MODIS false color RGB image (displayed using Google Earth)

A MODIS false color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (above; courtesy of Kathy Strabala, CIMSS) showed the areal extent of the unprecedented overland flooding that was occurring along parts of the Red River in North Dakota on 11 April 2011. Spring snow-melt along with recent heavy rainfall were contributing to the flooding. Interstate 29 north of Fargo was closed on the previous day due to rising floodwater covering the roadway.

AWIPS images of 1-km resolution MODIS 0.65 µm visible channel and 2.1 µm near-IR “snow/ice” channel data (below) was also useful for helping to highlight the location of the flooded areas. Both water and frozen lakes appear as very dark features on the 2.1 µm “snow/ice” channel image — but the frozen lakes are brighter white on the visible image.

MODIS 0.65 µm visible image + MODIS 2.1 µm near-IR "snow/ice" image

A comparison of 250-meter resolution MODIS true color and false color RGB images (below) offered a more detailed view of the flooding in the Fargo and Grand Forks areas. The flooded areas exhibited a “muddy” light brown appearance on the true color image. Farther to the west, the still-frozen Devils Lake (whose water level had reached a new record high level) and portions of northeastern North Dakota that still had snow cover (as much as 6 inches remaining on the ground) could also be seen (snow cover and frozen lakes appeared as lighter blue to cyan features on the false color image).

250-meter resolution MODIS true color and false color RGB images

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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)

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MODIS Red/Green/Blue (RGB) image, created using Bands 07/02/01

A McIDAS false-color Red/Green/Blue (RGB) image (created using MODIS Bands 07/02/01) showed numerous “burn scars” (red-enhanced features) that remained from recent fire activity across eastern Kansas and eastern Oklahoma on 05 April 2011 (above). Previous blog posts displayed imagery of the fires as they were burning on 23 March and 11 March.

========== 06 APRIL UPDATE ==========

An AWIPS image of MODIS 3.7 µm shortwave IR data (below) revealed widespread fire “hot spots” (black to red to yellow color enhancement) as fire activity flared up once again across this region on 06 April 2011.

MODIS 3.7 µm shortwave IR image

CIMSS participation in GOES-R Proving Ground activities includes making a variety of MODIS images and products available for National Weather Service offices to add to their local AWIPS workstations.

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Water vapor imagery from Monday 4 April 2011 over the Gulf of Alaska shows the development of what appears to be Kelvin-Helmholtz instability, an instability that occurs in regions of strong shear. In this case, the shear zone occurs within a gradient of moisture along the edge of a polar vortex, so the developing vortex deforms the water vapor field as detected by the GOES-11 Imager. The vertical circulation associated with the roll vortex can also change the detected moisture field: infer descent in the regions where the water vapor signal decreases with time, and ascent in regions where the water vapor signal increases with time. When these vortices are sampled by the GOES Sounder, it is common to see an enhanced ozone signal in the driest part of the developing vortex, suggesting the entrainment of dry stratospheric air into the vortex circulation.

The vortices have a signal only in the water vapor imagery. Visible imagery from AVHRR (here) show no evidence of wrapped-up vortices.

Note that the GOES-11 Imager was in eclipse between 0800 UTC and 1030 UTC and so no images were received then.

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