The middle part of April 2013 brought periods of very heavy rainfall to portions of Illinois and the Upper Midwest region, with many areas receiving 5-7 inches of rainfall. A map of the 14-day total observed precipitation during the 07-21 April period (above) shows the widespread distribution of the heavy rainfall, which was 4-5 inches above normal and 300-400% of normal at many locations for this time of the year. Additional information can be found at the NWS Chicago and NWS Lincoln sites.

The effect of this heavy rainfall was very apparent in a before (05 April) and after (21 April) comparison of 250-meter resolution MODIS false-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) — obvious changes can be seen in the width of sections of the Illinois River (which runs fron northeast through southwest across the center of the images) and many of its tributaries. 138 river gauges were reporting moderate to major flooding levels on 21 April.

AWIPS image comparisons of the standard 0.64/0.65 µm visible channel with the corresponding 0.86 µm visible channel from the VIIRS and MODIS instruments (below) show that the 0.86 µm imagery can be useful for helping to monitor the areal coverage of significant water inundation following heavy rainfall events such as this. Rivers, lakes, and flooded areas show up as darker features on the 0.86 µm images.

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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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