According to the National Snow and Ice Data Center, a large portion of the Wilkins Ice Shelf in the Antarctic (map) began to collapse during late February and early March 2008. A Terra MODIS visible image (above; courtesy of Shelley Knuth, SSEC Antarctic Meteorological Research Center) shows the extent of ice shelf disintegration on 10 March 2008.

The latest real-time IR satellite composite and Antarctic synoptic analysis chart from the SSEC AMRC is shown below.

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As a powerful winter storm intensified and produced heavy snowfall and blizzard conditions across much of the Ohio River Valley region of the US during the 07 March – 08 March 2008 period (Columbus, Ohio set new all-time records with a 20.4 inch storm total snowfall and 15.5 inches in 24 hours), a strong surge of cold air plunged southward across the Gulf of Mexico. This cold surge continued equatorward, crossed the terrain of southern Mexico, and emerged as a well-defined “Tehuano wind event“ over the Gulf of Tehuantepec along the Pacific coast (hence the name “Tehuantepecer“ given to this type of strong wind event). An AWIPS image of the GOES-12 10.7µm IR channel (above) includes plots of the surface frontal positions, the 850mb wind streamlines, and polar-orbiting microwave scatterometer winds from the QuikSCAT instrument on the morning of 08 March.

An AWIPS image of wind data from the QuikSCAT SeaWinds scatterometer instrument overlaid on the topography of the region (below) reveals the break in the higher terrain of the Sierra Madres mountain chain (known as the Chivela Pass), through which the northerly winds of a strong cold surge are able to pass from the Gulf of Mexico to the Pacific Ocean.

A closer view of the QuikSCAT wind data (below) shows that wind speeds at the 10-meter height were as strong as 46 knots (24 meters per second) as the cold “mountain gap winds” emerged over the Gulf of Tehuantepec. The accuracy of the QuikSCAT retrieved winds is probably very good in this case, since there is a very low rain contamination as noted by the Rain Falg value of only 6% (high rain contamination often leads to increased errors in QuikSCAT wind direction and speed magnitude).

An animation of GOES-12 visible images during the daylight hours on 07 March, followed by 3.9µm IR images during the overnight hours, and then visible images during the daylight hours on 08 March (below) shows the southward progression of a well-defined cloud arc (or “rope cloud”) that marked the leading edge of the cold surge.

A close-up animation of GOES-12 visible images (below) shows the period where the Tehuano wind event was moving through the Ixtepec, Mexico area (located just north of the Gulf of Tehuantepec) and flowing southward into the Gulf of Tehuantepec on 07 March. Note that the turbidity of the water in the small bay along the coast increased (as seen by the lighter gray, “muddy appearance” of the water).

The strong winds associated with a Tehuano wind event often cause upwelling of the coastal waters, which brings cooler and more nutrient-rich water to the surface. A comparison of MODIS true color and Land Surface Temperature images (below) from the MODIS Rapid Response System site indicated that a pool of colder offshore water temperatures (15º – 19º C, green to yellow colors) was in place in the Gulf of Tehuantepec, surrounded by warmer water temperatures in the 23º – 27º C range (orange colors). A closer view using 250-meter resolution MODIS true color imagery better shows the turbidity of the water in the bay just south of Ixtepec, as well as a plume of blowing dust being advected southward over the water.

Surface weather observations at Ixtepec, Mexico showed that winds changed to northerly and increased to 35 mph (16 meters per second) with the arrival of the Tehuano event (below). There was a ship report of winds as high as 50 knots (26 meters per second) over the Gulf of Tehuantepec at 18:00 UTC on 08 March; surface winds a day earlier were as high as 46 knots (24 meters per second) at Minatitlan, Mexico farther to the north (along the Gulf of Mexico coast).

Reference: Steenburgh, W. J., D. M. Schultz, B. A. Colle, 1998: The Structure and Evolution of Gap Outflow over the Gulf of Tehuantepec, Mexico. Monthly Weather Review: Vol. 126, pp. 2673-2691

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AWIPS images of the GOES-12 10.7 µm IR channel (above) revealed 2 separate periods where packets of “transverse banding” (thin, banded cloud elements oriented perpendicular to the ambient flow) were forming over parts of Florida, Alabama, and Georgia on 07 March 2008. These transverse bands were located at high altitudes along the western edge of the large convective cloud mass that was moving across the region; severe thunderstorms along the eastern flank of this line produced several tornadoes in northern Florida and southern Georgia (including a tornado responsible for 2 fatalities near Lake City, Florida).

