Ice motion in the Chukchi Sea

December 9th, 2014
Suomi NPP VIIRS 0.7 µm Day/Night Band images (click to play animation)

Suomi NPP VIIRS 0.7 µm Day/Night Band images (click to play animation)

AWIPS II images of Suomi NPP VIIRS 0.7 µm Day/Night Band data covering the 05 December – 09 December 2014 period (above; click image to play animation; also available as an MP4 movie file) revealed a fairly abrupt increase in the southwesterly motion of drift ice in the Chukchi Sea (off the northwest coast of Alaska), with giant ice floes beginning to break away north of Barrow (station identifier PABR) on 08 December. Although the northern half of the satellite scene saw little to no sunlight during this time, abundant illumination from the Moon (in the Waning Gibbous phase, at 82% of full) helped to demonstrate the “visible image at night” capability of the VIIRS Day/Night Band.

This change in ice motion was caused by an increase in northeasterly wind over that region, in response to a tightening pressure gradient between a 1040 hPa high pressure centered north of Siberia and a 958 hPa low pressure centered south of Kodiak Island in the Gulf of Alaska (below). The strong winds were also creating the potential for heavy freezing spray over the open waters north and south of the Bering Strait.

Suomi NPP VIIRS 0.7 µm Day/Night Band image, with surface analysis

Suomi NPP VIIRS 0.7 µm Day/Night Band image, with surface analysis

Along the northwest coast of Alaska, northeasterly winds at Point Hope (station identifier PAPO) gusted as high as 62 knots or 71 mph on 09 December (below). Not far to the north at Cape Lisburne (PALU), the peak wind gust was 39 knots or 45 mph.

Point Hope, Alaska meteorogram

Point Hope, Alaska meteorogram

Re-suspended volcanic ash from the Novarupta volcano in Alaska

September 29th, 2014
GOES-15 0.63 µm visible channel images (click to play animation)

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

McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the hazy signature of a plume of re-suspended volcanic ash originating from the region of the Novarupta volcano in Alaska, moving southeastward over the Shelikof Strait toward Kodiak Island on 29 September 2014. The 1912 eruption of Novarupta left a very deep deposit of volcanic ash, which often gets lofted by strong winds in the early Autumn months before snowfall covers the ash (another example occurred on 22 September 2013). Surface winds gusted as high as 30 knots at regional reporting stations, with numerical models estimating terrain-enhanced winds as high as 40-50 knots over the Novarupta ash field.

An AWIPS II image of POES AVHRR 0.86 µm visible channel data (below) showed the ash plume at 22:46 UTC; a pilot report at 22:45 UTC indicated that the top of the ash plume was between 4000 and 6000 feet above ground level.

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

POES AVHRR 0.86 µm visible channel image, with METAR surface reports and Pilot reports (PIREPs)

A sequence of 3 Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from the SSEC RealEarth web map server (below) indicated that the re-suspended ash plume had been increasing in areal extent during that period.

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

Suomi NPP VIIRS true-color images from 27, 28, and 29 September

A sequence of 4-panel products from the NOAA/CIMSS Volcanic Cloud Monitoring site (below) shows False-color images, Ash/dust cloud height, Ash/dust particle effective radius, and Ash/dust loading (derived from either Terra/Aqua MODIS or Suomi NPP VIIRS data).

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

4-panel MODIS/VIIRS products: False color image; Ash/dust cloud height; Ash/dust particle effective radius; Ash/dust loading

Hat tip to Mark Ruminski (NOAA/NESDIS) for alerting us to this event.

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