In order to determine cloud type over Montana and the Dakotas, we access GOES-10 satellite imagery and products on an individual basis, and then integrate this information to make a final determination. We begin with a frame-by-frame examination over Montana and the Dakotas:

1. Visible
Little to no evidence of clouds over the region of interest. A visible animation would help, but it would still be difficult to discern clouds. These observations indicate an optically-thin cloud, but give no indication of cloud height.

2. Short-wave infrared
Clouds appear dark grey against the light grey surface background. In short-wave imagery, water clouds generally appear light grey (e.g. offshore of northern California), while ice clouds appear black (e.g. Utah-Arizona border). The dark grey appearance of the clouds over Montana and the Dakotas may indicate mixed-phase clouds.

3. Water vapor
Clouds appear white and enhanced purple. Since the weighting function of the water vapor channel is around 400 mb, this image indicates that the cloud is at a mid- to upper-levels.

4. Window infrared
Clouds appear white against the black and dark grey surface background. The blackbody temperature of these clouds is near freezing (temperature scale not shown) or around 600 mb ( see Bismarck 00Z sounding ).

5. Split-window infrared
Clouds appear white against the black and dark grey surface background. This image is very similar to the window infrared image, although both clouds and background appear slightly warmer.

6. Reflectivity product
Clouds appear light grey against a grey surface background. In the reflectivity product, water clouds appear white (e.g. offshore of northern California), while ice clouds appear black (e.g. Utah-Arizona border). As with the short-wave infrared image, the reflectivity product may indicate mixed-phase clouds.

7. Long-wave difference product
Clouds appear black/dark grey against a grey surface background. In the long-wave difference product, most clouds appear light grey with the exception of thin cirrus, which appear black.

Taken together, these seven images/products suggest that the clouds over Montana and the Dakotas are thin cirrus. The visible image indicates that the clouds are optically thin, and the water vapor image indicates that the clouds are at mid- to upper-levels. In addition, the black/dark grey color of the clouds in the long-wave difference product is a common feature of thin cirrus.

Optically-thin cirrus can explain the appearance of the clouds in the window and split-window infrared channels as well as in the short-wave infrared channel. The near freezing temperature of the clouds in the window and split-window infrared channels can be attributed to transmission of surface radiation through the optically-thin clouds, making the clouds appear significantly warmer. The dark grey appearance of the clouds in the short-wave infrared channel is consistent with optically-thin cirrus, since optically-thick cirrus would appear black.

Evidence that these clouds are indeed thin cirrus comes from METAR observations from Dickinson (KDIK) in west-central North Dakota:

KDIK 222053Z 32009KT 20SM BKN250 28/03 SLP111 

which indicate that, on the 22nd at 2053Z, broken clouds were observed at 25,000 feet (BKN250).

A cloud top pressure product based on GOES sounder observations from the University of Wisconsin/CIMSS shows the clouds at or above 300 mb.
 

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We welcome your comments and discussion at ramsdis@comet.ucar.edu