Cold air outbreak (and ice formation) across Hudson Bay, Canada

November 18th, 2010
GOES-13 0.63 µm visible channel images

GOES-13 0.63 µm visible channel images

A strong cyclone was located over the northern portion of Hudson Bay, Canada on 18 November 2010 — and McIDAS images of GOES-13 0.63 µm visible channel data (above) showed the formation of widespread cloud bands due to very cold arctic air flowing over the still-unfrozen waters of Hudson Bay.

The strong westerly component of the surface winds was apparently helping to cause some of the land-fast ice along the far western shoreline to begin to drift eastward into the open waters of Hudson Bay. This was more easily seen on a zoomed-in version of the GOES-13 visible images. According to lower-tropospheric GOES-13 atmospheric motion vectors, the speed of motion of the cloud band features was generally in the 25-35 knot range.

A closer view using AWIPS images of 1-km resolution MODIS 0.65 µm visible channel data (below) revealed better detail in the cloud band structure — but also suggested the initiation of ice formation along the western and southwestern near-shore waters of Hudson Bay.

MODIS 0.65 µm visible channel images

MODIS 0.65 µm visible channel images

To verify that the brighter near-shore features seen on the MODIS visible images were indeed ice forming in Hudson Bay, a pair of false-color Red/Green/Blue (RGB) images were created using the MODIS 0.65 µm visible channel data as the Red component and the MODIS 2.1 µm “snow/ice channel” data as the Green and Blue components of the image. Snow cover (which was generally 3-5 inches at the first-order reporting stations in the region) and thick ice show up as darker red features on the RGB images.

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

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

An AWIPS image of the POES AVHRR Cloud Type product (below) indicated that many of the cloud bands likely consisted of supercooled water droplets (green color enhancement), although a number of the cloud bands were beginning to show signs of glaciating farther downstream (as indicated by the yellow and orange color enhancements).

POES AVHRR Cloud Type product

POES AVHRR Cloud Type product

The POES AVHRR Cloud Top Height product (below) showed that the tops of most of thee cloud bands were in the 3-4 km range.

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Top Height product

Another indication of the change from supercooled water droplets to more of a glaciated composition could be seen on the POES AVHRR Cloud Particle Effective Radius product (below), with an increasing presence of the larger size ice crystals showing up as increasingly darker blue colors farther downstream.

POES AVHRR Cloud Particle Effective Radius product

POES AVHRR Cloud Particle Effective Radius product

Blowing glacial silt from the Alaska Panhandle region

November 17th, 2010
GOES-11 0.65 µm visible channel images

GOES-11 0.65 µm visible channel images

McIDAS images of GOES-11 0.65 µm visible channel data (above) showed hazy plumes of glacial silt blowing southwestward from the Alaska Panhandle region out over the adjacent offshore waters of the Gulf of Alaska on 17 November 2010. A NOAA-19 false-color Red/Green/Blue (RGB) image created using AVHRR channels 1, 2, and 4 (below) offered another view with a bit more contrast, making the plumes of airborne particulate matter somewhat easier to see.

NOAA-19 AVHRR false-color Red/Green/Blue (RGB) image

NOAA-19 AVHRR false-color Red/Green/Blue (RGB) image

Mountain waves over the Mid-Atlantic states

November 17th, 2010
MODIS 6.7 µm water vapor and GOES-13 6.5 µm water vapor images

MODIS 6.7 µm water vapor and GOES-13 6.5 µm water vapor images

An AWIPS image comparison of  MODIS 6.7 µm and GOES-13 6.5 µm “water vapor channel” data (above) demonstrated the advantage of improved spatial resolution for detecting the structure and areal coverage of mountain waves that were present over the Mid-Atlantic states on 17 November 2010. The spatial resolution of the MODIS water vapor image is 1 km, compared to 8 km for the GOES-13 water vapor image (note that the native resolution of the water vapor channel on GOES-13 is actually 4 km, but this image was viewed on the AWIPS “CONUS” scale, which downgrades the resolution to 8 km).

