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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MODIS 3.7 µm shortwave IR and 2.1 µm near-IR "snow/ice" channel images

A large 16,000 acre wildfire was burning in the Bull Creek Run area near Kernville in central California on 27 July 2010. On a comparison of AWIPS images of the 1-km resolution MODIS 3.7 µm shortwave IR channel and the corresponding MODIS 2.1 µm near-IR “smow/ice” channel (above), the shortwave IR image displayed a large cluster of fire hot spots (dark black pixels) along the Kern / Tulare county line (northeast of Bakersfield KBFL and southeast of Porterville KPTV). Interrogation of this cluster of hot pixels with AWIPS cursor sampling activated would simply display “NO DATA” (since the IR brightness temperatures of the hot fire pixels exceeded that of the maximum IR threshold on AWIPS), which would not allow proper identification of the location of the hottest pixels denoting the most intense areas of fire activity. However, due to the thermal sensitivity of the 2.1 µm near-IR “snow/ice” channel, that particular image did display 3 distinct areas of brighter white pixels which helped to better highlight the location of the hottest, most intense fire activity at that time.

This fire was producing a large smoke plume, but at mid-day the boundary of the smoke plume was difficult to identify on 0.65 µm MODIS visible channel imagery due to the high albedo of the ground surface below. However, the MODIS 1.3 µm “cirrus detection” channel image (below) was helpful in locating the areal coverage of the smoke — this channel is sensitive to airborne particles that are efficient scatterers of light (such as smoke, dust, haze, volcanic ash, etc). By the way, the CIMSS Satellite Blog staff feels that the 1109 knot (1275 mph) wind barb at San Liuis Obispo KSPB is likely erroneous.

MODIS 0.65 µm visible channel and 1.3 µm "cirus detection" channel images

A comparison of 250-meter resolution MODIS true color (created using bands 1/4/3) and false color (created using bands 7/2/1) Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) clearly showed the thick smoke plume moving northward, along with the location of the fire hot spots (brighter pink pixels) at the far southern end of the smoke plume.

MODIS true color (bands 4/3/1) and false color (bands 7/2/1) RGB images

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GOES-11 (GOES-West)/ GOES-15 / GOES-13 (GOES-East) 10.7 µm IR images

Severe thunderstorms propagated southeastward across far northeastern Montana late in the day on 26 July 2010. McIDAS images of GOES-11 (GOES-West), GOES-15, and GOES-13 (GOES-East) 10.7 µm IR data (above; each image set is displayed in the naive projection of the respective satellite) showed that a subtle “enhanced-v” storm top signature first began to appear on GOES-13 imagery around 23:25 UTC, with this signature becoming more apparent by 23:45 UTC on all 3 satellite IR images. In addition, a well-defined cold/warm thermal couplet (with an IR brightness temperature difference of 11-14º C) was displayed on all three satellite IR images around 01:00 UTC. Note that more frequent images were available from GOES-11 and GOES-13, since both of those operational satellites had been placed into Rapid Scan Operations (RSO) mode. GOES-15 is providing images as part of its Post Launch Testing.

According to the SPC Storm Reports, these storms produced hail as large as 4.0 inches in diameter, and produced a tornado that was responsible for EF-3 damage and 2 fatalities. This was only the 4th EF3 damage producing tornado on record in Montana, and the deadliest tornado in that state since 1923.

The GOES-15 satellite (positioned at 89.5º West longitude) had the most direct view of the storm — and an animation of 0.63 µm visible channel images (below) showing some interesting cloud top structure, including several overshooting tops as well as a well-defined anvil plume later in the animation sequence.

GOES-15 0.63 µm visible images

The GOES-11 (GOES-West) satellite (positioned at 135º West longitude) offered a more oblique view of the severe thunderstorms (below). Viewing the storms from such a high western angle, one can see the appearance of low-level inflow feeder band clouds as the thunderstorms were intensifying. In addition, since GOES-11 was in Rapid Scan Operations (RSO) mode, more images were available compared to the normal 15-minute scan interval used with GOES-15 above.

GOES-11 0.65 µm visible images

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GOES-13 10.7 µm IR images

Several days before the largest hailstone on record in the US fell in central South Dakota, McIDAS images of 4-km resolution GOES-13 10.7 µm IR data (above) showed a cluster of severe thunderstorms that propagated southeastward across far northwestern South Dakota on 19 July 2010. From a satellite perspective, this convection did not appear to be unusually intense in terms of cold IR cloud top brightness temperatures (only as cold as -63º C, darker red color enhancement) or any “enhanced-V” or other typical severe storm top signatures, but it nonetheless produced a long-duration wind and hail event that resulted in a remarkably long and wide hail damage path.

This wind-driven hail damage path can be seen on the comparison of three 250-meter resolution MODIS true color Red/Green/Blue (RGB) images (created using bands 4/3/1) from 15 July (4 days before the event), 20 July (one day after the event), and 25 July (6 days after the event) acquired from the SSEC MODIS Today site. The hail damage swath appears as the distinct broad tan-colored feature that is oriented from northwest to southeast. According to the SPC Storm Reports, the largest hail size was 2.50 inches in diameter, and the maximum wind gust was 70 mph in that particular region. However, a number of the storm reports mentioned a wind-driven hail duration of 15-30 minutes, which exacerbated the crop damage. One storm report mentioned “1150 acres of corn stripped”.

MODIS true color RGB images from 15 July, 20 July, and 25 July 2010

According to Matt Bunkers (SOO at the NWS forecast office at Rapid City SD), this event "started with two HP supercells across southeastern Montana which then merged into a bow echo across western South Dakota". These 2 distinct storms in southeastern Montana show up with better clarity on the 1-km resolution NOAA-18 10.8 µm IR image compared to the 4-km resolution GOES-13 10.7 µm IR image (below). The cloud-top IR brightness temperatures are also significantly colder on the NOAA-18 image (-61º C) than on the GOES-13 image (-52“ C).

NOAA-18 10.8 µm IR and GOES-13 10.7 µm IR images

A false-color RGB image (created using NOAA-18 AVHRR channels 01/02/04) is shown below.

NOAA-18 false-color RGB image

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