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

On 17 July Tropical Storm Don became the 4th named storm of the 2017 North Atlantic Basin season. The satellite presentation improved somewhat on 18 July, with GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) displaying a few brief convective bursts (some of which exhibited cloud-top infrared brightness temperatures of -80º C  and colder).

A GOES-13 (GOES-East) Infrared Window (10.7 µm) image at 1845 UTC  with overlays of the Tropical Overshooting Tops and  Deep-Layer Winds products from the CIMSS Tropical Cyclones site is shown below.

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

On 15 July Hurricane Fernanda became the first Category 4 tropical cyclone of the 2017 Northern Hemisphere season. GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed the development of a well-defined eye during the period of rapid intensification. As the National Hurricane Center mentioned, it was unusual to have a hurricane of this intensity at such a low latitude in the Eastern North Pacific Basin.

#Fernanda is among strongest hurricanes in the East Pacific at such a low latitude (<12°N). 100 kt at 10.9°N! @UMiamiRSMAS @capitalweather pic.twitter.com/nVJm622tE6

— Brian McNoldy (@BMcNoldy) July 14, 2017

Fernanda fluctuated between Category 3 and Category 4 intensity during the 15-17 July period (ADT | SATCON) as it passed over the warm waters of the East Pacific Ocean (Sea Surface Temperature and Ocean Heat Content) — and trochoidal oscillations in the northwestward motion of the eye could be seen in GOES-16 Infrared Window (10.3 µm) imagery (below).

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

Strong summer monsoon season thunderstorms developed over Arizona in the pre-dawn nighttime hours on 17 July 2017, producing damaging winds across the Phoenix area (SPC storm reports). A Terra MODIS Infrared Window (11.0 µm) image (above) revealed cloud-top brightness temperatures as cold as -77ºC at 0508 UTC.

GOES-16 “Clean” Infrared Window (10.3 µm) images (below) showed the development and eventual dissipation of the overnight convection.

During the following daytime hours, GOES-16 “Red” Visible (0.64 µm) images (below) displayed the circulation of a Mesoscale Convective Vortex (MCV) as it propagated west-southwestward across southern Arizona. Note that surface dewpoint temperatures were in the upper 60s to low 70s F across southern Arizona, an indicator of the monsoon moisture that was in place across the region. The MCV appeared to play a role in helping to force the development of new thunderstorms later in the afternoon in the vicinity of the Arizona/Mexico border.

On the previous evening, a Mesoscale Discussion from SPC (below) mentioned the presence of weak deep-layer wind shear over the portion of Arizona affected by these nighttime severe thunderstorms — MCVs often form in such a low-shear environment.

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