MODIS true color and false color RGB images

The comparison of a 250-meter resolution MODIS true color Red/Green/Blue (RGB) image (created using Bands 1/4/3) with the corresponding MODIS false color (created using Bands 7/2/1) image from the SSEC MODIS Today site (above) showed intricate details of the surface oil slick in the far northern Gulf of Mexico on 19 June 2010. The glaciated cloud tops of deep convection appeared as darker shades of cyan on the false color image.

On the true color image, note the small black features located over the bright oil slick, toward the lower left portion of the image — this was smoke from small fires which were apparently being set to burn off some of the surface oil (the fire hot spots show up as shades of pink on the false color image). This was Day 61 following the explosion of the Deepwater Horizon offshore oil rig on 20 April.

The MODIS true color image displayed using Google Earth (below; courtesy of Liam Gumley, CIMSS) offers a different perspective and a larger-scale view of the oil slick.

MODIS true color image (displayed using Google Earth)

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GOES-13 0.63 µm visible images

McIDAS images of GOES-13 0.63 µm visible channel data (above) showed the development of a distinct convective outflow boundary along the coast of North Carolina on 17 June 2010. While appearing interesting on the satellite imagery, this outflow boundary dissipated quickly and did not appear to have any major impact on sensible weather or subsequent convective development.

A NOAA-19 false color Red/Green/Blue (RGB) image created using AVHRR channels 01/02/04 (below) offered another view of the outflow boundary at 18:53 UTC.

NOAA-19 false color RGB image (using AVHRR channels 01/02/04)

In contrast, another series of GOES-13 0.63 µm visible images (below) showed the development of a new convective cell as 3 outflow boundaries intersected over eastern Mississippi on 19 June 2010. This new convective cell produced hail of 1.00 inch in diameter (plotted as “A100” on the image) at 20:00 UTC and strong wind gusts that downed multiple trees (plotted as “W” on the image) at 21:27 UTC.

GOES-13 0.63 µm visible images (with severe weather reports)

AWIPS images of GOES-13 sounder Convective Available Potential Energy or CAPE product (below) indicated that the region of convective development was quite unstable during this period, with widespread CAPE values of around 6000 Joules per kilogram (darker purple color enhancement).

GOES-13 sounder CAPE derive product images

A MODIS false color RGB image using bands 01/07/07 (below) could be utilized to help discriminate areas of convection that were completely glaciated (darker red color enhancement) from those that were not (brighter white enhancement).

MODIS false color RGB image (using bands 01/07/07)

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POES AVHRR Cloud Top Temperature product

Severe thunderstorms that developed in the vicinity of a stationary frontal boundary over the northern Texas Panhandle region on 12 June 2010 produced unusually large hailstones (some as large as 5.5 to 6.0 inches in diameter) — additional details of this event can be found at the NWS Amarillo TX website. AWIPS images of the 1-km resolution POES AVHRR Cloud Top Temperature product (above) indicated that CTT values were as cold as -81º C at 19:42 UTC and -80º C at 20:07 UTC. By comparison, the coldest IR brightness temperatures seen on 4-km resolution GOES-13 10.7 µm imagery were -66º C.

The University of Wisconsin Convective Initiation product (below) flagged that particular area of developing convection at 18:40 UTC — about an hour before it produced the first report of 1.0 inch diameter hail at 19:40 UTC (and almost 2 hours before the report of 6.0 inch diameter hail at 20:32 UTC):

GOES-13 10.7 µm IR images (grayscale) + UW Convective Initiation product (colored boxes)

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A convective system over Texas spawned a Mesoscale Convective Vortex (MCV) during the day on 2 June, as shown in the 1.5-day loop above (color-enhanced GOES-13 11-micron imagery shown every 12 hours). The convection along the dryline at 0615 UTC on 2 June evolved into the MCV shown at 1815 UTC as a swirl of mid-level cloudiness over central Texas. That swirl supported the development of convection that subsequently evolved into a larger MCV on 3 June.

Atmospheric conditions that support MCVs are fairly well-understood. Wind shear acts to disrupt the warm core circulation of the MCV, thus small values of wind shear are commonly found near MCVs. In addition, MCVs are maintained by latent heat release in convection, suggesting the presence of abundant moisture. Low values of wind shear are noted on 3 June over eastern Texas: Model shear from the RUC (shown here overlain on the 11-micron imagery in a screengrab from AWIPS) has a wide region of weak shear over east Texas. The radiosonde from Fort Worth from 1200 UTC on 3 June also shows low values of shear. Abundant moisture is available to the system. Blended Total Precipitable Water (TPW) imagery (data from GPS over land and AMSU over water — click here and here for more information) from AWIPS shows values nearing two inches over east Texas. A loop of MIMIC TPW suggests moisture is being drawn into east Texas from the adjacent Gulf of Mexico.

Visible imagery from GOES-13 (above) shows convection developing rapidly over central Texas yesterday in the vicinity of the MCV. How well do CIMSS convective products do in predicting that development? Careful inspection of the loop above shows towering Cumulus at 1845 UTC and glaciating towers only 45 minutes later at 1932 UTC. (Click for imagery at 1902 and 1915 UTC). Screengrabs from a webmap server run at SSEC show UW Convective Initiation indicated as ongoing at 1915 UTC for a developing system that is warned as severe 45 minutes later. See the loop of screengrabs below.

Multi-day MCVs are infrequent: usually, an MCV will not persist for more than 12 hours, although famous multi-day examples exist (such as the MCV that spawned the July 1977 Johnstown, PA flood. That MCV could be traced to convective development over the Dakotas three days earlier). Note how the MCV over Texas grows in horizontal size from 2 June to 3 June. At 1200 UTC on 2 June the convective system was confined to a small region of north-central Texas. By 1200 UTC on 3 June, the region of influence has grown greatly, and the convective system covers all of eastern Texas and extends into the Gulf of Mexico. In addition, the strength of the accompanying 500-mb height field perturbation has increased. This upscale development — from smaller scale to larger scale — is one more interesting aspect of this system.

Added: Click here for a 2.5-day animated gif loop of 13-micron imagery data from GOES-13 (48 megabytes of data) produced using McIDAS-V.

This weather event is also discussed at the Hazardous Weather Testbed blog. Link.

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