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.

Heavy rainfall in Hawaii

March 6th, 2012
GOES-15 10.7 µm IR channel images (click image to play animation)

GOES-15 10.7 µm IR channel images (click image to play animation)

McIDAS images of GOES-15 10.7 µm IR channel data (above; click image to play animation) showed the cold cloud tops (some -60º C and colder, red color enhancement) associated with numerous large thunderstorms that moved across the northern Hawaiian Islands of Kauai and Oahu during the 04 March – 06 March 2012 period. Storm total rainfall amounts were as high as 35.97 inches at Hanalei on Kauai, and 15.64 inches at Punaluu Stream on Oahu. Lihue on Kauai set a new daily record rainfall amount with 8.64 inches falling on 05 March.

As one of the largest thunderstorm complexes was approaching the island of Kauai from the southwest around 03 UTC on 06 March (5 pm local time on 05 March), a comparison of a 1-km resolution NOAA-15 AVHRR 10.8 µm IR channel image to the corresponding 4-km resolution GOES-15 10.7 µm IR channel image (below) demonstrated the advantage of higher spatial resolution for identifying the location of colder cloud top IR brightness temperatures associated with convective overshooting tops. Southwest of Kauai the coldest IR temperature on the AVHRR image was -70º C, compared to -62º C on the GOES-15 image.

NOAA-15 AVHRR 10.8 µm IR image + GOES-15 10.7 µm IR image

NOAA-15 AVHRR 10.8 µm IR image + GOES-15 10.7 µm IR image

AWIPS images of the MIMIC Total Precipitable Water product with overlays of surface analyses (below; longer animation) showed that deep moisture was pooling along a stationary frontal boundary / wind shear axis that was situated between the islands of Kauai and Oahu. (Note to NWS forecast offices: MIMIC TPW is available in AWIPS, via LDM subscription)

MIMIC Total Precipitable Water product + Surface analyses

MIMIC Total Precipitable Water product + Surface analyses

GOES-15 6.5 µm water vapor channel images with water vapor Atmospheric Motion Vector (AMV) winds from the CIMSS Tropical Cyclones site (above) showed that a well-defined trough of low pressure was located to the northwest of the Hawaiian Islands during the 05 March – 06 March period.

GOES-15 6.5 µm water vapor images + water vapor atmospheric motion vector winds

GOES-15 6.5 µm water vapor images + water vapor atmospheric motion vector winds

Upper-tropospheric divergence derived from these satellite AMVs (below) revealed a trend of increasing divergence aloft over the northern Hawaiian Islands as the trough approached.

GOES-15 6.5 µm water vapor images + satellite wind derived upper-level divergence

GOES-15 6.5 µm water vapor images + satellite wind derived upper-level divergence

Juxtaposed beneath the strong upper-tropospheric divergence was strong lower-tropospheric convergence in the vicinity of the stationary front / wind shear axis, as seen in GOES-15 10.7 µm IR images with contours of IR satellite wind derived 850-925 hPa convergence (below). This created a favorable environment for upward vertical motion, with plenty of deep moisture to fuel the development of the strong thunderstorms.

GOES-15 10.7 µm IR images + satellite wind derived lower-level convergence

GOES-15 10.7 µm IR images + satellite wind derived lower-level convergence