A comparison of the MODIS “true color” RGB image (Red=channel 01, Green=channel 04, Blue=channel 03) and the corresponding “false color” RGB image (Red=channel 02, Green=channel 07, Blue=channel 07) from 19 November 2007 (above) shows snow cover over parts of New York, Vermont, New Hampshire, and Maine (extending northward into portions of southern Quebec in Canada). Both snow cover and clouds appear white on the true color image, but deep snow cover appears as darker shades of red (with clouds composed of ice crystals appearing as a lighter shades of red) on the false color image — this makes it relatively easy to discriminate snow cover from supercooled water droplet clouds (which appear as shades of white on the false color image). In fact, a few small patches of supercooled water droplet cloud can be seen over the region of deeper snow clover (along and just north of the US/Canada border). Snow depth data from the NOAA National Operational Hydrologic Remote Sensing Center (NOHRSC) indicated a number of sites reporting 5-10 inches (13-25 cm) of snow on the ground that morning.

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A NOAA-17 InfraRed (IR) image (above) depicted a well-defined eye and eyewall structure associated with Category 4 Cyclone Sidr while it was located over the Bay of Bengal on 15 November 2007. The CIMSS Advanced Dvorak Technique (ADT) intensity estimate around that time was 146 knots.

Animations of the Morphed Integrated Microwave Imagery at CIMSS (MIMIC) (above) showed Cyclone Sidr as it approached the coast of Bangladesh. This CIMSS MIMIC product was also featured on The Weather Channel by their tropical weather expert Dr. Steve Lyons (below).

Meteosat-7 IR images (below) indicated that Cyclone Sidr made landfall around 14:00 UTC between Calcutta, India (station identifier VECC) and Chittagong, Bangladesh (station identifier VGEG). Media reports suggest that the death toll in Bangladesh resulting from Cyclone Sidr is now greater than 3100 people.

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Meteosat-7 IR images sourced from the CIMSS Tropical Cyclones site (above) showed Category 4 intensity Tropical Cyclone Sidr as it moved northward across the Bay of Bengal on 14 November 2007. Increasing amounts of deep layer wind shear (below) to the north of the storm may act to diminish the intensity of Sidr somewhat as it approaches land, but catastrophic storm surge flooding will still be a danger across much of the flood-prone flat river delta regions along the coast of Bangladesh. A tropical cyclone with winds of 150 mph (240 km/hr) and a storm surge of 16-32 feet (5-10 meters) killed an estimated 500,000 people in Bangladesh in November 1970.

The CIMSS Advanced Dvorak Technique (ADT) plot (above) indicated an intensity estimate of 140 knots late in the day on 14 November — this was not long after the center of Sidr passed over a region of higher Ocean Heat Content over the Bay of Bengal (below).

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A major outbreak of Saharan dust was noted during the 06-11 November 2007 period — the Meteosat-9 Saharan Air Layer (SAL) tracking product (above) revealed an extensive signal of thick dust (orange to red enhancement) that was being transported westward across the tropical Atlantic.

The MIMIC Total Precipitable Water (TPW) product (below) showed the dry character of this large Saharan dust plume — TPW values as low as 10-20 mm (brown to violet enhancement) were seen over eastern and central portions of the tropical Atlantic basin as the dust and dry air layer streamed westward off the African continent.

An animation of daytime Meteosat-9 “true color” image composites at 12 UTC and/or 18 UTC (below) shows the hazy appearance of the large Saharan dust plume. The appearance of such a strong Saharan dust event in November is curious in light of two recent studies by Evan et al.: (1) November appears to be the minimum of the seasonal Saharan dust cycle, and (2) August-September 2007 showed little to no dust storm activity over the tropical North Atlantic basin.

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