Lake effect snow band over Lake Ontario

January 20th, 2011 |
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)

A long lake effect snow band became well-organized and stretched nearly the entire length of Lake Ontario on 20 January 2011. The cloud band was very evident on McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation). As the lake band moved onshore, it produced light to occasionally moderate snow at a few inland locations across central New York. In addition, if you look closely in the far northeastern portion of the lake you can also see ice floes that were drifting slowly eastward.

An AWIPS image of 1-km resolution MODIS 0.65 µm visible channel data (below) showed a more detailed view of the lake effect snow band feature. On the corresponding 1-km resolution MODIS Sea Surface Temperature (SST) product, relatively warm SST values as high as 40º F (lighter blue color enhancement) could be seen on either side of the cloud band.

MODIS 0.65 µm visible channel image + MODIS Sea Surface Temperature product

MODIS 0.65 µm visible channel image + MODIS Sea Surface Temperature product

A comparison of the MODIS 0.65 µm visible image with the corresponding 3.7 µm shortwave IR image (below) indicated that there was a significant amount of solar reflection off the center portion of the cloud band, suggesting a cloud composed of supercooled water droplets (darker gray enhancement) — perhaps with a very thin veil of cirrus cloud spreading out over the top of the supercooled water droplet clouds. At the time of the MODIS images, Fulton, New York (station identifier KFZY) was reporting moderate snow with a reduction in surface visibility to 0.5 mile.

MODIS 0.65 µm visible image + MODIS 3.7 µm shortwave IR image

MODIS 0.65 µm visible image + MODIS 3.7 µm shortwave IR image

However, the 4-km resolution MODIS Cloud Phase product (below) indicated that a good portion of the center of the cloud band had glaciated (salmon color enhancement), although this thin area of ice cloud was surrounded by a great deal of mixed phase (darker gray) or uncertain (lighter gray) and also water phase (blue color enhancement) cloud.

MODIS Cloud Phase product

MODIS Cloud Phase product

Mountain waves over Utah

January 19th, 2011 |
GOES-13 6.5 µm water vapor images (click image to play animation)

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

AWIPS images of GOES-13 6.5 µm ‘water vapor channel” data (above) showed a large area of dry air aloft moving southward across the state of Utah behind a shortwave trough axis on 19 January 2011. The 500 hPa wind fields from the RUC80 model indicated that winds turned more northerly and increased in speed behind the trough axis.

At 20:01 UTC, a comparison of the GOES-13 6.5 µm water vapor image with the corresponding 1-km resolution MODIS 6.7 µm water vapor image (below) demonstrated the value of higher spatial resolution for detecting the presence of widespread mesoscale mountain waves that covered a good deal of the state of Utah. Such a mountain wave signature on water vapor imagery can indicate the presence of a potential for turbulence — however, in this case there were no pilot reports of turbulence that showed up over Utah during that particular time period.

There was also an obvious northwestward parallax shift in the image features on the GOES-13 image, due to the large viewing angle from that geostationary satellite (which was positioned over the Equator at 75 degrees West longitude).

GOES-13 6.5 µm water vapor image + MODIS 6.7 µm water vapor image

GOES-13 6.5 µm water vapor image + MODIS 6.7 µm water vapor image

Cold temperatures in the Yukon Territory of Canada

January 14th, 2011 |
GOES-11 10.7 µm IR and POES AVHRR 12.0 µm IR images

GOES-11 10.7 µm IR and POES AVHRR 12.0 µm IR images

The surface air temperature at Watson Lake in the southern Yukon Territory of Canada (station identifier CYQH) fell to -56º F (-49º C) at 16 UTC on 14 January 2011. About 2 hours later, a comparison of AWIPS images of 4-km resolution GOES-11 10.7 µm IR and 1-km resolution POES AVHRR IR data (above) showed the signature of cold air that had settled into the valleys across that region — this signature was naturally much clearer on the higher resolution POES AVHRR image. The coldest surface IR brightness temperature on the POES AVHRR IR image was -52º C (-62º F) just to the southeast of Watson Lake. Also note the northeastward “parallax shift” of the warmer cloud features on the GOES-11 image, due to the high viewing angle from that geostationary satellite (which was situated over the Equator at 135º West longitude).

