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

During the week of 19 July – 26 July 2017, the Upper Midwest was affected  by a number of strong to severe Mesoscale Convective System (MCS) events, as shown in an animation of GOES-16 “Clean” Infrared Window (10.3 µm) images (above).

At the beginning of that time period, a derecho moved across the region on 19 July producing widespread damaging winds, large hail and a few tornadoes (blog post).

Following the derecho, a separate outbreak of thunderstorms exhibited well-defined “enhanced-V” storm top signatures in western Wisconsin (below).

Another MCS produced tornadoes and damaging winds across eastern Iowa and northern Illinois on 21 July (SPC storm reports) — at one point a storm in northern Illinois exhibited a seldom-seen “warm trench” surrounding an overshooting top (below).

Early in the day on 23 July, “transverse banding” — a signature indicating the likelihood of high-altitude turbulence — was seen around the northern periphery of an MCS that was centered in southern Illinois (below).

A pattern of mesoscale banding was displayed by thunderstorms that produced localized 1-2″ amounts of rainfall across southern Wisconsin on 26 July (below).

Also noteworthy was the swath of very heavy rainfall during this 1-week period across eastern Iowa, far southwestern Wisconsin and northern Illinois (below), which was responsible for flash flooding in those areas.

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

An isolated thunderstorm that was moving eastward across Maryland just after Midnight on 24 July 2017 intensified as it crossed Chesapeake Bay, eventually producing a waterspout which moved onshore near Bay City (just southwest of Stevensville/Bay Bridge Airport, station identifier KW29) — this tornado was responsible for 1 injury and EF2-rated damage (NWS Mount Holly PNS  | SPC storm reports). GOES-16 “Clean” Infrared Window (10.3 µm) images (above; also available as a 23-Mbyte animated GIF) showed that there were 3 distinct “pulses” when cloud-top infrared brightness temperatures cooled to the -71 to -75º C range (lighter gray pixels embedded within dark black regions) before the storm produced the tornado at 0529 UTC. Since one of the default GOES-16 Mesoscale Sectors was providing coverage over the eastern US, imagery was available at 1-minute intervals.

A comparison of 1-minute GOES-16 vs 15-minute GOES-13 (GOES-East) Infrared Window images (below; also available as a 17-Mbyte animated GIF) provided a convincing demonstration of the value of more frequent image scan intervals for monitoring severe convection. The improved spatial resolution of GOES-16 Infrared imagery — 2 km at satellite sub-point, vs 4 km for GOES-13 — also allowed for a more accurate depiction of cloud-top IR brightness temperature patterns and values.

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

Real-time GOES-16 Geostationary Lightning Mapper (GLM) data are now available for viewing using RealEarth™ (real-time GLM link). An example from 21 July 2017 is shown above, for an isolated thunderstorm that developed during the afternoon hours along a residual convective outflow boundary — which was evident on an animation of “Red” Visible (0.64 µm) imagery — draped across eastern Iowa. This storm produced 1.0-inch diameter hail and damaging winds within 7-22 minutes after the 2200 UTC end of the animation (SPC storm reports).  Both the GOES-16 “Clean” Infrared Window (10.3 µm) images and the GLM Group (GLM Events clustered by proximity; see this blog post) data points were available at 1-minute intervals, since the region was within the domain of one of the Mesoscale Sectors.

Note that during the early portion of the animation, a number of GLM Group points were located south of the rapidly-expanding cold cloud top shield — GLM data are parallax-corrected, assuming a cloud-top height of 12.5 km. The 18 UTC tropopause height was 15.0 km on the 18 UTC sounding at Davenport, Iowa.

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

A long-lived mesoscale convective system (MCS) known as a derecho produced swath of damaging winds — as well as some large hail and a couple of tornadoes — that stretched from north-central South Dakota to northwestern Indiana on 19 July 2017 (SPC storm reports | TWC summary). GOES-16 “Clean” Infrared Window (10.3 µm) images (above) showed the southeastward propagation of the storm system.

Closer views of the early stages of the derecho as it moved across central and eastern South Dakota are shown below, using GOES-16 “Red” Visible (0.64 µm) and Infrared Window (10.3 µm) images. The highest measured wind gust was 100 mph near Polo (1522 UTC), with 83 mph recorded at Huron (1636 and 1730 UTC). Hail of 2.50 inches in diameter fell near Cavour (1703 UTC). Note that most of the severe reports were in the general vicinity of the persistent cold overshooting top (black to white enhancement) seen on the Infrared imagery; due to parallax, the apparent location of this storm-top feature was shifted slightly north of its true location.

1-km resolution Terra MODIS Visible (0.65 µm) and Infrared Window (11.0 µm) images at (below) showed the MCS over the Huron (KHON) area at 1656 UTC. Since there is minimal parallax associated with polar-orbiter satellite imagery, the cluster of SPC storm reports (occurring within +/- 30 minutes of the time of the MODIS image) was much closer to the cold (-70 to -73º C, lighter gray enhancement) overshooting top. Another feature of interest seen on the Infrared image was a “warm trench” (exhibiting brightness temperatures as warm as -60º C, red enhancement) immediately surrounding the cold overshooting top — perhaps a result of compensating subsidence?

375-meter resolution Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 1846 UTC (below) provided a detailed view of the MCS as it was centered near the South Dakota / Minnesota border. The coldest cloud-top IR brightness temperature was -83º C (violet enhancement).

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