About 2 hours later, an AWIPS image of the POES AVHRR Cloud Top Height product (below) indicated that the tops of the mountain wave cloud bands at that time were generally in the 3-4 km range, which corresponded well to some of the altitudes of pilot reports of moderate turbulence (8,000-10,000 feet above ground level).

POES AVHRR Cloud Top Height product

POES AVHRR Cloud Top Height product

As part of the CIMSS involvement in GOES-R Proving Ground activities, MODIS and POES AVHRR satellite images and products are currently being made available in an AWIPS format for interested NWS forecast offices to add to their local AWIPS workstations (via LDM subscription). For more information, see the MODIS Imagery in D-2D and AVHRR Imagery and Products in D-2D sites. VISIT training lessons are also available for these MODIS and AVHRR images and products.

Upper Midwest snowstorm

November 13th, 2010
GOES-13 6.5 µm "water vapor channel" images + cloud-to-ground lightning strikes

GOES-13 6.5 µm "water vapor channel" images + cloud-to-ground lightning strikes

A major winter storm impacted parts of the Upper Midwest region on 13 November 2010, producing snowfall amounts as high as 14 inches at Emmetsburg, Iowa, 12.0 inches at Maple Grove, Minnesota (NWS MPX story), and 11.0 inches at Hawthorne, Wisconsin (NWS DLH story).

AWIPS images of 4-km resolution GOES-13 6.5 µm “water vapor channel” data (above) revealed a pronounced middle-tropospheric dry slot wrapping into the eastern sector of the storm. Thundersnow was reported at a few locations — note that there were a few cloud-to-ground lightning strikes showing up near the leading edge of the dry slot (over western Iowa after 05:15 UTC, and then over southern Minnesota after 12:15 UTC).

The corresponding 4-km resolution GOES-13 10.7 µm “IR window channel” images (below) showed that the cloud top IR brightness temperatures were not particularly cold across the areas that received the heavy snow (generally in the -30 to -40º C range, dark blue to green color enhancement), though there were bands exhibiting much colder cloud tops (colder than -60º C, red color enhancement) farther to the east within the warm conveyor belt of the storm.

GOES-13 10.7 µm "IR window channel" images + cloud-to-ground lightning strikes

GOES-13 10.7 µm "IR window channel" images + cloud-to-ground lightning strikes

A more detailed view of the storm’s cloud structures could be seen by examining a series of 1-km resolution MODIS 11.0 µm and POES AVHRR 10.8 µm “IR window channel” images (below). An overlay of the 12 UTC HPC-analyzed surface fronts and surface pressure on the 11:16 UTC POES AVHRR IR image showed that the center of the storm system was located over central Iowa at that time.

MODIS 11.0 µm and POES AVHRR 10.8 µm "IR window channel" images

MODIS 11.0 µm and POES AVHRR 10.8 µm "IR window channel" images

A 1-km resolution MODIS false-color Red/Green/Blue (RGB) image (below) showed the beginning portion of the heavy snow swath, which was stretching from southeastern Nebraska (where as much as 4.0 inches was reported at Gretna) into southwestern Iowa as the main cloud deck associated with the storm system began clear out over that region. In this false-color RGB image (created using the MODIS 0.65 µm “visible channel” image as the Red, and the MODIS 2.1 µm “snow/ice channel” image as the Green and Blue components), the deeper snow cover shows up as the darker red features.

MODIS false-color Red/Green/Blue (RGB) image

MODIS false-color Red/Green/Blue (RGB) image

========== 15 NOVEMBER UPDATE ==========

There was enough of a break in the clouds on 15 November to get a nice view of the southern portion of the swath of snow cover that stretched from Iowa into southern Minnesota — on the comparison of MODIS false-color RGB images at 17:35 UTC and 19:17 UTC  (below), the snow cover again appears as the darker red feature (in contrast to the brighter supercooled water droplet clouds, and the lighter pink ice crystal clouds).

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

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