Suomi NPP VIIRS 0.7 µm Day/Night Band image

The first accumulating snowfall of the season reported in the higher elevations of Colorado was on 19 September 2013 in the vicinity of Breckenridge Ski Resort, but a cold front associated with an upper-level trough of low pressure passing through the state on 22 September brought several inches of snow accumulation to much of the higher elevation mountain ranges. Once clouds had cleared the region, the coverage of the resulting snowfall could be seen on satellite imagery. A “visible image at night” was provided by Suomi NPP VIIRS 0.7 µm Day/Night Band data at 09:43 UTC or 3:43 AM local time on 24 September (above), which not only showed the bright lights from cities and towns, but also moonlight reflected by the snow cover located in the higher terrain (the Moon on this date was in the Waning Gibbous phase at 70% of full, providing ample illumination of the snow).

The following afternoon remained cloud-free over Colorado, allowing a good daytime view of the snow-covered mountains on a VIIRS 0.64 µm visible channel image at 19:29 UTC or 1:29 PM local time (below). A comparison with the corresponding VIIRS false-color Red/Green/Blue (RGB) image — which depicts snow as varying shades of red, depending on depth and water content — verified that the brighter white features seen on the visible image were areas with snow cover, and not clouds.

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

The MODIS Land Surface Temperature (LST) product at 20:33 UTC or 2:33 PM local time (below) showed a large range in LST values across the state, from 100-110º F (darker orange color enhancement) over the dry soils of the southeast, to lower to middle 30s F (darker blue color enhancement) over some the snow-covered higher elevations of the Rocky Mountains. The areas of black appearing within the coldest LST values were mistakenly identified by the LST algorithm as cloud, due to the very large gradient in LST values over the highest elevations.

MODIS Land Surface Temperature product

Note that the LST values over much of northeastern Colorado were significantly cooler (darker green color enhancement) than those over southeastern Colorado — the wet soils from the historic rainfall event about a week earlier in and east of the Front Range were not able to warm up as quickly as the dry soils farther to the south.

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

GOES-15 0.63 µm visible channel images (above; click image to play animation) showed a distinct hazy plume streaming southeastward from the Katmai volcano area in Alaska on 22 September 2013. This was a signature of re-suspended volcanic ash — a deep layer of ash has remained on the ground near the volcano following the massive 1912 eruption — which was carried aloft by strong winds on the back side of a deep area of low pressure over the Gulf of Alaska (below).

Suomi NPP VIIRS 0.7 µm Day/Night Band image

A closer view using a sequence of four Suomi NPP VIIRS 0.7 µm Day/Night Band images (below) showed the evolution of the ash plume as it moved over southeastward over Kodiak Island and then out over the Gulf of Alaska. Winds at Kodiak (station identifier PADQ) gusted as high as 55 knots or 63 mph. With limited snow cover and strong winds (which were enhanced by local terrain effects), the surface volcanic ash was easily lofted to great heights.

Suomi NPP VIIRS 0.7 µm Day/Night Band images

An image of a MODIS-based NOAA/STAR/CIMSS Volcanic Ash Height product is shown in combination with the Volcanic Ash Advisory that was issued by the Anchorage Volcanic Ash Advisory Center (below).

MODIS Ash Height product with Volcanic Ash Advisory

MODIS Ash Height product

A sequence of three MODIS Volcanic Ash Height product images (above) suggested that the average height of the re-suspended ash plume was around 9,000 – 11,000 feet. A vertical profile of CALIPSO satellite-based lidar data near the source of the ash plume (below; courtesy of Mike Pavolonis, NOAA/NESDIS/STAR) indicated that the top of the plume was around 3.5 km or 11,000 feet (at 12:57 UTC, near latitude/longitude 58 N / 155 W).

CALIPSO total attenuated backscatter

The corresponding MODIS Ash Mass Loading product (below) indicated values of 2-3 tons per square kilometer existed over much of the ash plume.

MODIS Ash Mass Loading product

Finally, the corresponding MODIS Ash Mass Effective Radius product (below) showed that much of the plume likely consisted of particles with radii in the 4-6 µm range, with a maximum value of 8.33 µm.

MODIS Ash Mass Effective Radius product

Additional information on the NOAA/UW-CIMSS GOES-R Volcanic Ash Products shown above can be found in this Java-based VISITview lesson (a separate Lesson Playback Control window will open to assist in viewing the lesson content).

===== 23 September Update =====

Suomi NPP VIIRS 0.7 µm Day/Night Band image

On the following day (23 September), a Suomi NPP VIIRS 0.7 µm Day/Night Band image (above) showed that the resuspended Katmai ash plume was still present, but was much less expansive than what was seen on 22 September.

Hat tip to Mark Ruminski of the NOAA/NESDIS Satellite Services Division for bringing this interesting event to our attention!

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MTSAT-2 10.8 µm IR images (click image to play animation)

McIDAS images of MTSAT-2 10.8 µm IR channel data (above; click image to play animation) showed Super Typhoon Usagi in the West Pacific Ocean as it continued to move northwestward across the Philippine Sea. Note the slight amount of “trochoidal wobble” seen in the path of the eye. The coldest IR brightness temperature seen on the MTSAT-2 IR images was -92º C at 12:32 UTC. At the time of these images, advisories issued by the Joint Typhoon Warning Center listed the maximum sustained winds at 140 knots, with gusts to 170 knots; at its peak intensity, Usagi had an estimated lowest pressure of 882 hPa, making it the most intense tropical cyclone so far in 2013.

TMI and SSM/I 85 GHz microwave brightness temperature images

From the CIMSS Tropical Cyclones site, a comparison of 85 GHz microwave images from the TRIMM Microwave Imager (TMI) at 10:35 UTC and the DMSP SSM/I at 19:13 UTC (above) displayed a very small ring of high brightness temperatures surrounding the “pinhole eye”.

MIMIC-TC morphed microwave images (below; click image to play animation) showed a well-defined closed eyewall during much of the early part of the day on 19 September.

MIMIC-TC morphed microwave imagery (click image to play animation)

MTSAT-2 IR image with AASCAT scatterometer surface winds

Scatterometer surface winds from the ASCAT instrument at 13:17 UTC  (above) and the OSCAT instrument at 15:10 UTC  (below) showed the large areal coverage of strong winds around the center of Usagi.

MTSAT-2 IR image with OSCAT scatterometer surface winds

 ===== 20 September Update =====

MTSAT-2 0.67 µm visible channel images (click image to play animation)

MTSAT-2 0.67 µm visible channel images (above; click image to play animation) showed the detailed structure of the compact eye of Super Typhoon Usagi.

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Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images

AWIPS images of Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm DayNight Band data showed Hurricane Manuel centered just off the west coast of Mexico at 07:54 UTC or 12:54 AM local time (above) and at 09:37 UTC or 2:27 AM local time (below) on 19 September 2013. Manuel had just reached hurricane intensity several hours earlier. In the 07:54 UTC images above, hints of an eye feature were present on both the IR and the Day/Night Band. In the 09:37 UTC images below, evidence of offshore convective bursts could be seen (many of which exhibited cloud-top IR brightness temperatures of -80º C and colder, violet color enhancement).

Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images

Manuel rapidly lost organization and intensity upon moving inland over the rugged terrain of the Sierra Madre Occidental, becoming a remnant area of low pressure over northern Mexico at the end of the day on 19 September.

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