NOAA/CIMSS ProbSevere Output from AWIPS on 24 April, 1902, 1908, 1912, 1930, 1938, 1944, 1948, 1950, 1954 and 1958 UTC (click to play animation)

Severe thunderstorms moved across central Texas on April 24th (Link). The NOAA/CIMSS ProbSevere product can be used with storms like this to alert a forecaster to when severe weather will develop. ProbSevere output tells you the probability that a given storm cell will first produce severe weather in the next 60 minutes. (The type of severe weather — hail, high winds or tornado) are not specified by the product. In the animation, a strong thunderstorm is just entering Coke county from Sterling county to the north of Tom Green county. The list below shows ProbSevere values with the three storms shown in the animation above.

1. 1902 UTC  (Northern Cell)  ProbSevere 46%
2. 1908 UTC (Northern Cell) ProbSevere 50%
3. 1912 UTC (Northern Cell) ProbSevere 85%
4. 1930 UTC (Northern Cell) ProbSevere 95%
5. 1932 UTC (Northern Cell) ProbSevere 95% (Severe Thunderstorm Warning active)
6. 1948 UTC (Southern Cell) ProbSevere 23%
7. 1950 UTC (Southern Cell) ProbSevere 50%
8. 1954 UTC (Middle Cell) ProbSevere 57%
9. 1956 UTC (Middle Cell) ProbSevere 70%

So, the northern cell crossed the 50% ProbSevere threshold at 1908 UTC, the southern cell crossed the 50% ProbSevere threshold at 1950 UTC, and the small middle cell had a >50% ProbSevere from the start, at 1954 UTC.

Severe hail (1.25″ in diameter) was reported at 1928 UTC (20 minutes after ProbSevere crossed the 50% threshold) 8 miles west (31.89 N, 100.62 W)of Robert Lee, TX (the county seat of Coke County). At 1957 UTC, 1.75″ Hail was reported four miles north (31.94 N, 100.30 W) of Bronte, TX (also in Coke County).

The middle cell in the animation above eventually merged with the southern cell, and intensified. The animation from 1958 through 2014 UTC is below. ProbSevere with the middle storm (that merges with the southern cell) is 70%, rising to 98% at 2014 UTC.

NOAA/CIMSS ProbSevere Output from AWIPS on 24 April, 1958, 2000, 2008, 2010, 2012, 2014 UTC (click to play animation)

At 2015 UTC, the National Weather Service issued a Severe Thunderstorm Warning. At this time, 2.75″ Hail was falling five miles northwest of Tennyson in Coke County. (31.79N, 100.35W). The 2016 UTC ProbSevere output is here.

The ProbSevere product is something that distills many bytes of information: model output that describes the environmental conditions, satellite data that describes the initial growth of convection, and MRMS radar data that captures the present state of a storm. The distilled data can be used to increase the confidence that a severe event will occur within the next 60 minutes.

An animation of the 10.7 µm imagery from 1800 through 2015 UTC is shown below. The locations of the severe hail reports noted above are included on the relevant images.

GOES-13 10.7 Brightness Temperature 1800-2015 UTC on 24 April 2015; Coke County is highlighted (click to play animation)

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Suomi NPP VIIRS 11.45 µm imagery, 0509 UTC 23 April 2015 (Click to enlarge)

Suomi NPP overflew the erupting Calbuco Volcano in southern Chile around 0509 UTC or 2:09 am local time on 23 April 2015. The image above is the VIIRS 11.45 µm infrared imagery (click here for a similar view).

The shock of the volcanic eruption generated mesospheric gravity waves (or “mesospheric airglow waves”) that were evident in the Day/Night Band, shown in the toggle below between the 11.45 µm and the night-time visible imagery. No lunar illumination was present, so the waves were apparent via the Earth’s airglow as the primary light source; this “night glow” is emitted from a variety of high-altitude (80-105 km) gases located near the mesopause (reference).

