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

McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed an excellent example of an undular bore propagating southeastward off the coast of Texas and out over the Gulf of Mexico on 27 April 2011. This bore exhibited multiple wave fronts, with as many as 10-15 being visible at various times. Also note the presence of thick haze both ahead of and behind the bore: this was due to smoke from fires burning in southern Mexico and Central America (which was moving northward across the Gulf of Mexico ahead of the bore) and also from fires burning in Texas and northern Mexico (which was moving southeastward behind a cold frontal boundary that was trailing the bore).

A comparison of AWIPS images of POES AVHRR and MODIS visible channel data with overlays of hourly MADIS atmospheric motion vectors (or cloud-tracked winds) showed that the undular bore was moving southeastward at a speed of 20-30 knots.

POES AVHRR and MODIS visible images + MADIS atmospheric motion vectors

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GOES-13 6.5 µm "water vapor channel" images (click image to play animation)

We received the following in an email message from Paul Fuentes at the National Weather Service forecast office at Key West, Florida:

“Just though you might be interested in a peculiar little feature we noticed at the WFO Key West on AWIPS from GOES-13 IR imagery on 4/23/11 starting at about 22:301Z over Andros Island (24.21N, 77.7W) and persisted to into the afternoon on 4/24/11. The feature looked almost like a smoke ring (several miles across) that was drifting off to the Northeast that emanated off of Andros Island and was also apparent in VIS/WV.”

McIDAS images of 4-km resolution GOES-13 6.5 µm “water vapor channel” data (above) showed the feature in question, as it first appeared along the east coast of Andros Island (the large island in the lower left corner of the images) at 22:45 UTC on 24 April 2011 — and then propagated northeastward, grew in size, exhibited progressively colder brightness temperatures, and at times took on a ring-like shape.

A closer look using 1-km resolution GOES-13 0.63 µm visible channel images (below) again revealed the ring-like structure that was evident at various times during the day on 25 April 2011.

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

The feature (as seen on 10.8 µm POES AVHRR IR imagery, below) seemed to follow the CRAS model 300 hPa wind flow — and southwesterly winds were not found until the 375 hPa pressure level on the 12 UTC rawinsonde report from Nassau in the Bahamas.

POES AVHRR 10.8 µm IR images + CRAS model 300 hPa wind flow

A comparison of the MODIS 0.65 µm visible channel, the 11.0 µm IR window channel, the 6.7 µm water vapor channel, and the 1.3 µm cirrus detection channel images at 15:57 UTC (below) seem to support the idea that this was a high ice cloud feature.

MODIS visible, IR window, water vapor, and cirrus detection channel images

So what exactly was this interesting satellite feature? Until an explanation is found, this blog posting shall remain in the “What the heck is this?” Category…

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MODIS false color image comparison between 11 April and 24 April 2011

A comparison of MODIS false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) shows the increase in areal coverage of flooding along the Red River of the North, from north of Grand Forks, North Dakota into southern Manitoba. Also evident is the melting of most of the snow cover across northeastern North Dakota, and the melting of portions of Devils Lake (snow and ice appear as cyan features on the false color images, while water has a darker blue appearance).

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GOES-13 10.7 µm IR image (click image to play animation)

AWIPS images of GOES-13 10.7 µm IR data (above; click image to play animation) showed a large line of severe thunderstorms that moved eastward across the middle Mississippi River Valley region during the evening of 22 April 2011. This storm produced a significant number of large hail, damaging wind, and tornado reports (including one that did damage to the St. Louis airport). The initial storm damage survey has found EF-4 damage in the northern St. Louis county area.

A 1-km resolution POES AVHRR image very close to the time that the tornado was moving through the St. Louis area is shown below, with an overlay of the SPC hail, damaging winds, and tornado reports. Though the time stamp of the AWIPS image was “01:00 UTC”, the actual time that the NOAA-16 satellite was making its overpass of that region was about 01:12 UTC. Note that the storm exhibited a very well-defined “enhanced-v” signature near St. Louis (with a minimum cloud top IR brightness temperature of -83º C) — this enhanced-v IR storm top signature is often observed with areas of strong convection that are producing (or are about to produce) either large hail, damaging winds, or tornadoes.

POES AVHRR 12.0 µm IR image + severe weather reports

On a larger-scale view, a comparison of the 1-km resolution POES AVHRR 12.0 µm IR image with the corresponding 4-km resolution GOES-13 10.7 µm IR image (below) demonstrated two things: (1) how an improvement in spatial resolution can aid in the detection of small-scale cloud top features and signatures, and (2) the parallax shift of the high cloud top features on the GOES-13 image (features are shifted farther to the northwest compared to the POES AVHRR image, due to the large viewing angle from GOES-13). In spite of the AWIPS time stamps of the 2 images being different, the times of the images are actually about the same: the GOES image began scanning southward from southern Canada at 01:10 UTC, while the Miami ground station began to receive to NOAA-16 AVHRR image over the Gulf of Mexico at 01:00 UTC. Both images are scanning the St. Louis region around 01:12 UTC.

POES AVHRR 10.8 µm IR image + GOES-13 10.7 µm IR image

As the line of convection was organizing across western Missouri during the afternoon hours, GOES-13 sounder derived product images (below) of Convective Available Potential Energy (CAPE), Lifted Index (LI), and Total Precipitable Water (TPW) showed that the air mass south of the warm frontal boundary across eastern Missouri was moist (TPW values of 30-40 mm or 1.2 to 1.6 inches) and unstable (CAPE values exceeding 4000 J/kg and LI values of -5 to -9 C).

GOES-13 sounder Convective Available Potential Energy derived product image

GOES-13 sounder Lifted Index derived product image

GOES-13 sounder Total Precipitable Water derived product image

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