MODIS and GOES-13 fog/stratus product images

Strong nocturnal radiational cooling beneath a large area of high pressure centered over the Ohio River Valley led to the formation of widespread areas of fog and stratus on 05 October 2011. AWIPS image comparisons of the 1-km resolution MODIS and the 4-km resolution GOES-13 fog/stratus products at 03:30 UTC or 11:30 pm local time (above) and 07:45 UTC  or 3:45 am local time (below) demonstrated the clear advantage of having improved spatial resolution to detect the more subtle features such as river valley fog.

MODIS and GOES-13 fog/stratus product images

To compliment the improved fog/stratus detection capabilities offered by higher spatial resolution, other products are being developed (as part of the CIMSS participation in GOES-R Proving Ground activities) that provide more quantitative information about areas of fog and/or low cloud: for example, Fog Depth, Marginal Visual Flight Rules (MVFR) Probability, and Instrument Flight Rules (IFR) Probability (below). In this case, the 07:45 UTC products indicated that the Fog Depth values were as high as 1231 feet (cyan color enhancement) over parts of northern West Virginia, where there were also MVFR Probabilities greater than 90% and IFR Probabilities greater than 75% (brighter red color enhancement).

GOES-13 fog/stratus product, Fog Depth, MVFR Probability, and IFR Probability

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MODIS true color images: 02 October (left) and 03 October (right)

As was highlighted in news stories posted by the National Weather Service forecast offices at Chicago and Milwaukee, a large amount of sediment was seen in southern Lake Michigan following a strong wind event which produced very large waves. A comparison of 250-meter resolution MODIS true color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed one particularly large sediment feature protruding northward from the southeastern part of Lake Michigan on 02 October and 03 October 2011.

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel data with the corresponding 1-km resolution MODIS Sea Surface Temperature (SST) product on 03 October (below) showed that while the prominent sediment feature was embedded within a larger scale area of warmer waters (SST values in the lower 60s F, darker red color enhancement) in the far southern part of the lake, there was not necessarily a 1:1 correspondence between the sediment pattern and the sea surface temperature pattern.

MODIS 0.65 µm visible channel image + MODIS Sea Surface Temperature product

GOES-13 0.63 µm visible channel imagery (below; click image to play animation) indicated that the prominent sediment feature was moving slowly northward early in the day on 03 October — however, once the northwesterly winds reported by the mid-lake buoy began to increase and gust to 16 knots later in the day, the northward motion of the sediment feature appeared to slow somewhat.

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

===== 06 October Update =====

A sequence of daily 250-meter resolution MODIS true color RGB images from 02, 03, 04, 05, and 06 October (below) show the changes in shape and location of the large sediment feature in the southeastern part of Lake Michigan.

MODIS true color images from 02, 03, 04, 05, and 06 October

In addition, daily 15-minute interval GOES-15 0.63 µm visible channel images from that same period (below; click image to play 5-day animation) further show how the sediment patterns were transported and morphed by the Lake Michigan water currents.

GOES-15 0.63 µm visible channel images (click image to play 5-day animation)

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

A McIDAS image comparison of GOES-11 (GOES-West) 0.65 µm visible channel, GOES-15 0.63 µm visible channel, and GOES-13 (GOES-East) 0.63 µm visible channel data (above) showed the dark smoke plume from a fire burning at a chemical plant in Waxahachie, Texas (about 30 miles south of Dallas) on 03 October 2011. (Note: GOES-15 is scheduled to replace GOES-11 as the operational GOES-West satellite in December 2011).

A similar comparison of the GOES-11, GOES-15, and GOES-13 3.9 µm shortwave IR channels (below) indicated that no obvious fire “hot spot” was evident before the appearance of the dark smoke plume — the brighter yellow colors highlight pixels which have an IR brightness temperature hotter than 45º C. This 45º C threshold was exceeded at 16:30 UTC on the GOES-15 and GOES-13 images, and at 16:45 on the GOES-11 images; on the visible channel imagery, the dark smoke plume was seen 30 minutes earlier at 16:00 UTC on all 3 satellites.

GOES-11, GOES-15, and GOES-13 shortwave IR images

A 17:32 UTC Terra MODIS Red/Green/Blue (RGB) true color image from the SSEC MODIS Today site (below, viewed using Google Earth) confirmed the very dark nature of the smoke plume from this particular fire, which was causing some evacuations (news media story).

MODIS true color RGB image (viewed using Google Earth)

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GOES-13 Visible images (click image to play animation)

Hurricane Ophelia, the fourth hurricane of the north Atlantic tropical season, is pictured above near peak intensity as it moves over the open waters of the Atlantic Ocean, northeast of Hispaniola (which island is visible in the southwest corner of the image loop). The hurricane displays a circular central dense overcast region around a eye in which one might infer the presence of small-scale vortices. Several factors argue for weakening with Ophelia. Note in the animation the motion of the cirrus clouds entering the frame from the west. These high-level winds suggest an increase the shear over Ophelia, and in fact the convective distribution around the storm shows an asymmetry with more convection east of the center. Further, Ophelia’s projected track takes it across a region of ocean that is cooler following the passage of major Hurricane Katia earlier in September. This cool wake limits the energy available to subsequent storms like Ophelia. This loop toggles between images retrieved from the CIMSS Tropical Weather website, showing an enhanced infrared image and a mapping of the sea surface temperatures over the Atlantic in which the wake of Katia is plain. Observations from AVHRR confirm the existence of the cooler SSTs ahead of Ophelia.

The vigor of the convection within a hurricane can be measured by the number of overshooting tops within the circulation. This plot, for example, shows a weakening in Katia as the number of overshooting tops dropped on 2 September. Overshooting tops can be inferred by differencing the 10.7 µm and 6.5 µm channels on the GOES imager. This animation shows only occasional evidence of overshooting tops. Visible imagery from GOES-15 shows evidence of a few overshoots possibly north of the center, and in a spiral band east of the center. A very oblique view from GOES-11 suggests a similar distribution to the overshoots, but also shows a mostly smooth cirrus canopy above the hurricane. The number of overshoots should decrease as Ophelia moves over the cooler waters to its north.

Added: This POES AVHRR Infrared image, showing half of the storm, shows cloud tops as cold as -77 C, but little in the way of overshooting tops. A comparison of this same POES AVHRR IR image (viewed using McIDAS)  with the corresponding POES AVHRR visible image (below) nicely shows the curved convective band that was wrapping around they eye of Hurricane Ophelia.

POES AVHRR 10.8 µm IR and 0.63 µm visible channel images

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