MODIS true color and false color Red/Green/Blue (RGB) images

The first major winter storm of the season to affect the central Rocky Mountains region produced up to 19.9 inches of snowfall across parts of Colorado on 26 October 2011. On the following day, 250-meter resolution Terra MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed a nice view of the resulting snow cover across northeastern Colorado (the snow cover was cyan-colored in the false color RGB image, with cloud features appearing as shades of white). The morning snow depths included 10 inches at Boulder and Greeley, with reports of 12 inches on the ground at a number of higher elevation stations.

A corresponding AWIPS image comparison of 1-km resolution MODIS 0.65 µm visible channel data and a false color RGB image created using the 2.1 µm “snow/ice channel” (below) further demonstrated the utility of using RGB imagery to discriminate between snow cover (which appeared red in this second RGB image) and cloud features (which again appeared as lighter shades of white).

MODIS visible and false color Red/Green/Blue (RGB) image

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18:13 UTC and 19:53 UTC MODIS false color RGB images

Some of the snow cover began to melt during the day across eastern Colorado, as could be seen in a comparison of the 18:13 UTC (12:13 PM local time) and 19:53 UTC (1:53 PM local time) MODIS false color RGB images (above). GOES-15 0.63 µm visible channel images at 15 minute intervals (below; click image to play animation) more clearly showed the temporal evolution of the melting snow cover.

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

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS.

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GOES-13 0.63 µm visible channel images + ASCAT scatterometer surface winds

Tropical Storm Rina rapidly intensified (CIMSS ADT plot) to hurricane intensity off the coast of Honduras on 24 October 2011 — GOES-13 0.63 µm visible channel images with an overlay of ASCAT scatterometer surface winds from the CIMSS Tropical Cyclones site (above) showed that Hurricane Rina exhibited a central dense overcast early in the day, with convective bursts near the center of the circulation.

A longer animation of GOES-15 10.7 µm IR channel images (below; click image to play animation) revealed a number of convective bursts, with large areas of the central dense overcast exhibiting cloud top IR brightness temperatures of -80ºC or colder (violet color enhancement).

GOES-15 10.7 µm IR channel images (click image to play animation)

AWIPS images of the MIMIC Total Precipitable Water (TPW) product (below; click image to play animation) suggested that Hurricane Rina may have been tapping moisture from the Eastern Pacific Ocean Intertropical Convergence Zone / Monsoon Trough.

MIMIC Total Precipitable Water product + tropical surface analysis (click image to play animation)

It is interesting to note that an increasing pressure gradient between high pressure located over the Gulf of Mexico and the deepening circulation of Hurricane Rina was beginning to enhance the intensity of dry Tehuano gap winds flowing southward into the Gulf of Tehuantepec (below).

MIMIC TPW + Tropical surface analysis + ASCAT scatterometer surface winds

===== 25 October Update =====

NOAA-16 false color Red/Green/Blue (RGB) image

On 25 October 2011, widespread high altitude cirrus “transverse banding” was seen along the western periphery of Hurricane Rina on a 1-km resolution NOAA-16 false color Red/Green/Blue (RGB) image (above), created using AVHRR visible channels 1 (0.63 µm) and 2 (0.86 µm) along with IR channel 4 (10.8 µm).

4-km resolution GOES-13 6.5 µm “water vapor channel” images (below; click image to play animation) showed that Hurricane Rina was a prolific producer of transverse banding during much of the day. The GOES-13 satellite had been placed into Rapid Scan Operations (RSO) mode, providing images as often as every 5-10 minutes.

GOES-13 6.5 µm water vapor channel images (click image to play animation)

1-km resolution GOES-13 0.63 µm visible channel RSO images (below; click image to play animation) revealed the formation of a well-defined eyewall during the afternoon hours.

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

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GOES-11, GOES-15, and GOES-13 visible channel images (click image to play animation)

A major blowing dust event occurred in the wake of a strong cold frontal boundary that moved rapidly southward across western Texas and eastern New Mexico late in the day on 17 October 2011 — the blowing dust reduced surface visibilities to near zero in some locations as winds gusted as high as 75 mph (see NWS Lubbock story). McIDAS images of GOES-11 (GOES-West), GOES-15, and GOES-13 (GOES-East) visible channel data during the daylight hours and shortwave IR data after sunset (above; click image to play animation) showed the southward propagation of the well-defined arc of blowing dust (or “haboob”), along with the surge of cooler air behind the cold front. A few wildfire “hot spots” (darker black pixels) were also evident on the GOES shortwave IR images, a result of fires started by downed power lines.

Much of that region had been experiencing long-term extreme to exceptional drought conditions — and an AWIPS image of the MODIS Normalized Difference Vegetation Index (below) showed very low NDVI values across much of western Texas the day before the dust storm.

MODIS Normalized Difference Vegetation Index

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GOES-15 6.5 µm water vapor channel images (click image to play 3-day animation)

McIDAS images of 4-km resolution GOES-15 6.5 µm water vapor channel data (above; click image to play 3-day animation) showed a plume of tropical moisture being drawn into the circulation of a large cut-off low that was part of a “Rex block” that had formed over the far East Pacific Ocean during the 11 October – 13 October 2011 period.

An AWIPS image of 1-km resolution MODIS 6.7 µm water vapor channel data with an overlay of 1-hour MADIS atmospheric motion vectors or “satellite winds” (below) showed better detail of the moisture plume structure, and indicated that this moisture was being drawn into the circulation of the cut-off low at speeds as great as 50-60 knots.

MODIS 6.7 µm water vapor image + MADIS atmospheric motion vector winds

AWIPS images of the MIMIC Total Precipitable Water product (below; click image to play animation) revealed that the plume of tropical moisture was likely composed of contributions from the remnants of Hurricane Jova (which had moved inland across western Mexico on 12 October) and Tropical Storm Irwin (which had been meandering across the Eastern Pacific Ocean for 8 days, reaching Category 1 hurricane intensity on 07 October).

MIMIC Total Precipitable Water product (click image to play animation)

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