Banner cloud in Alaska

November 7th, 2018 |

Topography + Suomi NPP VIIRS Infrared Window (11.45 µm) images, with/without overlays of NAM12 250 hPa winds [click to play animation | MP4]

Topography + Suomi NPP VIIRS Infrared Window (11.45 µm) images, with/without overlays of NAM12 250 hPa winds [click to play animation | MP4]

Suomi NPP VIIRS Infrared Window (11.45 µm) images (above) showed a well-defined banner cloud extending from the Brooks Range in northern Alaska to the Beaufort Sea on 07 November 2018. Overlays of NAM12 model 250 hPa winds revealed the presence of a branch of the polar jet stream flowing northeastward over the region. Strong southwesterly winds interacting with the topography of the Brooks Range created a standing wave which led to the formation of the banner cloud.

In a comparison of Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images (below), note the significantly warmer 3.74 µm cloud-top brightness temperatures — as much as 40 to 50ºC warmer at 2009 UTC when the sun angle was highest over Alaska — caused by enhanced solar reflectance off the very small ice crystals at the top of the banner cloud.

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to play animation | MP4]

Suomi NPP VIIRS Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to play animation | MP4]

GOES-15 (GOES-West) Water Vapor (6.5 µm) and Infrared Window (10.7 µm) images (below) showed that a large banner cloud had persisted downwind of the Brooks Range fpr much of the day.

GOES-15 Water Vapor (6.5 µm, top) and Infrared Window (10.7 µm, bottom) images [click to play animation | MP4]

GOES-15 Water Vapor (6.5 µm, top) and Infrared Window (10.7 µm, bottom) images [click to play animation | MP4]