Southeast US tornado outbreak of 27 April 2011

April 27th, 2011 |
GOES-13 0.63 µm visible images (click image to play animation)

GOES-13 0.63 µm visible images (click image to play animation)

The tornado outbreak that affected much of the Southeast US on 27 April 2011 was one of historic proportions, in terms of the number of strong to violent tornadoes produced and the number of resulting fatalities. McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above; click image to play animation; also available as a QuickTime movie) showed the multiple clusters of severe thunderstorms that developed across the region during the day. The GOES-13 satellite had been placed into Rapid Scan Operations (RSO), supplying imagery as frequently as every 5-10 minutes. Zoomed-in versions of GOES-13 RSO 0.63 µm visible images covering the period of the long-track (80 mile) EF-4 Tuscaloosa (KTCL) / Birmingham (KBHM) tornado are available here, which show that the storms exhibited a number of distinct overshooting tops during the time period between 20:40 UTC and 23:25 UTC.

AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data with overlays of severe weather reports (below; click image to play animation) showed the first round of large storms with cold cloud top IR brightness temperatures (red to black to white color enhancement) that moved through the area during the pre-dawn hours (which produced mainly damaging wind reports), followed by the development later in the afternoon and early evening hours of the stronger storms that produced numerous reports of large hail and strong tornadoes ahead of an advancing cold front (SPC storm reports). Zoomed-in versions of GOES-13 RSO 10.7 µm IR images covering the period of the long-track (80 mile) EF-4 Tuscaloosa (KTCL) / Birmingham (KBHM) tornado are available here — cloud top IR brightness temperature values during the 20:40 UTC to 23:25 UTC time period were as cold as -75º C at 22:25 UTC.

GOES-13 10.7 µm IR images (click image to play animation)

GOES-13 10.7 µm IR images (click image to play animation)

With the higher 1-km spatial resolution of the POES AVHRR IR imagery (below), more detail could be seen in the cloud top IR brightness temperature structure, and much colder cloud top temperatures could be detected in the vicinity of the strongest overshooting tops (as cold as -83º C, violet color enhancement). Other similar 1-km resolution POES AVHRR IR and MODIS IR image examples (with overlays of storm reports) are available at 16:28 UTC, 18:10 UTC, 18:12 UTC, 18:35 UTC, 19:48 UTC, 19:52 UTC, 20:13 UTC, 00:01 UTC, and 03:34 UTC.

POES AVHRR 12.0 µm IR image + SPC storm reports

POES AVHRR 12.0 µm IR image + SPC storm reports

Although there was widespread cloudiness across much of the Southeast US, hourly GOES-13 Sounder Convective Available Potential Energy (CAPE) derived product images (below) were still able to provide some indication as to the instability of the air mass that was feeding northward into the region that morning.

GOES-13 Sounder CAPE derived product imagery

GOES-13 Sounder CAPE derived product imagery

Another important ingredient was the approach of a strong trough aloft, along with an associated strong mid-level jet streak as seen in a comparison of 1-km resolution MODIS 6.7 µm water vapor imagery and CRAS model 500 millibar (hPa) wind speeds (below).

MODIS 6.7 µm water vapor channel image + CRAS model 500 MB wind speeds

MODIS 6.7 µm water vapor channel image + CRAS model 500 MB wind speeds

CIMSS participation in GOES-R Proving Ground activities includes making a variety of POES AVHRR, MODIS, and additional GOES Sounder images and products available for National Weather Service offices to add to their local AWIPS workstations. The VISIT training lessons “POES and AVHRR Satellite Products in AWIPS”, “MODIS Products in AWIPS“, and “Water Vapor Imagery and Potential Vorticity Analysis” are available to help users understand these products and their applications to weather analysis and forecasting.

To prepare for the upcoming GOES-R era, new products are being developed and tested at CIMSS using the current generation of satellite data — in fact, some of these new products are now being distributed to and evaluated by a few NWS Offices. Specially-tailored products such as Convective Initiation, Overshooting Tops, and Enhanced-V will allow for the automatic detection of the various developmental stages of convection.

 

Slide the “Set Fade Level” button located under examples of these images (above) to fade between the CIMSS Convective Initiation (CI) and CIMSS Overshooting Tops (OT) products (derived from satellite observations), along with Cloud-to-Ground (CG) lightning strikes observed from ground-based sensors. Note that there is good agreement between the locations of the satellite-derived CI and OT products and the SPC storm reports for the day (below).

 

 

Undular bore over the Gulf of Mexico

April 27th, 2011 |
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)

McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed an excellent example of an undular bore propagating southeastward off the coast of Texas and out over the Gulf of Mexico on 27 April 2011. This bore exhibited multiple wave fronts, with as many as 10-15 being visible at various times. Also note the presence of thick haze both ahead of and behind the bore: this was due to smoke from fires burning in southern Mexico and Central America (which was moving northward across the Gulf of Mexico ahead of the bore) and also from fires burning in Texas and northern Mexico (which was moving southeastward behind a cold frontal boundary that was trailing the bore).

A comparison of AWIPS images of POES AVHRR and MODIS visible channel data with overlays of hourly MADIS atmospheric motion vectors (or cloud-tracked winds) showed that the undular bore was moving southeastward at a speed of 20-30 knots.

POES AVHRR and MODIS visible images + MADIS atmospheric motion vectors

POES AVHRR and MODIS visible images + MADIS atmospheric motion vectors