Great Lakes ice

January 29th, 2014
Suomi NPP VIIRS 0.64 µm visible channel and Snow/cloud discrimination RGB images

Suomi NPP VIIRS 0.64 µm visible channel and Snow/cloud discrimination RGB images

An AWIPS II image comparison of Suomi NPP VIIRS 0.64 µm visible channel data and the corresponding “Snow/cloud discrimination” Red/Green/Blue (RGB) product (above) provided a glimpse of many of the areas of ice coverage on the Great Lakes at 18:06 UTC on 29 January 2014. Ice began to increase (especially across the western Great Lakes) in late January following one of the more significant arctic outbreaks of the 2013/2014 winter season. On the RGB image, snow and ice appear as varying shades of red, in contrast to supercooled water droplet clouds which appear as shades of white.

Terra and Aqua MODIS true-color images (28 January)

Terra and Aqua MODIS true-color images (28 January)

On the previous day (28 January), comparisons between 17:28 UTC Terra and 19:12 UTC Aqua MODIS true-color RGB images from the SSEC MODIS Today site revealed the amount of sea ice motion in the relatively short time (approximately 100 minutes) between the 2 images, a result of fairly strong winds blowing over the nearshore waters. The MODIS image comparisons are centered over the Upper Peninsula of Michigan (above), and over southern Lake Michigan (below).

Terra and Aqua MODIS true-color images (28 January)

Terra and Aqua MODIS true-color images (28 January)

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Terra and Aqua MODIS true-color images (29 January)

Terra and Aqua MODIS true-color images (29 January)

On 29 January, similar comparisons of the 16:34 UTC Terra and 18:16 UTC Aqua MODIS true-color RGB images showed a better view of the multiple long and narrow ice floes in northern lake Michigan (above), and showed how much ice in southern Lake Michigan had been blown across the lake and against the southeastern shore (below).

Terra and Aqua MODIS true-color images (29 January)

Terra and Aqua MODIS true-color images (29 January)

===== 31 January Update =====

Landsat 8 Panochromatic (0.59 µm Band 8) image

Landsat 8 Panochromatic (0.59 µm Band 8) image

A 15-meter resolution Landsat 8 Panochromatic (0.59 µm Band 8) image from the SSEC RealEarth web map server (above) showed the ice coverage in the far western portion of Lake Superior on 31 January. Land-fast ice in the Apostle Islands area of Wisconsin (located in the eastern part of the image) was thicker and snow-covered, giving it a brighter white appearance.

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

Snow, sleet and freezing rain across parts of Texas, Louisiana, and Mississippi

January 25th, 2014
Terra MODIS true-color image, with significant reports of snowfall, sleet, and ice accrual

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 January24 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

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)

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

Detecting snow cover at night with VIIRS Day/Night Band imagery

January 24th, 2014
Suomi NPP VIIRS 0.7 µm Day/Night Band image

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

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

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