Comparison of 8-day average MODIS SST (left) and 07 September MODIS SST (right)

A comparison of the MODIS 8-day average Sea Surface Temperature (SST) ending on 06 September 2011 (above, left) with the MODIS SST product on 07 September 2011 (above, right) revealed a dramatic cooling of the near-shore waters just off the east coastline of Lake Michigan. Persistent strong northerly daytime winds (gusting in the 20-30 mph range) induced an upwelling of colder water from below the surface, with 07 September values as cold as 6.8ºC (44ºF) at one location (Latitude/Longitude 43.63 North/81.96 West) — compared to the previous 8-day average SST of 22.8ºC (73ºF) at that same location. Unfortunately, the MODIS Cloud Mask that is applied to the SST product mistakenly identifies the strongest SST gradient as a cloud, and blanks out the SST product along the far western fringe of the ribbon of colder water.

AWIPS images of MODIS 0.65 µm visible channel and 11.0 µm IR channel data (below) showed greater detail in the ribbon of colder waters, with a series of eddies forming along the northern edge of the feature. Since no Cloud Mask is applied to the IR image, the full westward extent of the cold water feature can be seen.

MODIS 0.65 µm visible channel and 11.0 µm IR channel images

A sequence of four MODIS 11.0 µm IR images (below) shows the evolution of the eddy features along the western edge of the cold water. Note that the land surfaces exhibit cool IR brightness temperatures (blue to cyan color enhancement) on the first 2 night-time images (03:10 UTC and 07:21 UTC, or 10:10 pm and 2:21 am local time), but on the 2 daytime images (16:45 UTC and 18:27 UTC, or 11:45 am and 1:27 pm local time) urban areas and regions with less dense vegetation heat up and exhibit much warmer IR brightness temperatures (orange to red color enhancement). However, the Lake Michigan IR brightness temperatures generally remain constant during this time period.

MODIS 11.0 µm IR images

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. Currently there are 49 NWS offices receiving MODIS imagery and products from CIMSS. In addition, the VISIT training lesson “MODIS Products in AWIPS” is available to help users understand these products and their applications to weather analysis and forecasting.

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GOES-13 3.9 µm shortwave IR channel + 0.63 µm visible channel images

McIDAS images of GOES-13 3.9 µm shortwave IR and 0.63 µm visible channel data (above; click image to play animation) showed the fire hot spot (dark black pixels) and large smoke plume associated with the Bastrop County fire complex in eastern Texas on 04 September 2011. This fire went on to set a record for the highest number of homes damaged (over 500) by a single fire in Texas history.

A comparison of AWIPS images of 1-km resolution POES AVHRR 0.63 µm visible channel and 3.74 µm shortwave IR channel data (below) showed finer detail in the location of the individual fire hot spots (black to red to yellow color enhancement).

POES AVHRR 0.63 µm visible channel + 3.74 µm shortwave IR channel images

On the following day (05 September), the number of fires quickly grew to over 60 — a number of very large smoke plumes could be seen growing on GOES-13 0.63 µm visible channel images (below; click image to play animation). The thick smoke was causing air quality problems at a number of locations. Strong northerly winds around the circulation of the remnants of Tropical Storm Lee helped to create an environment that allowed many of the fires to quickly burn out of control.

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

The location of many of the larger fire hot spots (black to yellow to red color enhancement) could be seen on a comparison of GOES-15 and GOES-13 3.9 µm shortwave IR images (below; click image to play animation).

GOES-15 and GOES-13 3.9 µm shortwave IR images (click image to play animation)

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GOES-15 10.7 µm IR images (click image to play animation)

McIDAS images of 4-km resolution GOES-15 10.7 µm IR data (above; click image to play animation) showed the transition of Tropical Depression #13 into Tropical Storm Lee in the northern Gulf of Mexico on 02 September 2011. Deep convection persisted within the eastern semi-circle of the system, with large areas exhibiting cloud top IR brightness temperatures of -80º C and colder (violet color enhancement) prior to Lee reaching tropical storm intensity.

A comparison of AWIPS images of 1-km resolution POES AVHRR 0.63 µm visible channel and 10.8 µm IR channel data (below) revealed a few vigorous overshooting tops embedded within the convective region, with one feature located southeast of the circulation center having an IR brightness temperature value of -93º C (darker violet color enhancement).

POES AVHRR 0.63 µm visible channel and 10.8 µm IR channel images

About 2 hours later, a similar comparison of 1-km resolution MODIS 0.65 µm visible channel and 11.0 µm IR channel images (below) showed overshooting tops with IR brightness temperatures as cold as -89º C.

MODIS 0.65 µm visible channel and 11.0 µm IR channel images

===== 03 SEPTEMBER UPDATE =====

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

GOES-13 0.63 µm visible channel images (above; click image to play animation; also available as a QuickTime movie) revealed a curious “dual-vortex” structure to Tropical Storm Lee early in the day on 03 September 2011, with convective bursts developing in the vicinity of each of the two vortices. Later in the day, it appears that these dual vortices merged into a single vortex, as the center of Lee approachd the coast of Louisiana.

A comparison of 1-km resolution MODIS 6.7 µm and 4-km resolution GOES-13 6.5 µm water vapor images (below) showed that a significant tongue of dry continental air was being drawn into the western portion of the circulation of Lee.

MODIS 6.7 µm and GOES-13 6.5 µm water vapor channel images

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GOES-13 Visible (0.63 µm) image and auto-detected Overshooting Tops (click image to toggle)

Overshooting tops above a thunderstorm suggest an updraft powerful enough to penetrate through the tropopause into the stratosphere. In mid-latitudes, overshoots are well-correlated with both heavy precipitation and severe weather. In the tropics, overshooting tops are linked to intensification in tropical systems. In the image toggle above of an area of disturbed weather that may become a named tropical system in the Gulf of Mexico over the weekend, visible imagery and infrared data are shown with the automatically-detected overshooting tops (red being a more intense OT, that is, a bigger temperature difference between the tower top and the surrounding anvil cirrus through which the OT penetrates). Overshooting tops over the Continental United States are shown here (computed using data from GOES-13); Data from MSG are used to compute OTs over the tropical Atlantic, as shown here.

GOES-13 IR/WV (10.7 µm - 6.5 µm) used to detect Overshooting Tops

Difference fields between infrared data at 10.7 µm and the so-called water vapor channel (6.5 µm) can also be used to infer overshooting tops because Hot Towers push water vapor into the stratosphere and this alters the difference between the two channels. The image above, taken from the CIMSS Tropical Weather website, shows maxima in the difference field in the region where strong convection is occurring. (Click here for the toggle between the visible image and a similar WV/IR difference image). The automated detection algorithm seems to miss some towers; the wv/ir difference field identifies too many.

As the system in the Gulf of Mexico intensifies, the signal from the IR/WV difference and the number of autmomated detections should both increase. Intensification for now is inhibited by high shear over the region. The CIMSS Tropical Weather website offers information on this developing Gulf system.

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