“Cooling pond effect snow” in northern Illinois

December 30th, 2012
MODIS true-color and false-color Red/Green/Blue (RGB) images

MODIS true-color and false-color Red/Green/Blue (RGB) images

A comparison of 250-meter resolution MODIS true-color and false-color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) revealed an interesting snow cover feature (snow appears as white on the true-color image, and cyan on the false-color image) surrounding a small body of water in northern Illinois (just north of the cursor) on 30 December 2012.

A closer view of that area using Google Earth (below) indicated that the small body of water was the cooling pond of the LaSalle County Nuclear Generating Station.

MODIS true-color image (displayed using Google Earth)

MODIS true-color image (displayed using Google Earth)

An AWIPS image of the MODIS Sea Surface Temperature (SST) product (below) showed that SST values were as warm as 55.8 F in the cooling pond — so the flow of colder air (which was generally in the 20s to 30s F) from a variety of directions produced “cooling pond effect snowfall” immediately downwind of the pond.

MODIS Sea Surface Temperature product

MODIS Sea Surface Temperature product

 

Meso-vortex over Lake Superior

December 29th, 2012
Suomi NPP VIIRS 0.7 µm Day/Night Band images

Suomi NPP VIIRS 0.7 µm Day/Night Band images

AWIPS images of 1-km resolution Suomi NPP VIIRS 0.7 µm Day/Night Band data (above) served as “visible images a night” to reveal the formation of a mesoscale vortex that was moving southward over the northern portion of Lake Superior (northwest of Caribou Island, station identifier CWCI) at 07:01 UTC (2:01 AM local time) and 08:42 UTC (3:42 AM local time) on 29 December 2012.

During the following afternoon, a comparison of a 1-km resolution Suomi NPP VIIRS 0.64 µm visible image at 18:26 UTC or 1:26 PM local time with the corresponding 0.5 degree radar reflectivity (below) showed the meso-vortex as it was approaching the coastline of the Upper Peninsula of Michigan near Munising (station identifier KP53).

Suomi NPP VIIRS 0.64 µm visible channel image + Radar reflectivity

Suomi NPP VIIRS 0.64 µm visible channel image + Radar reflectivity

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

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

1-km resolution GOES-13 0.63 µm visible channel images (above; click image to play animation) and the 0.5 degree radar reflectivity from Marquette, Michigan (below; click image to play animation) showed the meso-vortex as it moved southward across Lake Superior and moved inland over the Upper Peninsula. Note how the surface winds at Munising became northeasterly at 13 knots as the meso-vortex reached the coast.

0.5 degree radar reflectivity (click image to play animation)

0.5 degree radar reflectivity (click image to play animation)

Mountain waves across the Mid-Atlantic region of the US

December 27th, 2012
Suomi NPP VIIRS 0.7 µm Day/Night Band + 11.45 µm IR channel image

Suomi NPP VIIRS 0.7 µm Day/Night Band + 11.45 µm IR channel image

Strong westerly to northwesterly winds in the wake of a departing winter storm were aiding in the formation of widespread mountain waves along and downwind of the Appalachian Mountains on 27 December 2012. A comparison of AWIPS images of 1-km resolution Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) with the corresponding 11.45 µm IR channel data at 07:39 UTC or 2:39 AM local time (above) showed how the DNB imagery could be used as a “visible channel at night” to aid in the detection and characterization of cloud features that are illuminated by moonlight. City lights could also be seen in cloud-free areas (or in areas covered by thin cloud layers) on the DNB image..

After sunrise, a 1-km resolution POES AVHRR 0.63 µm visible channel image at 14:48 UTC or 9:48 AM local time (below) showed how widespread the mountain waves had become across much of the Mid-Atlantic region of the US. At that time, surface reports showed wind gusts of 37 knots or 43 mph at Martinsburg, West Virginia (station identifier KMRB) and 39 knots or 45 mph at Jefferson, North Carolina (station identifier KGEV). The peak wind gust at Jefferson was 68 knots or 78 mph at 4:55 AM local time.

