Thunderstorms over the interior of Alaska

June 19th, 2014
Suomi NPP VIIRS 0.64 µm visible channel images, with contours of GFS90 500 hPa geopotential height

Suomi NPP VIIRS 0.64 µm visible channel images, with contours of GFS90 500 hPa geopotential height

AWIPS images of Suomi NPP VIIRS 0.64 µm  visible channel data (above) showed the development of early afternoon thunderstorms over the interior of Alaska as an upper-level low moved westward over the region on 19 June 2014.

An animation of VIIRS 11.45 µm IR channel images spanning the 18-19 June period (below) depicted large areas of cloudiness exhibiting cold cloud-top IR brightness temperature values in the -45 to -50º C range (darker red color enhancement). During this time some locations across the interior of Alaska received over 4 inches of rainfall, prompting the issuance of Flood Warnings for parts of the Goodpaster, Salcha, and Upper Chena Rivers.

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

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Blended Total Precipitable Water product (click to play animation)

Blended Total Precipitable Water product (click to play animation)

The Blended Total Precipitable Water (TPW) product (above; click image to play animation) showed areas where TPW values were in the 25-30 mm or 1.0 to 1.2 inch range (darker green to yellow color enhancement). The corresponding Percent of Normal TPW product (below; click image to play animation) indicated that these TPW values were generally in the 150-200% of normal range for this region and this time of year.

Percent of Normal Blended Total Precipitable Water product (click to play animation)

Percent of Normal Blended Total Precipitable Water product (click to play animation)

Record high January temperatures in Alaska

January 27th, 2014
Suomi NPP VIIRS 0.64 µm visible channel and False-color RGB images

Suomi NPP VIIRS 0.64 µm visible channel and False-color RGB images

A strong and persistent ridge of high pressure aloft (GOES water vapor image animation) along with a northward push of unusually warm air behind a poleward-moving frontal boundary (GOES IR image animation) helped some locations in Alaska set all-time record high temperatures for the month of January (including 51º F at Nome and 52º F at Denali National Park). An AWIPS I image comparison of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel data and the corresponding false-color Red/Green/Blue (RGB) product at 23:57 UTC on 27 January 2014 (above) showed generally cloud-free conitions over much of the northwestern quarter of Alaska — at that time Nome (station identifier PAOM) had a surface air temperature of 50º F, with offshore (east-northeasterly) winds. The Nome airport reported a snow depth of 12 inches on the morning of 27 January — however, there were several areas of bare ground (which appear as shades of cyan in the RGB image) scattered across the Seward Peninsula. Snow and ice appear as varying shades of red on the RGB image; supercooled water droplet clouds appear as shades of white, with ice crystal clouds taking on a pink to lighter red hue.

About an hour and a half earlier (22:14 UTC on 27 January), a closer look at the Seward Peninsula region using AWIPS II full-resolution (250 meter) Suomi NPP VIIRS visible and false-color RGB images (below) showed even more detail in terms of the location and size of the bare ground areas, with a few upwind of Nome (which was located approximately in the center of the images). Full sunshine and winds blowing across areas of snow-free ground likely helped to warm the air that was moving toward Nome. In addition to setting the all-time January high temperature of 51º F, the morning low that day of 38º F was also the warmest January minimum temperature on record for Nome.

Suomi NPP VIIRS 0.64 µm visible channel and False-color RGB images

Suomi NPP VIIRS 0.64 µm visible channel and False-color RGB images

Ice forming in Hudson Bay, Canada

November 19th, 2013
Suomi NPP VIIRS 0.64 µm visible channel images

Suomi NPP VIIRS 0.64 µm visible channel images

AWIPS II images of 375-meter resolution Suomi NPP VIIRS 0.64 µm visible channel data (above) showed the growth of new ice immediately offshore in the northwestern portion of Hudson Bay, Canada during the 17 November19 November 2013 time period. The northwesterly flow of cold arctic air in the Arviat, Nunavut (station identifier CYEK) region was also producing well-defined cloud streets over the open waters of Hudson Bay.

The corresponding false-color “Snow Cloud Discrimination” Red/Green/Blue (RGB) images (below) confirmed that the brighter white nearshore features seen on the visible images were ice — ice and snow cover appear as shades of red on the RGB images, in contrast to supercooled water droplet clouds which appear as varying shades of white.

Suomi NPP VIIRS "Snow Cloud DIscrimination" false-color RGB images

Suomi NPP VIIRS “Snow Cloud DIscrimination” false-color RGB images

On 18 November, a significant amount of young pack ice motion can be seen in the 104-minute period between the 17:16 UTC and 19:00 UTC VIIRS visible images (below).

Suomi NPP VIIRS 0.64 µm visible channel images

Suomi NPP VIIRS 0.64 µm visible channel images

Daily “stage of development” ice analyses from the Canadian Ice Service are shown below.

Canadian Ice Service daily ice analysis for northern Hudson Bay (17, 18, 19 November)

Canadian Ice Service daily ice analysis for northern Hudson Bay (17, 18, and 19 November)

Airborne glacial silt over the Gulf of Alaska

November 16th, 2013
GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

Hat tip to Mark Ruminski (NOAA/NESDIS) for directing our attention to a pair of airborne glacial silt plumes that were being drawn southward over the far northern Gulf of Alaska on 16 November 2013. McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the two distinct hazy plumes as they were being advected offshore east of the Cordova, Alaska (PACV) area. The tight cyclonic circulation of a mesoscale area of low pressure may have helped to increase the speed of the gap winds that were lofting the glacial silt particles from the Copper River Delta and Icy Bay regions.

Suomi NPP VIIRS 0.64 µm visible channel images

Suomi NPP VIIRS 0.64 µm visible channel images

AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel data (above) showed a better view of the 2 plumes at 21:23 and 23:04 UTC. The airborne glacial silt plumes appeared darker on the corresponding 3.74 µm shortwave IR images (below) due to enhanced solar reflection off the small particles.

Suomi NPP VIIRS 3.74 µm shortwave IR images

Suomi NPP VIIRS 3.74 µm shortwave IR images

MODIS Volcanic Ash Height product

MODIS Volcanic Ash Height product

MODIS-based products designed to monitor volcanic ash plumes were also able to detect the glacial silt plumes and provide quantitative information about these features. The mean plume height (above) was around 5000 feet, with a maximum around 9000 feet at some locations. The mean particle effective radius (below) was generally in the 4-7 µm range, with a maximum size of 9-10 µm.

MODIS Volcanic Ash Particle Effective Radius product

MODIS Volcanic Ash Particle Effective Radius product