SRSO scans over the eastern Great Lakes in support of OWLeS

January 7th, 2014 |

GOES-13 0.63 µm visible imagery [click to play animation]

GOES-13 0.63 µm visible imagery [click to play animation]

GOES-13 has been placed into Super Rapid Scan Operations (SRSO) mode today to support the OWLeS program over the eastern Great Lakes, providing periods of 1-minute interval imagery each hour. The extraordinary cold air over the eastern United States is producing heavy lake-effect snows over downwind of Lakes Erie (above) and Ontario (below). Storm total snowfall amounts were as high as 60 inches;  for additional information on this event, see the Wasatch Weather Weenies and Jim LaDue view blogs.

GOES-13 0.63 µm visible imagery [click to play animation]

GOES-13 0.63 µm visible imagery [click to play animation]

In a faster animation of GOES-13 SRSO visible images covering Lake Erie (below; click image to play animation; also available as an MP4 file), the motion of ice in the western portion of the lake could be seen; the formation and intensification of organized lake-effect snow bands occured over the ice-free open waters in the central and eastern parts of Lake Erie.

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

GOES-13 0.63 µm visible channel images [click to play animation]

To supplement the GOES-13 SRSO images, a comparison of AWIPS images of Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel data (below) showed the well-defined lake-effect snow (LES) bands streaming off of Lake Erie and Lake Ontario at 15:28 UTC (10:28 AM local time). At this time, surface visibility was restricted to 1/16 mile with heavy snow at Buffalo, New York (KBUF); other notable peak wind gusts included 46 knots at Waterton, New York (KART), 49 knots at Point Petre, Ontario (CQWP), and 50 knots at Long Point (CWPS) and Port Colborne (CWPC) Ontario. Metop ASCAT surface scatterometer winds were as high as 62 knots over Lake Erie and 46 knots over Lake Ontario. The coldest cloud-top IR brightness temperatures were -39º C immediately downwind of Lake Ontario, and -35º C immediately downwind of Lake Erie.

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

About 3 hours later (at 18:17 UTC or 1:17 PM local time), a similar comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (below) showed the 2 LES bands as they continued to organize and intensify. Surface visibility had dropped to 0 miles with heavy snow and blowing snow (and a peak wind gust of 41 knots) at Buffalo (KBUF). Other notable peak wind gusts included 41 knots at Watertown (KART) and 42 knots at Fort Drum (KGTB) in New York, 51 knots at Point Petre (CQWP), and 55 knots at Long Point (CWPS) and Port Colborne (CWPC) in Ontario. The Lake Ontario LES band had extended farther inland, with Saranac Lake, New York (KSLK) reporting visibility reduced to 1 mile with snow. Cloud-top IR brightness temperatures remained about the same: -39º C downwind of Lake Ontario, and -34º C immediately downwind of Lake Erie.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

It is interesting to point out that there were a few cloud-to-ground lightning strikes downwind of Lake Ontario during the preceeding night-time hours; 1-hour lightning strikes are overlaid on a comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR images at 06:54 UTC or 1:54 AM local time (below). In addition, note the small packet of gravity waves seen propagating southward (away from the area of lightning strikes) on the IR image. Isolated cloud-to-ground lightning strikes continued in this area until the early morning hours, as seen in an animation of GOES-13 IR images.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel image (with 1-hour lightning data)

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel image (with 1-hour lightning data)

While not related to the OWLeS field experiment, it was interesting to examine GOES-13 SRSO visible channel images farther to the west over Lake Superior (below; click image to play animation; also available as an MP4 file), which displayed the following: (1) widespead multiple LES bands over much of the lake, which produced as much as 12 inches of snowfall near Deer Park (snowfall reports | Google maps), (2) a curious “solitary standing wave” feature that was oriented roughly parallel to the coastline of the eastern Upper Peninsula of Michigan east of Munising (station identifier KP53), and (3) packets of terrain-induced gravity waves both upwind and downwind of Isle Royale in the northwestern part of the lake (in addition to patches of lake ice both northwest and northeast of the island).

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

GOES-13 0.63 µm visible channel images [click to play animation]

Sensing the surface on GOES-13 water vapor imagery

January 7th, 2014 |
GOES-13 6.5 µm water vapor channel images (click to play animation)

GOES-13 6.5 µm water vapor channel images (click to play animation)

Most users of water vapor satellite imagery interpret the patterns they see as variations in moisture within the middle to upper troposphere — and for the most part, this is often a good first-order assumption. However, one must keep in mind that the water vapor channel is essentially an InfraRed channel, which is sensing the average temperature of a layer of moisture — and the altitude and depth of the layer of moisture being detected can change significantly, based upon such factors as the temperature and/or moisture profile of the atmospheric column, and the viewing angle of the satellite.

During an unusually cold arctic outbreak over the north-central US during the 06 January07 January 2014 period, the outline of various portions of the Great Lakes (in particular, Lake Superior, Lake Michigan, and Lake Erie) could actually be seen on GOES-13 6.5 µm water vapor channel imagery (above; click image to play animation). So, how is it possible to see surface features on water vapor channel satellite imagery?

In helping to understand the vertical location and vertical extent of features seen on water vapor imagery, plots of the water vapor “weighting function” (or “contribution function”) can be generated by taking into account the temperature and moisture profile of that location, along with the satellite viewing angle (or “zenith angle”). For this example, plots of GOES-13 Imager 6.5 µm water vapor weighting functions for Green Bay, Wisconsin (below) showed how the altitude and depth of the moisture layer being sensed by the water vapor channel decreased from 12 UTC on 05 January to 12 UTC on 06 January as the core of the cold arctic air moved over the western Great Lakes region. After that time, both the altitude and depth of the moisture layer being detected (as seen on the water vapor channel weighting function plots) began to increase to approximately their pervious values as somewhat warmer and more moist air began to replace the arctic air mass.

GOES-13 Imager 6.5 µm water vapor channel weighting function plots for Green Bay, Wisconsin

GOES-13 Imager 6.5 µm water vapor channel weighting function plots for Green Bay, Wisconsin

Getting back to seeing the outlines of portions of northern Lake Superior, western Lake Michigan, and western Lake Erie: what was being seen on the water vapor imagery was not necessarily the actual surface per se, but the signal of the strong temperature gradient between the cold snow-covered land surfaces and the still-unfrozen waters — and the signal of this strong surface temperature gradient was “bleeding upward” through what little moisture was present in the atmospheric column, and reaching the GOES-13 Imager water vapor detectors.