Midwest derecho

July 19th, 2017 |

GOES-16 Infrared Window (10.3 µm) images, with SPC storm reports plotted in cyan [click to play MP4 animation]

GOES-16 Infrared Window (10.3 µm) images, with SPC storm reports plotted in cyan [click to play MP4 animation]

* 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.

GOES-16 Visible (0.64 µm) images, with SPC storm reports plotted in red [click to play MP4 animation]

GOES-16 Visible (0.64 µm) images, with SPC storm reports plotted in red [click to play MP4 animation]

GOES-16 Infrared Window (10.3 µm) images, with SPC storm reports plotted in cyan [click to play MP4 animation]

GOES-16 Infrared Window (10.3 µm) images, with SPC storm reports plotted in cyan [click to play MP4 animation]

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?

Terra MODIS Visible and Infrared Window (11.0 µm) images, with SPC storm reports [click to enlarge]

Terra MODIS Visible and Infrared Window (11.0 µm) images, with SPC storm reports [click to enlarge]

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).

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images, with SPC storm reports [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images, with SPC storm reports [click to enlarge]

Mesoscale Convective Vortex over Arizona

July 18th, 2017 |

Terra MODIS Infrared Window (11.0 µm) image, with SPC storm reports of severe winds plotted in cyan [click to enlarge]

Terra MODIS Infrared Window (11.0 µm) image, with SPC storm reports of severe winds plotted in cyan [click to enlarge]

* 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 -77º C at 0508 UTC.

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

GOES-16 Infrared Window (10.3 µm) images, with station identifiers plotted in yellow and SPC storm reports plotted in cyan [click to play animation]

GOES-16 Infrared Window (10.3 µm) images, with station identifiers plotted in yellow and SPC storm reports plotted in cyan [click to play animation]

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. Note that surface dew point temperatures were in the upper 60s  to low 70s F across southern Arizona.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with hourly surface reports [click to play animation]

Interesting Bore Features in Lake Superior Stratus

July 10th, 2017 |

GOES-16 Visible (0.64 µm) Imagery [click to play animated gif]

GOES-16 Visible (0.64 µm) Imagery [click to play animated gif]

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

High Dewpoints in mid-Summer in the Upper Midwest often leads to stratus and fog over Lake Superior. Such was the case on 10 July 2017, with dewpoints in the 50s and 60s F (GOES-16 Visible images with surface observations) and mid-lake water temperatures as cold as 40º F (buoy reports | MODIS SST values) — and very interesting waves were observed in the stratus deck. They had the appearance of Atmospheric Bores: parallel lines of clouds moving in one direction. It is unusual to have Bores moving in different directions at the same time, however.

One possible explanation for the differing motion of these undular bores could be internal reflection off the rugged northern and southern shorelines of Lake Superior.

The RTMA surface wind analyses at 17 UTC and 19 UTC, below, showed complex flow patterns over the lake — however, the surface wind flow did not always correspond well to the motion of the undular bores.

Terra MODIS Visible (0.65 µm) image, with RTMA surface winds [click to enlarge]

Terra MODIS Visible (0.65 µm) image, with RTMA surface winds [click to enlarge]

Aqua MODIS Visible (0.65 µm) image, with RTMA surface winds [click to enlarge]

Aqua MODIS Visible (0.65 µm) image, with RTMA surface winds [click to enlarge]

(Thanks to TJ Turnage, the SOO in Grand Rapids MI, for alerting us to this mesmerizing event).

Hail damage swath in South Dakota and Minnesota

July 4th, 2017 |

SPC storm report plots, from 12 UTC on 21 June to 12 UTC on 22 June 2017 [click to go to SPC storm reports list]

SPC storm report plots, from 12 UTC on 21 June to 12 UTC on 22 June 2017 [click to go to SPC storm reports list]

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

As seen on the map of SPC storm reports from 21 June 2017 (above), nighttime thunderstorms (during the pre-dawn hours of 22 June) produced a swath of hail (as large as 2.0 inches in diameter) that damaged emerging crops at some locations across eastern South Dakota and southwestern Minnesota (NWS Aberdeen summary).

