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

Persistent fog/stratus over the central and southern Rocky Mountains region

November 30th, 2013
Suomi NPP VIIRS fog/stratus BTD product (with overlays of METAR surface reports and ceilings/visibilities)

Suomi NPP VIIRS IR brightness temperature difference “fog/stratus product” (with overlays of METAR surface reports and ceilings/visibilities)

A night-time AWIPS image of the Suomi NPP VIIRS IR brightness temperature difference (BTD) “fog/stratus product” at 08:47 UTC or 1:47 AM local time (above) displayed an expansive area of fog and stratus cloud across much of the central and southern Rocky Mountains region on 30 November 2013. Overlays of the hourly METAR surface reports and plots of cloud ceilings and visibilities showed that the BTD “fog/stratus product” had no skill in determining whether there was fog or stratus cloud at any given location — and there was a lack of surface reports beneath large portions of the fog/stratus feature (especially across southwestern Utah).

Of the 3 rawinsonde sites in that area, Grand Junction, Colorado (KGJT) was the only one that remained covered by the fog/stratus deck; their sounding profile at 12 UTC showed a very strong temperature inversion whose base was around 7943 feet (2422 meters) above the surface. With a quasi-stationary ridge of high pressure over the region, this strong capping temperature inversion helped to hold the fog in place for several days.

A comparison of the 375-meter resolution (projected onto a 1-km AWIPS grid) VIIRS BTD fog/stratus product with the corresponding 4-km resolution GOES-15 image (below) demonstrated the advantage of higher spatial resolution in helping to diagnose the locations of edges and small-scale variations in coverage of the large fog/stratus feature.

Suomi NPP VIIRS vs GOES-15 IR brightness temperature difference "fog/stratus product" images

Suomi NPP VIIRS vs GOES-15 IR brightness temperature difference “fog/stratus product”

Products designed to provide qualitative information on fog and low stratus clouds have been developed for use on the future GOES-R ABI data; applying these GOES-R algorithms to current GOES-15 imagery offered some insight as to the low cloud thickness, as well as the probabilities of Marginal Visual Flight Rules (MVFR), Instrument Flight Rules (IFR), or Low Instrument Flight Rules (LIFR) conditions (below). Again, data-sparse regions such as southwestern Utah could benefit from the use of such products for aviation forecasting purposes. See the GOES-R Fog Product Examples blog for additional examples of these types of “data fusion” products.

During the subsequent daytime hours, McIDAS images of 1-km resolution GOES-15 0.63 µm visible channel data (below; click to play animation) showed that although the large area of fog/stratus persisted into the late afternoon hours, there was still a surprising amount of variability to the exact location of the edges of the features (which was likely driven by differential terrain heating and local wind circulations). Something to note in the visible imagery: fog in the eastern portion of the Grand Canyon in northern Arizona, which is apparently quite rare (photos)

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

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

A comparison of the 20:11 UTC (1:11 PM local time) Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding false-color Cloud-vs-snow discrimination Red/Green/Blue (RGB) image (below) helped to differentiate between the areas of snow cover (which appeared as varying shades of red on the RGB image) and the supercooled water droplet fog and stratus cloud features (which appeared as varying shades of white). Again, note the westward protrusion of fog located just to the north of Grand Canyon National Park (station identifier KGCN).

Suomi NPP VIIRS 0.64 µm visible channel and false-color Cloud-vs-snow discimination RGB image

Suomi NPP VIIRS 0.64 µm visible channel and false-color Cloud-vs-snow discimination RGB image

There were not many pilot reports availble to offer information on the height of the tops of the stratus clouds – however, one report placed the cloud tops at 8000 feet above ground level over far northwestern New Mexico at 19:08 UTC (below).

Suomi NPP VIIRS 0.64 µm visible channel image with pilot report of cloud top height

Suomi NPP VIIRS 0.64 µm visible channel image with pilot report of cloud top height

An image of the 1-km resolution POES AVHRR Cloud Top Height product at 21:00 UTC or 2:00 PM local time (below) indicated that the tops of the stratus clouds were generally in the 3-4 km range (green to yellow color enhancement).

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Top Height product

===== 01 December Update =====

On the following day, an AWIPS-2 image comparison of the afternoon Suomi NPP VIIRS 0.64 um visible channel data with the corresponding Cloud-vs-snow discrimination RGB product (below) again showed how entrenched the fog/stratus still was across that region at 19:54 UTC or 12:54 PM local time.

Suomi NPP VIIRS 0.64 um visible image and Cloud-vs-snow discrimination RGB image

Suomi NPP VIIRS 0.64 um visible image and Cloud-vs-snow discrimination RGB image

Tehuano wind event

November 27th, 2013
GOES-13 6.5 µm water vapor channel image, with surface pressure and surface front analysis

GOES-13 6.5 µm water vapor channel image, with surface pressure and surface front analysis

An AWIPS-1 image of GOES-13 6.5 µm water vapor channel data (above) showed a large storm that was affecting much of the eastern US during the 26 November - 27 November 2013 period. Arctic air surging southward behind this storm system crossed the Gulf of Mexico, was funnelled through the mountain passes of southern Mexico, and eventually emerged into the Pacific Ocean in the Gulf of Tehuantepec. This type of “Tehauno wind event” tends to occur a few times each year during the cold season — a few other cases have been documented on this blog.

A series of AWIPS-2 images of GOES-13 10.7 µm IR channel data with overlays of surface and buoy reports and tropical surface analyses (below; click image to play animation) showed that the Gulf of Tehuantepec region was highlighted on 26 November as a region susceptible to developing Storm Force (48-55 knot) winds as the cold front approached from the north. Once the strong gap winds emerged from the southern coast of Mexico, parts of that area likely began to experience storm force winds.

GOES-13 10.7 µm IR images, with surface and buoy reports and tropical surface analysis (click to play animation)

GOES-13 10.7 µm IR images, with surface and buoy reports and tropical surface analysis (click to play animation)

The plume of dry air associated with the Tehuano wind event could be seen on AWIPS-1 images of the MIMIC Total Precipitable Water product (below; click image to play animation).

MIMIC Total Precipitable Water product, with tropical surface analysis (click to play animation)

MIMIC Total Precipitable Water product, with tropical surface analysis (click to play animation)

During the day on 27 November, the hazy signature of blowing dust and sand could be seen streaming southward across the Gulf of Tehuantepec on McIDAS images of GOES-13 0.63 µm visible channel data (below; click image to play animation).

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

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