Tornadoes and large hail in Minnesota and Wisconsin

May 16th, 2017 |

GOES-16 Visible (0.64 µm, top) and Infrared Window (10.3 µm, bottom) images, with SPC storm reports plotted in cyan [click to play animation]

GOES-16 Visible (0.64 µm, top) and Infrared Window (10.3 µm, bottom) images, with SPC storm reports plotted in cyan [click to play animation]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

A significant outbreak of severe thunderstorms developed on 16 May 2017, producing damaging winds, large hail and tornadoes from Texas to Wisconsin (SPC storm reports). On the northern end of this outbreak, hail as large as 3.0 inches in diameter fell in northwestern Wisconsin, and a tornado resulted in 1 fatality and at least 25 injuries near Chetek (NWS Twin Cities MN summary). GOES-16 Visible (0.64 µm) and Infrared Window (10.3 µm) images (above) showed the development of the convective systems; surface-to-cloud-top parallax-corrected SPC storm reports are plotted on the images. Overshooting tops and above-anvil cloud plumes were evident on the visible images, with well-defined “enhanced-V” and “cold/warm thermal couplet” storm top signatures seen on the infrared imagery.

A closer view of the GOES-16 Visible and Infrared Window images (below) provided more detail of the supercell storm-top structure. Note that the pronounced enhanced-V Infrared signature began to develop near the Minnesota/Wisconsin border just before 2100 UTC, which was about 40 minutes before the first Wisconsin hail report of 2.5 inches, and about 90 minutes prior to the fatal Chetek tornado. Since the early 1980s (reference), the enhanced-V satellite signature has been recognized as a reliable predictor of supercell thunderstorms having a high potential to produce either damaging winds, large hail or tornadoes; an automated Enhanced-V / Overshooting Top product (reference) will be available using the ABI instrument on the GOES-R series of satellites..

GOES-16 Visible (0.64 µm, top) and Infrared Window (10.3 µm, bottom) images, with plots of SPC storm reports and hourly surface reports [click to play animation]

GOES-16 Visible (0.64 µm, top) and Infrared Window (10.3 µm, bottom) images, with plots of SPC storm reports and hourly surface reports [click to play animation]

A comparison of GOES-13 (GOES-East) and GOES-16 Infrared Window images (below) demonstrated the advantage of improved spatial resolution (2-km at satellite sub-point with GOES-16, vs 4-km with GOES-13) for identifying features such as cold overshooting tops.

Infrared Window images from GOES-13 (10.7 µm, top) and GOES-16 (10.3 µm, bottom) , with SPC storm reports plotted in cyan [click to play animation]

Infrared Window images from GOES-13 (10.7 µm, top) and GOES-16 (10.3 µm, bottom) , with SPC storm reports plotted in cyan [click to play animation]

True-color Red/Green/Blue (RGB) imagery (below; courtesy of Kaba Bah, CIMSS) offered another view of the storms on a regional scale.

GOES-16 true-color RGB images [click to play animation]

GOES-16 true-color RGB images [click to play animation]


Large hail in eastern Colorado

May 8th, 2017 |

GOES-16 Visible (0.64 µm, left) and Infrared Window (10.4 µm, right) images, with surface station identifiers in yellow and SPC reports of hail size in cyan [click to play MP4 animation]

GOES-16 Visible (0.64 µm, left) and Infrared Window (10.4 µm, right) images, with surface station identifiers plotted in yellow and SPC reports of hail size plotted in cyan [click to play MP4 animation]

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

Severe thunderstorms developed over eastern Colorado on 08 May 2017, producing large hail (especially in the Denver area: SPC storm reports | NWS Boulder summary). Both GOES-16 Mesoscale Sectors were positioned over that region, providing 30-second interval images — Visible (0.64 µm) and Infrared Window (10.35 µm) images (above; also available as a 161 Mbyte animated GIF) showed the convection in great detail, with parallax-corrected SPC storm reports of hail size (inches; H275 = 2.75 inches in diameter) plotted in cyan. Several of the storms exhibited well-defined overshooting tops in the Visible imagery, as well as “enhanced-V” and/or cold-warm “thermal couplet” signatures on the Infrared imagery.



A comparison of 30-second interval GOES-16 Mesoscale Sector and 15-minute interval GOES-13 (GOES-East) Routine Scan visible images (below; also available as a 179 Mbyte animated GIF) demonstrated the clear advantage of rapid-scan imagery for monitoring convective development. Also note the degradation of GOES-13 visible imagery (the cloud features do not appear as bright), due to the age of that satellite — the GOES-R series ABI instrument features on-board visible detector calibration, so this type of visible image degradation over time will not occur.

