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

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Terra MODIS true-color image, with significant reports of snowfall, sleet, and ice accrual

A relatively rare winter storm produced snowfall, sleet, and freezing rain (storm reports) across parts of far eastern Texas, central Louisiana, and southwestern Mississippi during the 23 January – 24 January 2014 time period. Numerous traffic accidents resulted from the ice-covered roads, with a few fatalities reported. A day after the event, a Terra MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Today site at 17:03 UTC on 25 January (above) showed the remaining swath of snow on the ground (including locations of some of the more significant reports of snowfall, sleet accumulation, and ice accrual from freezing rain). Also note the bands of “lake-effect” clouds streaming eastward from Lake Pontchartrain north of New Orleans.

Suomi NPP VIIRS 0.64 µm visible channel image

A little more than 2 hours after the MODIS image, there was no evidence of any snow cover seen on a Suomi NPP VIIRS 0.64 µm visible channel image at 19:20 UTC (above).  In fact, GOES-13 0.63 µm visible channel images (below; click image to play animation) showed just how quickly the 1-2 inches of remaining snow cover melted away under full sun and daytime heating.

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

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Suomi NPP VIIRS 0.7 µm Day/Night Band image

Due to illumination by moonlight — the Moon was in the waning crescent phase, at 40% of full — a broad area of snow cover could be seen over parts of the High Plains and Foothills regions of the US on an AWIPS image of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) data at 08:15 UTC or 1:15 AM local time on 24 January 2014 (above). This was what remained of the general 1-4 inches of new snow that fell over that area, aided by upslope flow in the wake of a southward-moving cold frontal passage on 23 January.

A comparison of this Day/Night Band image with the corresponding VIIRS 11.45-3.74 µm IR brightness temperature difference (BTD) “Fog/stratus product” and 11.45 µm IR channel images (below) confirmed that this feature seen on the DNB image was not an area of fog or low-level clouds (although some patches of cold high-altitude clouds were seen from far northern Colorado into Wyoming and Nebraska). On the 11.45 µm IR image, some areas in eastern Colorado exhibited IR brightness temperature values of -30º C or colder (yellow color enhancement) — these were likely locations where the snow cover was the deepest, allowing faster radiational cooling of the surface air layer.

Suomi NPP VIIRS 0.7 µm Day/Night Band, IR BTD “fog/stratus product”, and 11.45 µm IR channel images

A Suomi NPP VIIRS 0.64 µm visible channel image at 19:42 UTC or 12:42 PM on the following afternoon (below) showed that while the areal coverage of the snow cover had decreased with daytime heating, what snow cover did remain was acting to hold surface air temperatures down at least 10-15º F compared to adjacent bare-ground locations.

Suomi NPP VIIRS 0.64 µm visible channel image, with METAR surface reports

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GOES-15 6.5 µm water vapor channel images (click to play animation)

McIDAS images of 4-km resolution GOES-15 6.5 µm water vapor channel data (above; click images to play animation) showed the dramatic signature of rapid intensification of a very large mid-latitude cyclone over the eastern Pacific Ocean during the 20 January – 23 January 2014 time period.

A comparison of AWIPS images of 1-km resolution Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel data (below) revealed the tightly-wrapped center of circulation at 13:01 UTC on 20 January. Intricate mesoscale banding structures could also be seen within portions of the warm conveyor belt southeast and east of the storm center (which was analyzed to have a central pressure of 956 hPa).

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

A Suomi NPP VIIRS 0.64 µm visible channel image (below) showed a small but well-defined comma-shaped cloud feature marking the center of the storm at 00:13 UTC on 21 January (which was analyzed to have a central pressure of 952 hPa).

Suomi NPP VIIRS 0.64 µm visible channel image

A Suomi NPP VIIRS 0.64 µm visible channel image at 23:54 UTC on 21 January (below) depicted the band of clouds associated with the 950 hPa cyclone’s cold front as it approached the northwestern portion of the Hawaiian Island chain. A narrow “rope cloud” marked the leading edge of the cold frontal boundary.

Suomi NPP VIIRS 0.64 µm visible channel image

In a closer view centered over the Hawaiian Islands at 23:54 UTC on 21 January (below), a hazy “vog” plume (from the active Kilauea volcano on the Big Island) could be seen blowing northeastward ahead of the approaching cold front. Note how the areal coverage of the vog plume shows up better in the broadband 0.7 µm Day/Night Band image compared to the 0.64 µm visible channel image with its more narrow spectral width.

Suomi NPP VIIRS 0.64 µm visible channel and 0.7 µm Day/Night Band images

Finally, a Suomi NPP VIIRS 0.64 µm visible channel image at 23:35 UTC on 22 January (below) showed the cold frontal band as the leading edge was about to move southeast of the Big Island of Hawaii. Note that Honolulu (PHNL) had a temperature/dewpoint of 78ºF/45ºF, with northwesterly winds gusting to 34 knots at 00 UTC. Wind speeds on the summits of the Big Island of Hawaii were sustained hurricane force, with gusts to near 100 mph. The strong winds also caused a giant northwesterly ocean swell, with significant wave heights as high as 31 feet at Buoy 51101 (located 91 miles northwest of Kauai). There was also a notable air temperature drop at Buoy 51101 as the cold front passed, with a peak wind gust of 39 knots.

Suomi NPP VIIRS 0.64 µm visible channel image

GOES-15 0.63 µm visible channel images (below; click image to play animation) showed the cold front as it was passing through the Hawaiian Island chain on 22 January. A few areas of orographic wave clouds could be seen as the strong northwesterly winds in the wake of the cold front interacted with the topography of the islands.

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

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