GOES-13 6.5 µm water vapor channel images (click image to play animation)

A historic late-April “nor’easter” storm affected much of the northeastern US during the 22 April – 23 April 2012 period. This storm produced heavy snowfall (as much as 23.3 inches at Laurel Summit, Pennsylvania), heavy rainfall (as much as 5.74 inches at New Boston, New Hampshire), and wind gusts as high as 94 mph at Mount Washington, New Hampshire. AWIPS images of 4-km resolution GOES-13 6.5 µm water vapor channel images (above; click image to play animation) showed the development of various features of the storm on 23 April, including a large and well-defined comma head, dry slot, and deformation zone.

By tracking the movement of various water vapor image features between consecutive images, atmospheric motion vectors can be calculated which give an indication of the wind direction and wind speed within the middle to upper troposphere. GOES-13 6.5 µm water vapor images with overlays of MADIS 1-hour interval water vapor winds are shown below  (click image to play animation).

GOES-13 6.5 µm water vapor images + MADIS 1-hour water vapor winds (click image to play animation)

Satellite-derived water vapor winds can also be used to calculate an upper-tropospheric (150-300 mb) divergence product (below), which in this case showed persistent divergence aloft over much of the northeastern US on 23 April. This upper-level divergence created an environment that favored upward vertical motion within the atmospheric column, helping to enhance and prolong the ongoing precipitation over those areas.

GOES-13 water vapor images + Upper-level divergence derived from water vapor winds

A series of 1-km resolution MODIS 11.0 µm IR and POES AVHRR 12.0 µm IR images (below; click image to play animation) indicated that enhanced areas of colder clouds (some exhibiting a banding structure) developed over the region of persistent upper level divergence.

MODIS 11.0 µm IR + POES AVHRR 12.0 µm IR images

The 10-km resolution GOES-13 sounder Total Column Ozone (TCO) product (below; click image to play animation) revealed an anomalously large area of elevated TCO covering much of the eastern US, indicative of a lowered tropopause associated with the large upper-level trough of low pressure.

GOES-13 sounder Total Column Ozone + RUC 500 hPa geopotential heights

===== 24 April Update =====

MODIS 6.5 µm visible channel image + MODIS false-color RGB image

A comparison of the 1-km resolution MODIS 0.65 µm visible channel image at 16:09 UTC (12:09 pm local time) with a corresponding false-color Red/Green/Blue (RGB) image created using the MODIS 2.1 µm “snow/ice detection” channel (above) helped to identify high-elevation areas with significant snow cover remaining after the passage of the storm — snow appears brighter white on the visible image, and darker red on the false-color image. Note that cirrus clouds appear as a lighter shade of red in the RGB image.

A 250-meter resolution MODIS true color image from the SSEC MODIS Today site (below; viewed using Google Earth) showed even better detail of the snow-covered high terrain.

MODIS true-color RGB image (viewed using Google Earth)

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MODIS 0.65 µm visible channel image + MODIS Land Surface Temperature product

A comparison of AWIPS images of 1-km resolution MODIS 0.65 µm visible channel data and the corresponding 1-km resolution MODIS Land Surface Temperature (LST) product at 21:22 UTC on 22 April 2012 (above) depicted marine layer stratus clouds extending inland along much of the California coast — but farther inland most areas were cloud-free, with some of the interior deserts exhibiting very hot LST values (as high as 148º F in the Death Valley region of California, and 139º F in southern Nevada and southwestern Arizona).

An overlay of the 21 UTC METAR surface reports (below) showed that instrument shelter air temperatures were only in the 50s and 60s F beneath the marine layer stratus along coastal California, but many air temperatures were over 100º F in the interior deserts. A number of daily maximum temperature records were set on this day, including 113º F at Furnace Creek in Death Valley, California, 105º F in Phoenix, Arizona, and 99º F in Las Vegas, Nevada (which tied their record for the warmest high temperature for the month of April, and was also the earliest occurrence of a 99º F temperature).

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MODIS Land Surface Temperature product + METAR surface reports

===== 23 April Update =====

Following the hot daytime temperatures on 22 April, a night-time MODIS Land Surface Temperature image showed that many of the lower elevations were still quite warm at 09:19 UTC (below). In Death Valley, California LST values were still as warm as 86º F. Lower elevations in the Grand Canyon in Arizona exhibited LST values in the 60s and 70s F, while the higher elevation canyon rims had cooled into the 30s and 40s F. In Arizona, record high minimum temperatures for the date were set at Phoenix (77º F) and Yuma (74º F).

MODIS Land Surface Temperature product

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GOES-15 (left), GOES-12 (center), and GOES-13 (right) visible channel images (click image to play animation)

A small volcanic ash plume from Popocatépetl in central Mexico was seen streaming east-southeastward on GOES-15 (GOES-West), GOES-12, and GOES-13 (GOES-East) visible channel images (above; click image to play animation) during the early morning hours on 18 April 2012. Satellite imagery over this particular region is available every 15 minutes on a routine basis from GOES-13, but only every 30 minutes from GOES-15 and every 3 hours from GOES-12.

According to the advisory issued by the Washington VAAC (below), the volcanic ash was extending upward to an altitude of around 23,000 feet.

Washington VAAC advisory

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

A major outbreak of severe thunderstorms occurred across parts of the central US during the 14 April – 15 April 2012 period, producing widespread tornadoes, large hail, and damging winds (SPC storm reports). Noteworthy events included a tornado that produced EF-4 damage at Kanopolis Lake, Kansas, hail up to 4.5 inches in diameter at Randolph, Kansas, and a wind gust to 97 mph at Oskaloosa, Iowa. Six fatalities resulted from an EF-3 rated tornado that struck Woodward, Oklahoma.

