GOES-11 0.65 µm visible channel images

A persistent ridge of high pressure aloft was keeping the interior of Alaska unusually cloud-free, as was evident on McIDAS images of GOES-11 0.65 µm visible channel data on 19 September 2010 (above). Temperatures at many stations across the region had been averaging about 10 degrees F above normal during the previous week, with many daily high temperatures in the 60s and 70s F. On this particular day, the high temperatures ranged from 70º F (21º C) at Holy Cross (in the clear skies of the interior of southwestern Alaska) to only 37º F (+3º C) at Barter Island (beneath the stratus clouds along the northeast Arctic Coast).

The visible images showed that low stratus clouds and fog were attempting to work their way inland (southward) across the Arctic Slope region of northern Alaska. Widespread stratus clouds also covered much of the Gulf of Alaska, and was affecting some of the coastal regions in the far southern portions of the state. In addition, a smoke plume from a wildfire could also be seen drifting southwestward across the interior of Alaska later in the day.

AVHRR visible image + Cloud Type, Cloud Top Temperature, and Cloud Top Height products

AWIPS images of the 1-km resolution POES AVHRR visible channel data along with the corresponding Cloud Type, Cloud Top Temperature, and Cloud Top Height products (above) demonstrated how the various cloud features could be further characterized according to their type (for example, fog vs. supercooled clouds vs. cirrus clouds) along with the temperature and height of their tops.

AVHRR visible image + Cloud Type, Cloud Top Temperature, and Cloud Top Height products

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GOES-13 10.7 µm IR images

Severe thunderstorms that developed along an advancing cold frontal boundary during the pre-dawn hours of 18 September 2010, producing hail up to 1.75 inch in diameter in south-central Wisconsin (NWS Milwaukee/Sullivan news story). AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data (above) showed the development of increasingly colder IR cloud top brightness temperatures as the storms moved over the Madison, Wisconsin area (station identifier KMSN).

A series of 1-km resolution MODIS 11.0 µm IR and POES AVHRR 10.8 µm IR images between 03:32 UTC and 10:23 UTC  (below) displayed greater detail in the cloud top brightness temperature structure as the thunderstorms moved southeastward across the region.

MODIS 11.0 µm IR + POES AVHRR 10.8 µm IR images

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GOES-11 0.65 µm visible channel images

McIDAS images of GOES-11 0.65 µm visible channel data (above) revealed some interesting cloud features over the far eastern North Pacific Ocean on 17 September 2010: (1) a large “hole” in the stratoculumus cloud field, which contained an intersecting pattern of ship condensation trails (or “ship tracks”), and (2) a subtle train of von Karman vortices extending downwind of Guadeloupe Island off the coast of Baja California. These cloud features were propagating southeastward, due to northwesterly winds within the marine boundary layer.

The pattern of ship tracks on the corresponding GOES-11 3.9 µm shortwave IR images (below) displayed a darker (warmer) signature — this was caused by the reflection of incoming solar radiation off the tops of the ship track plumes (which were composed of rather small water droplets compared to the surrounding stratocumulus clouds) during the day when the sun angle was high. Note how this “dark/warm signal” disappeared at the end of the shortwave IR image animation, when the sun angle became lower in the early evening hours.

GOES-11 3.9 µm shortwave IR channel images

A bit more detail can be seen in AWIPS images of the MODIS 0.65 µm visible channel, the 3.7 µm shortwave IR channel, and the 11.0 µm IR window channel data (below). Note how the ship tracks exhibited very little signal in the IR window image, since that channel is not sensitive to the reflection of solar radiation.

MODIS 0.65 µm visible, 3.7 µm shortwave IR, and 11.0 µm IR window images

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GOES-13 0.63 µm visible channel images

McIDAS images of GOES-13 0.63 µm visible channel data on 16 September 2010 (above) showed a nice example of the role that a pre-existing convective outflow boundary can play in helping to act as a forcing mechanism for new convection — and also to help intensify existing strong convection that encounters the outflow boundary. Morning thunderstorms along the Texas/Oklahoma border region produced an outflow boundary that later moved southward and westward during the early afternoon hours. New convection was then seen to develop in Oklahoma and Texas along the old outflow boundary after about 20 UTC.

In addition, new thunderstorms that had developed in the Texas Panhandle around 19 UTC appeared to intensify once they moved eastward and encountered the aforementioned outflow boundary that was left behind from the earlier storms. According to the SPC Storm Reports, the large thunderstorms in the Texas Panhandle produced hail up to 4.00 inches in diameter, with surface wind gusts up to 75 mph.

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