GOES-16 Visible (0.64 µm, left) and GOES-13 Visible (0.63 µm, right) images, with surface station identifiers in yellow [click to play MP4 animation]

GOES-16 Visible (0.64 µm, left) and GOES-13 Visible (0.63 µm, right) images, with surface station identifiers plotted in yellow [click to play MP4 animation]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images (below; actual satellite overpass time 1943 UTC) provided a high-resolution (375 meter) view of the developing thunderstorms, about 17 minutes before the first report of hail northeast of Trinidad (KTAD) at 2000 UTC — a number of these storms exhibited cloud-top infrared brightness temperatures of -70 to -73º C (black enhancement). The VIIRS instrument will also be on the JPSS series of satellites, the first of which is scheduled to be launched in the 4th quarter of 2017.

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images, with surface station identifiers plotted in cyan [click to enlarge]

Undular bores over the Gulf of Maine

April 27th, 2017 |

** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

As pointed out by NWS Caribou:



numerous packets of wave clouds associated with undular bores were seen on GOES-16 Visible (0.64 µm) imagery over the Gulf of Maine on the morning of 27 April 2017. A longer animation with surface wind plots (below; also available as an MP4 animation) revealed the presence of 3 distinct bore structures: the largest and most well-defined which was moving eastward; a second (and much smaller) off the coast of Cape Cod which was moving southeastward; and a third which as moving northwestward  (and eventually intersected the northern end of the primary eastward-moving bore).

GOES-16 Visible (0.64 µm) images, with surface winds (knots) plotted in cyan [click to play animation]

GOES-16 Visible (0.64 µm) images, with surface winds (knots) plotted in cyan [click to play animation]

A comparison of GOES-16 and GOES-13 (GOES-East) Visible images (below; also available as an MP4 animation) showed that undular bore wave cloud structures were more clearly clearly seen with the higher spatial spatial resolution of GOES-16 (0.5 km at satellite sub-point, vs 1.0 km for GOES-13). The comparison also showed that the visible imagery from GOES-13 (launched in May 2006, and operational as GOES-East since April 2010) was not as bright as that from GOES-16; this is due to the fact that the performance of GOES visible detectors tends to degrade over time.

GOES-16 Visible (0.64 µm, left) and GOES-13 Visible (0.63 µm, right) images [click to play animation]

GOES-16 Visible (0.64 µm, left) and GOES-13 Visible (0.63 µm, right) images [click to play animation]

So what caused these undular bores to form and propagate across the Gulf of Maine? Such gravity waves are ducted within strong temperature inversions — and rawinsonde data from Chatham, Massachusetts and Yarmouth, Nova Scotia indicated that such inversions were in place above the surface that morning. The northwestward-moving bore could have been initiated by surface outflow from thunderstorms associated with a mid-latitude cyclone (which was producing storm force and gale force winds: surface analyses) — GOES-16 Infrared Window (10.3 µm) images (below; also available as an 88 Mbyte animated GIF) showed these thunderstorms which developed within the warm sector of the coastal low pressure system. However, the forcing mechanism(s) that generated the eastward and southeastward moving bores remains somewhat of a mystery.

GOES-16 Infrared Window (10.3 µm) images [click to play MP4 animation]

GOES-16 Infrared Window (10.3 µm) images [click to play MP4 animation]

Mountain waves over the Sierra Nevada

April 13th, 2017 |

GOES-16 7.3 µm (left), 6.9 µm (center) and 6.2 µm (right) Water Vapor images [click to play animation]

GOES-16 7.3 µm (left), 6.9 µm (center) and 6.2 µm (right) Water Vapor images [click to play animation]

 ** The GOES-16 data posted on this page are preliminary, non-operational data and are undergoing testing. **

A comparison of GOES-16 Lower-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed the presence of numerous mountain waves over parts of California and Nevada on 13 April 2017. The more pronounced of these waves were caused by strong southwesterly winds interacting with  higher terrain of the Sierra Nevada.

A 3-satellite comparison of GOES-15 (GOES-West), GOES-16 and GOES-13 (GOES-East) Water Vapor images (below) highlighted 2 factors that allowed better detection of these mountain waves by GOES-16 — improved spatial resolution (2 km for GOES-16 at satellite sub-point, vs 4 km for GOES-15/13), and a more direct satellite viewing angle (GOES-16 is positioned at 105ºW longitude, while GOES-15 is at 135ºW and GOES-13 is at 75ºW).

OES-15 (6.5 µm, left), GOES-16 (6.9 µm, center) and GOES-13 (6.5 µm, right) Water Vapor images [click to play animation]

GOES-15 (6.5 µm, left), GOES-16 (6.9 µm, center) and GOES-13 (6.5 µm, right) Water Vapor images [click to play animation]

Note that there were no Visible cloud features associated with many of the waves seen on Water Vapor imagery (below); encounters of Clear Air Turbulence (CAT) often occur with these types of mountain waves, as seen by scattered pilot reports of moderate turbulence (plotted as Category 4).

GOES-16 Visible (0.64 µm, left) and Water Vapor (6.9 µm, right) images, with pilot reports of turbulence [click to play animation]

GOES-16 Visible (0.64 µm, left) and Water Vapor (6.9 µm, right) images, with pilot reports of turbulence [click to play animation]