GOES-11 and GOES-13 water vapor images

A cyclone off the Pacific Northwest coast was maturing and entering the occluded stage on 23 February 2009. An animation of  GOES-11 and  GOES-13 water vapor channel imagery (above) showed a very compact “dry swirl” signature that often signals a cyclone’s transition to the occluded stage. Note that the subtle features and gradients are more clear on the 4-km resolution GOES-13 water vapor channel data (compared to the 8-km resolution of the GOES-11 water vapor channel data).

An AWIPS image of the GOES-11 water vapor image with surface reports and HPC-analyzed surface fronts  (below) displayed the relationship between the satellite features and the surface features. Note that ship 3FMH7 (located to the north of the occluded front) reported blowing spray (group 70722) at 18 UTC — the present weather symbol on the station model plot that is used for “blowing dust/sand” is also used for blowing spray at sea.

GOES-11 water vapor image (with surface fronts and surface data)

A comparison of the GOES-11 water vapor image and the GOES-11 sounder Total Column Ozone product at 16:00 UTC (below) indicated that ozone values were quite high (in excess of 450 Dobson Units, lighter red color enhancement) over the region of the occluding cyclone.

GOES-11 water vapor + GOES-11 sounder Total Column Ozone

A west-to-east cross section along Line G-G’ using 18:00 UTC NAM80 model fields (below) showed that the dynamic tropopause (taken to be the height of the PV1.5 potential vorticity surface) had descended to below the 500 hPa pressure level in the vicinity of the occluding cyclone.

Cross section of NAM80 model fields

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GOES-13 visible and 3.9 µm shortwave IR images

We received the following in an email from the  National Weather Service forecast office at Fort Worth, Texas:

Some of our forecasters noted an interesting feature on visible satellite imagery on Thursday, Feb 12, 2009. I would like to get an expert opinion on what was causing the observed features. There was a layer of ~ 15kft altocumulus along with some scattered-broken areas of cirrus.

Excellent question…and we appreciate the heads-up on this event. An animation of GOES-13 visible and 3.9 µm “shortwave IR” images (above; QuickTime animation) showed the evolution of two “hole punch” cloud features that were drifting eastward across northern Texas on 12 February 2009. The first hole punch cloud feature moved just to the north of Dallas/Fort Worth (DFW) around 14:45 UTC, while the second feature moved just south of DFW about an hour later (around 15:45 UTC). In addition, an elongated aircraft dissipation trail (or “distrail”) could be seen to the west of the first hole punch feature (oriented west-to-east on the 14:15 and 14:32 UTC visible images), with a second distrail forming about an hour later (oriented northwest-to-southeast on the 15:15 and 15:32 UTC visible images).

These aircraft “hole punch” and “distrail” cloud features form when an aircraft ascends or descends through a layer of supercooled water droplet cloud, with the engine exhaust causing the droplets to glaciate — the resulting ice crystals then fall toward the ground, creating a visible hole or trail in the cloud layer. Note that there is a subtle “brighter white” signal evident on the GOES-13 3.9 µm shortwave IR images in the area of the hole punch features — this colder signal confirms the idea that the aircraft engine exhaust was causing the supercooled water droplets to glaciate.

A NOAA-17 false color Red/Green/Blue (RGB) composite image using channels 01/02/04 (below) showed the second hole punch cloud as it was moving to the south of DFW at 15:58 UTC. Similar aircraft hole punch and distrail cloud features have been seen in the past: for example, over the southcentral US and also over Wisconsin.

NOAA-17 false color RGB image

GOES-13 visible and 10.7 µm IR images

GOES-13 10.7 µm IR data (above) showed cloud top brightness temperatures in the -20 to -30º C range (cyan to dark blue color enhancement) over much of the cloud patch where the initial hole punch feature was seen. Rawinsonde data from both Midland and Fort Worth in Texas (below) displayed a moist layer centered around 425 hPa that corresponded to those temperatures — this indicates that the hole punch and distrail features were at a fairly high altitude (around 20,000 feet or so). Dallas/Fort Worth METAR reports listed cloud bases at 15,000 feet during the period.

Midland TX and Fort Worth TX rawinsonde data

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GOES-12 10.7 µm IR images

The first tornado-related fatalities of the 2009 severe weather season occurred during a tornado outbreak that affected parts of Texas and Oklahoma (SPC storm reports) on 10 February – 11 February 2009. GOES-12 10.7 µm IR images (above; QuickTime animation) showed the development of multiple lines of severe convection during the afternoon and evening hours of 10 February, with large areas of cloud top temperatures in the -55º to -65º C range (orange to darker red color enhancement).