Toggle between VIIRS 11.45 µm infrared image and 0.70 µm Day/Night Band image, 0509 UTC 23 April 2015 (Click to enlarge)

(VIIRS images courtesy of William Straka, SSEC)

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GOES-13 (GOES-East) 0.63 µm visible and 10.7 µm IR channel images at 2138 UTC (with surface reports)

The Calbuco volcano in southern Chile erupted around 2103 UTC or 6:03 pm local time on 22 April 2015. The first good satellite view of the volcanic cloud was provided by the 2138 UTC or 6:38 pm local time GOES-13 (GOES-East) 0.63 µm visible channel and 10.7 µm IR channel images (above). The coldest cloud-top IR brightness temperature at that time was -65º C, which was very close to the tropopause temperature as indicated on the nearby Puerto Montt rawinsonde reports from 1200 UTC on 22 April and 23 April — the height of the tropopause was between 12.3 and 15.6 km on each day (there were 2 tropopause levels TRO1 and TRO2 coded in both of the upper air reports).

However, before the volcanic cloud was seen, a well-defined thermal anomaly or “hot spot” was evident on the previous GOES-13 3.9 µm shortwave IR image at 2045 UTC or 5:45 pm local time (below). The hottest 3.9 µm IR brightness temperature at that time was 340.8 K (red pixel), which is very close to the saturation temperature of the GOES-13 3.9 µm detectors.

GOES-13 3.9 µm shortwave IR image at 2045 UTC

An oblique view of the early stage of the volcanic cloud was captured on a 2100 UTC GOES-15 (GOES-West) 0.63 µm visible image (below; closer view).

GOES-15 (GOES-West) 0.63 µm visible image at 2100 UTC

A sequence of GOES-13 (GOES-East) 10.7 µm IR channel images (below; click image to play animation; also available as an MP4 movie file) revealed that there was a second explosive eruption that began sometime before the 0508 UTC or 2:08 am local time image on 23 April. The coldest cloud-top IR brightness temperature with this second eruption was -68º C at 0808 UTC. Also, at 0508 UTC mesospheric airglow waves were seen with Suomi NPP VIIRS Day/Night Band imagery.

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

On the morning of 23 April, a 1200 UTC GOES-15 (GOES-West) 0.63 µm visible image (below) provided a good view of the large areal coverage of volcanic cloud material resulting from the 2 eruptions.

GOES-15 (GOES-West) 0.63 µm visible image

Finally, a before-eruption (21 April) and post-eruption (23 April) comparison of Aqua MODIS true-color Red/Green/Blue (RGB) images as visualized using the SSEC RealEarth web map server (below) showed the effect of ashfall on some of the higher terrain downwind of Calbuco, which was particularly evident on the snow-capped summits of the Osorno and Puyehue volcanoes (yellow arrows).

Before (21 April) and after (23 April) Aqua MODIS true-color RGB images

—– 24 April Update —–

A series of GOES-13 and Terra/Aqua MODIS volcanic ash height retrieval images from the SSEC Volcano Monitoring site (below; click image to play animation) showed that the ash from each of the two explosive eruptions reached heights of 18-20 km (black color enhancement), which was well into the stratosphere.

GOES-13 and Terra/Aqua MODIS volcanic ash height retrieval values (click to play animation)

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Himiwari-8 AHI 0.63 µm visible channel images (click to play animation)

0.5-km resolution Himawari-8 AHI 0.63 µm visible channel images from the SSEC RealEarth web map server (above; click image to play animation) revealed a number of interesting features from the Sea of Okhotsk to the Bering Sea during the 18 April – 19 April 2015 period, which included (1) a series of lee waves immediately west of the Kuril Islands (the chain of islands south of the Kamchatka Peninsula), (2) the cyclonic circulation that formed over the western Bering Sea off the Russian coast, along the far northern edge of a remnant frontal boundary, and (3) cloud streets in the central Bering Sea, streaming southward and southwestward from the sea ice across the open waters.

A comparison of Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images with an overlay of the19 April / 00 UTC surface analysis (below) showed the location of the remnant frontal boundary, which was an axis of convergence between strong northerly winds over the central Bering Sea (causing the cloud streets and heavy freezing spray which would be a concern for shipping activities in that area) and a ridge of high pressure southeast of the Kamchatka Peninsula.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images.

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