1-km resolution GOES-13 0.63 µm visible channel images (above; click image to play animation; also available as a QuickTime movie) showed a number of overshooting tops associated with some of the stronger thunderstorms. A large plume of blowing dust can also be seen toward the end of the animation, moving northeastward across New Mexico and eventually over the Texas and Oklahoma panhandle regions.

A closer look at a strong thunderstorm in northwestern Oklahoma using 0.63 µm visible channel images from GOES-15 (GOES-West) and GOES-13 (GOES-East) (below) showed the development of bands of inflow feeder clouds along the southern edge of the storm — this satellite signature is often seen prior to the time that a supercell storm is about to begin a period of intensification. GOES-13 was in Rapid Scan Operations (RSO) mode, providing images twice as often as GOES-15; this allowed the development of the inflow feeder bands to be more easily identified and followed using GOES-13. This particular storm went on to produce the large tornado that inflicted EF-3 damage in the Wichita, Kansas area.

GOES-15 (left) and GOES-13 (right) visible channel images

4-km resolution GOES-13 10.7 µm IR channel images (below; click image to play animation; also available as a QuickTime movie) revealed that a large number of storms exhibited well-defined “enhanced-V” signatures (an indicator that a storm has a high probability of producing tornadoes, large hail, or damaging winds). The GOES-13 satellite was placed into Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-10 minutes from 15:45 UTC on 14 April to 01:15 UTC on 15 April.

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

Shown below is a sequence of five separate 1-km resolution MODIS 11.0 µm IR channel or POES AVHRR 12.0 µm IR channel images, with overlays of SPC storm reports of large hail, damaging winds, and tornadoes within +/- 30 minutes of the image time. Many of the enhanced-V signatures were much more detailed in the higher spatial resolution IR imagery.

POES AVHRR 12.0 µm IR image + SPC storm reports

MODIS 11.0 µm IR image + SPC storm reports

POES AVHRR 12.0 µm IR image + SPC storm reports

POES AVHRR 12.0 µm IR image + SPC storm reports

MODIS 11.0 µm IR image + SPC storm reports

A display of maps of the University of Wisconsin Convective Initiation (CI), Cloud Top Cooling (CTC) rate, Overshooting Top (OT), and Overshooting Top/Thermal Couplet (OT/TC) automated detection products showed a good correlation with the map of plotted SPC storm reports (below).

UW Convective Initiation, Overshooting Top, and Thermal Couplet detections

Finally, a comparison of 375-meter resolution Suomi NPP VIIRS 0.64 µm visible channel, 11.45 µm IR channel, and 3.74 µm shortwave IR channel images centered near the Dodge City, Kansas (KDDC) area (below) showed a pair of well-defined “enhanced-V” signatures (with cold/warm thermal couplet IR brightness temperatures in excess of 25º C), which also exhibited anvil plumes extending downwind (to the northeast) of the vertex of each enhanced-V. The enhanced-V storm just to the southeast of Dodge City was producing a tornado and 1.75-inch diameter hail at the time of the VIIRS images. In addition, the IR and shortwave IR images revealed a number of southwest-to-northeast oriented swaths of cooler ground (lighter gray enhancement) due to heavy rainfall from the recent passage of thunderstorms.

Suomi NPP VIIRS 0.64 µm visible channel, 11.45 µm IR channel, and 3.74 µm shortwave IR channel images

Farther to the northeast, a comparison of 375-meter resolution Suomi NPP VIIRS 0.64 µm visible channel and 11.450 µm IR channel images (below) showed that the thunderstorms over northeastern Kansas, southeastern Nebraska, and southwestern Iowa were exhibiting well-defined overshooting tops, with packets of concentric anvil-top gravity waves propagating away from some of the strongest overshooting top features. The satellite detected a cloud top IR brightness temperature as cold as -85º C (purple color enhancment) associated with the overshooting top over far southern Nebraska.

Suomi NPP VIIRS 0.64 µm visible channel and 11.450 µm IR channel images

On a side note, it is interesting to point out that a 1-km resolution MODIS 6.7 µm water vapor channel image at 04:17 UTC (below) displayed an elongated north-to-south oriented wave packet  from Nebraska into Kansas — and there was a pilot report of severe turbulence at a flight altitude of 31,000 feet over this water vapor wave signature. These waves were not seen in the corresponding 04:17 UTC MODIS IR image, implying that they were likely located within the middle troposphere (GOES-13 water vapor weighting function plot).

MODIS 6.7 µm water vapor channel image + Pilot reports of turbulence

4-km resolution 6.5 µm water vapor channel images from GOES-15 (GOES-West) and GOES-13 (GOES-East) (below; click image to play animation) suggested that this gravity wave may have formed in response to pronounced middle-tropospheric subsidence/drying related to the formation of a strong rear flank downdraft along the trailing edge of the thunderstorm that was located in central Kansas around 01:00 UTC (schematic diagram from Lemon and Doswell, 1979). This packet of waves generally remained quasi-stationary, but did begin to move westward around the time of the pilot report of severe turbulence. However, it is also possible that the severe turbulence was due to the aircraft’s proximity to a rapidly-developing thunderstorm in south-central Nebraska.

GOES-15 (left) and GOES-13 (right) 6.5 µm water vapor channel images (click image to play animation)

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