Historic Late April Nor’easter Storm

April 23rd, 2012
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)

A historic late-April “nor’easter” storm affected much of the northeastern US during the 22 April – 23 April 2012 period. This storm produced heavy snowfall (as much as 23.3 inches at Laurel Summit, Pennsylvania), heavy rainfall (as much as 5.74 inches at New Boston, New Hampshire), and wind gusts as high as 94 mph at Mount Washington, New Hampshire. AWIPS images of 4-km resolution GOES-13 6.5 µm water vapor channel images (above; click image to play animation) showed the development of various features of the storm on 23 April, including a large and well-defined comma head, dry slot, and deformation zone.

By tracking the movement of various water vapor image features between consecutive images, atmospheric motion vectors can be calculated which give an indication of the wind direction and wind speed within the middle to upper troposphere. GOES-13 6.5 µm water vapor images with overlays of MADIS 1-hour interval water vapor winds are shown below  (click image to play animation).

GOES-13 6.5 µm water vapor images + MADIS 1-hour water vapor winds (click image to play animation)

GOES-13 6.5 µm water vapor images + MADIS 1-hour water vapor winds (click image to play animation)

Satellite-derived water vapor winds can also be used to calculate an upper-tropospheric (150-300 mb) divergence product (below), which in this case showed persistent divergence aloft over much of the northeastern US on 23 April. This upper-level divergence created an environment that favored upward vertical motion within the atmospheric column, helping to enhance and prolong the ongoing precipitation over those areas.

GOES-13 water vapor images + Upper-level divergence derived from water vapor winds

GOES-13 water vapor images + Upper-level divergence derived from water vapor winds

A series of 1-km resolution MODIS 11.0 µm IR and POES AVHRR 12.0 µm IR images (below; click image to play animation) indicated that enhanced areas of colder clouds (some exhibiting a banding structure) developed over the region of persistent upper level divergence.

MODIS 11.0 µm IR + POES AVHRR 12.0 µm IR images

MODIS 11.0 µm IR + POES AVHRR 12.0 µm IR images

The 10-km resolution GOES-13 sounder Total Column Ozone (TCO) product (below; click image to play animation) revealed an anomalously large area of elevated TCO covering much of the eastern US, indicative of a lowered tropopause associated with the large upper-level trough of low pressure.

GOES-13 sounder Total Column Ozone + RUC 500 hPa geopotential heights

GOES-13 sounder Total Column Ozone + RUC 500 hPa geopotential heights

===== 24 April Update =====

MODIS 6.5 µm visible channel image + MODIS false-color RGB image

MODIS 6.5 µm visible channel image + MODIS false-color RGB image

A comparison of the 1-km resolution MODIS 0.65 µm visible channel image at 16:09 UTC (12:09 pm local time) with a corresponding false-color Red/Green/Blue (RGB) image created using the MODIS 2.1 µm “snow/ice detection” channel (above) helped to identify high-elevation areas with significant snow cover remaining after the passage of the storm — snow appears brighter white on the visible image, and darker red on the false-color image. Note that cirrus clouds appear as a lighter shade of red in the RGB image.

A 250-meter resolution MODIS true color image from the SSEC MODIS Today site (below; viewed using Google Earth) showed even better detail of the snow-covered high terrain.

MODIS true-color RGB image (viewed using Google Earth)

MODIS true-color RGB image (viewed using Google Earth)

Posted in AVHRR, GOES sounder, GOES-13, Google Earth, MODIS, POES, Red/Green/Blue (RGB) images, Satellite winds, Winter weather | No Comments »

Ice in the Bering Sea

March 11th, 2012
POES AVHRR 0.86 µm visible channel images

POES AVHRR 0.86 µm visible channel images

A sequence of AWIPS images of POES AVHRR 0.86 µm visible channel data (above) showed the areal extent of ice in the Bering Sea during the 09 March – 11 March 2012 period. The far southern edge of the ice could be seen moving a bit further to the south during this time.

The corresponding Sea Ice Analaysis chart issued by the Ice Desk at the Anchorage, Alaska National Weather Service forecast office (below) provided a more detailed analysis of the age and thickness of various portions of this ice in the Bering Sea.

National Weather Service Sea Ice Analysis chart

National Weather Service Sea Ice Analysis chart

Posted in Arctic, AVHRR, POES, Winter weather | No Comments »

Ice eddies in the Gulf of Saint Lawrence

March 6th, 2012

We received the following in an email from John Goff, lead forecaster at the Burlington, Vermont National Weather Service office:

“Couldn’t help but notice the apparent large ice eddies up in the Gulf of Saint Lawrence this afternoon (3/6) per the TERRA MODIS noon overpass (250m res). I thought that initially these were eddy/small-scale cloud vortices we sometimes see up there, but upon looping the GOES visible imagery on my AWIPS workstation it’s fairly obvious these are not clouds, but ice structures.”

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)

Thanks John for the heads-up on this very interesting example! McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation) showed the development and motion of the ice eddies on 06 March 2012. Note how many of the ice floe structures began to move toward the northeast by the end of the day, due to increasing southwesterly surface winds across the region.

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel data and the corresponding MODIS false-color Red/Green/Blue (RGB) image (below) demonstrated the value of using RGB imagery to aid in the discrimination between snow/ice (which appeared as varying shades of red in the false-color RGB image) and supercooled water droplet clouds (which appeared as the brighter white to cyan features on the RGB image).

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

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

An AWIPS image of the 1-km resolution POES AVHRR Sea Surface Temperature (SST) product at 18:55 UTC (below) indicated that SST values over the open waters were in the 30-31º F range (blue color enhancement), while the ice features exhibited colder values in the 23-25º F range (violet color enhancement).

POES AVHRR Sea Surface Temperature product

POES AVHRR Sea Surface Temperature product

Finally, a comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (below) showed a closer view of the ice eddies, and again demonstrated the value of using various RGB image combinations to discriminate between snow/ice (cyan in the false-color image) and supercooled water droplet low cloud features (white on the true-color image).

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

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

CIMSS participation in GOES-R Proving Ground activities includes making a variety of POES AVHRR and MODIS images and products available for National Weather Service forecast offices to add to their local AWIPS workstations. Currently there are 51 NWS offices receiving MODIS imagery and products from CIMSS.

Posted in AVHRR, GOES-13, GOES-R, MODIS, POES, Red/Green/Blue (RGB) images, Winter weather | No Comments »

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