A powerful and deadly explosion at a fertilizer plant in the city of West, Texas occurred on the evening of 17 April 2013. A thinning of the layered cloudiness across the region allowed the 4-km resolution GOES-13 3.9 µm shortwave IR channel image (above) to reveal a subtle “hot spot” (yellow color enhancement) signature of the large fire that burned into the night.

Shown below is a comparison of  images from the Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) at 08:00 UTC or 3:00 AM local time on 17 April (the night before the explosion) and 07:41 UTC or 2:41 AM local time on 18 April (the night after the explosion). The 18 April DNB image appears to display a brighter signal in the West, Texas area (circled), although it is unclear whether this brighter signal on the later Day/Night Band image is due to the fire, or the large amount of emergency response activity, or some combination of the two factors. The presence of optically-thick cloud layers across the region may also be playing a role in the apparent West, Texas brightness differences sensed by the DNB detectors; this effect is very notable in the city light signature of the Dallas/Ft.Worth area in the upper center portion of the 2 images.

 

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Strong southwesterly winds ahead of an advancing cold front caused large areas of blowing dust across parts of the “Four Corners” region of the western US on 16 April 2013. Wind gusts were as high as 68 mph at Winslow, Arizona — and Interstate 40 was closed between Winslow and Winona, as visibility was reduced to 50 feet at times in some areas. McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation) showed the growth of large plumes of blowing dust during the day, with primary source regions appearing in northeastern Arizona and northwestern New Mexico.

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and 11-12 µm IR brightness temperature difference (BTD) data at 19:49 UTC  (below) revealed the hazy signature (on the visible image) and large BTD values of -3 to -5 C (orange to red color enhancement) associated with the most dense plumes of blowing dust that were moving northeastward. In southwestern Colorado, surface visibility was reduced to 1 mile at Cortez (station identifier KCEZ), and winds gusted to 75 mph at Wolf Creek Pass (station identifier KCPW).

A 250-meter resolution MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below) showed the lighter tan-colored plumes of blowing dust in great detail.

Later in the day, there were public reports of “dirty rain” at Grand Junction, Colorado, as well as “dirty snow” in the Denver area.

In the Fort Collins, Colorado area, two photos (courtesy of Louis Grasso and Dan Bikos, CIRA)  showed (1) blowing dust sediment in a container of melted snow water collected on 17 April (above), and (2) dust residue on a vehicle after the snow had melted on 18 April (below).

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A comparison of McIDAS images of 1-km resolution GOES-13 (GOES-East) Visible (0.63 µm) and 4-km resolution Shortwave Infrared (3.9 µm) data (above) revealed a number of ship tracks in the marine boundary layer stratocumulus cloud deck over the western Atlantic Ocean on 13 April 2013. Aerosols from the exhaust of ships causes a “cloud seeding effect”, which results in a higher concentration of smaller cloud droplets compared to the surrounding undisturbed cloud deck. These smaller cloud droplets are more effective reflectors of sunlight, resulting in a warmer (darker gray) signature on the 3.9 µm imagery.

A more detailed view of the ship tracks was provided using AWIPS images of 1-km resolution MODIS Visible (0.65 µm), Shortwave Infrared (3.7 µm) and Infrared Window (11.0 µm) images (below). Note that the ship track features could not be identified on the 11.0 µm image, since the cloud-top infrared brightness temperatures were essentially the same over that region.

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A late-season winter storm brought heavy snowfall to much of the central US — Rapid City, South Dakota (station identifier RAP) set records that included 20.0 inches on 09 April 2013 (most snowfall on a calendar day) and 28.2 inches on 08 April – 10 April (greatest muti-day snowfall). McIDAS images of 4-km resolution GOES-13 6.5 µm water vapor channel data covering the 08 April – 10 April period (above; click image to play animation; also available as a QuickTime movie) showed the development of several convective elements that helped to enhance snowfall rates as they moved northward across the region on 09 April, as well deformation bands that formed as the circulation of the upper-level low slowly migrated over western South Dakota and western Nebraska on 10 April.

An AWIPS image of 1-km resolution MODIS 0.65 µm visible channel data (below) showed some of the convective elements responsible for producing a period of heavy snow at Rapid City on 09 April. Large thunderstorms were also seen at the time over notheastern Nebraska and southeastern South Dakota.

A surface meteorogram (below) shows the conditions at Rapid City Regional Airport during the 08-10 April period.

===== 12 April Update =====

Widespread cloudiness masked a good view of the areal extent of the resulting snow cover across South Dakota, but farther to the south over Nebraska and far northern Kansas an AWIPS comparison of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images (below) showed interesting detail in a number of mesoscale bands of snow cover. Snow appears as white on the visible image, and as darker shades of red on the RGB image; supercooled water droplet clouds are lighter shades of white, while ice crystal clouds appear as shades of pink on the false-color image.

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