Suomi NPP VIIRS 0.64 µm visible channel and false-color RGB images

In the wake of a strong cold frontal passage, a series of disturbances left swaths of snow, sleet, and ice (from freezing rain) across parts of Texas and Oklahoma during the 05 December – 06 December 2013 period. Snowfall accumulations were as high as 5 inches in Texas and 6 inches in Oklahoma; sleet accumulations reached 3-3.5 inches and ice accruals were as great as 1.0 inch in Oklahoma and 0.4 inch in Texas.

After clouds finally began to clear the region on 08 December, areas that still had snow/sleet/ice on the ground could be seen in comparisons of visible channel and false-color “snow-vs-cloud discrimination” Red/Green/Blue (RGB) images from Suomi NPP VIIRS at 19:20 UTC or 1:20 PM local time (above) and from Aqua MODIS at 20:14 UTC or 2:14 PM local time (below). Areas where the ground remained covered with snow/sleet/ice appeared as darker shades of red on the false-color RGB images (in contrast to supercooled water droplet clouds, which appeared as shades of white, and ice crystal clouds, which appeared as shades of pink to light red).

MODIS 0.65 µm visible channel and false-color RGB images

===== 10 December Update =====

Suomi NPP VIIRS 0.64 µm visile channel and false-color RGB images

On the afternoon of 10 December enough clouds had cleared across the central US to reveal the large swath of snow/sleet/ice that still covered the ground from Texas to Ohio, as seen in a comparison of Suomi NPP VIIRS 0.64 µm visible channel and false-color “snow-vs-cloud discrimination” RGB images at 18:42 UTC or 12:42 PM local time (above). Note the darker red appearance of the southeastern edge of the swath over parts of Texas, Oklahoma, Arkansas, and Missouri — since sleet accumulation and ice accrual (from freezing rain) are stronger absorbers of radiation than snow cover at the 1.61 µm wavelength used in the creation of the RGB images, those areas appear darker. Ice acrual from freezing rain reached 1.25 inches in southeastern Oklahoma and west-central Arkansas, and sleet accumulations were as deep as 2-3 inches in Arkansas.

A closer view (centered on northern Arkansas) is shown below. For additional details on the sleet and freezing rain aspects of this winter storm, see the event summaries posted by the National Weather Service forecast offices at Norman OK, Tulsa OK, and Little Rock AR.

Suomi NPP VIIRS 0.64 µm visible channel and false-color RGB images

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Meteosat-10 6.25 µm water vapor channel images (click to play animation)

Winter Storm Xaver (EUMETSAT Image Library) affected much of northern Europe on 05 December 2013, causing widespread power outages, storm surge flooding, and adverse impacts to transportation in several countries. As many as nine deaths have been blamed on the storm. Many areas experienced hurricane-force winds, with the highest wind gust of 142 mph (229 km per hour) reported at Aonach Mor in Scotland. EUMETSAT Meteosat-10 6.25 µm water vapor channel images (above; click image to play animation) showed the rapid intensification of the storm as the center moved  from south of Iceland late in the day on 04 December to southern Sweden late in the day on 05 December.

Meteosat-10 water vapor channel images with overlays of surface wind gusts (in knots) are shown below (click to play animation).

Meteosat-10 6.25 µm water vapor channel images with surface wind gusts (click to play animation)

Meteosat-10 0.7 µm broadband high resolution visible channel images (below; click image to play animation) offered a closer look at the center of the storm as it moved eastward across the North Sea and over southern Norway during the daytime hours on 05 December.

Meteosat-10 0.7 µm visible images (click to play animation)

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Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product” (with overlays of METAR surface reports and ceilings/visibilities)

A night-time AWIPS image of the Suomi NPP VIIRS IR brightness temperature difference (BTD) “fog/stratus product” at 08:47 UTC or 1:47 AM local time (above) displayed an expansive area of fog and stratus cloud across much of the central and southern Rocky Mountains region on 30 November 2013. Overlays of the hourly METAR surface reports and plots of cloud ceilings and visibilities showed that the BTD “fog/stratus product” had no skill in determining whether there was fog or stratus cloud at any given location — and there was a lack of surface reports beneath large portions of the fog/stratus feature (especially across southwestern Utah).

Of the 3 rawinsonde sites in that area, Grand Junction, Colorado (KGJT) was the only one that remained covered by the fog/stratus deck; their sounding profile at 12 UTC showed a very strong temperature inversion whose base was around 7943 feet (2422 meters) above the surface. With a quasi-stationary ridge of high pressure over the region, this strong capping temperature inversion helped to hold the fog in place for several days.