Nearly 2 weeks later, on 04 July, the hail damage swath was still apparent on GOES-16 imagery. In a comparison of “Blue” Visible (0.47 µm), “Red” Visible (0.64 µm) and Near-Infrared “Vegetation” (0.86 µm ) images (below), the northwest-to-southeast oriented hail damage swath was best seen on the 0.64 µm imagery (in part due to its higher spatial resolution, which is 0.5 km at satellite sub-point); healthy vegetation is more reflective at 0.86 µm, so the crop-damaged hail swath appears slightly darker in those images.

GOES-16

GOES-16 “Blue” Visible (0.47 µm, top), “Red” Visible (0.64 µm, middle) and Near-Infrared “Vegetation” (0.86 µm, bottom) images [click to play animation]

A signature of the hail damage swath was also seen in Near-Infrared “Snow/Ice” (1.61 µm) and Shortwave Infrared (3.9 µm) images (below). The hail damage swath warmed more quickly on the 3.9 µm imagery — exhibiting a darker black appearance with time — compared to the adjacent fields of healthy crops.

GOES-16

GOES-16 “Red” Visible (0.64 µm, top), Snow/Ice (1.61 µm, middle) and Shortwave Infrared (3.9 µm, bottom) images [click to play animation]

Why was the hail damage swath also seen on the 1.61 µm “Snow/Ice” (Band 5) imagery? A look at the Spectral Response Functions for GOES-16 ABI  bands 3, 4, 5 and 6 — plotted with the reflectance of asphalt, dirt, grass and snow (below) — show that the 1.61 µm Band 5 happens to cover a portion of the radiation spectrum where there is a minor peak in grass relectance (denoted by the green plot).

Spectral Response Functions for GOES-16 ABI Bands 3, 4, 5 and 6, along with the reflectance of asphalt, dirt, grass and snow [click to enlarge]

Spectral Response Functions for GOES-16 ABI Bands 3, 4, 5 and 6, along with the reflectance of asphalt, dirt, grass and snow [click to enlarge]

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Aqua MODIS Land Surface Temperature product {click to enlarge]

Aqua MODIS Land Surface Temperature product {click to enlarge]

Regarding the warmer temperatures seen on GOES-16 Shortwave Infrared images, the 1-km resolution Aqua MODIS Land Surface Temperature product at 1738 UTC (above) revealed a 10º F difference between the warmer hail damage swath (which appeared to be about 100 miles in length) and adjacent fields of undamaged crops. A similar result was noted on 03 July by NWS Aberdeen (below).

A comparison of before (21 June) and after (02 July) Aqua MODIS true-color Red/Green/Blue (RGB) images from the SSEC MODIS Direct Broadcast site (below) clearly shows the hail damage path.

Aqua MODIS true-color RGB images, before (21 June) and after (02 July) the hail event [click to enlarge]

Aqua MODIS true-color RGB images, before (21 June) and after (02 July) the hail event [click to enlarge]

On 05 July a closer view of the hail scar was seen using a Suomi NPP VIIRS true-color RGB image from RealEarth (below).

Suomi NPP VIIRS true-color RGB image [click to enlarge]

Suomi NPP VIIRS true-color RGB image [click to enlarge]

Incidentally, on 02 July the Sentinel-2A satellite provided 10-meter resolution true-color imagery of the hail swath:

===== 07 July Update =====

The hail damage swath was also evident on a 30-meter resolution Landsat-8 false-color RGB image from 07 July:

Landsat-8 false-color RGB image [click to enlarge]

Landsat-8 false-color RGB image [click to enlarge]

Landsat-8 false-color RGB image, zoomed in on Castlewood, South Dakota [click to enlarge]

Landsat-8 false-color RGB image, zoomed in on Castlewood, South Dakota [click to enlarge]

Other examples of satellite-observed hail damage swaths can be seen here and here.