The tornado fatalities occurred in the town of Lone Grove  — located just west of Ardmore in far southern Oklahoma — around 01:30 UTC (7:30 pm local time). A comparison of GOES-11, GOES-12, and GOES-13 IR images around that time (below) demonstrated the effect of “parallax”, which leads to the apparent displacement of the cold “overshooting top”  cloud feature due to varying satellite view angles. Using GOES-11 (positioned over the Pacific Ocean at 135º West longitude), the coldest overshooting top IR pixel (with an IR brightness temperature of -63º C, darker red color enhancement) was located about 5 km southeast of Ardmore (KADM). Using GOES-12 (positioned over the Atlantic Ocean at 75º West longitude), the coldest IR pixel (also -63º C) was located about 22 km west of Ardmore. Finally, the GOES-13 satellite (positioned at 105º West longitude) had a more direct viewing angle, and therefore less of a parallax error: the coldest IR pixel (-64º C) was located 12 km northwest of Ardmore — this places the “overshooting top” a few km to the north of Lone Grove, which would be the expected location.

GOES-11, GOES-12, and GOES-13 10.7 µm IR images

A closer view using the GOES-12 visible channel images (below; QuickTime animation) shows the development of the initial line of storms over Oklahoma. The storm that produced the fatal tornado at Lone Grove formed  to the east of the main line of storms, and began to appear  just south of the Oklahoma/Texas border near the end of the animation.

GOES-12 visible images

AWIPS images of the GOES sounder Lifted Index (LI) derived product (below) showed that the atmosphere was destabilizing during the afternoon hour, with LI values over Oklahoma as low as -8º C by 19:00 UTC and -13º C by 21:00 UTC.

GOES sounder Lifted Index derived product images

In addition, the GOES sounder Total Precipitable Water (TPW) derived product images (below) indicated  that there was a northward surge of moisture across Oklahoma during the hours leading up to convective development, with TPW values  exceeding 20 mm (0.8 inch) by 18:00 UTC, and TPW values exceeding 30 mm (1.2 inches) by 21:00 UTC.

GOES sounder Total Precipitable Water derived product images

A strong upper-level trough was moving eastward across the southern Rocky Mountains region, and the GOES sounder Total Column Ozone derived product images (below) depicted elevated values of ozone associated with this trough. Total Column Ozone values of 350-425 Dobson Units (green to red color enhancement) often correspond to a lowering of the dynamic tropopause and/or the presence of a potenial vorticity (PV) anomaly — and the approach of the trough and the associated PV anomaly likely helped to produce an environment that favored  upward vertical motions on a synoptic scale across the southern Plains region late in the day on 10 February.

GOES sounder Total Column Ozone derived product images

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MODIS true color and false color images

The National Weather Service at Milwaukee/Sullivan posted a nice animation of MODIS true color imagery (using the  AWIPS “MODIS True Color Imagery Viewer” that Jordan Gerth developed as part of the CIMSS/SSEC MODIS in D2D project) which shows the breakup of ice in southern Lake Michigan and the melting of snow cover over far southeastern Wisconsin during a 3-day period of warm temperatures in early February 2009. A comparison of MODIS “true color” (Red/Green/Blue composite using channels 01/04/03) and “false color” (Red/Green/Blue composite using channels 07/02/01) images from the SSEC MODIS Today site (above) also showed some interesting clues about the thinning of the ice on some of the inland lakes and rivers on 08 February 2008. Snow and ice appear as white features on the true color image, but appear as varying shades of cyan on the false color image — however, thinner ice shows up as a darker blue color on the false color image (due in part to a higher meltwater content within  the top layer of the ice).

Even though the appearance of the inland lake ice was beginning to show signs of degradation and thinning  on the MODIS imagery, recent reports of ice thickness (below, courtesy of Lake-Link.com) indicated that there was still over 20 inches of ice on some parts of the larger lakes such as Lake Winnebago (the largest lake in east-central Wisconsin), as well as on smaller lakes like Lake Mendota (the largest of the lakes in the Madison area). Note that some of the lakes in southern Wisconsin are already ice-free — these lakes exhibit a darker appearance on both the true color and the false color images. In addition, a significant amount of lake ice can still be seen along the eastern nearshore waters of Lake Michigan.

Lake Winnebago ice thickness (courtesy of Lake-Link.com)

Lake Mendota ice thickness (courtesy of Lake-Link.com)

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