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Southeast US tornado outbreak of 27 April 2011

April 27th, 2011

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)

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

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

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

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).

Posted in AVHRR, Convective Initiation, GOES sounder, GOES-13, GOES-R, Lightning, MODIS, POES, Severe convection | No Comments »

Record April tornado outbreak in Wisconsin

April 10th, 2011

Supercell thunderstorms developed along and ahead of an advancing cold frontal boundary and moved rapidly eastward across parts of northern and central Wisconsin on 10 April 2011. These severe storms produced widespread damaging winds, large hail (up to 3.0 inches in diameter), and a significant number tornadoes (see: NWS La Crosse | NWS Green Bay | NWS Milwaukee | SPC Storm Reports). With 11 tornadoes confirmed so far, this was the largest single-day April tornado outbreak on record in Wisconsin.

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

McIDAS images of GOES-13 0.65 µm visible channel data (above; click image to play animation; also available as a QuickTime movie) showed a number of overshooting tops associated with these severe thunderstorms. The corresponding GOES-13 10.7 µm IR images (below; click image to play animation; also available as a QuickTime movie) showed the cold cloud top IR brightness temperatures (as cold as -67º C at 01:33 UTC), as well as a few enhanced-v and cold/warm couplet signatures.

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

A comparison of a 1-km resolution NOAA-15 AVHRR 10.8 µm IR image with the corresponding 4-km resolution GOES-13 10.7 µm IR image at 21:33 UTC (below) demonstrates the advantage of higher spatial resolution to aid in the detection of enhanced-v and cold/warm thermal couplet storm top signatures, as well as a more accurate depiction of the coldest cloud top IR brightness temperatures associated with the more vigorous overshooting tops (-71º C on the NOAA-15 AVHRR IR image, compared to -58º C on the GOES-13 IR image).

NOAA-15 AVHRR 10.8 µm IR and GOES-13 10.7 µm IR images at 21:33 UTC

An AWIPS GOES-13 0.65 µm visible image at 23:45 UTC (below) was particularly interesting — a few overshooting tops could be seen over central Wisconsin, as well as long shadows being cast upon the hazy boundary layer by a narrow line of developing convection to the southwest. Cloud-to-ground lightning strikes and storm reports (damaging winds, large hail, and tornadoes) are also overlaid on the visible image.

GOES-13 0.63 µm visible image + cloud-to-ground lightning strikes + storm reports

In an effort to try and locate a satellite signature of the damage path of the EF3-rated tornado that moved from Hamburg to Merrill to Gleason in north-central Wisconsin, a comparison of 250-meter resolution MODIS true color images from 10 April (a few hours before the tornado) and 12 April (2 days after the tornado) were used (below). However, the lack of a deep snow cover or dense vegetation in this area made it very difficult to identify the tornado damage path. Note that on 10 April — the day of the tornado outbreak — there still was some light snow cover just to the northwest of the tornado track, with some sites reporting 2-3 inches of snow remaining on the ground that morning.

MODIS true color images on 10 April and 12 April (displayed using Google Earth)

Posted in AVHRR, GOES-13, Google Earth, Lightning, MODIS, POES, Red/Green/Blue (RGB) images, Severe convection | No Comments »

“Groundhog Day” Blizzard of of 01-02 February 2011

February 2nd, 2011

GOES-13 6.5 µm water vapor imagery (click on image to play animation)

AWIPS images of GOES-13 6.5 µm water vapor channel data (above; click image to play an animated GIF; also available as a QuickTime movie) showed the evolution of the “Groundhog Day Blizzard” of 01 February - 02 February 2011. This was a particularly large storm, impacting a swath of the US over 2500 miles long and 700 miles wide with snow, sleet, and ice from New Mexico to Maine — snowfall amounts were as high as 27.0 inches at Antioch, Illinois (HPC storm summary). As the storm developed, the water vapor imagery displayed a very pronounced dry slot, along with an extensive cloud shield.

MODIS 6.7 µm water vapor image

With higher spatial resolution (1 km) MODIS water vapor imagery, several interesting details could be seen, such as bands of convection in Texas (above) and “lee waves” within the dry slot, downwind of the areas of higher terrain on northern Arkansas and southern Missouri (below).

MODIS 6.7 µm water vapor image

One area that was hit particularly hard with heavy snow and blizzard conditions was northern Illinois (NWS Chicago summary) and southeastern Wisconsin (NWS Milwaukee summary) — in the Chicago area, the 20.1 inches of snow at O’Hare airport and 20.9 inches at Midway airport were the third largest snowfall amounts on record. Thundersnow was reported at a number of locations, where accompanying snowfall rates were several inches per hour; much of the lightning was likely in-cloud and/or cloud-to-cloud, but there were several cloud-to-ground lightning strikes seen overlaid on GOES-13 10.7 µm IR images (below; click image to play animation).

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

=========== 03 February Update ==========

: MODIS true color and false color images

In the aftermath of the winter storm, a comparison of MODIS true color and false color images from the SSEC MODIS Today site (above) showed extensive snow cover across the Upper Midwest region, along with ice forming in parts of Lake Michigan, Lake Huron, and most of Lake Erie (snow and ice appear as shades of cyan on the MODIS false color image, in contrast to supercooled water droplet clouds which are brighter white features). In fact, some movement of the ice features in the Great Lakes could be seen — especially in Lake Erie – in a comparison of MODIS false color images from the Terra satellite overpass at 16:03 UTC and the Aqua overpass at 19:23 UTC (below), due to brisk southwesterly surface winds across the region.