Elevated stratus cloud deck over Texas

January 13th, 2011 |
GOES-13 10.7 µm IR images (click image to play animation)

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

AWIPS images of 4-km resolution GOES-13 10.7 µm IR data (above; click image to play animation) showed an expansive deck of elevated stratus clouds covering much of eastern Texas and far southern Oklahoma on 13 January 2011.

The Blended Total Precipitable Water (TPW) product (below) suggested that this elevated stratus cloud feature may have been associated with a plume of moisture that was beginning to move northward from the Gulf of Mexico. The bulk of this moisture plume was likely confined to the lower troposphere, since the MODIS 6.7 µm water vapor image showed that the middle to upper troposphere was fairly dry across the region. The Fort Worth, Texas rawinsonde data indicated that the stratus deck was probably located near the 750-800 hPa pressure level, well aloft of the dry arctic air near the surface.

Blended Total Precipitable Water (TPW) product

Blended Total Precipitable Water (TPW) product

A comparison of the 1-km resolution POES AVHRR 10.8 µm IR image with the corresponding 1-km resolution POES AVHRR Cloud Type product (below) indicated that the stratus deck — which exhibited relatively warm cloud top IR brightness temperatures between -5º C and -12º C — was composed of primarily supercooled water droplets (green color enhancement on the Cloud Type product).

POES AVHRR 10.8 µm IR + POES AVHRR Cloud Type Product

POES AVHRR 10.8 µm IR + POES AVHRR Cloud Type Product

Even though the elevated stratus cloud deck did not exhibit much of a temperature contrast on the 1-km resolution MODIS 11.0 µm IR image, it’s appearance on the corresponding 1-km resolution MODIS 3.7 µm shortwave IR image was much more complex (below). Since the shortwave IR channel is very sensitive to reflected solar radiation, portions of the cloud top that were composed of smaller cloud droplets (which tend to be more effective reflectors of solar radiation) appeared warmer (darker) on the shortwave IR image.

MODIS 11.0 µm IR + MODIS 3.7 µm shortwave IR images

MODIS 11.0 µm IR + MODIS 3.7 µm shortwave IR images

This was confirmed by a comparison of the 1-km resolution POES AVHRR 3.7 µm shortwave IR image with the corresponding 1-km resolution POES AVHRR Cloud Particle Effective Radius product (below). The warmer (darker) areas on the shortwave IR image matched well with the areas of smaller cloud particles (10-20 µm radius, lighter blue color enhancement) on the Cloud Particle Effective Radius product — while the cooler (lighter gray) areas on the shortwave IR image corresponded to the larger cloud particle regions (25-35 µm radius, darker blue color enhancement).

POES AVHRR 3.7 µm shortwave IR image + Cloud Particle Effective Radius product

POES AVHRR 3.7 µm shortwave IR image + Cloud Particle Effective Radius product

The stratus cloud deck was beginning to move northward over areas that had received significant snowfall a few days earlier — deep snow cover that remained on the ground showed up as the darker red areas on a MODIS false-color Red/Green/Blue (RGB) image (below), which was created using the MODIS 0.65 µm visible image as the Red component and the MODIS 2.1 µm near-IR “snow/ice channel” as the Green and Blue components of the image.

MODIS false-color Red/Green/Blue (RGB) image (created using channels 01/07/07)

MODIS false-color Red/Green/Blue (RGB) image (created using channels 01/07/07)

The MODIS Land Surface Temperature (LST) product (below) indicated that LST values within the swath of snow cover remained in the upper 20s to low 30s F (darker blue color enhancement), in contrast to the warmer LST values in the low to mid 40s F (yellow to green color enhancement) over the adjacent bare ground areas.

MODIS Land Surface Temperature product

MODIS Land Surface Temperature product