Recent news articles (such as this one) have noted the unusual warmth present in the surface waters of the Great Lakes. Clear skies over the western Great Lakes on Sunday 8 August allowed MODIS instruments to measure sea surface temperatures, and the warm temperatures are plain to see. These warm temperatures have persisted for some time, and 5-day plots for the Buoy in central Lake Michigan (buoy 45007), northern Lake Michigan (buoy 45002), and the center of Lake Superior (buoy 45001) all confirm the MODIS readings: unusual warmth in the Lakes. In fact, many of the lake surface temperature readings are near the top of the 4th quartile in the statistical distribution (see data here for buoy 45001 and here for buoy 45007).

Data from the AVHRR on board the NOAA series of satellites show similarly warm temperatures. Here is an afternoon image from NOAA-19 from 8 August.

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POES AVHRR visible, IR, and IR + severe weather reports

A large Mesoscale Convective System (MCS) initially developed over Nebraska and quickly grew in size as it propagated eastward across the Missouri River Valley region of the north-central US on 08 August 2010. AWIPS images of 1-km resolution POES AVHRR 0.63 µm visible and 10.8 µm IR channel data (above) revealed an impressive back-sheared anvil structure, along with well-defined overshooting tops and very cold cloud top IR brightness temperatures (as cold as -91º C). SPC storm reports showed a number of hail an damaging winds associated with this MCS, as well as one tornado.

An alternative view of the storm can be seen using a false color Red/Green/Blue (RGB) image using POES AVHRR channels 1, 2, and 4 (below).

POES AVHRR Red/Green/Blue (RGB) false color image

On the back-sheared portion of the anvil, note how warm the IR brightness temperatures were on the AVHRR 10.8 µm IR image — due to the very thin nature of the cirrus shield, radiation from the warm ground below contributed to the IR brightness temperatures being warmer than -20º C on that portion of the cirrus shield. However, the more accurate AVHRR Cloud Top Temperature (CTT) product (below) gave a much more accurate CTT of -40 to -50º C.

POES AVHRR 10.8 µm IR image + AVHRR Cloud Top Temperature product

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(Click image for larger version)

GOES-15 is observing from a vantage point above the Equator at 89.5 W and GOES-13 is observing from a vantage point above the Equator at 75 W. The two satellites therefore have slightly different perspectives of cloud scenes over the southeast United States. These different perspectives can be exploited to yield stereoscopic views of cloud development, as shown above. Crossed eyes will yield a third image that shows three dimensions so that vertical cloud structures can be discerned. Note in particular the abundant cirrus in the image over the southeast United States.

A short tutorial on cross-eyed stereoscopy is here. Example images — non-meteorological — can be found here.

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The image loop above shows GOES-15 11-micron imagery every half hour as Tropical Depression #4 in the Atlantic strengthened to become a minimal Tropical Storm, gaining the name Colin in the process. The infrared imagery shows periodic bursts of convection with brightness temperatures colder than -70 C near the center of the storm, outflow to the northwest and to the south of the storm and brisk motion to the west-northwest. The National Hurricane Center forecasts limited strengthening of the storm, and a path that takes the storm north of the islands in the Caribbean, east of the mainland United States and west of Bermuda.

Colin’s placement in the tropical Atlantic means it can be viewed by three Geostationary satellites: GOES-12, over the Equator at 60 W, GOES-13, over the Equator at 75 W and GOES-15 over the Equator near 90 W. Careful inspection of the three images shows that GOES-15 brightness temperatures over Colin are colder than GOES-13 or GOES-12 brightness temperatures. This is because of the more oblique viewing angle from GOES-15, which is farther west than the other two satellites. Thus, the path from the cloud top to GOES-15 traverses more of the (colder) upper troposphere than the path from cloud top to GOES-13 or GOES-12, and that coldness shows up in the computed brightness temperature. The same behavior exists for one satellite as the zenith angle changes. This link shows GOES-13 weighting functions for a standard (clear) tropical atmosphere; note that the brightness temperature decreases as the viewing angle (zenith angle: ZEN in the figures) increases. Again, that’s because the path from surface to the satellite traverses more of the colder upper troposphere as the zenith angle increases.

The impulse in the tropical atmosphere that created an environment favorable for tropical cyclongenesis was easily trackable from the coast of Africa westward using Total Precipitable Water (TPW) as observed over the ocean by microwave instruments onboard POES satellites. The loop above shows the environment rich in moisture (an arc of large values of Total Precipitable Water) moving eastward across the tropical Atlantic.

For more information on Colin, refer to the CIMSS tropical website or to the National Hurricane Center. Wind shear plots at the CIMSS site suggest that Colin is moving towards a region of stronger shear (click here for the image from 1200 UTC on 3 August 2010); the more strongly-sheared environment should limit strengthening.

Update, late in the day on 3 August: Colin has lost its closed circulation and is no longer a tropical storm.

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