GOES-15 (left) and GOES-13 (right) 6.5 µm water vapor channel images (click image to play animation)

McIDAS images of 4-km resolution GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 µm water vapor channel images (above; click image to play animation) showed a well-defined high altitude mountain wave cloud (or “banner cloud”) immediately downwind of the high elevations of the Rocky Mountains in western Montana on 01 March 2013.

A comparison of AWIPS images of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel, 11.45 µm IR channel, and 3.74 µm shortwave IR channel image at 20:47 UTC (below) revealed that this banner cloud exhibited 11.45 µm IR cloud top brightness temperatures as cold as -70º C (darker black color enhancement), yet on the 3.74 µm shortwave IR image the cloud top brightness temperatures were as warm as +24º C. These very warm shortwave IR brightness temperature values indicated that the banner cloud was composed of ice crystals that were quite small, and were thus very efficient reflectors of incoming solar radiation (reference: Ackerman, S. A., C. C. Moeller, K. I. Strabala, H. E. Gerber, L. E. Gumley, W. P. Menzel, and S-C Tsay, 1998: Retrieval of Effective Microphyscial Properties of Clouds: a Wave Cloud Case Study, Geophys. Res. Lett., 25, 1121-1124.)

Suomi NPP VIIRS 0.64 µm visible channel, 11.45 µm IR channel, and 3.74 µm shortwave IR channel images

The 1-km resolution POES AVHRR Cloud Top Height product (below) indicated that portions of this banner cloud were as high as 12 km (or around 39,000 feet). While an AIRMET had been issued advising of the possibility of moderate turbulence below 20,000 feet across the region, there was one pilot report of moderate turbulence at 38,000 feet earlier in the day at 16:37 UTC in the vicinity of the banner cloud.

POES AVHRR Cloud Height product

Strong westerly to southwesterly winds flowing across the higher elevations of the Rocky Mountains were causing a chinook wind event to occur, as adiabatic compression of the downsloping winds warmed the air. Some of the warmest surface air temeratures were seen in areas of southern Alberta, Canada that were free of snow cover — in that region MODIS Land Surface Temperature values exceeded 60º F (below).

MODIS Land Surface Temperature product + MODIS 0.65 µm visible channel image

===== 02 March Update =====

In a night-time comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band, 11.45 µm IR channel, and 3.74 µm shortwave IR channel images at 09:02 UTC or 3:02 AM local time (below), note that in the absence of reflcted sunlight the coldest shortwave IR brightness temperatures seen within the banner cloud (-63º C) were much closer to those seen on the 11.45 µm IR image (-69º C).

Suomi NPP VIIRS 0.7 µm Day/Night Band, 11.45 µm IR channel, and 3,74 µm shortwave IR channel images

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

A powerful winter storm brought historic snowfall amounts and widespread blizzard conditions to parts of Texas, Oklahoma, and Kansas during the 25 February – 26 February 2013 period (see additional information from the NWS forecast offices at Amarillo TX, Norman OK, Dodge City KS, Wichita KS, and Topeka KS). AWIPS images of 4-km resolution GOES-13 6.5 µm water vapor channel images (above; click image to play animation) showed the evolution of the storm system on 25 February, which included the development of well-defined dry slot and comma head signatures.

A comparison of 1-km resolution MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images (below) revealed a snapshot of the storm at 20:00 UTC or 3 PM local time on 25 February. A line of deep convection exhibiting cold cloud top temperatures extended from the Gulf of Mexico northward into Missouri, which produced large hail, damaging winds, and a tornado (SPC storm reports).

MODIS 0.65 µm visible, 11.0 µm IR, and 6.7 µm water vapor channel images

Very strong winds were associated with this storm, which created a large area of blowing dust across southwest Texas and southeastern New Mexico on 24 February — and GOES-13 0.63 µm visible channel images (below; click image to play animation) revealed additional areas of blowing dust across drought-stricken areas of southern Texas on 25 February, where winds gusted as high as 56 mph and visibilities were reduced to 1 mile or less in some locations (see NWS Brownsville TX summary).

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

During the following overnight hours the clouds had cleared across the Texas panhandle region, which allowed the Suomi NPP VIIRS 0.7 µm Day/Night Band (below) to provide a “visible image at night” (aided by bright illumination from the “full snow moon”) to display the areal extent of the fresh snow cover at 08:38 UTC or 3:38 AM local time. While the deep snow pack appeared somewhat colder on the corresponding VIIRS 11.45 µm IR image, the exact edges of the snow cover were easier to see on the Day/Night Band image.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR images

During the afternoon hours on 26 February, a comparison of the Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding false-color Red/Green/Blue (RGB) image at 20:02 UTC or 3:02 PM local time (below) aided in the discrimination between snow cover (varying shades of darker red on the RGB image) and supercooled water droplet cloud features (lighter shades of white). Glaciated (ice crystal) cloud features exhibit a lighter pink appearance in the RGB image.

Suomi NPP VIIRS 0.64 µm visible and False-color Red/Green/Blue (RGB) composite images

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MODIS 0.65 µm visible channel and 6.7 µm water vapor channel images

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and 6.7 µm water vapor channel data (above) revealed the presence of widespread mountain waves across parts of the Mid-Atlantic states on 20 February 2013. Parallel bands of rotor clouds helped to identify the location of these waves (caused by strong northwesterly winds interacting with the terrain of the Appalachian Mountains) where ample moisture was present, but in many areas the atmosphere at that altitude was too dry to support rotor cloud development — this demonstrated the advantage that water vapor imagery has in helping to know the total areal coverage of such mountain wave activity.

Mountain waves can be an aviation hazard, since they are capable of generating turbulence. Plots o pilot reports of turbulence within +/- 30 minutes of the MODIS overpass time indicated that there was one report of severe turbulence in the 7000-9000 foot altitude range over extreme northwestern Virginia, along with moderate turbulence likely associated with rotor circulation wind shear in northern Virginia and southern Virginia. In addition, there was a report of moderate clear air turbulence at 36,000 feet over eastern Chesapeake Bay, suggesting that these mountain waves might be vertically propagating.

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GOES-15 0.63 µm visible channel images with surface wind barbs (click image to play animation)

McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the development of a mesoscale eddy immediately downwind of San Clemente Island off the coast of southern California on 17 February 2013. The eddy was helping to push the marine boundary layer farther inland, bringing stratus clouds and cooler temperatures to some coastal locations.

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel data (below) revealed that cloud top IR brightness temperatures of the marine layer stratus were in the 6-7º C range (darker blue color enhancement).

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

A 250-meter resolution Aqua MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Direct Broadcast site (below) showed the fine structure of the center of the eddy circulation.

Aqua MODIS true-color Red/Green/Blue (RGB) image

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