MODIS true color Red/Green/Blue (RGB) image

A significant rain and snow event occurred across parts of southeastern Wyoming and western Nebraska on 08 October 2011 (see NWS Cheyenne story) — snowfall amounts as high as 12.0 inches were reported near Cheyenne , Wyoming with 2.73 inches of rain reported farther to the northeast near Crawford in western Nebraska. Two days later (on 10 October 2011), a large patch of low-elevation snow cover could still be seen in far southeastern Wyoming  on a 250-meter resolution MODIS true color Red/Green/Blue (RGB) image  from the SSEC MODIS Today site (above, viewed using Google Earth).

MODIS 0.65 µm visible channel image + MODIS 2.1 µm "snow/ice channel" image

On a comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and MODIS 2.1 µm “snow/ice channel” data (above), snow cover (along with clouds) appears bright on the visible image, but snow appears very dark on the snow/ice image (since snow is a very strong absorber at that particular wavelength).

Another method to discriminate between clouds and snow cover is to use different MODIS images to create a 3-channel RGB false color image — snow cover appears darker red on such a false color image (below), which used MODIS channels 01/07/07 as the Red/Green/Blue components.

MODIS 0.65 µm visible image + MODIS false color Red/Green/Blue (RGB) image

In far southeastern Wyoming, the areas that still had significant snow cover exhibited much colder MODIS Land Surface Temperature (LST) values (below), with LSTs ranging from the middle 30s F (darker green color enhancement) over deeper snow cover to the upper 60s to low 70s (darker orange color enhancement) over adjacent areas of bare ground.

MODIS Land Surface Temperature product

With the high October sun angle helping to produce warm temperatures (the daytime high at Cheyenne, Wyoming that day reached 59ºF or 15ºC) the patch of lower-elevation snow cover just to the north of Cheyenne began to melt during the day, as can be seen on an animation of GOES-15 0.63 µm visible channel images (below; click image to play animation).

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

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MODIS 11.0 µm IR image + topography

Another feature of interest on the satellite images was the formation of a  “cloud banner” or “cloud crest” just downwind of the ridge of higher terrain that ran northwest to southeast across the Wyoming/Colorado border region — this cold cloud feature could be seen on the 1-km resolution MODIS 11.0 µm IR image (above). The 4-km resolution MODIS Cloud Phase product (below) showed this to be an ice phase cloud feature (salmon color enhancement), with the 4-km resolution MODIS Cloud Top Temperature (CTT) product indicating CTT values as cold as -45ºC (darker blue color enhancement).

MODIS Cloud phase product + MODIS Cloud Top Tempeature product

The 1-km resolution MODIS 6.7 µm water vapor channel image (below) revealed a signature of mountain waves farther downwind of the cloud banner feature. A few hours later (at 23:58 UTC), there was a pilot report of light turbulence in that region at an altitude of 37,000 feet.

MODIS 6.7 µm water vapor channel image

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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MODIS true color and false color images

A previous blog post discussed the sediment features seen in southern Lake Michigan in early October of 2011. However, looking a bit farther to the east over Lake Erie several days later, a 09 October 2011 comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed a notable contrast between the two lakes: large green colored features covered much of western Lake Erie, compared to the cyan colored sediment that was seen in southern Lake Michigan (as well as southern Lake Huron).

According to the NASA Earth Observatory site, this is one of the worst algae blooms in Lake Erie in decades, brought about in part due to large amounts of runoff into the lake following a period of above-normal precipitation. The thickest portions of the algae bloom appear brighter green in the false color images, similar to the way that dense vegetation does.

A comparison of the consecutive Terra (16:52 UTC) and Aqua (18:33 UTC) MODIS true color images (below, viewed using Google Earth) seemed to suggest a slight northward movement of the algae features during the 91 minutes between the two images.

Terra (16:52 UTC) and Aqua (18:33 UTC) MODIS true color images

An animation of GOES-15 0.63 µm visible channel images (below) confirmed the gradual northward movement to the algae bloom features over western Lake Erie during the day. Surface winds were generally light out of the south across the region, so most of this motion was likely driven by lake currents.

GOES-15 0.63 µm visible channel images

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

GOES-15 10.7 µm IR images (above; click image to play animation) showed a large area of very cold cloud top IR brightness temperatures associated with Tropical Storm Jova over the East Pacific Ocean on 07 October 2011. Embedded within the large region of cloud top IR temperatures colder than -80º C (light purple color enhancement) were smaller areas that exhibited cloud top IR temperatures of -90º C or colder (dark purple color enhancement) — and the coldest cloud top IR brightness temperature seen was -94.65º C at 09:30 UTC. It is unusual to see cloud top IR brightness temperatures of -90º C or colder on 4-km resolution GOES IR imagery.

===== 10 October Update =====

A comparison of GOES-11 (GOES-West), GOES-15, and GOES-13 (GOES-East) visible channel images (below) showed the eye of Category 3 Hurricane Jova on 10 October 2011. Note how the difference in satellite viewing angle produces very different eyewall illumination characteristics.

GOES-11, GOES-15, and GOES-13 visible channel images

GOES-15 is scheduled to replace GOES-11 as the operational GOES-West satellite in December 2011.

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06 October MODIS Visible Image

High pressure over the eastern United States on October 6th allowed a rare view of the (almost) cloud-free Great Lakes, above, from the MODIS instrument on board Terra. The clear skies also allowed observations of lake surface temperatures over the entire Lake system, shown below. (Click here for an animation between the Visible and Lake Surface Temperatures). Note that the region of turbulent, sediment-laden waters over southern Lake Michigan — (link for blog post) — are warmer than adjacent waters. The default AWIPS Lake-surface temperature enhancement shows little variations in temperature, when in fact the temperature ranges from 46 F in Lake Superior to 74 F in Lake Erie (near the mouth of Sandusky Harbor). An image with a stretched enhancement that more clearly shows the temperature variability is here. Lakes Michigan, Huron and Ontario continue to show the effects of persistent easterly winds associated with a series of cut-off lows that have passed south of the Great Lakes in the past weeks: cold near-shore temperatures associated with upwelling in the eastern part of the basins.

06 October MODIS Sea Surface Temperature Image

Screenshot of AWIPS including MODIS True-color image, 06 October

MODIS multi-channel data can be combined to produce a true-color image in the AWIPS environment. In this case, above, the sediment-laden lake waters over southern Lake Michigan jump out. Fall colors over northern Wisconsin and the southern Upper Peninsula of Michigan are also evident. More true-color imagery is available at the MODIS today site: Link.

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