We issued 7 Tornado Warnings today, the most we’ve ever issued in a single day or even a whole year until now! #mewx #nhwx pic.twitter.com/x8set1XxOi

— NWS Gray (@NWSGray) July 2, 2017

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

As noted in the Tweet above from NWS Gray/Portland ME, a record number of tornado warnings were issued by that office on 01 July 2017. According to their damage surveys, the tornadoes were rated EF-0 to EF-1, with some straight-line wind damage also seen. GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images with plots of SPC storm reports (below; also available as a 98-Mbyte animated GIF) displayed the overshooting tops and colder cloud-top infrared brightness temperatures associated with some of the thunderstorms. Note the significant offset between cloud-top features and storm reports — this is due to parallax from the large viewing angle of the GOES-16 satellite (which is positioned over the Equator at 105º West longitude).

A comparison of Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 1744 UTC (below) showed the early stages of convective development in far southwestern Maine, in addition to well-developed thunderstorms in eastern New York (which would later move northeastward to produce a swath of heavy rainfall that caused flooding at some locations).

Thunderstorm development was fueled by high amounts of moisture that had moved into the Northeast US, as shown below by the Blended Total Precipitable Water product (values in the 40-50 mm or 1.6-2.0 inch range) and the Blended Total Precipitable Water Percent of Normal product (with values in excess of 200%).

The hourly evolution of moisture was depicted by the MIMIC Total Precipitable Water product (below).

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

Softball-sized hail fell in northwestern Iowa on Thursday afternoon, 29 June (Storm Prediction Center Storm Reports). The visible animation above, from 1902 to 2307 UTC, shows the rapid development of convection over far northeast Nebraska. Woodbury County in Iowa is outlined in the animation, the largest reported hail occurred in that county along the shores of the Missouri River; the location of the 4.25″ diameter hail is shown as the green box on this image.  This visible image closely corresponds to the time of the hail fall.

Since a GOES-16 Mesoscale Sector was positioned over the region, imagery was available at 1-minute intervals — a comparison of “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images is shown below. Plots of SPC storm reports are parallax-corrected to match the location of the storm-top features. The rapid growth of the storm that produced the 4.25″ hail was apparent in the Infrared data, which showed cloud tops cooling from around -45ºC at 2000 UTC to -65.5ºC at 2130 UTC (the time of the hail report). Cloud-top cooling rates were consistently 3ºC/5 minutes during this time. Also, in far northeastern Nebraska, a supercell thunderstorm produced an EF-1 tornado that tracked 14.4 miles along with hail up to 2.75 inches in diameter (NWS Omaha summary).

One of the GOES-16 Baseline Products available to forecasters includes a series of stability parameters derived from the ABI channels (and using GFS data as a first guess): Legacy Atmospheric Profiles or LAP (Online Source). These products are similar to those produced from the GOES Sounder on GOES-15. The LAP Lifted Index at 2100 UTC, below, from the GOES-16 Mesoscale Sector sited over the convection, shows a remarkable pool of instability (Lifted Indices less than -8ºC) in the region near the developing convection (which was in the wam sector of an approaching surface low). CAPE values were in excess of 2000 J/kg. More information on the Legacy Atmospheric Profiles products is available here (as part of the Satellite Foundation Course for GOES-R).

LAP Profiles can be an excellent tool for situational awareness when convection develops in clear or partly-cloudy regions.

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

Consider the visible image above. Can you tell where the eastern and southern edge of the cirrus shield is over the eastern United States? When the Sun is not on the horizon, thin cirrus can be very hard to detect in visible imagery because cirrus clouds are not efficient back-scatterers of solar radiation (all clouds forward-scatter very effectively, but cirrus are optically thin). In a still image, then, with a high sun angle, cirrus can be hard to discern.  There are brightness temperature difference fields that can also be used to infer the presence of cirrus.  For example, the Split Window Difference field (10.3 µm – 12.3 µm) and the Cloud Phase Difference (8.5 µm – 11.2 µm), toggled below, will highlight regions of cloudiness.  But do they also capture very thin cirrus?

 

The Cirrus Channel on GOES-16 (1.38 µm), below, better captures the areal extent of the cirrus.  This is because it is very sensitive to reflective features such as cirrus clouds, and because it is in a region of the electromagnetic spectrum where water vapor absorption occurs — so surface features that might complicate the interpretation are masked (Note, for example, that cumuliform clouds over Northwestern Pennsylvania are not apparent in the Cirrus Band imagery). Click here to toggle between all 4 images.

One of the GOES-16 Baseline Products is a Cloud Mask — this is important because many other Baseline Products use the output from the Cloud Mask in decision trees. The toggle below shows the Cirrus Band (1.38 µm), the Red Visible (0.64 µm) and the Cloud Mask for 1557 UTC on 28 June 2017.

 

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

Clusters of severe thunderstorms developed over eastern Wyoming and the Nebraska panhandle during the afternoon on 27 June 2017, and increased in areal coverage and intensity as they moved eastward into the overnight hours. 1-minute interval Mesoscale Sector GOES-16 Infrared Window (10.3 µm) images with plots of SPC storm reports (above) showed a number of locations with wind gusts in excess of 60 mph — including 79 mph in Rapid City SD at 2341 UTC and 100 mph in Custer NE at 0200 UTC. Many of these high wind reports were in the general vicinity of thunderstorm overshooting tops, which exhibited cloud-top infrared brightness temperatures in  the -70 to -80º C range (black to white enhancement).

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