Historic blizzard affects parts of Texas, Oklahoma, and Kansas

February 26th, 2013
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 powerful winter storm brought historic snowfall amounts and widespread blizzard conditions to parts of Texas, Oklahoma, and Kansas during the 25 February26 February 2013 period (see additional information from the NWS forecast offices at Amarillo TX, Norman OK, Dodge City KS, Wichita KS, and Topeka KS). AWIPS images of 4-km resolution GOES-13 6.5 µm water vapor channel images (above; click image to play animation) showed the evolution of the storm system on 25 February, which included the development of well-defined dry slot and comma head signatures.

A 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) revealed a snapshot of the storm at 20:00 UTC or 3 PM local time on 25 February. A line of deep convection exhibiting cold cloud top temperatures extended from the Gulf of Mexico northward into Missouri, which produced large hail, damaging winds, and a tornado (SPC storm reports).

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

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

Very strong winds were associated with this storm, which created a large area of blowing dust across southwest Texas and southeastern New Mexico on 24 February — and GOES-13 0.63 µm visible channel images (below; click image to play animation) revealed additional areas of blowing dust across drought-stricken areas of southern Texas on 25 February, where winds gusted as high as 56 mph and visibilities were reduced to 1 mile or less in some locations (see NWS Brownsville TX summary).

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)

During the following overnight hours the clouds had cleared across the Texas panhandle region, which allowed the Suomi NPP VIIRS 0.7 µm Day/Night Band (below) to provide a “visible image at night” (aided by bright illumination from the “full snow moon”) to display the areal extent of the fresh snow cover at 08:38 UTC or 3:38 AM local time. While the deep snow pack appeared somewhat colder on the corresponding VIIRS 11.45 µm IR image, the exact edges of the snow cover were easier to see on the Day/Night Band image.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR images

During the afternoon hours on 26 February, a comparison of the Suomi NPP VIIRS 0.64 µm visible channel image with the corresponding false-color Red/Green/Blue (RGB) image at 20:02 UTC or 3:02 PM local time (below) aided in the discrimination between snow cover (varying shades of darker red on the RGB image) and supercooled water droplet cloud features (lighter shades of white). Glaciated (ice crystal) cloud features exhibit a lighter pink appearance in the RGB image.

Suomi NPP VIIRS 0.64 µm visible and False-color Red/Green/Blue (RGB) composite images

Suomi NPP VIIRS 0.64 µm visible and False-color Red/Green/Blue (RGB) composite images

Mountain wave turbulence over the Mid-Atlantic states

February 20th, 2013
MODIS 0.65 µm visible channel and 6.7 µm water vapor channel images

MODIS 0.65 µm visible channel and 6.7 µm water vapor channel images

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and 6.7 µm water vapor channel data (above) revealed the presence of widespread mountain waves across parts of the Mid-Atlantic states on 20 February 2013. Parallel bands of rotor clouds helped to identify the location of these waves (caused by strong northwesterly winds interacting with the terrain of the Appalachian Mountains) where ample moisture was present, but in many areas the atmosphere at that altitude was too dry to support rotor cloud development — this demonstrated the advantage that water vapor imagery has in helping to know the total areal coverage of such mountain wave activity.

Mountain waves can be an aviation hazard, since they are capable of generating turbulence. Plots o pilot reports of turbulence within +/- 30 minutes of the MODIS overpass time indicated that there was one report of severe turbulence in the 7000-9000 foot altitude range over extreme northwestern Virginia, along with moderate turbulence likely associated with rotor circulation wind shear in northern Virginia and southern Virginia. In addition, there was a report of moderate clear air turbulence at 36,000 feet over eastern Chesapeake Bay, suggesting that these mountain waves might be vertically propagating.

Eddy off the coast of southern California

February 17th, 2013
GOES-15 0.63 µm visible channel images with surface wind barbs (click image to play animation)

GOES-15 0.63 µm visible channel images with surface wind barbs (click image to play animation)

McIDAS images of GOES-15 0.63 µm visible channel data (above; click image to play animation) showed the development of a mesoscale eddy immediately downwind of San Clemente Island off the coast of southern California on 17 February 2013. The eddy was helping to push the marine boundary layer farther inland, bringing stratus clouds and cooler temperatures to some coastal locations.

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel data (below) revealed that cloud top IR brightness temperatures of the marine layer stratus were in the 6-7º C range (darker blue color enhancement).

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

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

A 250-meter resolution Aqua MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Direct Broadcast site (below) showed the fine structure of the center of the eddy circulation.

Aqua MODIS true-color Red/Green/Blue (RGB) image

Aqua MODIS true-color Red/Green/Blue (RGB) image

Polar low over the western Bering Sea

February 16th, 2013
MTSAT-2 0.73 µm visible channel images (click image to play animation)

MTSAT-2 0.73 µm visible channel images (click image to play animation)

McIDAS images of MTSAT-2 0.73 µm visible channel data (above; click image to play animation) showed a small polar low that was developing just south of the sea ice edge in the western Bering Sea on 15 February 2013. Widespread cloud streets could be seen streaming southwestward off the sea ice edge as colder air was being drawn into the circulation of the low as it propagated westward.

Greater detail in the sea ice, the cloud streets, and the curved cloud bands associated with the circulation of the polar low could be seen in an AWIPS comparison of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel and false-color Red/Green/Blue (RGB) images (below). In the RGB image, snow and ice appear as darker shades of red, in contrast to supercooled water droplet clouds (which appear as varying shades of white) — and clouds that are becoming glaciated also exhibit a pink to lighter red appearance.

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

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

Several hours later, a comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 3.74 µm shortwave IR images at 15:00 UTC on 16 February (below) showed the tight circulation of the polar low approaching the east coast of Russia’s Kamchatka Peninsula. Even though a thin veil of high clouds covered most of the Kamchatka Peninsula (VIIRS 11.45 µm IR image), another feature of interest was the large (but diffuse) bright spot seen on the DNB image, which coincided with a small shortwave IR thermal anomaly or “hot spot” (darker black to yellow enhancement) which exhibited a maximum IR brightness temperature of 43º C. This feature was the Plosky Tolbachik Volcano, which was experiencing strong seismic activity and producing effusive lava flows at the time (KVERT site).

Suomi NPP VIIRS 0.7 µm Day/Night Band and 3.74 µm shortwave IR images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 3.74 µm shortwave IR images