POES AVHRR 0.63 µm visible channel image with METAR surface reports

POES AVHRR 0.63 µm visible channel image with METAR surface reports

Suomi NPP VIIRS 0.64 µm visible channel image + False-color Red/Green/Blue (RGB) image

Suomi NPP VIIRS 0.64 µm visible channel image + False-color Red/Green/Blue (RGB) image

Comparisons of visible channel images with their corresponding false-color Red/Green/Blue (RGB) images from Suomi NPP VIIRS (above) and Aqua MODIS (below) demonstrated how RGB imagery can be used to aid in the discrimination of cloud vs snow cover — for example, there was a large area with snow on the ground (darker shades of red on the RGB images) seen in the Shenandoah Valley and the surrounding mountains of northwestern Virginia. Gaps in the clouds also revealed patchy areas of snow cover which extended northeastward into south-central Pennsylvania.

MODIS 0.65 µm visible channel image + False-color Red/Green/Blue (RGB) image

MODIS 0.65 µm visible channel image + False-color Red/Green/Blue (RGB) image

The appearance of mountain waves on satellite imagery — either on visible imagery, or on water vapor imagery — often suggests an enhanced potential for turbulence. While there were isolated pilot reports of light to moderate turbulence across the region throught the day (some of which were seen on the VIIRS and MODIS images above), there was one incident of severe turbulence encountered in Maryland at 18:49 UTC or 1:49 PM local time (below).

Suomi NPP VIIRS 0.64 µm visible channel image + Pilot report of severe turbulence

Suomi NPP VIIRS 0.64 µm visible channel image + Pilot report of severe turbulence

Christmas Day storm across the southern US

December 25th, 2012
Suomi NPP VIIRS 0.64 µm visible and 11.45 µm IR channel images

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

A large and intense storm system moved across the southern US on 25 December 2012, producing a wide variety of weather that included heavy snow from Texas and Oklahoma into Arkansas (HPC storm summary), and hail, damaging winds, and tornadoes from eastern Texas into Alabama (SPC storm reports).

AWIPS images of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel data with overlays of surface reports and the corresponding surface analysis (above) showed great detail in the cloud structure, as well as the variety of weather conditions across the region at 19:41 UTC. At 19:48 UTC, a similar comparison of 1-km resolution MODIS 0.65 µm visible channel, 11.0 µm IR channel, and 6.7 µm water vapor channel images (below) also showed the detailed cloud structure associated with the storm, as well as the well-defined dry slot associated with an upper-level cyclonically curved jet streak that was wrapping around the base of the storm.

MODIS 0.65 µm visible, 11.0 µm IR, and 6.7 µm water vapor images

MODIS 0.65 µm visible, 11.0 µm IR, and 6.7 µm water vapor images

GOES-13 10.7 µm IR channel images (below; click image to play animation; also available as a QuickTime movie) included overlays of the SPC storm reports of hail, damaging winds, and tornadoes. This event may turn out to be one of the largest outbreaks of tornadoes on record for Christmas Day — and the EF-3 rated tornado that struck Pearl River County in Mississippi was the strongest tornado on record for Christmas Day.

GOES-13 10.7 µm IR channel images (click image to play animation)

GOES-13 10.7 µm IR channel images (click image to play animation)

GOES-13 6.5 µm water vapor channel images (below; click image to play animation; also available as a QuickTime movie) showed the dry slot (associated with the upper-level jet streak) as it approached the rear edge of the squall line which formed in eastern Texas and intensified as it moved eastward into Mississippi and Alabama.

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

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

===== 26 December Update =====

Suomi NPP VIIRS 0.7 µm Day/Night Band and IR brightness temperature difference

Suomi NPP VIIRS 0.7 µm Day/Night Band and IR brightness temperature difference “Fog/stratus product’ images

A “night-time visible image” provided by the Suomi NPP VIIRS 0.7 µm Day/Night Band (above) showed the hook-shaped signature of moonlight-illuminated snow cover across the Texas/Oklahoma Pandandle region and surrounding areas at 07:58 UTC or 1:58 AM local time on 26 December. The corresponding VIIRS IR brightness temperature difference “Fog/stratus product” image showed that while there were some patches of low cloud (yellow to red color enhancement) in the central and eastern portions of the satellite scene (as well as high cirrus clouds, black enhancement, approaching from the west), the majority of the bright areas seen on the Day/Night Band image were fresh snow cover.

Later in the day, a comparison of the 19:22 UTC VIIRS 0.64 µm visible channel image with the coresponding false-color Red/Green/Blue (RGB) image (below) demonstrated the value of using RGB images to help discriminate between snow cover (shades of red) and supercooled waater droplet cloud features (shades of white). Storm total snowfall amounts in Arkansas were as high as 15.0 inches.

Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) image

Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) image