through Maryland and Pennsylvania into western New York. GOES-East DCPD RGB imagery showed the evolution of clouds in the area, including individual convective elements streaming north behind the main upper cloud shield 9Fig 17).

The VIIRS Snowmelt RGB on the 16th was able to capture signs of where the freezing rain had fallen, between still abundant cloud cover, including western Maryland and central PA (Fig 18). Recall, darker shades of blue represent ice cover in this RGB, while fresh snow cover will be lighter shades of gray, such as further to the west.

Continued strong winds and clear skies across the plains on the 17th resulted in continued blowing snow being observed in both GOES-East and VIIRS Blowing Snow RGBs over southeast South Dakota (Fig 19 and 20).

Bill Line, NESDIS/STAR

A previous blog post highlighted the eruption of the Mauna Loa Volcano in Hawaii. This past week, the volcanic activity quickly quieted down, with very little activty present by Dec 13. Satellite imagery also showed the progressive calming of the volcano over the last 7+ days. Specifically, the VIIRS Day Night band from SNPP and NOAA-20, each evening, captured the decrease in light emitted from the volcano and adjacent lava flow (Fig 1). Toggling through the images from Dec 6-12, the light coming from the volcano and adjacent lava flow area quickly decreases to only a faint signal at the Volcano.

Figure 1: 4-12 Dec 2022 NOAA-20 and S-NPP VIIRS Day Night Band Near Constant Contrast product centered over the Mauna Loa Volcano. See below for Animation form.

Volcano procedure imagery from the 14th, similar as that shown in the aforementioned blog post (but with Geocolor used instead of VIS), shows only a faint hot spot centered over the volcano, with no lava flow heat signature. The SO2 signature previously present was also not detected.

Bill Line, NESDIS/STAR