A comparison of the 375-meter resolution (projected onto a 1-km AWIPS grid) VIIRS BTD fog/stratus product with the corresponding 4-km resolution GOES-15 image (below) demonstrated the advantage of higher spatial resolution in helping to diagnose the locations of edges and small-scale variations in coverage of the large fog/stratus feature.

Suomi NPP VIIRS vs GOES-15 IR brightness temperature difference “fog/stratus product”

Products designed to provide qualitative information on fog and low stratus clouds have been developed for use on the future GOES-R ABI data; applying these GOES-R algorithms to current GOES-15 imagery offered some insight as to the low cloud thickness, as well as the probabilities of Marginal Visual Flight Rules (MVFR), Instrument Flight Rules (IFR), or Low Instrument Flight Rules (LIFR) conditions (below). Again, data-sparse regions such as southwestern Utah could benefit from the use of such products for aviation forecasting purposes. See the GOES-R Fog Product Examples blog for additional examples of these types of “data fusion” products.

During the subsequent daytime hours, McIDAS images of 1-km resolution GOES-15 0.63 µm visible channel data (below; click to play animation) showed that although the large area of fog/stratus persisted into the late afternoon hours, there was still a surprising amount of variability to the exact location of the edges of the features (which was likely driven by differential terrain heating and local wind circulations). Something to note in the visible imagery: fog in the eastern portion of the Grand Canyon in northern Arizona, which is apparently quite rare (photos)

GOES-15 0.63 µm visible channel images (click to play animation)

A comparison of the 20:11 UTC (1:11 PM local time) Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding false-color Cloud-vs-snow discrimination Red/Green/Blue (RGB) image (below) helped to differentiate between the areas of snow cover (which appeared as varying shades of red on the RGB image) and the supercooled water droplet fog and stratus cloud features (which appeared as varying shades of white). Again, note the westward protrusion of fog located just to the north of Grand Canyon National Park (station identifier KGCN).

Suomi NPP VIIRS 0.64 µm visible channel and false-color Cloud-vs-snow discimination RGB image

There were not many pilot reports availble to offer information on the height of the tops of the stratus clouds – however, one report placed the cloud tops at 8000 feet above ground level over far northwestern New Mexico at 19:08 UTC (below).

Suomi NPP VIIRS 0.64 µm visible channel image with pilot report of cloud top height

An image of the 1-km resolution POES AVHRR Cloud Top Height product at 21:00 UTC or 2:00 PM local time (below) indicated that the tops of the stratus clouds were generally in the 3-4 km range (green to yellow color enhancement).

POES AVHRR Cloud Top Height product

===== 01 December Update =====

On the following day, an AWIPS-2 image comparison of the afternoon Suomi NPP VIIRS 0.64 um visible channel data with the corresponding Cloud-vs-snow discrimination RGB product (below) again showed how entrenched the fog/stratus still was across that region at 19:54 UTC or 12:54 PM local time.

Suomi NPP VIIRS 0.64 um visible image and Cloud-vs-snow discrimination RGB image

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GOES-13 0.63 µm visible channel images (click to play animation)

McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed the well-defined circulation of a mesocale vortex over far western Lake Superior on 28 November 2013. During the day, this mesovortex was slowly migrating southward toward the Apostle Islands of Wisconsin. As much as 7.5 inches of snow was reported north of Bayfield in far northern Wisconsin, likely a result of enhanced snowfall rates associated with the passage of the mesovortex.

Suomi NPP VIIRS 0.64 µm visible channel images (17:27 and 19:07 UTC)

AWIPS images of VIIRS 0.64 µm visible channel data from consecutive overpasses of the Suomi NPP satellite at 17:27 and 19:07 UTC (above) showed better detail in the structure of the mesovortex; the corresponding VIIRS 11.45 µm IR images (below) indicated that cloud top IR brightness temperatures were generally in the -25 to -30º C range (darker blue color enhancement), suggesting that cloud glaciation was likely.

Suomi NPP VIIRS 11.45 µm IR channel images (17:17 and 19:07 UTC)

A comparison of the 17:27 UTC VIIRS visible image with the 17 UTC RTMA surface winds and the 18 UTC NAM12 surface, 925 hPa, and 850 hPa winds (below) showed that neither the RTMA nor the NAM12 wind fields did a good job of locating the actual center of primary mesovortex circulation — demonstrating the value of satellite imagery for a more accurate diagnosis of such small-scale features.

Suomi NPP VIIRS 0.64 µm visible image (with RTMA surface winds, NAM12 surface, 925, and 850 hPa winds)

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