A comparison of the 4-km resolution GOES-12 IR image at 16:32 UTC with the 1-km resolution NOAA-17 AVHRR IR image at 16:20 UTC (below) shows a closer view of one area of transverse banding moving over the Florida panhandle region, and demonstrates that more accurate identification of this type of small-scale cloud feature is possible with improved spatial resolution satellite imagery. The IR channels available on the Advanced Baseline Imager (ABI) instrument on GOES-R will provide 2-km resolution data, which should improve the ability to detect subtle features such as transverse banding.

There were large areas across the southeastern US that were covered by aviation AIRMET (Airmen’s Meteorological Information) turbulence advisories (outlined in yellow, below), but these advisories were for locations a bit farther to the west than the transverse banding seen on the satellite imagery. In fact, there were indeed a couple of pilot reports of high-altitude turbulence indicated near the regions of transverse banding.

In addition to the AIRMET advisories, there was also a SIGMET (Significant Meteorological Information, outlined in red) that had been issued due to isolated aircraft reports of severe to extreme turbulence at the 28,000-29,000 feet altitude range over northern Alabama and western Tennessee during the 15:00-16:00 UTC period. Note that there were also some transverse banding signatures evident in the patch of cloud that was located over northern Mississippi at that time — once again, the structure of these banded cloud features was much more obvious when viewed using the 1-km resolution NOAA-17 AVHRR IR imagery (below).

On that same day, a Lufthansa Airbus A340 passenger jet flying from Frankfurt, Germany to Atlanta, Georgia encountered severe turbulence around 19:15 UTC, at an altitude of 36,300 feet (while over the Atlantic Ocean, about 80 nautical miles southeast of Charleston, South Carolina):

CHS UUA /OV 80SE CHS/TM 1915/FL363/TP HA343/TB SEV FL350-FL363/RM CLIMB 130 FT ZJX=

The aircraft apparently lost about 1300 feet of altitude after encountering the severe turbulence. Ten persons aboard that flight received injuries (with a few requiring hospitalization), and the plane landed with priority clearance at Atlanta around 20:07 UTC. While the GOES-12 10.7 µm IR imagery in the vicinity of the incident (below) did not exhibit any of the transverse banding signatures that were seen farther inland, there were some rapidly developing thunderstorms in the vicinity (around 80 nautical miles southeast of Charleston, CHS) that likely contributed to the high-altitude turbulence. Note that the Lufthansa pilot report of turbulence did not show up in the database that was plotted by the McIDAS software shown below, but it was plotted by the AWIPS software (although in the wrong location, directly over Charleston, instead of 80 miles southeast of CHS).

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Several inches of snow fell in parts of Texas, Oklahoma, Arkansas, and Missouri during the evening of 03 March 2008 into the morning of 04 March 2008 — snowfall amounts included 8.5 inches at Springfield, Missouri, 8.0 inches at Broken Arrow, Oklahoma, 6.0 inches at Bella Vista, Arkansas, and 5.0 inches at Pottsville, Texas. Snow was even reported briefly at Shreveport in far northwestern Louisiana, and the 1.0 inch of snow at Dallas-Ft. Worth in Texas set a new daily snowfall record for 03 March. GOES-12 6.5 µm water vapor images (above) show that many of the reports of snow (along with some rain and freezing rain) were occurring along the periphery of a well-defined dry slot that was advancing northeastward from Texas into Arkansas. In addition, a deformation zone just northwest of the dry slot was also acting to help organize the southwest-to-northeast oriented banded structure of the resulting precipitation.

AWIPS images of the GOES sounder Total Column Ozone product (below) depicted a lobe of high values of ozone (greater than 400 Dobson units, red colors) associated with the sharp trough aloft that was swinging eastward across the southern and central Plains. Such elevated ozone levels are often seen in regions where the tropopause altitude is quite low — in fact, the NAM fields indicated that the “dynamic tropopause” (taken to be the pressure level of the 1.5 Potential Vorticity Unit surface) was as low as the 700 hPa pressure level at 12:00 UTC.

GOES-12 visible images from the following morning (below) revealed several large patches of snow-covered ground as the clouds began to retreat eastward. Note the aforementioned southwest-to-northeast orientation of the bands of snow cover in Oklahoma, Arkansas, and Missouri. The snow on the ground melted quickly under the warmth of the March sun, eroding quickly from the edges inward on the visible satellite imagery. Also, if you look closely, you can see a small puff of smoke move northward from a fire that was burning briefly in west-central Oklahoma (toward the end of the animation).

If we compare AWIPS images of the MODIS visible channel and the 2.1 µm near-IR “snow/ice channel” at 16:57 UTC 0r 11:57 am local time (below), we see that both clouds and patches of snow cover appear as brighter white features on the visible channel image; however, on the snow/ice image the snow cover features appear much darker (in contrast to the much lighter appearance of supercooled water droplet clouds). Cloud features in Missouri and Arkansas that were composed of ice crystals also appear darker on the snow/ice channel image.

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